CM_1970_symposium_19.pdf (1.297Mb)

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This paper is not to be cited without prior reference to the author"

International CotL~cil for the Explorati on of'.·'the Sea

With collaboration of FAO and ICHAF

C .M. 1970 Symposium

on

"Stock and Recruitment"

No.

19

RECRUITT,1ENT OF YOUNG ARCTO-NOR'VlEGIAH COD AND HADDOCK IN RELATION TO PAl"'{EHT STOCK SIZE

By

Arvid Hylen and Olav

Dragesuu~d

+)

+)Institute of' Marine Research Bergen, Norvlay

. '

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INTRODUCTION

Variations in abund&Lce of recruits in the Arcto-Norwegian cod and haddock stocks have been described by Hjort (1914), Rol1efsen (1930, 1954), Sund (1924, 1936), Hy1en (1962) and Garrod (1968). The relative strengths of poor and rich year-classes in the cod stock measured at age

~3 years were found to be in the order of 1:20 for cod and haddock in the period 1946-1968. Also the time hLterval between the appearence of rich year-classes in these stocks cm~ be relatively long in some periods even more thm~ ten years (Anon. 1970).

Tne causes of the variation are not ]:-,.nown, but current hypothesi·s concen- trate on possible variability of parental factors and of environmental conditions in the sea shortly after hatching. Since Hjort (1914) demon- strated the great fluctuations in year-class strength of fish stocks in the Northeast At12.ntic the general view has been that 1'1Tithin the range of stock size variations studied, the numerical strength of a year-class is independent of the size of the parent stock in fish species with high f e cUJ.l.di ty • The evidence supporting this concept of stock size and re- cr~itment has been reviewed by Beverton and Holt (1957). Recently this theory has been challru~ged by data from North At12ntic cod and haddock stocks (Garrod 1966, 1968, Anon. 196Ga, 1969a). Garrod found evidence fcr a decrease in recruitment with decreasing parent stock size for Arcto- Norwegirul. cod and claimed that the decliDing trend in recruitment that has been observed in this stock, is assiciated with an increasing fishing

effort. He assumed that i f the spal~ing stock remains stable i t will on the average produce enough young to replace the average of its constituent year-classes.

In the present investigations the series of observations is too short to give firm conclusion of the relationship between the parent stock size

(the spatlTl1.ing potential) and the subsequent abundance of the resulting year-class. The paper attempts to present relative estimates of year- class strengths at the O-group stage (i.e. about 6 months of ag~ of Arcto- Horwegia.L"l. cod and haddock and to correlate these vIi th subsequent year-

class strengths in the young adolescent phases. Abundance estimates of the 1963-1969 year-classes Clre used to discuss the relationship bet1;-men recJ.:ui truent of young Arcto-HoTI-J"egian cod al1.d hClddock in relation to the parent stock size.

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}!Ili. TERIAL AND lljETI10DS

i-group fish surveys

Joint investigations were carried out during the period 1965-1969 by 1abatories conducting fisheries research in the Barents Sea in order to estilnatG year-class strength at the O-group stage (Anon. 1965a, 1966, 1967, 1969b, 1969c). ?rior to this period (in 1963 and 1964) data are available from surveys conducted by Institute of Marine Research, Bergen (Dragesund and Olsen 1965, DragesUi""1.d 1970b). The O-group survey in 1963 was restricted to the Barents Sea (Figs. 1 and 8), m~d data from the USSR young fish survey in 1963/64 to the Bear Island/Spitsbergen area were taken into consideration (Hizovtsev 1964, 1968a and Baranova 1964).

The basic tecl~ique employed in the O-group surveys was echo sounding and sampling "tvith mid"tvater trawl (Dragesund and Olsen 1965, Dragesund, Hidt- tun and Olsen 1970).

Experience has shovln that i f the Barents Sea surveys for O-group· fish arc carried out from L::te August to early September, the fish are large enough to be detected. They are pe1agically distributed and occur generally in the upper 100 metres of water. During the dark period the O-group fishes form more or less ~Liform scattering layers. vlhen concentrations are not too dense single individuals can be distinguished~ In day-time, however, the fish cluster together forDir~ either small schools or discontinous layers of schooling concentrations.

