SOME ASPECTS OF THE ECOLOGY OF LANTERNFISHES(MYCTOPHIDAE) IN THE PACIFIC OCEAN NEAR HAWAIl

THOMAS A. CLARKE!

ABSTRACT

Most species of myctophids collected near Hawaii showed ontogenetic differences in verticaldistribution and migration. Newly transformed juveniles of several species did not regularlymigrate. Within both day and night depth ranges, the smaller fish tended to occur shallowerthan the adults. Few differences were related to sex or reproductive condition. Largefractions of populations of three species appeared not to migr<jte at certain seasons. Seasonalchanges in size composition of populations and ripeness of mature females indicated thatmost abundant species spawn principally in the spring and summer and live about I year.The size-depth patterns of congeners and closely related species were quite different, whilesimilar-sized individuals of dissimilar species tended to co-occur at the same depths.

Comparison of day and night estimates of abundance and .size composition indicatedthat there was little differential avoidance by most species. There were differences betweencatches by a IO-ft Isaacs-Kidd trawl and a modified Cobb pelagic trawl related toboth species and size with neither trawl showing a distinct advantage for all species. Com­parison of catches at full and new moon indicated that at full moon most species occurredabout 50 m deeper and avoided the Isaacs-Kidd trawl better than at new moon.

The average standing crop of myctophids was about 0.32 g(wet weight)/m2 , and theyearly turnover rate was estimated at roughly twice the standing crop. Myctophids andother vertically migrating micronekton appear to be very important in the trophic structureof the tropical open ocean and probably account for most of the consumption ofzooplankton.

l\1yctophids or lanternfishes are one of thedominant families of mesopelagic fishes and aregenerally thought to be important in the openocean ecosystem because of their frequentoccurrence and apparently great abundances.The bulk of early work was concerned primarilywith taxonomy and distribution. Most recentWork has concentrated on one aspect of theirecology, diurnal vertical migration. Myctophidshave been shown in a number of cases, e.g.,Paxton (1967), Badcock (1970), to undertakesubstantial migrations from depths of severalhundred meters during the day to the upper100-200 m at night, but few studies have donemore than describe the vertical distributionpatterns and suggest possible relationships ofthese to gradients in temperature or light withdepth or with the position of sonic scatteringlayers. There are numerous gaps in our knowl-

f! Hawaii Institute of Marine Biology and Department96820ceanOgraphy, University of Hawaii, Honolulu, HI

2.

-----~aSnUSCriP! accepted November 1972.

HERY BULLETIN: VOL. 71, NO.2, 1973.

edge of other aspects of the ecology of thisubiquitous group of fishes. Moreover, previouswork has not been equitably distributed in ageographic sense; most has been carried out athigher latitudes.

Among others, Badcock (1970) has indicatedthat there are size-specific differences in migra­tion patterns of some species of myctophids, butontogenetic changes in depth distribution havenot been studied quantitatively. Similarly,Nafpaktitis (1968) has indicated that in somespecies of the genus DiapJL'Us the mature femalesdo not migrate. It is not known whether eitherof these patterns is typical or widespread withinthe family. Extensive life history data have beenpresented for some abundant northern species,Benthosoma glaciale (Halliday, 1970), Steno­branchus leucopsaurus (Smoker and Pearcy,1970), and Myctophulil alft/Ie (Odate, 1966), butthe life histories of most species, particularlytropical ones, remain unknown.

This paper presents and discusses data onmyctophids collected in several series of mid-

401

water trawl samples taken in the Central PacificOcean near Hawaii. The majority of the sampleswere collected during four series which at­tempted to cover the upper 1,000 m day andnight at 3-mo intervals over a period of 1 year.The aims of the sampling were to determine thevertical migration patterns of the species presentand to examine changes in abundance, sizecomposition, and reproductive state with depthand season. In addition, changes in verticaldistribution and avoidance with changing phasesof the moon were investigated, and the catchingability of a 10-ft Isaacs-Kidd mid-water trawlwas compared with that of a much largeranchovy trawl. The results allow detaileddescription of many aspects of the life historyand ecology of myctophids. It is possible fromthese data to consider interspecific relation­ships with respect to time and space and toestimate the importance of myctophids andother micronekton in the tropical, open oceanecosystem.

MATERIALS AND METHODS

A total of 221 mid-water trawl samples weretaken for this study. Fifty-four were taken witha 6-ft Isaacs-Kidd OK) mid-water trawl, 157with a 10-ft IK trawl, and 10 with a modifiedCobb pelagic trawl (CT). All trawls were fishedwithout opening-closing devices. Thirty-sevenIK tows were taken during September andNovember 1969 to provide preliminary data.The remaining tows consisted of four generaltypes: a series of 31 6-ft IK tows taken inJuly 1970 to check various aspects of sampling,four series of 26-35 10-ft IK tows each takenat 3-mo intervals from September 1970 toJune 1971, 17 10-ft IK tows taken in Sep­tember and October 1971 to determine effectsof moon phase on sampling, and 10 CT towstaken in conjunction with the 10-ft IK towsduring February-March 1971.

All tows except those of November 1969 weretaken west of the island of Oahu, Hawaii,roughly along a line between lat. 21 °20'N;long. 158°20'W and lat. 21 °35'N; long. 158°35'W.The depth of water for all tows was 1,800 m(1,000 fm) or more. BT casts to 300 m madeduring the study indicated that seasonal tem-

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FISHERY BULLETIN: VOL. 71. NO.2

perature changes in the study area were nearlythe same as for a nearby station (lat. 22 °10'N;long. 158°W) studied more thoroughly by Gor­don (1971). Presumably the depth profiles ofother physical-chemical factors given by Gordon(1970, 1971) are also representative of the studyarea. The November 1969 tows were taken nearGordon's station.

The IK trawls were of standard dimensionsand were lined with 6.35 mm (% inch) knotlessnylon mesh anteriorly and 4.75 mm (3/16 inch)knotless nylon mesh posteriorly. The 10-ft IKterminated with a 1.0-m diameter planktonnet of333 f.1 nitex; the 6-ft, with a 0.5-m diameternet. The CT, described in detail by Higgins(1970), had 19-mm stretch mesh in the mainbody and a cod end lined with 6.35-mm mesh.Diver observations of the CT have indicatedthat the mouth opening under tow is about 12 mwide by 8 m high (Higgins, 1970).

IK trawls were fished from the Universityof Hawaii RV Teritu. Unless otherwise noted,the procedure was the same for all tows. Thetrawl was shot with the ship moving about 1.75m/sec (ca. 3.5 knots), and the cable, was paidout so that just enough tension was maintainedto keep the net from fouling. For deeper (over300 m) tows, the ship was slowed to ca. 1.0m/sec for a few minutes after the cable waspaid out to allow the trawl to sink farther. Theseprocedures were designed to minimize forwardmotion while the trawl descended to towingdepth. The trawl was towed at depth for 2-3hr at a speed of about 1.75 m/sec. For retrieval,the ship was slowed to ca. 1.0 m/sec, again tominimize forward" motion while the trawl wasabove sampling depth. Cable was retrieved asfast as possible; the average rate varied between30 and 60 m/min. The rate was considerablyfaster than 60 m/min when there was morethan 1,000 m of wire out. The CT was fished ina similar manner from the National MarineFisheries Service (NMFS) RV TownsendCromwell.

Depth of tow was determined by time-depthrecorders (Benthos, Inc.)2 attached to the trawl.For depths of less than 300 m the trawl reached

2 Reference to trade names does not imply endorsementby the National Marine Fisheries Service, NOAA.

CLARKE: ECOLOGY OF LANTERNFISHES

towing depth within a few minutes after cablewas paid out and usually stayed within 5 m ofthis depth during the entire tow. For deepertows, the trawl frequently took some time todescend to maximum depth and often moved upand/or down gradually during the tow. In allcases, however, a single, most frequently fisheddepth was assigned to each tow.

For some IK tows an acoustic telemeter(Benthos, Inc.) was used to determine depthwhile underway and to reach desired depth, butin most cases the amount of cable required toreach a given depth had to be estimated before­hand. This method required some practice, and,needless to say, depth coverage was more evenfor the later cruises.

Towing speed for the IK was, in some cases,measured by a TSK flowmeter attached to thetrawl and rigged to signal, through the tele­meter, every 500 revolutions. In all cases,Position of the ship was determined by visual orradar fixes at 1/2 - to I-hI' intervals during thetow and speed calculated from these data. Thetowing speed for the IK varied between 1.54and 1.98 m/sec with most tows about 1.75m/sec. The CT was towed at about 1.5 m/sec.

Assuming 100% filtering efficiency and aspeed of 1.75 m/sec, the 10-ft IK sampled about9.4 X 104 m 3 per 2-hr tow. At 1.5 m/sec,the CT sampled just over lOll m3 per 2-hr towor about 11 times the IK tows. Only fish over10-mm long were considered sampled quantita­tively by the IK since smaller individuals couldpass through the meshes. Larger fish, up to25-30 mm long, appeared to escape through theCT meshes.

The July 1970 (5-10 July 1970) series of towswith the 6-ft IK were designed primarily todetermine whether significant changes in verti­cal distribution occurred in the upper layersduring the course of night and to obtain anestimate of sample variability. At depths of50 m and 100 m, five 2-hr tows were taken fromdusk to dawn on a single night, and one replicatetow Was made during the following night. Dusk,?awn, and night tows were taken .at other depths.In the upper 400 m. In addition, day tows weretaken between 500 and 1,125 m.

The four quarterly series of 10-ft IK towswere designed to sample for seasonal changes

and were intended to be replicate surveys ofthe upper 1,000 m both day and night. Sincepreliminary day tows caught no nonlarvalmyctophids above 300 m, no attempt was madeto cover the upper layers during the day. Thedates of the cruises were 14-17 and 20-24September 1970; 8-10 and 13-17 December1970; 26 February-3 March and 19 March1971; and 8-11 and 15-19 June 1971. The serieswill subsequently be called September 1970,December 1970, March 1971, and June 1971.Depths sampled for these series and the July1970 series are given in Figure 1.

In addition to some gaps in depth coverageduring September 1970, the shallow nighttows were made at both full and new moon.Subsequent analyses showed that the depthdistribution and avoidance for many specieschanged considerably with moon phase, and asa consequence, some populations were sampled

403

twice and others not at all during the September1970 series. This also occurred to a lesser extentduring the December 1970 series. All nighttows above 200 m were made during new moonfor the March 1971 and June 1971 series. TheMarch 1971 series was incomplete due to astorm, and the 400-700 m zone was not sampledat night. Such limitations are taken into accountin interpreting the data.

The CT tows were taken in conjunction withthe March 1971 IK series. Eight night towswere taken at 25-m intervals between 25 and200 m during the same three nights that IKtows were taken at or near these depths. TheIK-CT pairs were unfortunately not all takensimultaneously. All tows but one were 2 hr atdepth; the 25-m CT tow was only 15 min long,but catches of some species were sufficient foruseful analyses. Two day tows at 300 and 400 mwere also taken with the CT during this period.

To determine effects of moon phase on verticaldistribution and avoidance at night, 10-ft IKtows of 11/2 hr each were made at depths of15,45,65,80, 100, 125, 145, and 165 m on 17-19September 1971 (new moon) and at 20, 50, 75,100, 130, 170, and 190 m on 4-6 October 1971(full moon). This series, designated September1971, also provided useful data on other aspects.

During December 1970 and June 1971, threeand four, respectively, short oblique tows weremade to depths of 250-300 m at night in orderto roughly estimate the catch due to ascentand descent through the upper layers. Thecable was paid out as described above, but theship was slowed and the trawl retrieved im­mediately. A longer oblique tow was made inJune 1971 to 330 m at night. Fifty meters ofcable was paid out every 15 min in an attemptto sample all depths equally.

The dusk and dawn tows taken during July1970 indicated that myctophids had completedtheir upward migration by 2000 hr and hadbegun to descend by 0400-0500 hr. All sub­sequent night tows were taken between thesetimes. DifferenceI'. between tows taken insequence at 50 and 100 m through the nightwere not markedly greater than differencesbetween tows taken at the same hour on twosuccessive nights. There was no trend amongthe species which indicated that anything

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FISHERY BULLETIN: VOL. 71. NO.2

analogous to a "mid-night dispersal" occurred.Therefore, all night tows were considered to­gether regardless of what period of the nightthey were taken. No comparable study wasmade to check on possible changes in depthdistribution during the day. It was assumedthat no changes took place during the daybetween 0800 and 1600 hr.

Specimens were preserved in Formalin.Standard length was measured to the nearestmm for all collected by IK. For some CT collec­tions of over 1,000 individuals per species, asubsample of several hundred was measured.Wet weights of blotted specimens were deter­mined to the nearest mg for small individualsand to the nearest 10 mg for larger fish orwhole samples.

Insufficient replicate samples were taken toreliably specify the variance associated with theestimate of abundance from a single tow. Therewas considerable variability in the catches ofthe two series of four tows each taken at 50and 100 m in July 1970. (Appendix Table 1.)In particular, one tow in the 100 m seriescaught much higher numbers of several species.This variability, probably related to patchinessin the organisms sampled and differences inavoidance due to differences in ship's speed,cloud cover (light), etc., limits interpretationof some of the data. Where I have drawn con­clusions without statements of statistical sig­nificance, I have attempted to be conservative.Features not consistently evident from a seriesof tows should be regarded as tentative.

The significance of differences between twosamples in size composition was determinedusing the Kolmogorov-Smirnov test (Tate andClelland, 1957). Two samples were consideredsignificantly different if the probability (one­tailed) associated with the maximum differencebetween the cumulative size-frequency curveswas less than 0.05. The overall significance ofthe differences is somewhat altered becausemultiple tests were often made with the samedata. In most cases, the trends observed wereobvious and consistent, and it is doubtful thatlarge errors resulted from the procedure.

There were relatively few significant dif­ferences in size composition between replicatesat the same depth. For 10 sets of data for eight

CLARKE: ECOLOGY OF LANTERNFISHES

species caught in abundance in the replicatesat 50 and 100 m during July 1970, there wereno significant differences between size-frequencycurves in seven and only one sample in each ofthe other three sets differed significantly fromone or more of the other replicates.

Not all individuals were sexed and no detailedgonad studies were done. Size at maturity wastaken as the minimum size at which femaleswere found with obviously ripened ova. A vari­able number of each species were examined.For abundant species, sex was determined forabout 50 juveniles, and sex ratio of mature fishand ripeness of mature females were determinedfor samples from several depths and seasons.If significant or nearly significant differencesbetween samples were noted, a larger seriesWas examined to determine trends. It wasassumed that the percentage of females amongmature fish and the percentage of ripe out oftotal mature females were distributed as abinomial and that the differences in percentagesWere considered significant ifthe 95% confidencelimits did not cross zero.

