JAMES 1. GOLDEN, ROBERT L. DEMORY,and WILLIAM H. BARSS

Abundance, Size and 'ge Composition,and Growth of Pacific Ocean Perch,Sebasfes alufus, Sampled During 1977

Introduction

Marine resource surveys providemeasures of abundance and size andage composition of rockfish that are in­dependent of commercial landing data.This report contains a summary ofanalysis of data obtained on Pacificocean perch, Sebastes alutus, from the1977 coastwide rockfish survey. Be­cause of the large number of speciesinvolved and the discontinuous dis­tribution of major species within thegeographic range of the survey, dataanalysis responsibilities were dividedamong the participating agencies. TheOregon Department of Fish andWildlife (ODFW) elected to analyzedata collected from Pacific ocean perchbecause it has a particular interest inthis species, both in terms of stock as­sessment and the commercial fishery.The ODFW routinely samples com­mercial landings of Pacific ocean perch

The authors are with the Oregon Department ofFish and Wildlife Research Laboratory, MarineScience Drive, Newport, OR 97365.

ABSTRACT-The 1977 rockfish surveyprovided the first opportunity for a detailedexamination of Pacific ocean perch,Sebastes alutus, stocks inhabiting waters offthe coasts of California, Oregon, andWashington. From catch data, estimates ofbiomass, age and size composition were de­termined. Estimates of marketable biomass(~30 cm) were 175 t in the 1NPFC Eurekaarea, 6,467 t in the Columbia area, and7,685 t in the southern portion of the Van­couver area. The Columbia area estimate iswell below that of the 1966-68 period butsubstantially greater than the estimate for

March-April 1980

for age, size, sex, and maturity, and thesurvey provided a means of obtainingadditional biological data on thisspecies. The survey also provided theopportunity to sample deep water(>150 fathoms or 274 m) segments ofperch stocks only lightly fished by thecommercial fishery.

Methods

Catch Composition

Commercial landings of perch-likespecies (those hailed as nominal perchby commercial fishermen) must be in­terpreted using catch composition sam­ples to determine the landings of Pacificocean perch. The proportion of Pacificocean perch (by weight) in all rockfishas well as other perch-like rockfishcaught during the 1977 rockfish surveywas determined for each 30' intervalfrom Cape Blanco (Jat. 42°30' N) northto Cape Flattery (Jat. 48°30' N). Perch­like species that were included in thecalculations were darkblotched rock­fish, S. crameri; splitnose rockfish, S.

the 1973-74 period. The 1970 year classdominated catches ofPacific ocean perch inmost strata sampled. They were particularlyabundant in the 100-149 fathom (183-272m) depth strata. There were marked differ­ences in age composition from south tonorth in the Columbia and Vancouverareas. Older fish were more abundant in thenorthern one-third of the Columbia areaand throughout the Vancouver area. Statis­tical comparison of growth rates betweenthe Columbia and Vancouver areas showedno significant difference in growth rate.

diploproa; redstripe rockfish, S. pro­riger; yellowmouth rockfish, S. reedi;stripetail rockfish, S. saxicola; andsharpchin rockfish, S. zacentrus. Onlytows made at depths greater than 100fathoms (183 m) were used in calculat­ing the proportions for both indices.

Biomass

Biomass estimates (metric tons) ofPacific ocean perch were determined asoutlined by Gunderson and Sample(1980), for International North PacificFisheries Commission (lNPFC)Eureka, Columbia, and Vancouverstatistical areas. Since the survey esti­mates included small fish ( <30 cm) thatare not suitable for market use, biomassestimates were adjusted downward sothat they would be useful in comparisonwith biomass estimates derived fromcommercial catch per unit effort(CPUE) data (CPUE in t/hour). To ac­complish this, a length-weight key wasused to determine the weight of fishsmaller than 30 cm, which was sub­sequently subtracted from the surveyestimate. Biomass estimates based oncommercial CPUE for the INPFC Co­lumbia area were determined by divid­ing the total area available to the fleet(717 square miles) by the area swept bythe trawl in I hour and multiplying thequotient by the average commercialCPUE. This method is based on an as­sumed towing speed of 2.5 knots with ahorizontal trawl opening of 35 feet.Commercial biomass estimates werenot stratified by depth or geographicarea.

