Herring Inrvae to th~ west of Seotland

in the autumn of 1911

)

International Couneil for theExploration of the Sea

•. i(-.,

, ~

•

Bundesforschung30n,tQllfür Fischerei Homburg

Bibliothek

C.M.1972/H:6

Pelagie Fish (Uorthern) Committee

•

by

R. J. Wood

Fisheries LaboratoryLowestoft, Suffolk, England

INTRODUCTlON

The first extensive survey of herring larvae over the autumn-spawning

grounds to the west of Seotland was earried out by the English research vessel

CLlONE in Ootober 1965 (WOOD, 1966). Considerable numbers of herring larvae

were oaught over an area of approximately 18 200 square miles extending from

Donegal l3a.y to beyond the Butt of Lewia and Cape Wrath (see Figurea 1 and 5)

and the total number of herring larvae in the aurvey area during the period

16-25 Ootober 1965wna estimated to be 1 159 x 109• When allowance was made

for a difference both in fecundity and in the a1ze of the adult spawners in the

two areaa it was oonoluded that the eize of the total autumn-spawning herring

population to the west of Scotland in 1965 was probably of the same order as .

that of the Downs stook in the North Sea dur1ng the years 1946-51, i.e. approxi-

mately 700 000 tons (ANON., 1911).

Aoting on arequest from the Liaison Committee of lCES the North Sea

Herring Assessment Working Group met in December 1969 to consider the state of

the herring stocks around Ireland and north-west of Scotland (ANON., 1971).

In addition to noting the above oomparison the Working Group compared the esti-

mated abundance of larvae to the west of ScotJ.and in the autumn of 1965 with the

abundance estimates for larvae in the central and northern North Sea in the two

periods 1957-60 and 1961-64 and ooncluded that a stock s1ze to the west of

Scotland of between 960 000 and 620 000 tone was lndicated. Further esti~too

by the Working Group based oncatoh-fishing mortality estimates gave however a

much lover stock aizo, betWeen 460 000 and 330 000 tons, although it was pointcd

out that none of the eatimates was very preoise. The Working Group Report

1

',·la recommended that in order to be able to use abundance estimates of larvae for

future stock assessment in this aren regular sampling ror herring larvae should

be initiated.

As no further surveya for herring larvae had, however, been carried out

in the area west of Scotland following the 1965 RV CLIOlffi survey it was decided

to repeat the October survey in 1911 using RV CIROLANA and, in addition, to exa-

mine the early September production of herring larvae off the Jmtt of Lewis and

Cape Wrath, after completion of the Lowestoft laboratory's share in the lCES

•

•

coordinated surveys over the apawning grounds adjacent to the Orkney and

Shetland Islands •

MATERIAL AND METIIODS

The first aurvey comprising a grid of 24 stations was carried out durine,

8 and 9 September 1911 by RV CORELLA over an area lying north of the :Butt of

Lewis and Cape Wr~th usinG a Dt~dard English 20 inch (50.8 cm) high-speed

sampIer fitted with an 8 inch (20.4 cm) nose cone and 60 meshes per inch

(23.6 per co) nylon filter. The sane D~pler was used on the second survey,

which was carried out by RV CIROLANA in October. With only a few minor excep-

tions the station positions for this survey were identical with those worked

in 1965 and the period of sampling was virtually the same, being 16-24 October

(16-25 October in 1965). It was most unfortunate that mechanical troubles

reduced the duration of the cruise, thus leaving insufficient time to werk the

stations through the I>1inches or the' full arid off Cape Wrath. In spite of thio,

a total of 83 stations was completed during the October 1911 survey, which

adequately covered the area from Donegal Bay to north of the Butt of Lewis,

along the western side of the Outer Hobrides.

From the sampIes at each station on both surveys the herring larvae were

picked out and identified. All were then measured and examined for the presence

of yolk sacs unless the nUI:1bers were very largo, in which case only sub-samples

were completely examined. The total number of herring larvae at each station

2

.. \lüS afterwards converted to the number bancath one aquare metro of uurface and

for the October survey the area was thon contoured and planimetered in cxactly

,the same way as whon thc 1965 survey was worked up (WOOD, 1968). The total

number of herring larvae for tho curvey ~~s thon ealeulated.