In general the identification of O-group fish from the echo reording paper alone is not possible. However, in the Barents Sea surveys i t has been possible to distinguish between several types of recordings which have been identified by mid1'la ter traw·ling. In theis area, therefore, analysis of echo recordings combined "'vi th frequent sa.'1lpling with fishing gears seems to be possible for establishing the geographical distribution of O-group fish in August-September.

Tne catching gear used by all participating vessels was a small meshed pelagic midwater trawl with headline and footline of l8,3 rn, sideline of l5,3 m and .mesh size from 100 mm (Wll~gS and square) graded down to 8 mm

(cod end). The catchability of the trawl was tested by intership compari- sons carried out during the surveys. The depth of trawling was checked by a depth recorder attached to the trm·ll.

O-group echo abund~nce

A simple counting method Clli~ be applied as long as the single fish can be distinguished on the echo paper. L~ dense layers and in schools this met-

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hod can not be used on standard echo sounder equipment the O-group fish are oost frequently recorded as craltiple echo traces. Exact weasurement of' r::lultiple echoes is possible, but some'vhat sophisticated instl."'UJnel1.t- ation is necessary. However, Dragesund (1970b) hQS shown that fairly reliable relative abundance estimQtes could be obtained by visual classi- fication or grading of paper recordings of multiple scatters in 1) very scattered, 2) scattered, J) dense and L~) very dense echo recordings.

The best conditions for estimating abundance exists during the dark period

",'hen the fish fry occur in more or less continuous scattering layers.

Since the surveys are carried out also in day time, a conversion factor between day and night recordings ,vas es tabliahed by frequently surveying

the same area both by day and by night.

The abundance of O-group fish is Cl. function of the area of the horizontal distribution, the vertical extension and the density of the scattering layer. In the present investigations the area of distribution of O-group

cod and haddock together "od th the del1.si ty of the echo recordings (the echo abundance) have been used to study the variation in abundance from year to year. The results of some preliminary experiments on O-group herring (Dragesund 1970b) gave a ratio of the order 1:10 between catch in numbers in a scattering layer by night of' density 1) and 2) compared with

that of density J) and

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l'!Thich li1ight be the correct order of magnitude for other species too. Indices of total echo abundance, were therefore estimated by multiplying the area of dense recordings by a factor of 10 and adding these estimates to those of the area with scattered recordings.

Tne vertical ext 3nsion of' the scattering layer varied. This feature is not taken into aCC01U1.t and night g'ive a bias in the abundence indices.

Young fish surveys

The USSR Polar Institute of Harien Fisheries a11.d Oceanography has since 1946 made yearly surveys of young cod ~~d haddock to determine aIll~ual

recrui tmel1.t to the Arcto-Norvlegian cod and haddock stocks. .A 25 m bottom trm'll inserted w'i th a cotton net in the cod end has been used for sampling (Baranelikova 1957). The cover net was 6-8 ^ill long with 10 mm mesh size.

Ages were determined from otoliths.

The number of fish in each age-group caught per hour trawling is taken as abundance index. The indices are obtained by dividing the total catch in number of different age-groups in the Barents Sea and the Bear Island/

Spitsbergen areas by the respective hours trmvling during the survey period. The abUl1.d~~ce indices for cod (Nizovtsev 1966, 1967, 1968b, 1968c, _ 1969 and Nizov·tsev and Trambachev 1969) and haddock (Baranova 1966, 1967, 1968a, 19680 and 1969) are given separately for each year-class at an age c

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0+ (i.e. from age 6-13 months), 1+ and 2+ for the Barents Sea m~d for the Bear Island/Spitsbergen areas respectively. Thes e t-.;·w regions have different areas. Consequently the catch per hour fishing in the tvw regions is not directly comparable in terms referring to the total stock. It is therefore necessary to weight the abundance indices for the h17"o regions in order to combine the data. As supposed by Garrod (1967) the catch per unit effort data for the two regions Clli~ be combined by supposing that

the Bear Islan.d/Spitsbergen "stock" 117"aS distributed over an area equiva- lent to that of the Barents Sea "stock". The weigh3d abundance indices for the Bear Island/Spitsbergen areas are therefore estimated by dividing the catch per UL~it effort figures by 3:54, which is the ratio between the Barents Sea ffiLd the Bear Island/Spitsbergen areas.