Age and Size Composition

Age and size composition sampleswere collected for Pacific ocean perchusing the sampling scheme describedby Gunderson and Sample (1980) at thelatitudes and depth intervals withinINPFC areas listed in Table 1. Sampleswere not available for all depths insome of the normal sampling densityareas (tracklines spaced every 10 nauti­cal miles). This was due in part to thelow abundance of Pacific ocean perch at50 to 99 fathoms (91-181 m).

The ages of the individuals sampledwere determined by counting the trans­lucent winter growth bands on the

41

otoliths following the method describedby Westrheim (1973).

Age and length frequency samplesfor individual tows were weighted tothe total catch from which the sampleswere taken. The expanded age or lengthcompositions (sexes combined) werethen combined within area and 50­fathom depth strata for each INPFCarea, and further expanded to the totalestimated population.

Growth

Table 1,-Numbers of Pacific ocean perch sampled for age and length composition at dillerent latitudes anddepth Intervals within INPFC Eureka, Columbia, and Vancouver areas during the 1977 rockfish survey(number of otoliths read is shown in parentheses).

Sampling Depth interval (fathoms)INPFC densityarea type' Latitude (N) 50-99 100-149 150-199 200-260

Eureka N 40'26'-43' 0 (0) 81 (0) 132 (0) 0 (0)Columbia N 43'_45° 0 (0) 439 (155) 247 (112) 6 (0)

H 45'-46'44' 307 (190) 1,741 (982) 664 (304) 259 (23)N 46'44'-47'30' 0 (0) 283 '(72) 270 '(0) 131 (0)

Vancouver N 47'30'-47'50' 0 (0) 130 (129) 0 (0) 0 (0)H 47"50'48"30' 70 (70) 1,040 '(539) 383 (262) 136 (135)

IN =tracklines 10 nmi apart: H=tracklines 5 nmi apart.'In INPFC Columbia area from lat. 46'44' to 47"30'N, 126 and 67 otoliths from 100-149 and 150-199 fathoms,respectively, were unusable, and were not included in the totals in parentheses. Similarly, in INPFC Vancouver areafrom lat. 47"50' to 48'30'N at 100-149 fathoms, 93 otollfhs were unusable.

Figure I, - The percentage of Pacific ocean perch in surveycatches of rockfish (solid line) and perch-like rockfish(dashed line) by 30' intervals oflatitude from south to north,

of perch-like species in commerciallandings in Pacific Marine FisheriesCommission (PMFC) areas 2B (lat.42°50'-44°18'N), 2C (lat. 44°18'­45°46'N), and 3A (Iat. 45°46'­47°20'N), respectively,

Biomass

Estimated biomass based on the sur­vey data is shown in Table 2. In theColumbia area, the estimate of biomassbased on CPUE of the commercialcatch was 9,600 t.

Although the survey estimate is 33percent less than the estimate based oncommercial CPUE data, this is to beexpected as a consequence of the factthat commercial trawlers bias theirfishing towards areas of high localabundance. Both estimates showed an

increase in stock biomass relative to the1973-74 estimate reported by Gunder­son et al. (1977) but remained wellbelow the estimated biomass of 35 ,000t reported during the 1966-68 period(Westrheim et a!., 1972).

1977 Exploi-INPFC Biomass 95% C.E. land- tation

area (I) ("'%) Ings rate

Monterey 2 "'82Eureka 223 "'76 65 0.29

(175)Columbia 7,105 ",49 '479 0.07

(6,467)Vancouver 7,728 "'136 817 0.11

(7,685)

1 Includes foreign catch.

Table 2.-Biomass estimates, 95 percent confidence in­tervals, 1977 landings, and estimated explonation rate.Numbers in parentheses are adjusted biomass est~

mates of marketable fish ;,,30 cm.