For species collected in low numbers, thedata from each series were simply pooled toestimate overall size composition and relativeabundances. For abundant species, total num­bers and overall size composition for the entirewater column were computed by a rectangularintegration of the depth-abundance curves.Numbers collected were adjusted to a 2-hrtowing time. It was assumed that abundanceand size composition from the depth sampledwere the same for the layer between the mid­Points between that depth and the next shallowerand next deeper depth sampled; i.e., abundanceestimated from a sample at depth zi wasassumed constant throughout (zi _ 1 + zi)/2 to(zi + zi + 1) /2 where zi _ 1 was the next shal­lower depth sampled and zi + 1 the next deeper.The number of individuals of each size in eachRample waR weighted accordingly.

Differences in the numbers and size com­Position of these calculated totals could not becompared statistically since no estimate of thevariances of the data were available, but wheredepth coverage was adequate, calculated totalsand size-frequency curves were used to roughlycompare whole series for day and night, sea-

sonal, full and new moon, and IK and CTdifferences. The calculated size-frequency curvesfor December 1970 and June 1971 could becompared with those of the oblique tows whensufficient specimens of a given species weretaken in the latter. Unless there were obviousdeficiencies in depth coverage, etc., the cal­culated curves agreed closely with those fromthe oblique tows.

RESULTS

A total of 47 species of myctophids werecollected. The number collected, size range, sizeat maturity fOI" females, and day and nightdepth ranges are given in Table 1. Unless notedunder individual species headings (below), theindividuals caught did not deviate from speciesdescriptions in Wisner (1971, manuscr. 3),

Nafpaktitis (1968), or Nafpaktitis and Nafpak­titis (1969).4 The percentage of ripe femalesamong total mature females examined for eachof the four quarterly cruises is given for severalabundant species in Table 2.

The depth ranges given in Table 1 are thebest estimates based on all available data.Because the trawl was open during descentand ascent, some individuals were caught intows made below the levels where they occurred.For abundant species, catches below the depthranges given were low and consistently closeto those of short oblique tows (see AppendixTable 2). A few cases where substantial numberswere caught near the day depth at night arediscuRsed below under the species headings. Forrarer species, where the chances of being caughtin a tow at their actual depth were not muchgreater than the chances of being caught intransit by deeper tows, catches due to contami­nation could not be readily distinguished andthe lower depth limits in Table 1 may beerroneous. In most cases, the values given areconservative.

3 Wisner, R. L. Unpub!. manuscr. Annotated andillustrated key to the identification of fishes of thefamily Myctophidae of the eastern Pacific Ocean, east·ward of 160 0 West Longitude.

4 Specimens of most species will be deposited at theU.S. National Museum, Los Angeles County Museum,Scripps Institution of Oceanography, and the BerniceP. Bishop Museum in Honolulu.

405

FISHERY BULLETIN: VOL. 71, NO.2

TABLE 1,-List of myctophid species collected, the number collected, size range, size at maturity, night and daydepth ranges, and seasons when juveniles were present or present in markedly higher abundances. Under "Numbercollected" the figures given are the totals from the four quarterly series of samples; where few or none were caughtin these series, the total number caught in all other samples is given in parentheses. Figures in parentheses under"Size range" are for dipnetted specimens,

SpeciesNumber

collected

Sizerange(mm)

Size otmaturity

(mm)

Nightdepth

(m)

Daydepth

(m) Juveniles

Pr010m}'CIOphum beckeriBenthosema suborbitaleBemhosema jibu/awmDiogenichth}'s at/anticusHygophum proximumH)'goplwm reinhardt;Myctophum nitidulumMyclophum ob/llsirostrumM.vctophum spinosunlMyclophum selelloidesSymbolophorus evermann;wweinQ lauraeuJ}l,'eina terminataCentrobru1lcJws choerocephalusCnltrobranchus andreaeLobianchia geme/lariLobiunchia urolampaDiaplws berte/sen;DiapllllS. "glondulifer"Diaplws schmidt;Diaplllls frallilisDiaphus ro/j1Jo/illiDiaphus ellleensDiap/ll/s adenv,,"/.>Diaplllls chrysorhYflchus

Diaphus metopoclampusDiaphlls theraDiaphus sp. ADiaplllls sp. BDiuphus anderseniDiaphll.\· brachycepiJalusNOlo/ychnus va/diviaeLampadena luminosaLampadella urophaosLClmpadena anomalaTaallillgichthys bathyphilusTaaninrsichfhys minimumTaaninxichfhys paurolychmgLampanycfus nigerLampanycfus nobi!isulInpanycfus S/cinbcckiLampanJ'cfus fenui!ormisTripho/uruJ nigrescensBo/inichth}'!i [ongipesBolillichthus .Hlpra/ateralisCeratoscopelus »'unninxiNotoscope/us caudispinoswi

o (3)

1.15714 (30)27

696413

lB (34)15 (59)5 (32)

14 (24)lB6

2 (3)1

224 (6)

1771 (1)6 (79)

37823

56104132

77 (27)1o (I)

253165261100

1,2677744

1 (2)

55712

1,946384

2,36214

2,1201,45B

853,911

6 (17)

34-389-38

10·7212-2212-5112-4813-5412-6334·93

9-6715-8622-432212-3714-479-59

25-2617-3812-739-47

10-839-767-65

71·12611·844923

9-369-64

10-299-619·25

15·7717·11530·4920·7220·6420·2212·13515·11414·562B·136

9·3811·5612-9011·7920-125

( 65)( 77)(115)

25

1738335758

1106270

29

41

5531616548

2542202820

100 ?

5153

609843

125303788 ?45

111 ?

400 ?15·7515·16515·10025-15050·1750·15?0·15?0·15?

25·1500·125

250 ?

0·150100-16525·360

100 ?100-150

95·22515·8015-12050·20015·100

75·125185145

25·8530·19095·26030·20080,15075-25095·140

300·400590·930150·475

1,175100·31040·14080·275

250·30025·7550·15095·22515·14075-125

400 ?490·620500·550400·600500-700550·900600·Boo500·700600 ?300-500600·900690 ?825490·650640·650410·560

300 ?425·600490·625520·600490·690490·600495-550550

490·525490·560300·560?300·6OO?525·640525-725620·775BOO620·BOO640·775

1,000640·900590.1,200625·1,000640·775540·775525,725490·690620·1,000590·680

June (Mar.)

June, Julyall ?

Mar., June

June, July, Sept.

June, July, Sept.Sept.June, July, Sept.Sept.

July, Sept.JuneJune, July, Sept., Dec,June, July, Sept.Sept. (Mar" June)June, July, Sept.

Mar.

Dec. (Sept.)all ?July, Sept.

June, JulyJune, July, Sept.Sept., Dec.Mar., June, July

moon;dance,

Eight species-Protmnyctophurn beckeri,Loweina laurae, L, tenninata, Centrobranchusandreae, Diaphus metopoclampus, D. theta,Larnpadena anornala, and Taaningichthys pau­rolychnus-were taken so rarely that littleother than their capture in the area can benoted, For 39 species, the individual accounts

406

below include where possible the followingaspects: deviations from depth ranges given inTable 1; changes in size composition and sexratio with depth; differential avoidance betweenday and night, IK and CT, and full and new

and changes in size composition, abun-and reproductive state with season.

CLARKE: ECOLOGY OF LANTERNFISHES

TABLE 2.-Proportion of females with developed ova among total maturefemales (figures in parentheses) examined for 10 species from September 1970and 1971, December 1970, March 1971, and June 1971 samples. Significantdifferences between values arc noted in text.

Species September December March June

Bem!losema suborbitale 0.39 (18) 0.98 (62) 1.00 (38) (0)

HYKOplllll1l proxil1lum .78 (37) .72 (7) 0.91 (22) 0.86 (22)Diaphlls schmilit; .375 (8) (0) .88 (59) 1.00 ( 11)

Diap!lus sp. A .96 (46) 1.00 (8) .89 (9) 1.00 ( 14)No[o!)'clulll.\' lluJdil'iae .70 (54) .71 (69) .91 (11) .89 (38)Lampall)'cfus "iKer .35 (51) .76 (95) .8S (69) .53 (47)LampUIJ)'cIUS steinbecki .64 (42) .44 (22) .81 (103) .78 (122)Triplwturus lligrescell.~ .54 (13) .39 (142) 1.00 (41) .94 (36)Bolillichthys I01lf.:ipes .67 (12) .12 (17) .81 (70) .SS (17)Ceratos('opelus warming; .60 (102) .62 ( 124) .52 (48) .70 (27)

Differences in sex ratio with size and seasonare of somewhat dubious significance and willbe treated in the discussion.

BelltboselJ/i./ slIborbittde

Small (10-12 mm) B. 8uborbitale tended toremain at depth both day and night. On allthree cruises where night samples were takennear the day depth, low but probably significantnumbers of small fish were taken. In June 1971,the number caught at about 550 m was nearlyequal to that caught at 25 m at night and at thesame depth during the day. In all cases exceptthe June 1971 series the size-frequency curvesof the deep night catches differed significantlyfrom those of most other tows, the differencesbeing due to much greater proportions of 10- to12-mm fish in the deep night tows. There wasno evidence that larger fish did not migrateregularly.

The depth ranges for this species were rathernarrow relative to the sample spacing, andpopulations at a given time were usually madeup of one size class. There were, however,significant differences between the size-frequencycurve at 25 m and those at 50 and 80 m inMarch 1971. The difference was due to theabsence of fish <25 mm at 50 and 80 m ratherthan a decrease of larger fish at 25 m. Othernight series also showed a trend for smallerfish to occur higher in the water column.

There was no indication of differential day­night avoidance. The calculated size-frequencycurves for day and night samples from eachseries agreed quite well with each other, except

for June 1971. The total calculated numbersagreed well in June 1971, but for the otherseries, the day totals were 1.5 - 2 X higher thanthe night totals. This difference was probably aresult of the weighting factors assigned to theday tows being too large, Le., the depth rangewas probably narrower than the relativelywide-spaced samples indicated.

The IK appears to sample B. 8uborbitale aswell or better than the CT. The calculatedtotal for the CT series was 7 x that for the IK;factors for individual pairs varied between 4.2and 8.8 x. There were no significant differencesbetween size-frequency curves of IK-CT pairsat the same depths, and the calculated curvesfor the two series agreed well. The fact that theCT size-frequency curves did not differ fromthose of the IK suggests that the lower CTestimates of abundance were not due to escape­ment through the meshes. If the latter had beensubstantial, the smaller fish would have escapedmore frequently, and size composition of thecatches would have differed from those of theIK.

At new moon, B. 8uborbitale occurred mostlyabove 50 m at night; at full moon the populationwas centered at about 75 m with practicallynone above 50 m (Figure 2). The size-frequencycurves of both the individual samples and thosecalculated from the new and full moon seriesagreed closely. The numbers at peak depthswere similar, and the calculated total for newmoon was only 1.25 x that for full moon. Thusthe change in depth distribution apparent inthe full moon samples was mainly if 110t totallydue to a depression of the night depth by about50 m.

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FISHERY BULLETIN: VOL. 71, NO.2

FIGURE 2.-Number of individuals of B£'/1tlws£'lIla mb­orbiwl£' (left) and HygophulIl proxilllulIl (right) caughtper tow at several depths in the upper layers at nightduring new moon (solid circles and lines) and full moon(open circles, dashed lines) during September 1971.

Be1Jthosellltl fiblllatllJJl

by September, but apparently not all havereached the minimum size caught by the trawluntil later. Most fish are mature by Decemberwhen maximum abundance occurs. There isapparently little growth in size between Decem­ber and March and a decrease in total numbers.By June, most of the adults are gone and thenext generation has begun to reach trawlablesize. The percentages of mature females withripe ova (Table 2) correlate with these trends;they were significantly higher in December andMarch, before the periods when juvenilesappeared.

'\'b..,

20 40 60

NUMBER /TOW

20 40 60 80

150

100

200

10 20 30STANDARD LENGTH (mm)

FIGURE 3.-Cumulative size-frequency curves for B£'/1­tlws£'lIla suborbital£' at four seasons. Size compositionwas calculated (see text) from samples taken throughoutthe water column in June 1971 (A), September 1970 (B),December 1970 (e), and March 1971 (D).

Size composition and abundance showed adefinite seasonal pattern. In June 1971, about70% were 10-15 mm; there were a few adultsand practically no intermediate sizes. Thecalculated size-frequency curves (Figure 3)shifted to the right from June to March indicat­ing changes in size-composition due to growth.Though calculated day totals were higher thannight totals for all but the June 1971 series, therank order was the same for both, abundancesbeing highest in December, lowest in June, andintermediate and nearly equal in Septemberand March.

It appears that B. suborbitale spawns prin­cipally in the spring and summer. A few young(10-15 mm) are present by March and many byJune. A substantial portion are 20-25 mm long

HygophllJJl pro.'\.'iIJlIIJJl

Diogellichthys .tlla1Jticlls

D. atla/lticlls, although quite abundant in theEquatorial Pacific (Hartmann, 1971), wascaptured rarely in Hawaiian waters. About 80%of the individuals collected were adults, but thepresence of 11- to 15-mm fish several times ofthe year suggests some spawning may occur inthis area.

B. fi·bulatum is apparently epibenthic orrestricted to nearshore areas. In Hawaii, largeindividuals (45-95 mm) are regularly taken inbottom trawls at depths of 100-190 m at night(P. J. Struhsaker, pers. comm.), and largecatches have been made by NMFS in CT towsat 25-100 m over areas where the bottom depthis about 600 m. Only eight of the individualstaken during this study were of the size takenby inshore trawls, 40-72 mm. The rest were15-27 mm and mostly taken in the upper 100 mat night.

In June 1971, nine small H. pTO;J.;imum (12-14mm) were caught at about 650 m at night. Aslow as this catch was, it was higher than anyshallow night catch and unlikely due to con­tamination. Similar numbers of this size werecaught near this depth during the day andnone in the shallow night tows, suggesting thatthe smallest H. proximum caught by the trawldo not regularly migrate. Individuals of this

100

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I­ZILlU

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408

CLARKE: ECOLOGY OF LANTERNFISHES

FIGURE 4.-Cumulative size-frequency curves for HYI~{)­~hllm proxilllllm collected at different depths in theaPPer layers at night. Top: Cobb trawl samples takenn new moon during March 1971; depths of tows and7~mber of individuals were: 25 m, 14 (A); 50 m, 150 (B);Sa m, 276 (C); and 100 m, 83 (D). Bottom: Isaacs-Kidd:, 3m(PAles taken at full moon in September 1971 at 20 m,~ ); 50 m, 30 (B); 75 m, 48 (C); and 100 m, 43 (D).

size were, however, taken in shallow nighttows during July 1970 and March 1971.