The year-class strength in nwnbers ut 3 years of age have been estimated by virtual population an.alysis (Anon. 1965b) by ass1.L'11ing a natural

mortality rate of I;;I= 0,30 for cod aJ.1.d M= 0,20 for haddock (Anon. 1969a, 1970 and Hylen and Eide 1969). A fishing mortality rate of F= 0,80 for older cod and haddock is applied in the calculations. This method gives only the numerical strength of the 1963 and 1964 year-classes in the period studied. HO'wever, by comparing the abundance ip.dices from the USSR young fish surveys in the period 1946-1964 the respective yec,r-class

strengths at 3 years of age for the same year-classes, the numerical strength of the 1965-1968 year-classes might be given (Anon. 1969a, 1970

~~d Hy1en and Eide 1969).

The virtual population ancdysis gives estimatos of the absolute numerical strength of each age-group each year. irJhen a oaturation ogive is applied to the estimated age composition of the stock for each year, estimates of the spawning stock size and its age composition are obtained. The spawnin~

potential can be estimated from the estimated age-composition when the fecundity is YJ1own. Fecundity data for cod and haddock in the Northeast Arctic are insufficient, but the fecundity is assumed to be approximately propotionnl to the weight of the fish, and the total weight of the parent stock is used as an index of the spawning potential. According to Botros (1959) the suggested fecundity/weight relationship underestimates the true relationship as far as cm is concerned.

RELATIONSHIP BETdEEN MEASURES OF YEAR-CLASS ABUJ:.JDANCE

Cod

The echo abundance indices of O-group cod distributed north of 670

:n

^are

estimated for the year~classes 1963-l969 (Figs. l-7). These indices are plotted against the abundance indices at 0+, l+ and 2+ years of age

-'

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respectively (Fig. 15). ^A correlation is indicated between the echo abundance of O-group cod and the abundsnce at 0+. No correlation could be found for O-group echo abundance and the other measures of year-class abundance estimated from the young fish surveys. TI~is is mostly caused by the low abundance indices of the 1963 year-class at 1+ and 2+ (Fig.

l5B-C). In Fig. 15D the O-group echo abundance is plotted against the numerical strength at 3 years of age, obtained from the virtual population analysis. The numerical strengths of the year-classes 1965-1968 can not be measured from this analysis, since they have not yet been available in

the fishery for long enough time. E011Tever, i t is no doubt that they are very poor year-classes, and a correlation betl'leen the two measures of ⁷ year-class strength is suggested.

Haddock

The relationship between O-group echo abundance indices of haddock and the abundance at 0+, 1+ and 2+ is sho,,]n in Fig. 16. rJo correlation vJas found betweon the O-group abundance and the abundance at 0+, whereas

correlations are observed between O-group abundance and year-class strength at subsequent stnges,(-Fig. l6B-C). Excluding the year-class of 1967 Cl.

correlation is also indicated bet"lGon O-group abundance and subsequent year-class strength at 3 years of age (Fig. l6D).

Re^l 2.tionship betHeen parent stoct.:: size and subseguent ye er-clGss strength.

Cod

Virtual population analysis give for each year estimates of the numerical strength of each age-group in the stocl~. By applying a maturation ogive to these numbers an estimate of the spavming stock size is obtained.

Garrod (1967) used a maturaton ogive derived from the relative number of first tine spawners (Rol1efsen

1954)

by a nethod described by Gulland

(196~~). Ro1lefsen found first time spawners up to

14

years of age, but first time spawnors havo in the last 3-5 years only been represented by a small number at 13 years of age and none at lL~ years of age (unpublished Norwegian data). i1 similar maturation ogive to that given by Garrod (1967) has been drm'l11. (Fig. 17), starting vJith 100% maturation at 13 years of' age and ending with

2%

mature fish in age-group six. vn1.en applying this

maturation ogive on the absolute numerical stock composition the age distribution of' the spawning stock cnn be estil":mted for the period 1963- 1969. These age-distributions are similar to those obtained from the

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otolith samples of long line 'oatchos 01' spmvning cod (Fig. 18). HOvlevor, the older age-groups are more abunda11.t in th estimated spmming stock than in the samples of long line catches •. The purse seine catches which are expected to be more reprosentative for the spavming stock than long iine catches (Rollef'sen :LS'56 8.1"C.d. Iiylon 196:2) consisted of older fishes.

I t is therefore suggestoG ~~2t the absolute numerical estimated compo- si tion of the spawning s ':~" ,)~:::. is fairly good.