,..... /~

" ..........._--"/

//

//

/,---...... I

., .... J

lat, 430

N

20

10

70

80

UJ

u 40

'"UJ 30"-

Individual length observationsweighted to the raw age composition ofPacific ocean perch were fitted to thevon Bertalanffy growth in length curvefollowing the procedure used by Tom­linson and Abramson (1961). Growthrates by sex were compared between100-149 fathom (183-272 m) and 150­199 fathom (274-364 m) depth inter­vals within INPFC Columbia and Van­couver areas. Growth rates were thencompared between INPFC areas afterpooling the age composition for alldepth intervals (i .e., 100-199 fathoms),Perch from 6 to 18 years of age wereused in making estimates of L"" k, andto'

Results

Catch Composition

Pacific ocean perch represented 22,7to 73.8 percent of the total weight ofrockfish caught between Cape Blancoand Cape Flattery with the proportionof perch caught increasing withlatitude. Similarly, Pacific ocean perchranged from 30.7 to 83.7 percent of theweight of associated perch-like species(Fig, I). Of the perch-like species(other than the Pacific ocean perch), themost important contributors to the catchcomposition were spl itnose rockfish(9. I percent), sharpchin rockfish (8.2percent), and darkblotched rockfish(8.1 percent). Of non-perch-likespecies, shortspine thornyhead, Sebas­tolobus alascanus (8.2 percent), yel­lowtail rockfish, S, fiavidus (4.6 per­cent), and rougheye rockfish, S.aleutianus (4.3 percent), were impor­tant in making up the catch of totalrockfish. Pacific ocean perch rep­resented 16.2,62,3, and 92.3 percent

42 Marine Fisheries Review

100·149 latham (1m)

the data for all strata were combinedand expanded to the total population foreach INPFC area. The 1970 year classwas dominant in the Columbia area andobvious but not dominant in the Van­couver area (Fig. 6). The modal agewas 19 years in the Vancouver area.Secondary modes within the two areasoccurred at 13 and 14 years, respec­tively.

In addition to survey age data fromthe Columbia area, age compositiondata from commercial landings werealso available for comparison. Surveyage composition showed a greaterabundance of older fish because thesurvey included samples from depthsgreater than those which are normallyfished by the fleet in the summer (Fig.7). In addition, the depleted state ofolder fish combined with the presenceof the strong 1970 year class have con­tributed to a concentration of effort bythe fleet in areas of local high abun­dance (i.e., in shallower water).

Length frequency data for Pacificocean perch were compiled for com­bined sexes and were expanded to thetotal population for each stratum where

greater than 200 fathoms (366 m). Asingle sample from lat. 46 0 44' to47 °30 ' N indicated the presence of fishII years and older in the 100-149fathom (183-272 m) zone (Fig. 4).Another sample from the region im­mediately to the north (Jat. 4r30'­4r50' N) once again showed thedominance of the 1970 year class in the100-149 fathom depth interval, how­ever (Fig. 4).

Due to the presence of a large catchof Pacific ocean perch that was notsampled for otoliths in the areabounded by lat. 4r51' -48 0 30' N, theage composition for the 100-149fathom interval was estimated using anage-length key derived from othersamples taken in the same area. Al­though the 1970 year class is still ob­vious, it was far overshadowed by thepresence of older, larger fish. The1970 year class was present, but notdominant, in 150-199 fathoms (274­364 m) and was absent in depths greaterthan 200 fathoms (Fig. 5).

After adjusting the age compositionto the total population estimate withineach depth zone and geographic area,

>201510

150-199 1m

AGE (yeo')

Figure 2.-Age composition ofPacific ocean perch in the southernportion of the INPFC Columbia area(Iat. 43°00' -45°00'N), expanded tothe total population.

~ 200u:

U)

I :::Li:':~==

Age and Size Composition

The presence of a strong 1970 yearclass was evident in depths from 50 to199 fathoms (91-364 m) in the Colum­bia area (Fig. 2, 3). Secondary modesoccurred at 13-14 years from lat.43 °00 ' to 45 °00' N and at 10-16 yearsfrom lat. 45 °00' to 46 °44' N with the1970 year class being absent at depths

Figure 5.-Age composition ofPacific ocean perch in the middleportion of the Vancouver area (Jat.47°5I'-48°30'N), expanded to thetotal population.