H. proximum appeared to avoid the IK atnight more during new moon (see below) andWas sampled best by the CT and by the fullmoon IK series. Both of these series indicatedsimilar depth distribution but different trendsin size composition with depth (Figure 4). Inthe CT series the curves for 75, 100, and 125 mwere all similar and differed significantly fromthose at 25 and 50 m. Over 50% of the deepercatches were less than 30 mm, most about 20mm. In the 25- and 50-m catches, which alsodiffered significantly from each other, only 30%and 10% individuals were under 30 mm. Com­parison of curves from IK catches at new moonduring December and March 1971 also showedsignificant differences, with only the larger fishoccurring above 50-60 m and smaller onespredominating deeper.

In the September 1971 series, the size­frequency curves for full moon tows at 25 and50 m differed significantly from each other and

from the curves at 75 and 100 m. The catchwas almost all < 15 mm at 25 m, 20-30 mm at50 m, and over 30 mm for the deeper tows. Infull moon tows during September 1970 at 80and 100 m, the size-frequency curves differedsignificantly and indicated that most fish at 80 mwere <30 mm and most at 100 m were >30 mm.

In the daytime during September 1970, size­frequency curves for H. pro:rillluill differedsignificantly, with a greater proportion ofjuveniles in shallower water. In March 1971and June 1971, similar nonsignificant trendswere present. All data indicated that individualsover 40 mm rarely occurred above 600 m.

At new moon during September 1971, highcatches were made at 125 and 150 m with afew at 80 m (Figure 2). At full moon, catcheswere high between 20 and 100 m with practicallynone deeper. The calculated total for full moonwas 3 x that for new moon, and the calculatedsize-frequency curves indicated that new moontows had missed most of the larger fish. Thesedata, combined with the changes in size com­position with depth, indicate that the smallerfish occur about 75-100 m deeper at new moonand the adults about 25-50 m shallower at newmoon. The latter, however, appear to avoid theIK much more at new moon. Consequently,H. proxilnulll was not sampled well by mostIK night series.

The CT data also indicate that avoidance ofthe IK by larger fish was substantial. Thecalculated total for the CT series was 14.5 xthat for the March 1971 IK night series, andcalculated size-frequency curves indicated muchlower proportions of larger fish in the IKcatches. The greatest difference was at 75 mwhere the IK caught only 5 as opposed to theCT's 276. Comparison of individual size­frequency curves indicated that some fish under20 mm probably passed through the CT'smeshes. Thus avoidance of the IK by larger fishis even greater than indicated by comparisonof the calculated totals.

The calculated totals were much larger forthe day series in March 1971 and June 1971, butday and night totals were close for September1970 when the night tows in H. pro:rilllum'sdepth range were taken during full moon. (Fewwere caught in December 1970 during day or

40

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100

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409

night.) Both of the September 1970 estimateswere close to that for full moon in September1971. Thus there appears to be less avoidance ofthe IK during the day than at night during newmoon.

For March 1971, the calculated total fromthe CT series was only about 3.7 X that of theday IK series, and the calculated size-frequencycurves for the two series agreed closely. Thusthe IK appears to sample H. proximum by daybetter than the CT at night. Since day tows andfull moon night tows with the IK appear tosample this species about equally well, the IKmay give better estimates of abundance andsize composition than the CT at full moon.Kuba (1970) found that the IK sampled H.proximum better than the CT in night tows inequatorial waters. Most of his tows where thisspecies was caught were taken near full moon.

The calculated day totals indicated that H.proximum was distinctly more abundant inSeptember and March than in December orJune. The calculated size-frequency curves forMarch 1971 and September of both years weresimilar and indicated that most fish weremature or nearly so. None less than 15 mm werecaught in September or December, but a few10-15 mm were caught in March 1971. Fish12-14 mm long were present in fair numbersduring the June 1971 series and abundant inJuly 1970. This suggests that H. pTOximumspawns principally in spring or early summer.The percentages of mature females with de­veloped ova were highest in March and June butdid not differ significantly from the other values.

Hygoph'"l1 reillhttrdti

H. reinhardti was less abundant and occurredslightly deeper than its congener, H. proximum,but the data indicated that similar samplingproblems existed. So few H. reiuhardti werecaught in the March 1971 IK series that it wasimpossible to make quantitative comparisonswith the CT data. but it appeared the IKmissed substantial numbers at 75-100 m andsampled about as well as the CT in deeperwater. Though catches were low during bothSeptember 1971 series, the full moon seriescaught overall higher numbers and indicated a

410

FISHERY BULLETIN: VOL. 71. NO.2

shallower night depth than the new moon series.In all four regular series, catches of day towswere generally higher than those of night tows.

Size-frequency curves from the CT seriesindicated no trends in size composition withdepth. The curves for IK tows in September1970 at 150 and 195 m differed significantlywith few fish >20 mm at 195 m and few <20mm at 150 m. Three-day tows in September1970 showed no individuals over 20 mm at 520m and most over 20 mm at 775 and 900 m. Therewere no obvious seasonal changes in abundance.Juveniles ( < 15 mm) and females with developedova were present at all seasons.

MyctophlllJl spp.

Three species of M!Jctophull/-M. ititidululII,M. obtusirostrulI/," and M. spii/osuill-ap­parently occur at or near the surface at night.They were regularly dipnetted at the surfaceat night, but few were caught in the trawls,even in preliminary tows at 10-m depth. In­dividuals considerably larger than the trawl­caught specimens were frequently taken by dipnet. These species are relatively solid-bodiedand are probably strong swimmers. Theyprobably avoid the trawl easily in the processof avoiding the ship itself.

The few day catches of these species weremostly from 500 to 800 m but may well havebeen due to contamination. These species aredistinctly countershaded, and in life the uppercolor is quite blue, suggesting that they occurat shallow, well-lighted depths during the daywhere they can avoid the trawl. Nevertheless,the rarity of even small individuals in the trawlcatches indicates that none of the three wereabundant.

MyctophlllJl selelloides

At night, small «30 mm) M. seleuoides weretaken mostly between 50 and 100 m. The largerfish were below 100 m and mostly around 150 m.Only three were taken during the day, one by

"Myctophl/ln "btl/sirostrum is the correct name forthe species ~alted M. Imlllchygnllthl/111 by Nafpaktitisand Nafpaktltls (1969) and others (8. G. Nafpaktitis,pers. comm.).

CLARKE: ECOLOGY OF LANTERNFISHES

CT at 300 m and two by IK at 500 m. The lownumbers of juveniles as well as adults in thetrawl catches suggest that rarity of M. selelloideswas not due to avoidance. Small fish (8-13 mm)were caught only in March and June 1971,indicating that this species spawns locally­probably in the spring.

SY1Jlbolophorus etJer1Jlanni

The larger individuals of S. eveJ'mallili areundersampled by the IK. Kuba (1970) showedthis in Equatorial Pacific waters. During March1971 CT catches were 28-35/tow as comparedwith 1-2/tow for the IK at similar depths. TheCT tows indicated that S. evermal/IIi was mostabundant at 50-100 m at night and showed nodifferences in size frequency with depth. On oneoccasion, November 1969, several large indi­viduals were dipnetted at the surface.

Day tows with the IK caught no individualsabove 500 m and most between 600 and 800 m.A few substantial catches, 6-8/tow, came from800 to 900 m. There was some indication thatfish <20 mm do not regularly migrate; par­ticularly in September 1970, most of the shallowcatches were larger fish, and most small in­dividuals were taken in night tows around800 m.

Centrobrtl11chus choe1'ocephalus

Most catches of C. choerocephalus were at550-650 m during the day. The night depthappeared to be between 100 and 200 m for bothII{ and CT samples, but on one occasion,September 1969, seven individuals were dip­netted at the surface.

Lobianchia gewelliwi

L. gemello1'l was never taken in large num­bers. At night, all individuals caught above100 m were < 25 mm, and those over 40 mmwere caught only below 150 m. The CT series,which caught fair numbers, also showed thistrend with significant differences in size­frequency curves. Substantial catches of largerfish were made as deep as 300 m at night, butthere were no differences in sex ratio or

percentage of ripe females between deep andshallow catches of adults.

There was no evidence that this speciesavoided the IK better than the CT nor thatthere was a day and night difference in avoidanceof the IK. Also the depth distributions andabundances in full and new moon were notgrossly different.

The pooled IK data indicated that juveniles,<25 mm, were most abundant in the summer(July 1970, June 1971) and least so in December1970. Curiously, there were few juvenilespresent in September 1970 but many in Septem­ber 1971. Adults were most abundant in March1971 when few juveniles were present.

Lobia1/chia IIrolawpa

Only two juvenile L. Ilrolompa were taken inthis study. This species is apparently nearshoreor epibenthic. Adults (48-99 mm) have beentaken in bottom trawls at depths between 124and 190 m at night (P. J. Struhsaker, pel's.comm.).

Diaphlls berte/selli

The identity of this form with the AtlanticD. bel'telselli is not certain since only one largeindividual was taken. The species was caughton only two occasions. Many were taken in theMarch 1971 series including 70 in one CT towat 125 m at night. One each was taken at 300and 400 m with the CT during the day suggest­ing that this species has a shallow day depth.All March 1971 specimens were between 17 and31 mm-most between 17 and 25 mm. The onlyother individual taken was a 38-mm specimenfrom 100 m at night during the July 1970series.

Diaphlls "glandulifer"

The form designated here as D. "glandulifer"appears to be an undescribed species (R. L.Wisner, pel's. comm.). Gill raker counts weremostly 8 + 1 + 15 - 16, lower than those forD. gla mllllljel' from the Western Pacific (Wisner,see footnote 3). Accessory luminescent tissueoccurred regularly in specimens over 30 mm

411

at POL, VLO, SAO-3, Pol, and Prc-4. In 8 outof 20 specimens over 50 mm, there was acces­sory tissue at PO-4, V03, or both.

Only small «20 mm) D. "glandulifer" werecaught above 150 m, the larger individualsbeing around 200 m and deeper at night. Thisspecies was rare at all seasons, and mostspecimens were either in a 27-39 mm group orover 45 mm. Catches of a few less than 20 mmsuggest that this species may occasionallyspawn in the area.

Diapblls scblllidti

There was no indication that any sizes ofD. schrn'idti sampled by the trawl did notregularly migrate to the upper layers at night.There were significant differences in size­frequency curves from different depths at night.The number and percentage of juveniles «25mm) were greatest around 25 m. The number oflarger fish was greatest at 50 m, but thepercentages of small and large fish wereroughly equal. At 75-80 m most or all theindividuals were larger. Only the day samplesfrom March 1971 were spaced closely enough tosuggest that there were similar size-frequencychanges within the day depth range.

Because D. schmidti occurred over arelatively narrow depth range during the dayand was frequently caught in only one towper series, it was impossible for some seriesto assign realistic weighting factors for calcula­tion of total numbers. However, the calculatednight size-frequency curves agreed closely withthose of the day samples.

The calculated size-frequency curves for CTand IK in March 1971 agreed quite closely, butthe calculated total for the CT was 15 x that ofthe IK. The difference in totals was due to rela­tively much greater catches by the CT at 75and 100 m. The CT caught only 1.7 and 6.3 xthe IK at 25 and 50 m, but caught 65 and 45 xmore at 75 and 100 m, respectively. The pairsof individual size-frequency curves at 25 and50 m differed significantly and indicated thatthe IK caught more larger fish, while the curvesat 75 and 100 m from the CT did not differ fromthose of the IK at 80 m. Since both large fishand juveniles occurred shallower and only

412

FISHERY BULLETIN: VOL. 71, NO.2

large fish deeper, it appears that the CT under­sampled larger fish in shallow zones and theIK undersampled them in deeper zones.

The full moon samples indicated that peakdepth was around 75 m and caught none at20-50 m where new moon tows indicated maxi­mum abundance. The calculated total for fullmoon was about three-fourths that of newmoon, and the calculated size-frequency curvesindicated a somewhat larger proportion ofjuveniles during full moon. Thus D. schrnidt'ioccurs deeper at full moon, and larger indi­viduals may avoid the net more frequently.

D. schmidti apparently spawns in late springand summer and matures in about 1 year. InJune 1971, the population consisted mostly ofeither juveniles or adults with few individualsbetween 20 and 30 mm. Both juveniles and 20­to 30-mm individuals were present in September1970 and 1971. In December 1970, almost allwere 20-30 mm, and in March 1971, almost allwere over 30 mm. Percentages of ripe femaleswere significantly higher in the March andJune 1971 series than in the September 1971series. Practically none were mature in De­cember 1970.

Diapblls jragilis

D. jragilis was caught most frequently atnight at 25-50 m (new moon) and 100-125 m(full moon). The CT catches were low and didnot indicate that this species was avoiding theIK in appreciable numbers. D. jragil'is wasdistinctly more abundant in September 1970and 1971 and least so in December 1970 andMarch 1971. It is one of the dominant speciesof myctophids in Pacific equatorial waters(Hartmann, 1971) but its presence in lownumbers near Hawaii cannot be ascribedentirely to immigration. Fair numbers of small«20 mm) individuals were caught in Septem­ber, suggesting that some spawning occurs inthe summer.

Diaph/ls rolfboli1Ji

Pooled size-depth data indicated that D.roljIJolin'i <20 mm occurred principally above100 m, those 20-45 mm around 100 m, and

CLARKE: ECOLOGY OF LANTERN FISHES

those over 45 mm below 125 m. D. TOlflJolilliwas caught in roughly similar numbers at allseasons; however, trends in size compositionWere evident from the pooled data. In July1970, September 1970 and 1971, and June1971, 50% or more of the catches were <20 mm.In December 1970, almost all were between20 and 40 mm, and in March 1971, both CT andIK catches were mostly between 45 and 55mm. Individuals over 55 mm were present inlow but consistent numbers all year round andmay be more than 1 year old.

D;,lphllS elllce1Js

D. elucells showed definite changes in sizecomposition with depth at night. Size-frequencycurves from the CT series in March 1971differed significantly. There were two sizegroups present at that time, 32-47 mm and49-63 mm. The smaller size group made up80%,73%, and 20% of the catches in tows at 50,75, and 100 m, respectively. The number ofsmaller fish was roughly equal in the twoshallower tows and those of larger fish compar­able in the two deeper ones. In September 1971,fUll moon, 98 individuals 7-11 mm long werecaught at 20 m, and 12 of 13-17 mm at 50 m.Few of these sizes were taken in deeper waterwhere some larger individuals were caught. Notrends could be recognized in the daytimesamples.