A propotional relationsbj_I' ")Gt'fJGOn uoight and fecundity is assumed. This implies propotional relatl,:;::lSilip oetvloen spawning potential an,d the lveight of the s tocl-:. "trThen esti.r:-::nti~g the liOight of the spawning stock the same age/weight relationship is used as by the North-East Arctic Fisheries

~rJ'orking Group. The absolute size of the parent stock in hundreds of

metric tons is plotted against subsequent year-class strength at about

6

months of age (Fig. 19). A relatively small variation in parent stock size has been observed in this period. The year-classes 1963, 1964 and

1969 1t10re the most abundant year-classes. A relationship between the

parent stock size a11.d the abundance of the resulting year-class at 6

months of' age may exist f;::)}~ 'the most 2.bundant year-classes in the period studied, but not for the "t~lCJ2 group of year-classes.

Haddock

The n~~erical strength of each age group each year in the period 1963-

1969 is estimated by using virtual population analysis. A maturation.

ogive estimated from material sar;.lp1ed in the Barents Sea (Saetersdal

1954)

during autunm 1953 (Fig. 17) ,vas applied to the absolute numerical stock size when calculating the age composition of the spawning stock. Otolith readings of lTorwegian date:. tc1r.eD. from research vessel catches during

vlinter and spring on t::1.G s~)c:rv.m:inG ni.:::;rQtion along the coast from lVi:alangen to R0st, Sh01'l none firs:; -:,~,'::;2 G:pc"·'j.rn:::::.~s among the age-groups 10 and older and very fe .. .r of the 3 T,:'::L'S ;:;lc1. ~::':.[~:o. (i.:1.1:"lpublished IJor""egian data). These informations are in good 2;:::'OO'TIGli.'':; ~Jit:Ll Scstersdalfs findings (Fig. 17).

Tnese calculations g.ive 2 .. :::1. 2..-:;.:) CO::2D22ition of the spawning stock each year in the period 196J-~l9SS 'i1[::,io1::. dgro'3 fairly good with the age compo-

si tions (Fig. 20) of the G8:r::i12,l1. lcl.ll,:..lings from the area R0st-Mal8..l"1.gen during January-J~pril 196:3-1968 (Neyer 1969) and the age-dis tribu tion in Norwegian long line catches from the area MalangenTNorth Cape during February 1969 (unpublished HOY'V10gian data). Both the German and the NorvlGgian lcandings are expected to be mostly oatu:r;'e haddock on spawning migration.

Also for haddock fecundity is assumed to be proportional to the weight of the fish, which implies that the spawning potential is proportional to the parent stock size. EstiQates of the parent stock size is obtained

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by using the sw~e age/weight relationship us by the North-East Arctic vlorking Group. In Fig. 21 the purent stock size is plotted against the abundance of the resulting year-class at

6

months of age. A relationship may exist under certain conditions within the period considered.

HO'j,vever, under other conditions the effect of the spawning stock size is ruled out.

DISCUSSION

When estimating the echo abundance of the 1963 year-class of coel and

haddock a scattered distribution of O-group fish was assumed for the areas around Bear Island and along the Spitsbergen ccast (Figs. land

8).

^High

ahuJ:.Ldance indices of cod for this year-class vlere found in the young lli1.d adolescent phases (Hizovtsev 1963a) and at least some of the areas might have been popluated with dense concentrations of O-group fish. The O-group

echo abundanceO:.1ight therefore be underestiw2.ted.

The figures for catch per unit effort are compararable from one year-class to another, when the same relative Mlo~Lt of the year-classes at 0+, 1+ and 2+ years of' age are at the bottom each year during the young fish survey.

H01'lever, sone year-classes migrate to the botton later in the year than others, and a bias may be introduced in the 0+ abund~~ce indices. Few specimens of the 1947 year-class were caught with bottom trawl as late as December 19L~7 in the eastern Barents Sea, but in December 19L~8 a great number of' this year-class ,-ms caught together >vi th O-group cod of the 1948 year-class (Barm~ecl~ova 1957). Diurnal, vertical nigration of O-group cod (Baraner.J::ova et. al. 1963) and of' 1, 2 and 3 years old haddock ('G'food- head 1964) "lill affect the abundance indices in the young fish surveys.