2001 50-99 lathom (1m)

o I ~ '---'"'='=

BOO100-149 1m

600

'1:r: I,':' 400 I~

I

0200 -JkDI

U)

o rfh-0z..:U)

"O~I::::>

150-199 1m0:r:>- 200

o ~2]

>200 1m

:::::iIJt--,

5 10 15 > 20

AGE (yeo, I

>20

100-1491athom (1m)

100-149 1m

5 10 15

AGE (year)

400

I200"2

~

~

0

V)

0

'''jz..:V)

::::>0I>-

200

Figure 4.-Age composition ofPacific ocean perch in the north­ernmost portion of the INPFC Co­lumbia area (Jat. 46°44' -47°30'N)(top) and the southernmost portionof the INPFC Vancouver area (Jat.47°30'-47°50'N) (bottom), ex­panded to the total population.

>200 1m2001oLl_---,---__--,-:=rcfIb-o--,="--Ll.-.e:t::'--==--_

10 15 >20

AGE tyeor)

400,

Figure 3.-Age compositIOn ofPacific ocean perch in the middle por­tion of the INPFC Columbia area (Jat.45°00'-46°44' N), expanded to thetotal population.

200

400

200

March-April 1980 43

1879

Figure 6.-Age composition ofPacific ocean perch in INPFC Co­lumbia (Iat. 43°00' -47°30'N) (top)and Vancouver (lat. 47°30'-48°30'N) (boltom) areas, all depth in­tervals combined. Samples ex­panded to the total population.

samples were taken. Figures 8 throughII show the length frequency composi­tion by depth interval in the Eureka,Columbia, and Vancouver areas. Themodes in length frequency compositionreflect the modal distribution in agecomposition in most strata where agesamples were taken.

In the Eureka area (lat. 40°26'­42°59'N) there was a conspicuous ab­sence of larger, presumably older fishat all depths. The mode at 33 cm in100-149 fathoms (183-272 m) indi­cated the presence of the 1970 yearclass. Within the Columbia area the1970 year class was dominant from100 to 250 fathoms (183-457 m) be­tween lat. 43°00' and 44°59'N andfrom 50 to 199 fathoms (91-364 m)between lat. 45°00' and 46°43'N.Further north in the Columbia area(tat. 46°44'-47°29'N), the length fre­quencies shifted to larger fish.

Size composition data from samplesof commercial landings were also

Growth

The growth of Pacific ocean perchsampled in depths of 100-149 fathoms(183-272 m) was compared with theirgrowth in 150-199 fathoms (274-364m) for lat. 45°00' -46°43'N (Columbiaarea) and lat. 47°50'-48°30'N (Van­couver area). No significant differences(P~0.05) were detected between Lx,k, and to parameters of males andfemales between depth intervals in theColumbia area (Table 3). Highly sig­nificant differences occurred betweendepth intervals for estimates of k formale perch in the Vancouver area (2 =2.61, P~O.OI), together with sig­nificant differences between estimatesof to (2 = 1.97, P~0.05). There wereno significant differences in L x be­tween the two depth strata. Males sam­pled in 100-149 fathoms had highervalues for k and to (k = 0.170 and to =-1.64) compared with those in 150­199 fathoms (k = 0.080 and to =

-8.65). No significant differenceswere found between depth strata forestimates of Loo , k, and to for femalePacific ocean perch in the Vancouverarea.

Male Pacific ocean perch sampledfrom 100 to 149 fathoms (183-272 m)in the Columbia area had a significantlyhigher estimate for L x (L x = 47.0 cm)compared with the Vancouver area

The appearance of larger fish with in­creasing latitude may be an indicationof a pattern of recruitment from south tonorth. Evaluation of this hypothesis,however, is confounded by the fact thatclosures to foreign fishing exist fromlat. 46 °00' to 47 °00' N and from47 030' to 48 °30' N which may haveallowed the build-up (and conserva­tion) of older, larger perch. In addition,there were 60 percent females in theVancouver area as opposed to 49 per­cent in the Columbia area, a situationwhich would account for some of thedifferences in size composition. Also,the inherent patchiness and variabilityof rockfish size and abundance betweensamples make it difficult to generalizeabout length frequency distributions forPacific ocean perch from one geo­graphic area to the next.