The pooled IK data indicated that D. elucellssPawns in late summer and reaches maturityin about 1 year. In June 1971 and July 1970,most individuals were over 40 mm. In Septem­ber 1970 there were two distinct size classes,10-13 mm and over 46 mm with practicallynone in between. In September 1971, new moon,there was a broad group 10-29 mm and a fewOVer 50 mm. In the full moon series, there wasa distinct group at 7-11 mm, a smaller group at12-18 mm, and practically none larger. InDecember 1970, 70% were 23-41 mm, and inMarch 1971, the two size groups mentionedabove were present in both IK and CT data.

D;,lpIJl/S sp. A and B

D. sp. A and B are superficially similar to

each other and resemble most closely D. mol/isfrom the Atlantic, but both appear to be distinctspecies. All but the smallest specimens can bereadily distinguished. Species A has a roundedopercular margin, and the eyes of Formalin­preserved specimens are distinctly green. Inspecies B, the upper opercular margin is dis­tinctly angular or hooked, and the eyes areyellow-white. The counts for fully developedgill rakers were usually 4 + 1 + 10 for speciesA and 5 + 1 + 10 -12 for species B. Species Bmatures at and reaches a much larger sizethan species A.

Species A was taken in abundance (> 10/tow)only 13 times, and size-frequency curves couldbe compared unly for samples from the July1970 and March 1971 CT series. These bothindicated significant differences with the smallerfish occurring in shallower water. The onedaytime comparison possible, in September1970, showed no difference between tows at 500and 575 m. There was no evidence that anysizes did not migrate regularly.

There were no obvious differences in abun­dance and size frequency between day and nighttows. Two CT tows in March 1971 caughtspecies A similar in size composition to thetwo positive IK tows, but the CT catches werehighest at 50 m and substantial at 75 m whereasthe IK indicated a peak at 25 m and only a fewat 50 m. At new moon, the depth of highestcatch was at 45 m and at full moon was at75 m. The catch at new moon was about 5 xthat at full moon, indicating greater avoidanceas well as depression during full moon.

Abundance was distinctly higher duringJuly 1970 and September 1970 and 1971 withthe largest proportion of small fish at thesetimes. Abundance was distinctly lowest inJune 1971 and almost all were adults. Thesedata suggest that species A spawns in thesummer and reaches maturity in about 1 year.However, the condition of the ovaries did notindicate a restricted spawning season; 89-100%of the mature females were ripe at all seasons(Table 2).

Only the juveniles « 15 mm) of species Boccurred above 100 m. Abundance was highestin June 1971 and most of the catch was juveniles

413

at that time. Juveniles were also present inJuly 1970 and September 1971.

Diapblls aJlderseJli

At night, adults of D. QlldCI'SClli occurredmostly around 200 m whereas the juveniles(< 13 mm) were found only around 100 m. D.QlldcrsClli had one of the shallowest day depths(Table 1) and most limited migrations of allthe species considered, the adults covering onlyabout 100-200 m each night. In all series butMarch 1971, catches were mostly small juvenilesand adults, but in March 1971 both CT and IRtows indicated the population was composedentirely of intermediate-sized fish. Apparentlythis species spawns over the greater part of theyear.

Diapblls bracbycep/:htflls

Numbers of D. bl'QchyccphQlas were quitelow except in September 1970 when largenumbers of juveniles «20 mm and most < 15mm) were collected around 50 m at night. Thelarger individuals caught at 150-200 m weremostly females. Five of the 10 larger males(over 40 mm) taken at night were caught below300 m, suggesting that the larger males migratelittle or not at all. Presence of 9- to 12-mm fishin June, July, and September and their absencein December and March indicated that D.brachyccphalus spawns in the summer. The Juneand September samples included both very smalland adult fish; the March samples were mostlyintermediate sizes (15-30 mm) suggesting thatthis species reaches adult size within 1 year.

Di'Ipblls adeJlo/llIIs andD. cbrysorbYllcblls

D. adcl/omas and D. chl'ysol'hYl/chus are bothapparently epibenthic and associated withshallow water. D. chl'ysorhyllchus (54-98 mm)is frequently taken in bottom trawls at 75-190 mat night and D. udc/IO/llas (41-153 mm) at180-185 m at night. Both are taken down to500-600 m during the day (P. J. Struhsaker,pers. comm.). Individuals of the sizes takennear the bottom were rarely caught in mid-

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FISHERY BULLETIN: VOL. 71. NO.2

water. The D. adcllomus were all taken duringthe day by IK. Thirteen of the D. chJ'ys01'hYII­chus collected were larger fish (56-84 mm).These were taken sporadically at all seasons,eight of them in the upper layers at night. Theremaining 21 specimens were all 11-17 mmand all taken in the upper layers at night duringthe September 1971 series, 11 of them in onetow at 80 m. This suggests that this speciesspawns in late summer and that the young arepelagic. Unless substantial numbers of adultsof these species are able to avoid both CT andIR, it appears that the larger fish caughtpelagically were wanderers.

N ofofycb JI liS l"tfdi l'iae

Significant differences in size-frequency curvesfrom several series indicated that smaller N.valdiviac occurred higher in the water column.In both September 1970 and 1971 series, thecatch at night at 80-100 m was almost totally< 15 mm and at 115-145 m mostly over 20 mm.In other series, single pairs differed significantly,but trends were not as obvious because most ofthe fish were of one size class. Two day tows inSeptember 1970 at 525 and 725 m also differedsignificantly with 60% of the fish < 20 mm inthe shallow tow and over 90% > 20 mm in thedeep tow.

In September and December 1970, nightcatches of N. valdiviac near the day depth werelarger than that expected from contamination.Substantial catches were also made in theupper layers during these series. In September1970, roughly 70% of the population remainedat depth. There were relatively more largerfish in the nonmigrating fraction (Figure 5).In December 1970, roughly 50% did not migrate,but there was little difference in size composi­tion between shallow and deep catches. Therewere no significant differences in either sexratio of mature fish or ripeness of maturefemales between the shallow and deep nightcatches. There was no indication that anysizeable fraction of the population did notmigrate in either March or June 1971.

The calculated totals for day and nightagreed fairly closely and indicated no differen­tial avoidance. Likewise, the calculated size-

CLARKE: ECOLOGY OF LANTERN FISHES

FIGURE 5.-Cumulative size-frequency curves calculatedfor NOlolyclullIs valdiviae (left) from samples takenduring September 1970 in the upper layers at night (A),near the day depth at night (B). and during the day (C)·and (right) from samples taken throughout the wate;~?lumn in September 1970 (A). December 1970 (B),"'arch 1971 (C). and June 1971 (D).

with developed ova for March and June weresignificantly higher than those for Septemberand December.

No individuals of L. luminosa over 32 mmwere caught above 100 m at night, but a few,16-24 mm, were taken shallower. The restof the catches, of both large and small fish,were mostly between 150 and 250 m. Five fish,16-18 mm, were taken during the day at 525­550 m, but most day catches of all sizes werebetween 650 and 750 m. In June 1971 andJuly 1970, the catch was almost exclusively< 25 mm fish; in September these small fishstill predominated but there were also several25- to 40-mm individuals caught. Only onespecimen was caught in December 1970, andin March 1971, 80% of the catch was over 35mm. None of the individuals captured weremature, suggesting that the adults are largerthan the maximum size collected and likelytake more than 1 year to mature.

(

50

20 10 20STANDARD LENGTH (mm)

10

f­ZWUa:w0-

w 50>f=<i-':::l~:::lU

100

frequency curves were quite similar. Theagreement of numbers and curves was closestfor June 1971. This indicates that since thenight data were all from shallow tows, most, ifnot all, of the population migrated at that time.There was little point in comparing CT-IKdata since most fish were apparently smallenough to pass through the coarser CT meshes.

The new moon series in September 1971indicated the population was mostly between75 and 145 m while at full moon it was between130 and 190 m. The calculated size-frequencyCUrves agreed closely, but the new moon seriescalculated total was about 3 X that of full moon.This suggests that N. valdiviae occurs about50 m deeper and avoids the net better duringfUll moon. The latter seems questionable sinceeven adults are quite small and unlikely toavoid the trawl. Although full moon tows below200 m in other series made no substantialcatches, it is possible that some of the popula­tion was below the deepest depth sampled duringthe September 1971 full moon series.

Both day and night calculated totals indicated~hat N. valdiviae was distinctly most abundantIn September and least so in March; the valuesfor December were slightly higher than thosefor June. Both September series indicated largeproportions and numbers of smaller « 15 mm)fish. A few small fish were present in Marchand June, but in December none were < 17 mm(Figure 5). The percentages of mature females

L/lllp"dell" /I ropb"os

L. u1'ophaos was caught rather sporadically;only one each was caught at night in Septemberand December 1970, and none during the dayin December 1970 or June 1971. All sizesappeared to be present throughout the rangesgiven. One fish 18 mm long was caught inDecember and several <30 mm were taken inMarch, June, and July. Otherwise, most of thefish were 35-65 mm with a few individuals over90 mm. One ripe female, 98 mm, was collectedin March.

'1'"" IIi II gicbtbys h"tbypbilm

T. bathllphilu8 was taken regularly between600 and 1,000 m and occasionally deeper bothday and night. Highest catches were between700 and 800 m. It was the only myctophidwhich definitely did not migrate. Size composi­tion of the catches was roughly similar at allseasons with most individuals 30-60 mm long.

415

FISHERY BULLETIN: VOL. 71, NO, 2

T,WI/i1/gicbtbys lIlil/illlllS NUMBER I~ 105 m3

W ~ W W ~ W W 00

400

EJ:I-0.. 600w0

800?----II

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II

II cI

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FIGURE 6,-Depth-abundance profiles for LumpullyClllsniKer from samples taken by Isaacs-Kidd trawl duringJune 1971 (left) and December 1970 (right), Nightsamples are designated by solid circles connected bysolid lines; day samples by open circles and dashedlines. Numbers collected were adjusted to a 2-hr towingtime with volume filtered of ca, 105 m3 •

juveniles at depth at night. The discrepanciesfor June 1971 were principally due to anexceptionally large catch of 30- to 36-mm fishat 140 m at night.

L. lIiger, especially the larger individuals,apparently avoided the CT more than the IK.The ratio of CT to IK catches was low (1.2-5.8)for all depth pairs except at 100 m where theCT caught 18 to only 1 in the IK. The calculatedtotal for the CT was only 2.3 X that for theIK tows above 200 m. The individual size­frequency curves were significantly differentin three of four pairs but not consistent indirection. The calculated size-frequency curvesindicated that the CT caught lower percentagesof 50- to 70-mm individuals.

During the new moon series, L. lIigcr wascaught at 145 and 165 m-the deepest samples,but at full moon none were caught. It is notknown whether all of the population occurredbelow 190 m, the deepest depth sampled at fullmoon, or whether there was increased avoidance.

Ul1l1Ptl11yctllS niger

Other reports, e.g., Davy (1972), have statedthat T. minimus does not migrate, but all nightcatches in this study were well above the daydepth range. Individuals 20-30 mm long were 200

caught between 150 and 250 m at night andlarger fish between 200 and 400 m. None weretaken in night tows below 475 m. Of 32 fishcaught in March 1971, 27 were 20-24 mm andonly 1 was over 50 mm. In other seasons, allwere over 30 mm, and most over 50 mm,suggesting that T. minimus spawns principallyin late winter or early spring. Too few maturefemales were taken to correlate gonad ripenesswith the changes in size composition.

Most L. niger less than 25 mm long weretaken at depth both day and night, indicatingthat the majority of the smaller fish do notregularly migrate. In December 1970, noindividuals under 50 mm were caught in theupper layers, and large catches with about 50%larger than 50 mm were taken near the daydepth at night (Figures 6 and 7). The matureindividuals taken in deep night samples did notdiffer from those of shallower samples in sexratio or percentage of ripe females. Smallerpeaks at depth during the night were presentduring other series, but catches of fish over25 mm could not be discriminated fromcontamination.

In the upper layers at night, the size­frequency curves from catches above 150-165 mwere usually significantly different from thosein deeper tows (Figure 7). Few individualsover 50 mm were caught above 165 m, andbelow 200 m, 50-100% of the catches were over50 mm. Similar stratification by size was evidentin some day series and suggested, nonsignifi­cantly, that individuals less than 50 mm rarelyoccurred deeper than 750 m.

The calculated totals for day and night agreedwell for all but the June 1971 series (daywas 1.6 x night), The calculated size-frequencycurves differed greatly for the September 1970and June 1971 series. The difference for Sep­tember 1970 may well have been due to missing

416

CLARKE: ECOLOGY OF LANTERNFISHES

FIGURE 7.-Cumulative size-frequency ~urves for samplesof Lampanyc/lls niger collected at different depths atmght. Top: December 1970-two samples from 750 mof 119 and 174 individuals (A); 320 m, 10 (B); and2(50 m, 39 (C). Bottom: June 1971-140 m, 60 individuals3A.); 165 m, 12 (B); 185 m, 41 (C); 260 m, 14 (D); and00 m, 25 (E).

. The name Lampanyctus lIiger, used above,Illcluded both individuals with weakly developedpectoral fins and those without pectoral fins.Recently, M. A. Barnett informed me that, inSPecimens collected north of Hawaii, there aredifferences in other features which correlate

The calculated totals indicated for both dayand night series that L. niger was most abundantduring December 1970; the figures for otherseries were all similar and about one-half ofthose from December 1970. Except for slightlyhigher percentages of smaller «40 mm) fish inDecember and September 1970, there were nodistinct differences in the calculated sizefrequencies. The percentages of mature femaleswith developed ova for both December 1970and March 1971 were significantly higher thanthose for June 1971 and September 1970.Together these data indicate that L. nigersPawns principally in the early part of the yearand that most of the juveniles are recruitedto the trawlable population by December.

NOTE (Added in press)

with the presence or absence of pectoral fins.All of our specimens have been reexamined and,regrettably, there appear to be at least twoforms present. The taxonomic status of theseforms cannot be evaluated. A world-widerevision of species of the Lampanyctus niger­ater-achints complex will be necessary to fullyelucidate the problem (cf. Nafpaktitis andNafpaktitis, 1969). Consequently, the text abovewas left unaltered, and the following supple­mentary data is offered here. The latter must beregarded as tentative since it was impossibleto identify all specimens with certainty due todamage during collection.

Roughly one-half the specimens have nopectorals. These, designated as Form A, alsodiffer from the others in that the PV02 photo­phore is well separated from PVO. and abovethe level of P0 4 • The SA03 is usually posteriorto AOalo and AOa + AOp is 5-6 (rarely 4)+ 6-7 (rarely 8) = 12-13 (rarely 11). FormA appears to reach maturity at about 57-58mm and reaches a maximum size of 74 mm.