Tl1.ese might be responsible for some of' the variations observed in Figs.

15

and

16.

On the other hand a reduced abundance of the 0+ group relative to the O-group echo abundance l:light be caused by s!:12.11 predators as 1, 2 and 3 years old cod (Ponomarelu~o 1961). Variation from year to year in discarding snall fish at sea by trawlers (Hylen 1967 and 1969), is a factor which might cause some variation in the data presented in Figs.

15D and l6D. This is not tak.en into account in the virtual population . analysis. At present only the numorical strength of the 1963 and 1964 ye2cr-classes of' cod and haddock can be estimated with some confidence.

No"l firm conclusion of the relationship between the O-group abundance and the year-class strength at 3 years of age can therefore be drawn from the availnble data. HOvlever, i f a close correlation exists between the echo abundance of' O-group cod and haddock and the numerical strength of the year-classes at the beginning of' their third year of' life, an estimate of' the year-class strength can be given the same year as i t is spawned.

vfuen alinear regression between the O-group abundance and the year-class strenGth at 3 years of age i~-_~;;Slirrigci; ^thG 1969"'year::'class of cod- 8.1'1cl- haddock is expected to -be ropresei1.teCl: in' the sea at the be- - , ~

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giPJling of 1972 with about 680 and 730 millions of cod and haddock respec- tivcly (Figs. 15D and 16D). Applying the same method :for the 1967 year-, . clacE' of haddock this year-:'class is expected to be repr~ented in the sea

by a·,:,:::-.t1 t ~-20 millions of :fish at 3 years of a.ge. However, since the 0+

abuI:.;i:""l].ce is 101'! in the young fish survey (Fig. l6A), the year-class might have been reduced by predators in this stage, or i t ~ight havo been reduced due to unfa.vourablo enviroluuental conditions. I t is known from the O-group survey in 1967 that O-group saithe 1'lere numerous west of Bear Island 8..."ld off the Spitsbergen coast, up to about BOON (Anon. 1967). Th.e prc::S'3:'1.Y may have been transported northwards from the spawning areas at Viki,V: Ban..k, off M0re and Hal ten Bank. A northward transport of haddock

eggs ~nd larvae from the same areas may also have taken place, and the 1967 .l0ar-class in the Barents Sea might have got a significant number of

post.~irval fish from the spawninG areas mentioned. These fish might be exposGd to more extreme enviror~ental conditions than they are adapted to, and tho natural mortality rate during the O-group bottom stages may have been higher than those of tho .Arcto-lJoJ."1;rogian haddock. This may explain

the :::"01'[ abundance of the 1967 yoar-class (Fig. 16;.). On the other hand

this yoar-class was relatively numerous in catches taken along the Firill- mark Coast and in the Barents Sea during a Nor1'!egain trawl survey in r4ay 1970.

1<111en Gstima ting the numerical spawning stock size one maturation ogive

for cod fu""ld one for haddock ,-vere applied :for the ·whole period 1963 -69 •. Long

and ;:.~_:>,:t term ,changes ·will therefore introduce bias in the estimated spaTrr-

nin{t stock age compositions (Rollefsen 1954). These may be responsible for -v~1.() disagreeraent between the relative strength of some year-classes in t::-~:.; estimated spawning stock and those in the catches of spawning fish,

as o~sGrved for the 1956 m~d 1959 year-classes of cod and of the 1964 year-

class of haddock (Figs. 18 and 20). HOvlevor, the agreement is fairly good

for t;~lG period studied.

The aGo/fecundity relationships are not lll~own for Lrcto-Norwegian cod and hadd'):::;l;:: and a linear regression betv18en the weight and the :fecundity is as s :",::K<1. This assumption implies a proportionality betvreen parent stock siz.:.- iJ:: metric tons and spm'1Tlling po tentia1 •

/ However, this method may give

anu;--:.::~.8restil:12te 9'f the spnwning potential (Botros 1969). Data of parent

.'

stoc:';': ;:::ize al'ld subsequent year-class strength nre available oP~y for a

lJ..~_c_,,~.,_, ~t~u.io.JGr ·,-'~·I·.·-,,' ",_.,.C-. - OI ~ years (F· 1 9 S . 19 auQ ~1 ...,...) ^~• The relationship indicated for coG.:'.';.c. h2ddock aro similar to that found for ITorwegian spring spm-ming herT:',::-lLS (Draeesund 1970£1). These studies suggest a relationship betvveen spm,,-c':::'l'le; potential nnd O-group abundance for cod, haddock and herring, when the conditions for the progeny are favourable. Under less favourable conditions the effect of spaWl'ling potential is ruled out. H01,vever, an

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assosiation in time between the var~ables, spavnling stock, recruitment, fishing₇effort and some undetected trends in the environment CalTIlot be avoided in the methods used to denonstrate a stock/recruitment relation.