RESULTS AHD conCLUSIO:lS

The results of the firut s~{ey n~de duxin« thc 8 and 9 September 1971

are prosented in Fiauro 2. A hiG~ d~noity p~tch cf alrnont entirely reeontly

hatched horring Inrt~:::.e \lO.13 fo12,,::,;1 c:::te~dir'..c frc:1 the llElotCr:l edG'o cf t~e curye~"

ßrid off tho :Butt of L'3~iD, c.ero::::J '~hc ITorth lIinch ~d l:.orth-o~st\'!'ards bcyond

• Cilpe vTro.t~. This p;.tch uao al:eo:::t eot!:?lotcly cep:u:a.ta fro~ thc high densi ty

patch just 'Wost of Orknej 'tJhich hD.d bo~n Eluxveyed du=ing the prccodins 2 days

(SCIDiLCIr, C.H. 1972/11: '~Rcport 0::1 t:lo Intc::l.'l.tion:u Su--v't'ys of II3xrin3" L:lrV&.c

•

b thc l~~,:,th S~~ on.i Acjcecnt \:::r'.;::rs in 1971/12"). 'l11c e~1.11 sizc of th3 hcrrit".f:

la...~ao off tho :E-.ltt of Lel,io nn.1 Cc..pe \{ro.th. pluß thc feet that a ccnsiderablc

in eIoee proxicity to their h~tching arena. At one station a few milco north

of Cape ~!ro.th thc vCr'J hi&:l l!'l...~ber of 2 689 herring ln.rvac 'Wao fcund benC:l.t11

one equz:.re cctro of curfo.co v..,1 cf t1:lio tot:J.l 1 527 bad yolk Co,co.

Tho C\U;IOY during the e and 9 Sopt~ber 1971 did not co~~lctcly cover

the ~holc arca of poosible distribution cf horring larvno off thc ~~tt of Lc,:io.

HOW3vcr, in vicw of thc ror.rt11t~ of an ~~xlicr Ct~ey c~~i~d out ~c·b.fnc~

30 August and 5 Sept~ber 1965, end rcproduced here aa Fi~~e ;, it r.~~~n l~oly

that the grec.tcr :p~t of tb.e a.ren of diotribution \l!!.3 covc::.-~d. Tho c~ti'C..."l.tcd

tota,l n~'bor of· h~rrinc larWlf} .f=o~ "thc t'.rc~ C'.l..-voycd du't'i:t~ 0 c.n1 9 SO:;>tc!:b3r

ria c:.trc~lyhicI1 rold cf the order of 2 000 x 109 • Ao appro~i~n.tel:r half cf

:hio figure is rclo.tcd.ho~ovcr.toyoJk G~C otncos of lar'r~c tho n~~b~r of

1 200 x 109 for tee rc:::idno ~.G nO~'e ~c~incrful end thio io olmlu to an coti­

t'.ato of 1 517 x 109 her.i:'inG la..'t"J"r-.e dorivod fron n bloc1: cf 14 otationa "!orkcd

off Cape Wrnth during 23 c:nd 24 8optcobar 1970 by nv SCOTIA (ZIJLSTRA, 1972).

3

A matter of some importance arises from this in connection with the

• North Sea international surveys of herring larvae. It is quite probable that

many of the larvae which originate from the Butt of Lewis-Cape Wrat~ area in

early September are carried enstwards where they would later be includcd in

the estimates of abundanco for northern North Sea herring larvae.

•

Tbe results of the socond survey to the.west of Scotland and north-west or

Ireland carried out in October 1971 aro preBent~d in Figures 4 and 6, while those

from October 1965 are rcproduced in Figures 5 and 7 for comparison. The pattern

of distribution of the herring larvne in both years can be seen to have been

very similar, the chief differonce being the occurrence of recently hatched

herring larvae at several stations along the western extremity of the grid off

the north-west Irish coast in 1971, where rew, ir any, herring larvae were eaUßht

in 1965. T.his, however, could weIl be duo to the fact that these particular

stations were workcd a few days Inter in 1971 than in 1965. The abundance esti­

mates for total herring larvae in the area south of latitude 560 north, which

includes the Donegal :Bay and Tory Island spawning grounds, are almost identical

in both years, being 516 x 109 in 1971 nnd 484 x 109 in 1965 (see Table 1).

An exact comparison between the abundance estimates northwards of

latitude 560 north in both years unfortunately cannot be made in the same way,

• as the area off Cape Wrath was not cO::lpletely covered by the survey in

October 1971, !l0r were stations worked through the Minches. Tbe Minches did

not, however, constitute an important area of distribution in October 1965 and

those stations which were not covered by the survey in 1971 only contributed

80 x 109 herring larvae towards the total abundance estimate of 1 275 x 109 for

the whole of the surveyed area northwards of latitude 560 north in Octob~r 1965.

:Because of the poor coverage of the area off Cape Wrath in October 1971 the

total number of herring larvae was, as a consequence, probably somewhat under-

estlmated. T.he best comparison that can be made for the aren northwards of

latitude 56° north, excluding the Minches, is between a total abundance est~ate

4

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of herring larvae in Oetober 1971 of 909 x 109 and or 1 195 x 109 in

Oetober 1965. It ~~st theref~re be eoncluded thnt the total nucbers of herring

larvae which were distributed to the west of Seotland andnorth-west of Ireland

during the month Of October in both 1971 and 1965 were ver,y much the same andmtlst have been

thus the she of the adult spawning population/fairly siml1ar in both years.