In the remaining specimens, the pectoralfin was variously developed but always present.The PV02 was closer to PVO. and at or belowthe level of P0 4 • SA03 was usually anterior toor above AOa•. The majority of these had AOcounts of 5(4) + 6(7) = 11. These, Form B,reached maturity at about 70 mm, and themaximum size was 84 mm. Among the speci­mens with pectorals, the eleven largest indi­viduals (85-125 mm) and about two percentof the smaller ones had higher AO counts­5-6 + 6-7 (rarely 8) = 12-13 (14). None ofthese larger fish were mature, suggesting thepresence of a third form, Form C.

Thus there appear to be two very similarforms that were common and roughly equal inabundance and a larger, much rarer form. Thedepth distributions, migrations, size-depth pat­terns, and seasonal changes of Forms A andB are quite similar and essentially as describedabove under Lampa lIyctU8 Iliger. The co­occurrence in abundance of two such similarforms contrasts with the patterns of most otherclosely related species. Further investigationof not only the taxonomic status, but also thegeographic distribution of these forms will benecessary to determine if, as with the Hygoplw 11/

80604020

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50

50

>­zwU0::W0.-

W>~SIOO::;;::>u

100

417

FISHERY BULLETIN: VOL. 71, NO.2

50

NUMBER /~105m3

20 40 60

FIGURE S.-Estimates of abundance of LumpwIYC(IISlIobilis at different depths at night during March 1971from samples with the Cobb trawl (CT) (solid circlesand lines) and Isaacs-Kidd trawl (IK) (open circles.dashed lines). CT catches were adjusted to the samevolume filtered by 2-hr tows with the IK, ca. 105 m3 .

150

100

200

J:l­e.wCl

L. Iwbi/is was probably about twice as abundantas the IK tows indicated.

At new moon in September 1971, L. lIobilisoccurred between 60 and 125 m with peakabundances at 75 and 100 m. At full moon, theonly individual caught was from 190 m. Towsbelow 200 m taken during full moon in' otherseries made no substantial catches. Thus thedifference between the new and full moon serieswas probably due to greatly increased avoid­ance at full moon.

There were no gross seasonal differences inabundance or size composition apparent fromthe IK data except that L. }wbilis may havebeen slightly less abundant in June 1971. Small«25 mm) fish were present in comparable

\numbers in September 1970, December 1970,and June 1971 (the proper depth zone was notadequately sampled in March 1971 day ornight).

With the exception of a 78-mm individual,all ripe females were over 97 mm and wererarely caught-once in September, once inMarch, and twice in June. The presence ofjuveniles indicated that spawning regularlyoccurs in the area, and the presence of immaturesizes in fair abundance suggests that adultsshould be more abundant than catches ofeither IK or CT indicated. It seems likely thatthese larger fish avoided both trawls in sub­stantial numbers.

LUI/pm/yell/s llob;l;s

spp., Hawaii is near the edge of their ranges.Little can be said about Form C; it appears tohave a depth distribution and migration patternsimilar to those of the other two.

L. nobilis apparently does not begin migratinguntil about 25-30 mm long. A few small fishwere taken in shallow tows at night, but mostwere taken at 625 and 750 m at night duringSeptember and December 1970. The absence ofsmall individuals in deep night tows duringMarch and June 1971 was probably due towidely spaced sampling since substantial num­bers of small ones were caught in day tows then.There was no evidence that other sizes did notmigrate regularly.

There were few instances where enough L.lIo/J'ilis were taken to make comparisons of sizecomposition and depth, but several pairs ofsize-frequency curves showed significant dif­ferences. Individuals <30 mm were mostlyabove 75-80 m at night, and most fish below100 m were >40 mm. All night catches ofexceptionally large individuals (16 of >95 mm)were below 100 m. During the day, catchesabove 750-800 m were almost all <25-30 mm,and the only substantial catches of fish >40 mmwere at 1,150 and 1,200 m in September 1970.The only mature individual caught during theday, 100 mm long, came from a tow at 1,250 m.It is possible that the lower end of the daydepth range was not adequately sampled.

L. lIobilis avoids the IK in substantial num­bers. In March 1971, the CT tows indicated adepth range similar to that of the IK series(Figure 8), except that a large catch was madeat 175 m, below a catch of almost none at 150 m.The size-frequency curve from the 175 m CTtow looked like a composite of the shallowertows. This catch was likely due to excessivecontamination and was disregarded. The cal­culated total for CT was 18 x that for the IKprincipally due to catches at 100 and 125 mwhich were 21.4 x and 24.8 x the IK catchesat these depths. The size-frequency curves forindividual pairs differed significantly and likethe calculated total curve indicated that theIK missed individuals over 40-45 mm. Thus

418

CLARKE: ECOLOGY OF LANTERNFISHES

20 30 40 50STANDARD LENGTH (mm)

LWIPtwyctlls steinbecki

~IGURE 9.-Top: Cumulative size-frequency curves. fordam.Ples of Lampanyctus steinbecki collected at night5Mn.ng .new moon, September 1971, at depths of 80 m,46 Individuals (A); 100 ro, 59 (B, solid line); 125 ro,165 (8, dashed line); 145 m, 49 (C, dashed line); andfr m, 28 (C, solid line). Bottom: Cumulative size­tatquency curves for L. steinbecki calculated from samples(A)7n throughout the water column in September 1970197'1 December 1970 (8); March 1971 (C); and June

(0).

value and the two lowest ones. There were somesignificant differences among the June 1971night samples, but no trend with depth wasevident.

The calculated totals were higher for the dayseries in all cases. The day totals wererelatively highest for the September and De­cember 1970 series (2 x and 1.6 x night totals,respectively) and were probably in part a resultof poor timing of the night samples withrespect to moon phase. For March and June1971 the day totals were about 1.5 x higherthan night. Except for December 1970 thecalculated size-frequency curves for day andnight series were quite similar. Thus all sizesappear to avoid the IK better at night.

The individual CT tows caught from 0.7 to4.5 x their paired IK tows, and there was noobvious trend in differences of the size-frequencycurves. The calculated curve for the CT wasdisplaced slightly to the right of both night andday IK curves for March 1971, but the calculatedCT total was only 3.4 x the night IK total.Apparently L. steillbeck-i avoids the CT morethan the IK.

During new moon in September 1971 thepeak depths were at 80 and 100 m, and at fullmoon none were caught above 120 m. Thecatches at 170 and 190 m at full moon bothexceeded the peak catches at new moon. Thewater column totals were nearly equal, but thefull moon calculated curve and the individualcurves were displaced far to the left of newmoon curves indicating substantially greaternumbers of 20- to 40-mm individuals. The newmoon tows seemed to miss substantial numbersof juveniles; and if large numbers of largerfish occur below 190 m at full moon (there wassome evidence for this from full moon tows inother series), it is possible that full moon towsmay also sample the larger fish better. Theincrease in night depth with full moon, about100 m for the juveniles, was about twice thatobserved for other species.

Both day and night calculated totals indicatedthat L. steillbeclc7: was least abundant in March1971 and present in comparable numbers duringthe rest of the seasons. The calculated size­frequency curves (Figure 9) indicated that 80%of the individuals were immature in September

504030

50

f­zwU0::W0-

W> 20

1'''150~

100

All postlarval L. steillbeclci appeared tomigrate regularly. Within the night and daydepth ranges, the size-frequency curves wereUSually displaced to the right with increasingdepth (Figure 9). The differences were signifi­cant only in September and December whenseveral size classes were present in abundance.In these cases the differences were due tochanges in absolute numbers of both small andlarge individuals, the shallower samples beingcomposed almost entirely of juveniles and thedeeper ones of adults only. Consistent, signifi­cant differences in size-frequency curves of daysamples indicated that adults (> 40 mm)occurred mostly below 850-900 m and fewsmaller fishes occurred at these depths.

The percentages of females among maturefish tended to decrease with depth in the March1971 night samples. The values for samplesfrom 95, 120, 135, 175, and 265 m were 82,63, 64, 55, and 44%, respectively. The onlySignificant differences were between the highest

419

1970, with 50% under 30 mm. In December1970, most fish were still immature, but thepeak size group was 30-40 mm. In March andJune 1971, about 65 and 90% of the fish,respectively, were mature. The percentages ofripe females among mature females were highestin March and June 1971 and were significantlylower than all others in Decemher 1970. ThusL. steinbecki appears to spawn principally inthe spring and summer and to reach trawlablesize by September. Most fish appear to liveabout 1 year.

UlmpmlY ct /IS t ell/liformis

L. tenuiformis differs from L. steinbeclciprincipally in size at maturity and relativepositions of a few photophores. Counts of finrays, etc., for the two species were eitheridentical or overlapping. Individuals over about40 mm could be distinguished by the relativedevelopment of the gonads, but it is possiblethat some smaller, damaged L. tenuiformis wereerroneously identified as L. steinbeclci. Owingto the former's rarity, as evidenced by the fewlarger individuals, any error is almost certainlynegligible.

Only four L. tenuiforrnis were taken atnight, and the larger two of these (120 and 138mm) were taken in tows near the day depths.Thus the night depth range given in Table 2is quite uncertain. L. tenuiformis appearsto spawn near Hawaii; four females (123-138mm) with ripened ova and two small juveniles(28 and 32 mm) were collected.

Triphoturus nigrescens

T. nigrescens < 15 mm were caught only ina night tow at 650 m in June 1971, suggestingthat small juveniles do not migrate. In December1970, high catches of larger fish were madeduring the night both in the upper layers andat the day depths. Calculated totals indicatedroughly 60% of the population did not migrate.Calculated size-frequency curves for shallownight, deep night, and day samples all werequite similar and also agreed closely with thecurve from fish taken in three short night

420

FISHERY BULLETIN: VOL. 71, NO.2

oblique tows from 0 to 300 m. Differences insex ratio and percentage of mature females withdeveloped ova between the deep and shallowsamples were small and nonsignificant.

Large numbers of more than one size classwere caught only in July and September 1970.There were significant differences between size­frequency curves indicating that fish <20 mmoccurred mostly above 50 m at night and above650 m during the day. Adults occurred mostlybelow 50 m at night and below 650-700 mduring the day.

Owing to low numbers in June 1971 and poortiming of shallow night tows in September1970, day and night comparisons could bemade only for December 1970 and March 1971.The day calculated totals were larger in bothseries, 1.3 x for December 1970 and 3.8 x forMarch 1971. The larger discrepancy in March1971 may have been due to missing nonmigrat­ing fish at night. The calculated size-frequencycurves for day and night agreed closely.

The CT tows in March 1971 caught only2.5-4 x the IK tows; the calculated total forthe CT was 2.6 x that for the IK night series.The calculated size-frequency curve for the CTwas nearly identical to both the day and nightIK curves, and most fish were over 30 mm.Apparently T. nigrescens is better able to avoidthe CT, but it is possible that some fish of eventhe larger sizes could have escaped through thecoarser CT meshes.

T. nigrescens appears to have a I-yeargeneration cycle with spawning principally inspring and summer. Abundance was distinctlyhighest in December and extremely low inJune and September 1971 with substantial androughly equal numbers present in September1970 and March 1971. T. nigrescens wasalso abundant in July 1970 with most of thepopulation either adults or <20 mm. In Sep­tember 1970, 65% of the population was 20-28mm with few adults, and in December, 85%were over 25 mm. In March 1971, 85% wereover 30 mm and none <24 mm. In June 1971,the catches were made up almost entirely ofadults or fish < 15 mm. The conditions of theovaries were correlated with the changes insize frequency. The percentages of maturefemales with developed ova (Table 2) were low

CLARKE: ECOLOGY OF LANTERNFISHES

in September and December 1970 and weresignificantly higher in March and June 1971.

The decline in abundance observed for T.nigrescens in June and September 1971 was themost dramatic change observed among all thespecies during the study period. The differencebetween the series in July and September 1970and those of June and September 1971 suggestthat either spawning success or larval survivalWas markedly lower in 1971. The only obviousfactor correlated with this change was a sig­nificant increase in the percentage of femalesamong mature fish in June 1971. Whetherthere was a causal relationship between thetwo changes cannot be determined from the data.

Bolinicbtbys longipes

Apparently almost all B. longipes of the sizessampled regularly migrate. The only indicationof nonmigration was a catch of seven small(12-14 mm) individuals at 650 m during thenight in June 1971; individuals of these sizeswere caught frequently during the day towsbut rarely at night in the upper layers suggest­ing that some small individuals do not migrate.Within each series there were relatively fewsignificant differences between size-frequencycurves of the separate tows. These indicatedthat the smaller fish tended to be found shal­lower at night. Differences between day towsclearly indicated (Figure 10) that few fish lessthan 20 mm occurred deeper than 625 m andfew larger than 30 mm occurred above thisdepth.

In the March 1971 night samples, the per-

100>-zwU0:WQ.

~ 50i=..,...J::l

'"::lU

10 20 30 40 50

STANOARO LENGTH' (mm)

~IGURE. IO.-Cumulative size-frequenc~ curves for samI?les/ Boll/lIeht h.l's IUllgipe.\· collected dunng the day dunngl~n(e 1971 at depths of 560 m, 11 individuals (A); 600 m,

B); 620 m, 21 (e); and 640 m, II (0).

centages of females among mature fish de­creased with depth. The values were 73% at 80m, 59% at 95 m, 32% at 120 m, and 46% at 135 m.The first two values were significantly differentfrom the latter two. Insufficient mature fishwere caught to compare values at differentdepths in other series.

The calculated totals agreed well for the dayand night series, but calculated size-frequencycurves differed for almost all pairs. Depthcoverage was best for the March and June 1971series, and the calculated curves were closestfor the March 1971 series. The curves for theJune 1971 series differed mostly because of agreater frequency and number of small indi­viduals in the day. The numbers caught werequite low for all tows of this series, andinclusion of seven small individuals from a deepnight tow (see above) in the calculations broughtboth the calculated totals and curves into veryclose agreement for the June 1971 series.

The CT tows indicated that peak depth wasat 75-100 m and caught fair numbers of B.longipes at 25-50 m where the IK caught fewor none. The IK peak depth was at 100 m andsubstantial numbers were caught at 125 and135 m where CT catches were relatively low.The ratios of CT to IK numbers were 9.4 and5.6 at 75 m and 100 m, respectively, but only1.1 at 125 m. The calculated CT total was 5 xthat for the IK. The IK and CT size-frequencycurves were similar at 75 m but differed sig­nificantly at 100 and 125 m due to largerpercentages of fish over 35 mm in the CTcatches. The calculated CT curve was displacedto the right also due to higher percentages offish over 35 mm. Thus it appears that the CTsampled B. longipes as well or better than theIK above 100 m, but in the deeper zones theIK gave higher estimates of abundance in spiteof missing some larger fish.