ROCKFISH

_._ ..... ~~RVEY

'--,'-

10 15 > 20

AGE Iyear)

COMMERCIAL

35 40 45

LENGTH (em)

30

1

'lI"5

~

30ZwU'"w

200-

10

30

Figure 7.-Top: Age composition ofPacific ocean perch sampled at thedock (open bars), and sampled dur­ing the rockfish survey (dark bars), in1977 in the INPFC Columbia area.Bottom: Length frequency distribu­tion of Pacific ocean perch sampled atthe dock (solid line), and sampledduring the survey (broken line), forsame.

'Unfortunately, no otolith sample was collectedfor this tow.

52%

COMME RC IAl

available for comparison with the sur­vey data for the INPFC Columbia area(Fig. 7, bottom). The commercial dataalso showed the dominance of the 1970year class, but contained a smallerproportion of larger fish than the surveydata. Again, this reflects the fishingstrategy of the commercial fleet.

The influence of the 1970 year classappears to diminish northerly into theVancouver area, as greater numbers oflarge fish appear. One of the Vancouverarea samples (tat. 48°0I'N, 140 fath­oms) appeared to influence the lengthfrequency distribution substantially dueto a very large catch (3,020 kg) with amodal length of 46 cm. l A geographicshift in length can be clearly seen in thecomposite Figure 12, where all depthintervals were combined for each area.

>20

>201510

10 15

AGE (year!

5

5

lI1l-TI -m

f

1,1 ~~

400

1200-

400

200

</)

oz«~ 800oI~

600

600

800

44 Marine Fisheries Review

150-199 fm

5045

>2001m

100-149 fathom (fm)

150-199 fm

25 30 35 40LENGTH (em)

20

400:

~200

u.. 0 '-- ~=--==____=:,_

u..0 400

~20016 0 ----------~---------------='-------===-~-

~400J

2oo,lo"-,,,,"'I" ,','"""-,,,," " " ",''1"4~=;==ITTT"r,,,"""-,,,,'"j

2' 100-149 latham (1m)

1O:1'- ~=.:=_____''''''~''___=~ _

200

1100l

;;; 0 L,I'"" -r-F'T,Tj7:::rrn=n,r~r:rrrTT""""'" ""TT,""",',''''"'"

u..oVJoZ<!VJ

§2°:lL__~=~=~=1",00,--1_4_9_fm-----,=",,-_~ _

2°:1L ~1~50""~:::.19_9_fm_=:::===== _

Figure 10.-Length frequency distribution of S. alutus sampledduring the 1977 rockfish survey for the northernmost portion of theINPFC Columbia area (Iat. 46°44 '-47"29 'N), expanded to the totalpopulation.

2OOol-""",,,,"""""""",>"20,,Or,~mf''<>''?r'""-,--,,,,,,,,,,,--,--,,I I I I I I I i J I j I I I Iii

Figure 8. -Length frequency distribution of Pacific ocean perchsampled during the 1977 rockfish survey for INPFC Eureka area(Iat. 40°26 '-42°59 'N) (top) and the southern pOf1ion of the INPFCColumbia area (Iat. 43°00' -44°59'N) (bottom). Samples were ex­panded to the total population.