A slightly different approach is made by Garrod (1968) and Ancn. (1969).

This approach is based on the assumption that i f the stock is to remain stable the spmro.ing stock should in average produce enough young to replace the averD."ge of its constituent year-classes. t-Jhen the potential

spmm.~ng stock is reduced by fishing, the recruitment can be held constant by a corresponding increase in the survival of the progeny~ This is

expressed -(Anon. 1969a) as by S= (~3/R R ) sp

H' R

• e~ or log S = 3/R + F.

e sp

Using the age groups 7-13 and 5-11 t~ represent the spawning stocks of cod and haddock respectively, R

sp denotes the average numerical strength at 3 years of age of the year-classes in the parent stocks. R3 is the year-class strenGth of the resulting generation at 3 years of age. F is

the mean fishing mortality rate per year-class sU!11ITled ')ver 3-9 and 3-7 years for cod w~d haddock respectively, and S is a survival indax'from

the eggs stage to 3 years old fish. The relationship log S

=

^F represents e

the hypothesis that recruitment is independent of the spawning potential (Fig. 22). Recruitment is held constm~t by ~ncreased survival rate of eggs and larvae as the spawning stock is reduced. The replacement rate

(R / )

3 Rsp for the year-classes up to 1964 are calculated from year-class strengths given by virtual population analysis. For recent year-classes estimates have been obtained from Figs. 15D and 16D, assuming a linear

regression between O-group echo abundance and nUPJerical year-class strengtt at 3 years of age. Since the late fifthies only

5

of II year-classes of cod and 8 of 13 year-classes of haddock have replaced its constituent year-classes (Fig. 22). A great variation is observed in the data! and a longer series of observations are necessary to establish a relationship.

SUM!YIARY

1. The relationship between the O-group echo abundance of Arcto-Nor- wegian cod fu~d haddock (i.e. about

6

months of age) of the 1963-1969 year-classes 2~d the abundru~ce at subsequent stages of the sa~e year- classes (at 0+, 1+ and 2+ years of age) ruld between the O-group

abundance and the numerical strength at 3 'years of age were analysed.

(FiGS. 15 and l6). O-group echo aDillldrulce indices were obtained from combined acoustic and fishinG surveys (Figs. 1-14). Abundance indices -at 0+, 1+ ru~d 2+ were taken from the USSR young fish surveys. The

numerical year-class strengths at

3

years of age were estimated by virtual population analysis. Correlations were indicated l6tween

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the abundm1.ce of O-group cod and the abundance at 0+ and bet";;Teenthe O-group abundance and the nlli~erical strength at

3

years of age.

For haddock correlations 1vere indicated between the O-group abundance lli~d the abundance at l+, 2+ and the numerical year-class strength at 3 years of age.

2. Variation in O-group abundmLce was studied in relation to the parent stock size in metric tons (assTh~ed proportional to spawning potential). Relationships were suggested for cod and haddock between the parent stock size and the strengths of the resulting generations at

the O-group stage in years 'iv-hen the conditions for the progeny w·ere favourable (Figs. 19 and 2l). The effect of the parent stock size in determining the year-olass s trongth vlas ruled out in years wi t11.

less fa.vourable conditions •.

3. The survival from the egg staGe to 3 years old fish was studied in relation to the fishing mortality rate per year-class in the

spmming stock. (Fig.22). These investigations suggests that since the late fifthies only

5

^of11 year-classes of cod and 8 of 13 year- classes of haddock have replaced its constituent year-classos.

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Anon.

Anon.

Anon

1965a. Preliminary report of the joint Soviet-NorwegilliL investigations in the Barents Sea and adjacent waters September 1965. Couu. Heet. into Coun. Explor. Sea, 1965

(161): ~-5, 10 figs. l11ime~

(Gu1land, J.A.) 1965b. Estimation of mortality rates. Anex to Arctic Fisheries Working Group. Report of meeting in Haiu- burg 18-23 January 1~§5. Couu. Meet. int. Coun. EJ..:p1or.