At new moon, B. IO/lgipes was abundantbetween 60 and 125 m and peaked at 80-100 m.At full moon, practically none were caughtabove 130 m and the peak was at 170-190 m.Full moon tows in other series indicated thatfew occurred deeper. The new moon catch at60 m and the full moon catches at 130 and170 m were similal' in size composition; almostall fish were <20 mm. The 190-m curve at full

421

moon resembled those from 125 m and 145 mat new moon. The calculated total for fullmoon was 1.4 x that for new moon and thecalculated size-frequency curves differed con­siderably. Both differences were due to largercatches of 17- to 23-mm fish at full moon. Boththese data and the CT-IK comparisons indicatethat the IK missed some smaller fish in theupper layers at new moon. If these differencesare real, they could in part account for theapparent lower numbers and percents of ju­veniles estimated in night series (see above).

There were substantial numbers of juveniles«20 mm) in the June, July, and Septemberseries with few in December 1970 and practicallynone in March 1971. The percentages of maturefemales with developed ova (Table 2) werehighest in March and June 1971 and significantlylower in December 1970. These suggest thatspawning occurs principally in spring andsummer and that the juveniles have reachedtrawlable size within a few months.

Bolillichthys wprtlltltertllis

No B. 8upralateralis over 53 mm long weretaken above the day depth range. Out of 15such individuals, only 3 were caught duringdeep night tows. These could well have beencontaminants and do not clearly confirm thatthe larger individuals do not migrate. However,out of 50 smaller fish caught at night, 10 werecaught in tows within the day depth rangesuggesting that all sizes may not regularlymigrate. In the upper layers at night, fish lessthan 20 mm occurred between 100 and 200 m,but only two between 20 and 30 mm and noneover 30 mm were caught above 200 m. All sizesappeared to occur throughout the day depthrange.

The pooled IK size-frequency data indicatedthat B. supralateralis spawns principally inlate summer and fall and that it may take atleast 2 years to reach maturity. There weredistinct, well-separated size classes in all butthe March 1971 series where only 11 fish werecaught. Small fish, 12-20 mm long, were mostabundant and made up the majority of thecatch in September and December 1970. Itappeared that this group was represented by

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FISHERY BULLETIN: VOL. 71, NO.2

24- to 35-mm individuals in June 1971. Asecond year class was suggested by size classespresent only in the December 1970 and June1971 series (41-53 mm and 47-59 mm, respec­tively). A few fish larger than 60 mm werecaught in all series and may represent a thirdyear class. The only female with developedova was 88 mm long, almost the largest speci­men taken. It is likely that such large individualsavoid the trawl in addition to being rather rare.

CertlfoJl.:opellls U'tlrlJlingi

The smallest C. warmingi regularly collectedin the trawl do not appear to regularly migrate.At night, individuals 15-19 mm long werecaught both between 20 and 100 m and at600-700 m. In June 1971, when these sizeswere most abundant, about two-thirds of thejuveniles remained at depth. There was noindication that larger fish did not regularlymigrate.

Within both day and night depth ranges thesize-frequency curves differed significantly.Except during June 1971, at night few fishover 40 mm were caught above 50 m and fewsmaller individuals were caught below 75 m.In the June 1971 series, however, large num­bers of 15- to 19-mm fish were caught downto 140 m, throughout most of the nightrange. During the day, few individuals over20 mm occurred at 600-700 m, and largerindividuals occurred principally below 750­800 m.

At night the percentage of females amongmature C. warmingi tended to decrease withdepth. In March 1971, when large numbers ofmature fish were caught at several depths, 89%of the mature fish from 25 to 30 m werefemales. At 50 and 80 m the value was 64%,significantly lower. The value at 95 and 100 mwas 33%, and at 120 m was 31%. Both weresignificantly lower than the values from shal­lower tows. Similar, but nonsignificant, trendswere present in the September and December1970 series. The only day series where suf­ficient numbers of mature fish were collectedat several depths was in December 1970; therewere no trends or significant differences inpercentages of females.

CLARKE: ECOLOGY OF LANTERNFISHES

DISCUSSION

Rare species

Notoscopellfs CtllfdispillOSlfS

6020 30 40 50STANDARD LENGTH (mm)

10

50

N. cuudisphlOSU8 was captured very rarely,but several fish, 20-25 mm, caught in Marchand June 1971 suggest that it may spawn in thisarea or nearby. It is possible that the largerindividuals avoid both the CT and IK and aremore abundant than the collections indicate.

FIGURE 11.-Cumulative size-frequency curves of Ceralo­SCOpe/liS warl/lill/(i calculated from samples taken through­out the water column in September 1970 (A); December1970 (B); March 1971 (C); and June 1971 (D).

but adults were definitely most abundant inDecember 1970 and almost absent in June 1971.

The large numbers of immature fish in March1971 (particularly, a peak at 25-30 mm) suggestthat some recruitment had taken place betweenDecember and March. The size composition ofthe population in June 1971 indicated a spring­time spawning also. The percentage of ripefemales was highest in June 1971, but none ofthe differences between series were significant.It appears that C. warmillgi spawns over a longseason, but principally during the first half ofthe year, and that there are either peaks withinthis season or marked fluctuations in larval andjuvenile mortality.

100

The majority of the species collected wererather rare. Only 19 species were present inmoderate to high abundance and showed strongevidence of spawning in the area. A few of therarer species appear to have primary centers ofabundance elsewhere. The single Diaplllls thetacollected was certainly an expatriate from NorthPacific transitional waters (Paxton, 1967), andfour species are restricted to nearshore waters

Comparison of day and night series wasPossible only for the June 1971 series due topoor timing of the night samples with respectto moon phase in September and December 1970and inadequate coverage in March 1971. Boththe calculated totals and size-frequency curvesfor June 1971 agreed quite closely. Since about85% of the fish in this series were < 20 mm,any differences for larger fish would be difficultto detect, but the other series showed noobvious indications of differential day-nightavoidance.

The CT caught only 4 x as many C. warmillgias the IK at 25 m, but outfished the IK byfactors of 12-14 x between 50 and 100 m. Thecalculated CT total was 7.4 x the IK total;when only fish over 25 mm were included, thefactor was 8.3. The size-frequency curves weresimilar at 25 m but differed significantly forthe deeper tows, the CT catching larger propor­tions of larger individuals. The calculated curvesdiffered similarly, even when only fish over25 mm were included. Apparently, some of thesmaller fish passed through the CT meshes,thus accounting for the differences at 25 mwhere these fish were more abundant, but theCT appeared to sample the larger fishes, par­ticularly those over 35 mm, better than the IK.

At new moon in September 1971, the depth ofPeak abundance was at 45 m, and the majorityof the population was between 15 and 100 m.During full moon, the peak depth was at 130 m,and the population was mostly between 100and 170 m. The calculated total for new moonwas about twice that for full moon, and then.ew moon tows caught slightly larger propor­hons of fish over 35 mm.

The calculated totals indicated that C. wurmill­gi Was present in comparable numbers inDecember 1970, March 1971, and June 1971and much less abundant in September 1970,but the calculated size-frequency curves differedg.reatly (Figure 11). In June 1971, the popula­tion Was about 90% juveniles (14-17 mm), and inDecember 1970, about 60% were over 40 mm with:ew under 20 mm. In March 1971, 70% of theJUveniles were 20-40 mm and in Sel)tember19 '70, most were either under 25 mm or over45 mm. Changes in the numbers of juvenilesaccounted for most of the changes in abundance,

423

(Benthosema fibulatum, Diaphus adenomus,D. chrysorhynchus, and Lampadena urolampa).Diogenichthys atlanticus and Diaphus fragilisare more abundant in Equatorial Pacific waters(Hartmann, 1971). The principal range ofLampanyctus tenuifonnis is not clearly known.

Nineteen of the rarer species-Prot01nyc­tophum beckeri, Myctophum spp., Loweinaspp., Centrobranchus spp., Diaphus bertelseni,D. metopoclampus, D. "glandulifer, " Lampadenaluminosa, L. anomala, Taaningichthys spp.,Bol'inichthys supralateralis, and Notoscopeluscaudispinosus-appear to be typical of centralor equatorial-central waters but are nowherecommonly collected (Bekker, 1966; Nafpaktitis,1968; Nafpaktitis and Nafpaktitis, 1969; Gibbset al., 1971; Wisner, 1971; Davey, 1972). Fiveof these species-Myctophum selenoides, Dia­phus "glandulifer," Lampadena luminosa,Taaningichthys minimus, and Bolinichthyssupralateralis-appear to spawn in the studyarea. Lampadena urophaos, although designatedas a transitional water mass species by Paxton(1967), would appear to belong with the abovegroup. It appears to spawn in this area, and arough comparison of the present study's andPaxton's catch per effort indicates that it ismore abundant near Hawaii.

Avoidance

Although it was not possible to set confidencelimits for the calculated totals and size-frequencycurves, in most species the differences betweenday and night totals were not large enough tosuggest that there was substantially greateravoidance at either time. The exceptions,Lampanyctus steinbecki and the Hygophumspp., were sampled better during the day thanat new moon at night. They also apparentlyavoid the IK better at new moon than at fulland may be sampled equally well by night towsat full moon and day tows.

These results contrast with those of Pearcyand Laurs (1966) off Oregon. They noted sub­stantial differences in day-night avoidanceamong mesopelagic fishes. The differences werein the opposite direction of the few noted in thisstudy; most of their species avoided the netbetter during the day. Pearcy and Laurs used

424

FISHERY BULLETIN: VOL. 71. NO.2

a 6-ft IK, and perhaps the larger trawl used inthe present study sampled fishes relativelybetter during the day.

The IK-CT comparisons show that, as Har­risson (1967) and others have suggested, nosingle net will adequately sample all species.The IK gave higher estimates of overall abun­dance than the CT for many species analyzed,but greatly underestimated the abundance oftwo species, Symbolophorus evermanni andLampanyctus nobilis. The CT sampled theHygophum species better at night during newmoon, but the IK probably samples them aswell or better during the day or during fullmoon at night. Even allowing for escapementof small fishes through the CT meshes, the CTcaught higher proportions of larger fishes ofsome species, e.g., Ceratoscopelus warmingiand Lampanyctus steinbeclci. Neither net ef­fectively sampled the mature sizes of Lam­panyctus nobilis, Lampadena luminosa, andBolillichthys supralateral'is.

There was evidence for some species thatone trawl sampled better at some depths only.The IK appeared to sample Hygophum reiu­hardti and Bolinichthys longipes as well orbetter than the CT at the deeper end of theirnight depth ranges, but the CT sampled as wellor better at the shallower end. For Diaphusschmidt'i and Diaphus species A, the CT appearedto underestimate abundance at the shallowerend of the depth range and caught relativelymore fish at the deeper end. Obviously, moredata are needed since one or two very high orlow catches could have produced these results.

Harrisson (1967) using only roughly com­parable pairs of samples, suggested that alarger otter-type trawl towed at 1 mlsec caughtmore larger fish than an IK towed at 1.5 m/sec.Aron and Collard (1969), however, have shownthat towing speed had an important effect onan IK's estimates of abundance and size com­position for one of the more abundant speciescollected in their study. Kuba (1970) foundthat in the Equatorial Pacific, the IK at 2 mlsecsampled most species' abundance and sizecomposition as well or better than the CT at1.5 m/sec. It would appear that the higherspeed used for the IK tows in this study gave

CLARKE: ECOLOGY OF LANTERNFISHES

a greater overall advantage than the increased"stealth" of the larger CT.

The full-new moon series indicated that mostspecies occurred deeper at full moon and thatseveral avoided the trawl better at full moon.The Hygophum species appeared to do just theopposite. The changes suggest that it is bestoverall to sample the upper 200 m at new moononly. A mixed sampling program can result insome populations being sampled twice and thedepth range and abundance overestimated, ormost of the population being missed andabundance underestimated.

Most species appeared to occur 50-75 mdeeper at full moon. Data presented by Clarke(1970), however, indicate that in clearest oceanwater, the depths of isolumes at full moon areabout 200 m greater than at new moon. ThisSuggests that the fishes occurred at higher lightlevels at full moon and may explain the in­creased avoidance noted then. The data ofBlaxter and Currie (1967) indicate that this isPossible. They observed that the depth of asonic scattering layer was depressed by artificiallight but to a light level about 10 times brighterthan that at which the layer normally occurred.

Intraspecific Variations inMigration

Most myctophid larvae appear to occur in theupper layers (Ahlstrom, 1959). Whether theydescend just prior to or just after metamorphosisis not known, but at least some species do notbegin to undertake regular, extensive diurnalmigrations immediately after metamorphosis.The data indicate that the recently meta­morphosed juveniles of Benthosema suborbitale,Lampanyctus niger, L. nobilis, and Cerato­scopelus warmingi, and possibly Hygophumproximum, Symbolophorus evermanni, andBolinichthys longipes, do not regularly migrate.l\iore thorough sampling of the deeper layers atnight with opening-closing devices may showthis to be a general feature of myctophids.

Nafpaktitis (1968) has suggested that gravidfemales of some myctophids do not migrate.No evidence of this was found. The larger males?f Diaphus brachycephalus and the largerIndiViduals of Bolinichthys supralateralis ap-

peared to remain at depth both day and night,but in both cases data were too few to becertain. In the latter species, there was noclear relation to maturity or reproductivecondition. Most of the "nonmigrating" B. su­pralateralis were immature.

Large fractions of the populations of threespecies, Notolychnus valdiviae, Lampanyctusniger, and T1'iphoturus nigrescens, appeared toremain at the day depth during the night onsome occasions. It is unlikely that the deepnight catches were due to contamination, Le.,encountering aggregations in the upper layerson the way up or down. The numbers caught atdepth during the December 1970 series were inall cases considerably larger than those caughtin short oblique tows made during the sameseries. Also it seems unlikely that patcheswould be encountered only by tows made to thesame depths where the species were found duringthe day. Finally, the day and night calculatedtotals and size frequencies agreed well for allthree species in December. If the deep nightcatches had been contaminants, the night totalswould have been much larger than those forthe day.