100-149 falhom (fm)20 25 30 35 40

LENGTH (em)45 50

200

lo "'",,',',','"""r,,,," 'I-r',,.,9'1=r-n=TTTT?n==ro"'T-ri'-rrT"r1,I""r,,,,'IT'1[120 25 30 35 40 45 50

2°:lL- 5_0_-~=9"'fm::::,=~ _

100-149 fm

150-199 1m

100-149 fm

150-199 fm

u.. 600oVJ 40oZ 20<!VJ

:::> 0 L-==-="-===.e:::::=- hoIf- 40J

2°:l ~o--------~-"----------==~

I~8002°:1.__~_~__~==:::::...5_0_-9_9_fa~th",o=m=(f=m=)=~::::::..._....:::::==-

~ 400i

:200 ~o 0 --~===~=-----=::~VJo~ 400i:g 200

§ 0 -------~~"'--------~"'==-

201llltlll~illl

5045

>200 fm

25 30 35 40LENGTH (em)

20

400

l200

lo """r'," " " " """-""'"" " " " ,','"-,'-,~r;=::r::;:,.:=r=r=;-,""''''" "'1I

50I I I

45

>200 1m

25 30 35 40LENGTH (em)

i I I

400

J200,1

o I I I I I

Figure 9.-Length frequency distribution of Pacific ocean perchsampled during the 1977 rockfish survey for the middle portion ofthe INPFC Columbia area (Iat. 45°00'-46°43'N), expanded to thetotal population.

Figure II. -Length frequency distribution of Pacific ocean perchsampled during the 1977 rockfish survey for the INPFC Vancouverarea (Iat. 47°30' -47°50'N, top; lat. 47°51' -48°30'N, bottom), ex­panded to the total population.

March-April 1980 45

20:J E_U~.E=K_A<'__==_=_A"'.=E_A<'c=__..._=(1"'0_t_40_0_3_0~'-~4_3°_0_0_'_N_I _

MALES

fEMALES

FEMALES

MALES

COLUMBIA AREA

VANCOUVER AR EA

20

10 ......_-....,~__...,.. ,...__...

30

40

30

Z 10 ...... ~__.... .,... _

UJ

:E 20u

5045403530

VANCOUVER AREA

:101 47°30'- 4S026'NI

20

LENGTH lem)

800

1600

400

2001o~M'T=rr"::;::;rFfTr'i'Ti=-",.-rrT"T"TnCTT"-T'-l+'

25'

u..oV>oz«V>

=>oI>-

IV>

Figure 12. -Size composition of Pacific ocean perch (sexes anddepth intervals combined) caught by INPFC area during the 1977synoptic rockfish survey,

5 10AGE IN

15YEARS

20

Table 3.-Estimates 01 Pacilic ocean perch growth parameters at depths of 10C).149 lathoms compared with estimates at lSC).199 lathoms in two InternationalNorth Pacific Fisheries Commission (INPFC) areas,

Depth l.L.3 L.l.3 L.l.3

INPFC area (im) n' k' U.L. Lx(cm)' U.l. to' U.L.

Figure 13 ,-Growth- in-length curves fitted by von Bertalanffyequation for Pacific ocean perch from INPFC Columbia and Van­couver areas (100-199 fathoms),

ColumbiaMales 100-149 433 0.099 0.062 47.00 43.28 -4.86 -7.57

0.137 50.72 -2.15150-199 '184 0.125 0.057 43.92 3988 -4.09 -8.02

0.193 47.96 -0.16Females 100-149 474 0.105 0.074 49.10 46.00 -382 -5.83

0.137 52.20 -1.82150-199 74 0.071 0.000 53.01 38.74 -6.92 -14.74

0.142 67.26 0.90

VancouverMales 100-149 304 0.170 0.130 42.30 41.17 -1.64 -3.25

0.210 43.43 -0.02150-199 '176 0.080 0.026 46.17 40.00 -8.65 -15.42

0.134 5234 -1.87Females 100-149 128 0096 0.049 51.30 45.60 -4.05 -7.32

0.142 57.00 -0.79150-199 '64 0.110 -0.011 45.07 37.67 -5.76 -15.76

0230 52.47 4.25

ColumbiaMales 100-199 621 0.110 0.079 45.74 43.28 -4.36 -6.41

0.141 48.20 -2.31Females 100-199 548 0.100 0.071 49.53 46.44 -424 -6.20

0.128 5262 -2.28

VancouverMales 100-199 481 0.134 0.102 43.14 41.73 -3.57 -5.48

0.166 44.55 -1.67Females 100-199 191 0.097 0.046 49.39 43.98 -4.67 -852

0.148 54.80 -0.82

lSample size.2Growth coefficient.395 percent confidence interval, L.l. = lower limit, U.L. = upper limit.'Asymptotic length.'Hypothetical length (em) at age O.'Pacific ocean perch ages trom 6 to 16 years.7Pacific ocean perch ages from 7 to 18 years.