The importance of the various spawning areaa a.lso nppeared to be unc1langed.

The grounds off the north-west Irish eoaet eontributed roughly one-third of

the total estimated number of herring larvae both in October 1911 and 1965, .

while the most important concentration of larvae was aituated to the west and

north of the islands of Harrie and Lewia in the Outer Hebrides.

Tbe apparent magnitude of the hatching of herring larvae off the :Butt

of Lewis and Cape Wrath in early September is a striking feature of the recent

investigations. Few larvae were sufficiently large in the October survey to

have been derived from thia apawning (see Figure 8) so that the estimates of

abundance for October herring 1nrvae are probably related ver,y largely to

hatchings in late September and early October. It was on these later larvae

that the original estimate of stock eize to the west of Scotland and north-west

of Ireland was based (WOOD, 1968). If ,the abundance estimate for herring ll:--vae

in early September is also considercd in conjunction with both the October esti-

mates a stock eize in excess of 700 000 tons must sure1y be indieated•

SUMMARY

1 Two surveys of the abundance and distribution of autumn-spawned herring

larvae to the west of Scotland were carried out by English research vessels

during the autlll'JIl of 1971.

2 The first survey by RV CORELLA during 8 and 9 September revealed a

dense patch of newly-hatched herring larvae extending from off the :Butt of

Lewis to north-east\i3Xds of Cape Wrath. The total number of herring larvae in

the area surveyed at that time was estimated to be approximately i 000 x 109,

of whieh roughly half were in the yolk aae stage.

•

•

:; 'Ibe second survey b:r nv ClROI.JJlA cnrricd out betwecn 16 and 24 October

covered the aroa from Donegnl Day to north of thc Butt of Lewio and Caps Wrath.

The total number of herrincr larvllc in thc c.rco. e1.~rva:red W3.0 ostiLl!l.ted to

bc 1 425:x 109•

4 This estimate ,mo reaßcnabl;r si:nilnr to tL'1e cs'tion.ted mmbe~ of he~rinG'

le.rvae in approx~?taly tho na'C'.o Dxr:m c,nu. Utr1:,inC the c:nne pericd of O::tobcr 1965,

and i t \1:lS concluded thn.t the ßpa....'l1ing otock aize related to these 13.tor lnrvae

,-ras probably si:rllllr in t!!13 wo yell:rs.

5 It ~~s aIDO co~cluded that,:lo vc~~r few of th3 e~rly Sapte~~e~ le=vno

appcarcd to have been incluied in the Octobcr abundanco eotim~tos,n 7o~al

opa.lnline stock aize fo~ tue whole ~xen to th~ \reet of Scotlnnd end north-west

of Ireland in exceso of ths 1955 esti~te of 700 000 tons wao ir.dicatcd.

REFERillJCES

AlION. , 1971. "Report on thc Stnto of the Her:::-ing Stocks around Ircll!.nd and

North-west of Scotl~Jld". lCES, Coop. Res. Rap., Serien A, No. 21:

1-29.

\OlOOD, R. J., 1968. "Autw..n-:;:p:.~ming G:::c~ds of Ecrring to thc \Jest of Scotll'\Ild".

ICES, C.M. 1968, S~:poo~.v.n on "r:ne BioloC'J of E:u-l:r Sh.zes and Recrui t­

ment Mcchanif:'l!ln of Herrin!;". Dcc. l~o. 0, pp. 1-8 (oi:c.'9o.) •

ZlJLSTRA, J. J., 1972. "Roport on thn Interrntional Surveys of H3rring Larvae

in the North Se:\. and Adja~ent ,,raters in 1970/71". ICES, Coop. ROB. Rep.,

Seriea A, No. 28: 1-24.

6

• •

Table 1 Abundance estimates of herring larvae in October to the west of Scotland x 10-9

I

I

III

l....

Year

1965

1971

North of lat. 56°N(excluding Mlnches)

1 195

909

°South of lat. 56 N

484

516

lUnch area

80

IVhole ares.(excluding 11inches)

1 679

1 425

Whole area(including Minches)

1 759

-J

I

suLA 'SGEJ.R:-, ,RONA:

Figur~...!.:. Islands and het?,dlonds to ths~eßt of Scotl~nd referred toin tho text.

FLANNANISLES

BARRA

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FigurA 2. Numbers of herr1ng larvaebeneath 1 square metre,.8-9 September 1971.

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,E1nure 7. l\unbcrs cf herring larvaee!n.ller than 10 rnn inl€>ngth benca.th 1 square~etre, 16-25 October 1965.

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Figure 8. Numbers of herring l~elarger than 15 Irl inlengtil bencath 1 cqUßrereetre, 16-24 October 1971.

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