There were no obvious differences betweenthe migrating and nonmigrating fractions ofthe populations. The nonmigrating fraction ofLampanyctus niger tended to be smaller andthat of Notolychnus valdiviae, larger in Sep­tember 1970, but there was considerable overlapbetween both fractions of the populations inboth cases. For Triphoturus nigrescens andN. valdiviae in December 1970, both fractionsof the populations were nearly identical in sizecomposition. Thus the difference in behaviorwas not entirely a function of size. There was nocase where shallow and deep night samplesdiffered in sex ratio or percentage of ripefemales. The number of specimens involved wasrather large in all cases, so it is doubtful thatmore data would produce clearer trends or anyexplanation related to the parameters measuredhere.

Most species showed significant differencesin size composition with depth. Symbolophoruseve1'manni was the only species present inabundance for which all sizes appeared to occurthroughout the depth range. In the great

425

majority of species, the juveniles tended tooccur shallower than adults. The trend wasmore obvious in the night samples due to closersample spacing, but probably holds for thedaytime depth distribution in most cases.Hygophum proximum and H. reiuhardti wereanomalous in that at night during new moonthe adults tended to occur shallower than thejuveniles.

The changes in size composition with depthmay be an artifact caused by larger fish avoid­ing the trawl better at lesser better-lighteddepths. However, many small species such asBeuthosema suborbitale, Diaphus schmidti,Triphoturus nigrescells, and Notolychuus val­diviae are unlikely to avoid the trawl even asadults, and the trends with depth were asevident with these species as with the largerspecies. Also the same trends were evidentfrom CT data for species which the CT appearedto sample larger individuals relatively better.Furthermore, avoidance by larger fish wouldonly partly explain the changes noted for manyspecies, Le., the smaller fish were absolutelyless abundant with depth.

The ecological significance of the trends insize with depth is not clear. The juveniles areremoved to some extent from predation byadults, but this is of doubtful significance sinceother predators are probably more important.Possibly the smaller fish are less visible topredators than are the adults in the better­lighted shallow layers. In those species whereadults occur farther below the juveniles in theday than at night, it may be related simply tothe juveniles being unable to make longermigrations. This pattern could be related todistribution of food. It is quite likely thatjuveniles require greater concentrations andsmaller average particle size of food than adults,and optimal conditions for juveniles may occurshallower than for adults.

Sex Ratios

Sex ratios of mature and juvenile fish ofseveral species are compared in Table 3. Thedifference is significant for only one species,Diaphus schmidti, and in that case, the ratiosdid not differ significantly when data for mature

426

FISHERY BULLETIN: VOL. 71, NO, 2

TABLE 3,-Proportions of females amon/l juveniles andmature fish for nine species of myctophlds. Number ofspecimens examined is given in parentheses.

Species Juveniles Adults

Benthosema suborbital£' 0.48 (54) 0.51 (230)HrgopllllnJ prox;mum .58 (67) .46 (192)Diaphlls schmidt; .43 (56) .62 (127)NOlolychltlls valdiviae .50 (70) .45 (402)LampaflycIlls n;Ker .65 (55) .57 (456)Lampallyctus Heillbecki .65 (48) .51 (535)TriphotllTuS lli!?rescens .59 (49) .48 (452)Bo/i/lichth}',,' /o/lKipes .58 (66) .48 (239)Ceratoscopellls wurmillKi .59 (96) .58 (456)

fish from a single sample with a very largeproportion of females was not included. Formost species there was a tendency for higherproportions of females among immatures, butthe figures are suspect in the sense that thedata were not properly weighted to account forpossible trends with depth or season. Legandand Rivaton (1970) have noted opposite trendsin sex ratio with size for three species ofmyctophids. (However, their criteria for separat­ing "larger" from "smaller" fish is not entirelyunbiased and the proportions given for onespecies, BentJwsema simile, do not differsignificantly.)

Given that there may be trends in sex ratiowith size, recognition of trends with depth orseason was made difficult because there wereonly a few series where sufficient numbers ofsimilar-sized fish were captured at severaldepths or several seasons. Thus, significanttrends in sex ratio with depth were observed formature fish of only a few species. Quite possibly,more data would show that these trends are therule rather than the exception. When datawere pooled for all mature fish examined fromeach series (Table 4), some significant dif­ferences in sex ratio were observed. In mostcases one series showed significantly higher orlower percentage of females than the rest withno suggestion of seasonal trends. Again, how­ever, differences in depth composition of thesamples or size composition of the fishes pooledfor a series may have either obscured trends orhave been responsible for the few significantdifferences observed.

Seasonal Trends

In considering seasonal trends, it was assumed

CLARKE: ECOLOGY OF LANTERNFISHES

TABLE 4.-Proportion of females among total mature fish at different seasonsfor 10 species of myctophids. Total number examined is given in parentheses.

Species September December March June

Belllho.\'ema suborbitaJe 0.51 (35) 0.59 (105) 0.42 (90)

Hn.:ophum prOXim1l11l .56 (66) .32 (22) .34 (64) 0.55 (40)Diaphus schmidti .36 (22) .71 (100) .52 (21)

Diaplllls sp. A .57 (81) .32 (28) .52 (27)

NOlo/)'ell,,"s l'uldil-'iae .48 ( 133) .49 ( 141) .23 (48) .48 (80)

Lampall)'ClliS "i~e,. .58 (86) .52 (183) .58 ( 119) .69 (68)Lampall}'C!llS steinbeck.; .42 (99) .55 (40) .63 ( 163) .52 (233)TriphOlurus "igrescen.\' .52 (25) .45 (314) .48 (85) .80 (45)

Bolillichthys [ollRipes .41 (29) .43 (40) .50 (139) .55 (31)CerwlJ.\'copelus warm;u!:; .73 ( 15) .59 (29) .32 (41) .46 (26)

that the same or equivalent populations weresampled on each cruise. Possible changes dueto horizontal advective transport were ignored.Advection rates, especially for organisms whichspend one-half of their time below the surfacelayers, and horizontal gradients in the pal'ame­tel'S measured-abundance, size composition,etc.-are probably low. It seems unlikely thatpopulations which had been subjected to greatlydifferent environmental conditions were advectedinto the study during the periods betweencruises.

The most likely possibility of change due toadvection would be related to seasonal north­south shifts of water masses. Near Hawaii inthe upper layers, water transitional betweenNorth Pacific Central and North Pacific Equa­torial displaces North Pacific Central waterduring the summer. This shift is known to affectthe abundance of skipjack tuna (Seckel, 1969).

The absence of marked changes in speciesComposition and relative abundance of themyctophid fauna suggest that north-southshifts of water masses did not, during the studyperiod, markedly affect populations. Twoexamples illustrate this particularly well.Diaphus schmidti, a species of myctophid whichapparently does not occur much further souththan Hawaii, was consistently taken here inabundance, while a very similar congener,D. ga1'lnanni, which is very abundant from atleast lat. 12°30'N and further south (Hartmann,1971), was never taken. Two species, Dio­genichthys atlant-icus and Diaphus fragi/is,Which are very abundant in equatorial waters(Hartmann, 1971), were taken consistentlybut never in great numbers near Hawaii.

Most species that showed seasonal changes in

size composition appeared to reach maturityin about 1 year. The larger species-Lampadellaspp., Lampanyctlls lIobilis, Boli lIichthys sllpra­lateralis, and Notoscopeills caudispillOSIIS­probably take longer. In many species theadults nearly or completely disappeared atabout the same time that juveniles becamemost abundant suggesting that few individualslive longer than 1 year.

The ages at maturity and life spans of colderwater species of myctophids, e.g., BCllthosclllaglaciale (Halliday, 1970), Stelloln'allchllSleucopsall1'IIs (Smoker and Pearcy, 1970), areconsiderably greater than those suggested herefor tropical species. Murphy (1968) has pre­sented data on epipelagic clupeoid fishes whichshow a marked decrease in age at maturity, thenumber of reproductions, and life span relatedto year-to-year variability in spawning success.He suggests that the latter is directly relatedto year-to-year variability in the physicalenvironment. It is not unreasonable that thesame trend exists for a mesopelagic familythat occurs in both variable high-latitudewaters and in the more stable tropical openocean.

Most species appear to spawn predominatelyin the spring or summer. Primary productionmeasurements taken by S. A. Cattell nearHawaii during 1969-70 indicate that primaryproduction and productivity index are muchhigher during March-June than the periodfrom October to January. Zooplankton pro­duction probably lags behind the peaks inprimary production only slightly. Assumingthat this seasonal pattern recurred during thepresent study, the period of principal spawningfor most myctophid species appears to be timed

427

with respect to the seasonal peak in productionof food.

In many of the abundant species, the seasonalchanges in abundance and size compositionwere quite pronounced. When these were com­bined with size-dependent differences in migra­tion habits, the depth-abundance profile alsochanged with season. Consequently, samplesfrom only one period may give a misleadingpicture of vertical distribution and abundance.This would be particularly true in the tropicswhere, as opposed to longer-lived species athigher latitudes, several different size classesare not often present in abundance at allseasons.

Interspecific Relations

Many species of myctophids, including somecongeners that are very similar morphologically,occur together in the water column yet must beecologically segregated. From this study it ispossible to examine several relevant factors:depth distribution, size range, and size changeswith depth and season. Owing to better data forsome of these aspects for the nighttime, onlynight distributions will be considered. There are,however, some data (Backus et al., 1968Barham, 1970) that suggest that myctophidsare rather inactive during the day and thatinterspecific patterns at night are probablymore meaningful ecologically.

In Figure 12, depth-size patterns are dia­grammed for 16 of the 19 most abundant

FISHERY BULLETIN: VOL. 71, NO.2

species. For each species, a straight line isdrawn connecting the size-depth coordinatefor smallest size-shallowest depth with that forlargest size-deepest depth. Syrnbolophorus ever­manni, which showed no trend, and the Hy­gophus species, which will be discussed separ­ately, have been omitted. Extremes of depth ofcapture and size range have been ignored;consequently, the ranges shown in Figure 12are, in some cases, narrower than those givenin Table 1. The straight lines are of course onlya rough approximation to the actual patternsof size and depth; it is realized that more datawould probably result in polygons for eachspecies.

The species can roughly be separated intothree groups. The first group includes eightspecies whose young occur principally at about25 m and the adults between 75 and 125 m,depending on size, In the second group of threespecies, the pattern is similar except that theyoung occur principally at 80-100 m and theadults down to 150-250 m, again depending onsize. The third group includes four specieswith sharper gradients in size with depth wherejuveniles occur around 50 m and larger fish aremostly between 150 and 200 m. Two of therarer species, Myctophum. selenoides andLarnpadena lurninosa, appear to have patternslike those of the third group. Diaphus andersenihas a depth-size pattern different from any ofthose illustrated, but two rarer species, Taan­ingichthys minirnus and Bolinichthys supra­lateralis, appear to have similar patterns.

10STANDARD LENGTH (mm)

30 50 70 90

~IOO

E

:r:t­e..wCl

200

428

FIGURE 12.-Depth-size profiles (see text) inthe upper 250 m at night for 16 species ofmyctophids: Diaphlls schlllidli (A), Diaphlls sp.A (B), B('llIhos('lIIa .whorhila/(' and Tripho{lIfl1slligr('sc('lls (e), Bo/illicll/hys /ollgip('s (D), Diap/Illse1I1C('1lS (E), Cera{oscopeilis wa/"ll/il/gi (F), La111­

pallyc{lIs I/ohi/is (G), Diaphlls ro/jlJU/illi (H),Diap/lI/s sp. B (I), LWl/pal/ycllls Iliger (J), No/O­/ychl/liS va/dil'ia(' (K), Diaphlls <IIll/ers(' IIi (L),

Lobiallchia gI'I/lI'//ari (M), Diaphlls brachyc('ph­a/lis (N), and Lal/lpal/ycllls s{('il/h('cki (0).

CLARKE: ECOLOGY OF LANTERN FISHES

Within the first two groups, similar sizes ofthe species tend to occur at similar depths. Thedepth-size patterns of four species in the firstgroup-Benthosema suborbitale, Diaphusschmidti, D. sp. A, and Triphotu1'Us lIigre­scens-are nearly identical. Within the thirdgroup, the juveniles co-occur with similar­sized individuals of the first group and theadUlts with larger fish of the second group.

Judging from the seasons of peak juvenileabundance (Table 1) most species in group onehave similar reproductive cycles; large numbersof juveniles were present in the June or Julysamples. Juveniles were present in substantialnumbers also in September for Diaphus 8chmidti,D. sp. A, and Bol-inichthys longipes. D. elucensshowed a peak in September only. Benthosemasuborbitale and Ceratoscopelu8 warmingishowed large numbers ofjuveniles also in March.In group two, Notolychnus valdiviae and thesmaBest Lampanyctus steinbecki co-occur insummer and fall. L. niger, in spite of its apparentlater season of maximum recruitment, is re­cruited at a larger size and co-occurs withsimilar sized L. steinbecki over much of theYear. Thus there is a good deal of overlap intime as weB as depth and size range for theseSPecies.

In general, congeners and closely relatedspecies, except Hygophum spp., have differentsize-depth patterns at night. Within each of theabove groups, there are few congeners, and theco-occurring congeners are rather dissimilar.The four species of group one whose patternsare closest are of three genera, and the twoCongeners, Diaphus schmidti and D. sp. A, arequite different morphologically. Similarly, ing~ouP two, the Lampanyctus spp. belong todIfferent groups within the genus.

. Taan'ingichthys minimus and T. bathyphilusdIffer in that only T. minimus migrates.~olinichthys longipes and B. supralateral'isd~ffer not only in morphology, size, and depthdIstribution but also in overaB abundance. Thetwo most similar Lampanyctus species, L.~teinbecki and L. nobil'is, which were presentIn abundance, have different night depth rangesa~d different sizes at maturity. Among theDtaphus species, closely related or similarSpecies-pairs are distinctly separated even

though most species appear to have similarreproductive cycles with peak juvenile abun­dance in June or September and nearly thesame day depths. D. roljbolini and D. elucel/shave different depth distributions at night. D.sp. A and D. sp. B differ in depth distributionand also in size at maturity. The species-pairof D. anderseni and D. brachycephalus differssimilarly.

The depth-size patterns of the different speciessuggest that closely related species differ intheir responses to physical factors and thatgenera or groups within genera have differentbiological requirementI:'. Strong gradients intemperature, salinity, and light exist in theupper 250 m, particularly for temperature andsalinity between 100 and 250 m. These are themost obvious factors to explain the differencesin patterns of closely related species. Withineach group, however, similar-sized individualsof dissimilar species co-occur under identicalphysical conditions. For them to co-exist, itwould seem that they must be specialized withrespect to biological factors.

A likely hypothesis is that the species withina group have different food preferences. Morpho­logical differences between species within thegroups include many features probably relatedto finding or capturing food; relative size of theeye and gape and the number, spacing, andstructure of gill rakers. Closely related speciesof different groups are often rather similar inthese respects.