46 Marin.e Fisheries Review

males from the same depth (L x = 42.3cm, 2 = 2.37, P ~0.02). For thesame comparison, estimates of k weresignificantly lower for Columbia areamales (k = 0.099) compared withthose in the Vancouver area (k =0.170,2 = 2.52, P~0.02). Significantdifferences occurred between to esti­mates for male Pacific ocean perchsampled from 100 to 149 fathoms be­tween the Columbia and Vancouverareas with to = -4.86 and -1.64, re­spectively (2 = 2.00, P~0.05). Nosignificant differences for estimates ofL oc , k, and to were detected betweenmales sampled from 150-199 fathomsbetween the Columbia and Vancouverareas. There were also no significantdifferences for estimates of L GO, k, andto between females sampled in the Co­lumbia and Vancouver areas in eitherdepth interval.

The width of the 95 percent con­fidence intervals indicated that morevariation was associated with estimatesof L oc, k, and to for Pacific ocean perchsampled in the deeper interval whencompared with those sampled from 100

March-April 1980

to 149 fathoms. This may be due to thesmaller sample sizes in deeper water aswell as the effects of changes in agecomposition between depth strata.

After pooling the data from eachdepth interval (even though some dif­ferences occurred for estimates ofk and to for Vancouver males betweendepth strata), no significant differencesin the L GO, k, or to values were presentbetween Pacific ocean perch from theINPFC Columbia and Vancouver areas(P~0.05). Age-length relationshipspredicted by the von Bertalanffyparameters from the pooled samples areshown in Figure 13.

Growth parameters estimated fromthe 1977 rockfish data for the INPFCVancouver area are similar to those re­ported by Gunderson (1977) for Pacificocean perch sampled in 1972. Malesfrom the Vancouver area in that studyhad L oc, k, or to values of 43.15 cm,0.1320, and -2.1186 years, respec­tively, with a standard error of theestimate equal to 0.68. Females hadvalues of 48.47 cm, 0.0908, -3.5041years, respectively, with a standard

error of the estimate equal to 0.45. Allof these values fell within the 95 per­cent confidence interval of the 1977rockfish survey estimates for the Van­cou ver area.

Literature CitedGunderson, D. R. 1977. Population biology of

Pacific ocean perch, Sebasles alulus, stocks inthe Washington-Queen Charlotte Sound re­gion, and their response to fishing. Fish. Bull.,U.S. 75:369-403.

____, and T. M. Sample. 1980. Distribu­tion and abundance of rockfish offWashington, Oregon, and California during1977. Mar. Fish.Rev. 42(3-4):2-16.

____, S. 1. Westrheim, R. L. Demory, andM. E. Fraidenburg. 1977. The status of Pacificocean perch (Sebasles alutus) stocks off BritishColumbia, Washington, and Oregon in 1974.Environ. Can., Fish. Mar. Serv., Tech Rep.690,63 p.

Tomlinson, P. K., and N. J. Abramson. 1961.Fitting a von Bertalanffy growth curve by leastsquares. Calif. Dep. Fish Game, Fish Bull.116,69 p.

Westrheim, S. J. 1973. Age determination andgrowth of Pacific ocean perch (Sebasles alulus)in the northeast Pacific Ocean. J. Fish. Res.Board Can. 30:235-247.

____, D. R. Gunderson, and 1. M.Meehan. 1972. On the status of Pacific oceanperch (Sebasles alutus) stocks off British Co­lumbia, Washington, and Oregon in 1970.Fish. Res. Board Can., Tech. Rep. 326,48 p.

47