The behavior of the HygophulII speciesappeared to be different from that of the othermyctophids. The change in size-depth patternbetween new and fuB moon was unique. Thejuveniles of H. proximum co-occurred withthose of species of the second group at newmoon and occurred shallower than those ofthe first group at fuB moon. The changesin avoidance with moon phase were also uniqueand suggest that the HygophulII species re­sponded to something besides the visual stimulusof the trawl.

The HygophulII species were the only twocongeners that occurred together in evenroughly comparable numbers [see Note (Addedin press) under Ln mpn II!/ct /IS Ilifjcrl. The twospecies are quite similar morphologically. H.

429

)'ei I/lwrdti is more slender and has higher num­bers of AO photophores, gill rakers, and fin rays.There was, however, a great deal of overlap inthese features, and except for adult malesseparation of the two species was the mostdifficult of all species collected. (Indeed, com­parison of Hawaiian specimens with H. proxi­mum from equatorial waters, where H. rein­hardti does not occur, indicated that thespecimens from Hawaii were more like H.reiuhardti in body proportions than those fromthe equator.)

The seeming overlap between these twospecies may be anomalous in that the studyarea is at the edge of the principal ranges ofboth. According to Bekker (1965), H. proximumoccurs principally below lat. 20 0 N and H.reiuhardti above lat. 20 0 N in the central partof the Pacific. Over most of their ranges thesetwo species do not appear to occur together inabundance, and Hawaii appears to lie in thetransition zone between one species and theother.

Importance in the Ecosystem

The estimated total numbers of individualsper 103 m 2 for nine abundant species is givenin Table 5 for each of the quarterly series andthe CT series in March 1971. These numbersare the calculated totals from the best series·(day or night) from each quarter. Using thesame weighting factors, the biomass per 103 m 2

TABLE 5.-Estimated number (individuals/10 3 m2) fornine species of myctophids at different seasons. Numbersare totals calculated (see text) from samples takenthroughout the water column by Isaacs-Kidd trawl OK)during September 1970, December 1970, March 1971,and June 1971 and by Cobb trawl (CT) during March1971.

Number/lO" m2

Species Sept. Dec. March June

IK CT

Belllhosema suborbital£' 23 40 26 20 14Hn:uphu11l proximu11l 26 6 49 14 14Diaphus schmidt; 21 14 19 30 25NoIO/)'e/lIllI.\' \'u/dil'iue 104 68 12 23LampUllyclUS nigcr 57 163 62 9 55U1I11pllll)'ctus steinbeck; 82 75 43 16 81Trip/wIllY/I.\" n;gre.\'('('lJs 45 248 96 7 23Bo/inichthys !olJ/;ipes 58 23 44 24 13Ceru/(Hcope!US H'tlrmillKi 55 176 196 153 155

Totol 471 813 547 273 403

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FISHERY BULLETIN: VOL 71. NO.2

TABLE 6.-Estimated biomass (wet weight in g/103 m2 )

for nine species of myctophids at different seasons. Figureswere calculated by the same method as those In Table 5.

9/10" 2m

Species Sept. Dec. March June

IK CT

BentllOsema suborbital!! 4 11 10 7 1Hygoplwm proximum 19 2 29 11 2Diaplws schmidti 4 3 10 17 4No{o/ychflliS valdivicu! 6 5 1 2La/llpllll)'C!1l5 l1if,:l'r 59 244 102 18 37Lampanyctus steinbecki 34 34 43 11 61Triphoturus niKrescens 5 41 19 1 3Bo/inicJlthY5 /Oll!{ipl'.~ 13 5 30 20 8CerlltoscopelltS wllrmillKi 56 221 103 130 40

Totol 200 566 347 215 158

for each species was calculated and is given inTable 6.

The figures are probably low for severalreasons. Neither IK nor CT filtered with 100%efficiency; Pearcy and Laurs (1966) estimatedthat filtering efficiency was 85% for a 6-ft IKwith coarser mesh than used here. There is anegative bias due to avoidance. Substantialavoidance of either the IK or CT was demon­strated for many species, and some likelyavoided both. This probably affected the biomassestimates more since the larger fish are morelikely to avoid the net. (The CT figures forLampauyctus I/iger are deceptively low sincesubstantial numbers were caught by IK belowthe deepest depth sampled by the CT.) ForMarch 1971, the estimated total number isabout 7% higher and that for biomass about20% higher if CT estimates for Hygophuillreil/hardti and Lampallyctus uobi/is are includedand the higher of the two estimates OK or CT)is used for the other species. It was not possibleto estimate reliably numbers and biomass forthe less abundant species. They amounted toabout 10% of the total numbers caught by thefour quarterly series and would probably in­crease the estimates of total numbers andbiomass by a similar factor.

The low totals in June reflect the fact thatfor most species few adults were present andthe juveniles of the next generation were notfully recruited to the population. Other dif­ferences were largely due to changes in oneor two important species. The peak in totalnumbers in December was due principally to

CLARKE: ECOLOGY OF LANTERN FISHES

high values for Triphoturus nigrescens andLam.panyctus niger, and the peak in totalbiomass then was caused mainly by the largernumbers of L. niger, a large species, and thefact that Ceratoscopelus wannillgi had thehighest percentage of adults at this time. Over­all, C. wanningi and L. niger were clearly thedominant species with respect to both numbersand biomass.

The average number of myctophids per m2

Was about 0.55 and the average biomass wasabout 0.32 g/m 2• These figures are lower thanthose given by Pearcy and Laurs (1966) fortotal mesopelagic fishes in the upper 1,000 moff Oregon-1.5 individuals and 3.6 g/m2 forthe night tows. The total number of the threedominant myctophids off Oregon was aboutO.78/m2 • Analyses of other fishes collected offHawaii is not yet complete, but inclusion ofother groups, particularly the hatchetfishes,CYclothone, and larger stomiatoids would likelyraise the average number and possibly theaverage biomass to values comparable to thoseof Pearcy and Laurs.

Preliminary analyses of the biomass ofother groups of micronekton indicate that mostof the biomass in the upper 250 m at night is inthe form of vertically migrating groups whichare not present during the day and that themyctophids dominate the fauna as a whole. Theonly other important group of verticallymigrating fishes were the gonostomatids whosebiomass, principally from Gonostoma spp., wasabout one-fourth that of the myctophids. ThemYctophid biomass was one to two times thatof the caridean shrimps and about one to fourtimes that of the larger euphausiids, Tll]j.~(!II()P()­da sPp.

The biomass of epipelagic fishes and larvalfiShes over 10 mm was about one-sixth that ofthe myctophids. The figure for epipelagic fishesmay be low due to higher concentrations very~ear the surface, where the sampling wasInadequate, and possibly greater avoidance. Ingeneral, however, the data agree with Ahlstrom's(1969) conclusions, based on abundances oflarval fishes, that vertically migrating, meso­Pelagic groups-principally myctophids andgonostomatids-dominate the open ocean fishfauna.

Conservatively, the average biomass ofmicronekton is at least three times that of themyctophids or about 1.0 g/m2 • Most myctophidsappear to have a I-year life cycle, and in manyspecies, the population is nearly totally replacedby each new generation. The difference betweenthe highest and lowest estimates of myctophidbiomass is greater than the average value.Yearly production is then probably higher thanthe average standing crop. It is not unreasonableto assume that the dynamics of other groups ofmicronekton are similar and that micronektonproduction is about twice the average standingcrop.

If, following Ryther (1969), it is assumedthat ecological efficiency in the open ocean isabout 10% for each trophic level and theorganisms are about 10% carbon, then a pro­duction of 0.2 g C/m2 by the micronektonwould require production of 2 g C/m 2/yr bythe trophic level below. The yearly primaryproduction in this area is about 50 g C/m 2/yr(S. A. Cattell, pel's. comm.) with about 5 gC/m2/yr available to the third trophic leveland 0.5 g C/m 2/yr to the fourth. For the ratherconservative estimate of micronekton produc­tion to result, ecological efficiencies must behigher than 10% or the food chain in the openocean must be shorter than generally assumedby Ryther (1969) and others, i.e., the micronek­ton must be consuming a large fraction ofproduction by herbivores.

A final point concerns the fate of micronektonproduction; about 2 g/m2/yr must be consumedby higher carnivores. Studies of the feedinghabits of such predators as tuna; dolphin,Coryphaena; and lancet fish, Alepisau1'us(Gibbs and Collette, 1959; King and Iversen,1962; Haedrich and Nielsen, 1966; Fourmanoir,1971) indicate that these predators consumefew vertically migrating forms such asmyctophids or gonostomatids. Tuna and dolphinappear to eat mostly epipelagic forms. Unlessthe standing crop of epipelagic micronektonhas been greatly underestimated here or itsturnover rate is greater than that of verticallymigrating forms, the "typical" predators of theopen ocean are consuming only a fraction of theproduction by micronekton. In order to identifythe principal energy pathways in the open

431

ocean, more work is needed on the food habitsof poorly studied pelagic predators such assharks, porpoises, gempylids, and squids.Further attempts, such as those of Forster(1971), to collect potential mesopelagic preda­tors are also needed.

ACKNOWLEDGMENTS

I am grateful to all the people who struggledwith the trawls day and night during thework at sea. Among the many who assistedare A. R. Hartmann, D. M. Kuba, T. Okamura,J. P. Vansant, and D. A. Ziemann. I alsothank Captain Red Scholtz and the crew ofthe venerable RV Te1'itu.

The comparative series between IK and CTwas made possible by the cooperation andassistance of the Southeast Fisheries Center,Honolulu Laboratory, National Marine Fish­eries Service, NOAA. B. E. Higgins was incharge of the RV Townsend Cromwelloperations.

Numerous others assisted in sorting thesamples; special thanks are due to BarbaraBaldwin and Kay Koons. Patricia Wagnerassisted in all phases of the work. I am par­ticularly grateful for her conscientious andcareful efforts. I also thank John Caperonfor use of his computer facilities. B. G. Naf­paktitis and R. L. Wisner assisted in identifi­cation of specimens, and the latter kindly madeavailable a very useful unpublished manuscript.R. E. Young critically reviewed the manuscriptand made helpful suggestions.

This research was supported by NSF GrantGB-23931 and funds from the University ofHawaii, Hawaii Institute of Marine Biology.

LITERATURE CITED

AHLSTROM, E. H.1959. Vertical distribution of pelagic fish eggs and

larvae off California and Blija California. U.S.Fish Wildl. Serv., Fish. Bull. 161:107-146.

1969. Mesopelagic and bathypelagic fishes in theCalifornia Current region. Calif. Coop. OceanicFish. Invest, Rep. 13: 39-44.

ARON. W .• AND S. COLLARD.

1969. A study of the influence of net speed oncatch. Limno!. Oceanogr. 14:242-249.

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FISHERY BULLETIN: VOL. 71. NO.2

BACKUS, R. H., J. E. CRADDOCK, R. L. llAEDRICH,

D. L. SHORES, J. M. TEAL, A. S. WING, G. W. MEAD,

AND W. D. CLARKE.

1968. Ceratoscopelus maderensis: peculiar sound­scattering layer identified with this myctophid fish.Science (Wash., D.C.) 160:991-993.

BADCOCK,J.

1970. The vertical distribution of mesopelagicfishes collected on the Sond cruise. J. Mar. Bio!.Assoc. U.K. 50: 1001-1044.

BARHAM, E. G.

1970. Deep-sea fishes: Lethargy and vertical orienta­tion. 111 G. B. Farquhar (editor), Proceedings ofan international symposium on biological soundscattering in the ocean, p. 100-118. U.S. Gov.Print. Off., Wash., D.C.

BEKKER, V. E.1965. Lanternfishes of the genus Hygophlllll (Mycto­

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1966. Slendertailed luminescent anchovies (generaLoweina, Tarletunbeania. Gonichthys and Centro­branch liS) of the Pacific and Indian Oceans.Systematics and distribution. lilT. S. Rass (editor),Fishes of the Pacific and Indian Oceans biologyand distribution, p. 10-78. (Translated by IsraelProgram Sci. Trans!., 1966; available U.S. Dep.Commer., Natl. Tech. Inf. Serv., Springfield, VA,as IT 65-50120.) (Original 1964 in Akad. NaukSSSR, Tr. Inst. Okeana!. 73: 1-74.)

BLAXTER, J. H. S., AND R. I. CURRIE.

1967. The effect of artificial lights on acousticscattering layers in the ocean. Symp. Zoo!' Soc.Lond. 19: 1-14.

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433

FISHERY BULLETIN: VOL. 71, NO.2

ApPENDIX TABLE I.-Catches of myctophids in twoseries of four night tows each taken at 50 m and 100 mduring July 1970. Only species with an average catchof JO/tow or more are considered separately. All towswere 2 hr at depth. The first three tows of each serieswere taken successIvely on tne same mght; the fourthwas taken on the night immediately preceding (50 m)or following (100 m) the other three.

Catch/tow

Species 2 3 4

SO·rn series:

Bent!lo5ema suborbitale 38 57 22 30Djaplllls schmidti 18 21 23 29Diap/JUs sp. A 14 22 8 20Triphoturus lliKreSCells 32 46 22 40Bolinichlhys !OllRipeJ 24 49 40 38Ceratoscopellis warmi,,!:i 237 226 120 214

Total myctophids in SO-m series 399 437 267 446

lOO-m series:

H.n~()pllUm proximu111 8 9 11 25NOlolycll1111S l'uldiviae 1 2 3 46Llimpan)'ClllS steinbeck; 7 30 47 73La11lpWl.l'ctus nohilis 0 12 20 64Bo/inichllly.'! !ullRipes 45 51 38 141Ceratoscopelus warmillKi 37 25 31 32

Totol myctophids in lOO·m series 127 164 184 447

ApPENDIX TABLE 2.-Catches of several species of myctophids in short oblique tows and ranges of catches fromhorizontal tows. Given for each series are the range of catches considered positive in estimating lower limits of depthranges (+ 's) and the range considered negative and due to contamination (-'s). For the December 1970 and June 1971series, the catches of short oblique tows are also given. Each of the four December tows made two cycles simulatingdescent and ascent of the trawl during horizontal tows, each of the three June tows made one descent and ascent.

Species

September1970

+ +

December 1970Oblique

2 3

March1971

+ +

June 1971Oblique

234

Bellthosema suburb;la/eHn:ophl/11l proximu111

Diaplllls schmitlliDiaplws sp. ANOIOI_\,{~}J1JllS vllldivillt'Lampllll}'clliS niKerLumpanyctlls steinbeck;Triphoturus nigrescellsBoliIJichthJ's [onKipl'sCerwoscopellis l\'arminJ,:i

434

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