Sea, 1965 (3): l-9. ll:1ime§l

1966. Preliminary report of the joint international O-group fish survey i~ tp~~ ?arents Sea and adjacent waters August/

September 196b. ·-~Coiiri"';.j JI1eet. into Coun. Explore Sea, 1966 (I-I: 23): l-9, 13 figs. L~Iime2:.;

1967. Preliminary report of the international O-group fish survey in the Barents Sea and adjacent waters August/Septem- ber 1967. Coun. Heet. into Coun. Explor. Sea, 1967 (H:31):' 1-8, lb^r figs. LMime~

1962a. Horth-East Arctic Fisheries Working Group_ Report of the meeting at Copenhagen, December 4th-14th 1967.

Coun. Meet. into Couu. Explor. Sea, 1968 (F:19): 1-10, 14 tables, 7 figs. '1J1ime?~

1969a. North-East Arctic Fisheries Working Group. Report of the meeting at Copeilhpgen, January l3th-l7th 1969.

Coun. Meet. into Coun. E .... lore Sea 1969 (F:2): l-21, 8 figs,

1 Appendix \ 3 pages • IHimeq,j

1969b. Preliminary report of the O-group fish survey in the Barents Sea at"Ld adjacent "tvaters in August-September 1968.

Coun. Meet. into Coun. Explore Sea, 1969 (F:33): 1-4, 13 figs. ~Iime~

1969c. Preliminary report of the O-group fish survey in the Barents Sea ruLd adjacent waters in August-September 1969.

Coun. Meet. into Coun. Explor. Sea, 1969 (F:34): 1-5, 15 figs.

[~1ime~

1970. Report of' the meeting of the Horth-East Arctic Fishe~·_

ries vlorking Group Copenl'lagen, January 14th-16th 1970.

Coun. Meet. into Conu. Explor. Sea, 1970: 1-15, 1 Appendix.

Q1ime~

Baranenkova, A.S. 1957. Fore10pig medde1else om den kvantitative utbred- else av yngel av torsk og hyse

J.-

Barentshavet. TrydY mur- mansk biol. Sta. , 3: lL:-8-l58. LIn RussiarY

BAx:<:1:l1.enkova,

Barfu"'1.0Va,

z.

A.S., Drobysheva and Ponomarenko, I.Ja. 1963. Vertical migration and f'ee_ding of' O-group cod in the Barents Sea in

September-O~tobe~. Coun. Heet. into Coun. Explor. Sea, 1963

(84): 1-6. \ Himeo.l

'-- -.~

1969. Soviet investigations on young haddock of' the 0, I, II al'ld III age groups in the Barents Sea. Annls __ bio1., Copenh. ,"

2S: 124--125. .'

Baranova, Z.P.

196h.

Results of determining the abundance of' young had-.

dock in the Barents Sea in ,·lin"ter 1963/6^lJ

r.

Hater. ryb. Iss- 1ed~ Sever. bass., 4- : 18-21. JIn Russian~

.... -

1966. Soviet inves tigations on young haddock (0-3 age--groups) in the Barents Sea. Annls bio1." ,Copeill'l., 21: 91-92.

1967. Soviet investigations on YOILYl.g haddock. on the 0, I, II and III groups in the Barents Sea in 1964/65. Annls biol., Copelih., 22: 92-94.

1968a. Soviet investigations on young haddock of' the 0, I, II aJ.1.d III age-groups in the Barents Sea. Annls bio1. , Copenh., 23: 108-109.

(13)

-13 -

Bar~~ova, Z.P. 1968a. Soviet investigations on young haddock of the 0,

I, II and III agE't-groups in the Barents Sea. AIUlls bioI.,

Coper~., 23: 108-l09.

196Gb. Soviet investigations on young haddock of the 0, I, II and III age-groups in the Barents Sea. Ann1s bioI., CoperJa., 24: 102-103.

Beverton, R.J.H. and Holt, S.J. 19570 On the dynamiCS of exploited fish population. Fishery, Invest., Lond., Ser. 2, 19: 1~533.

Botros, G.A.

Dragesund, O.

1959.

A comparative study on the fecundity of Norwegain and Baltic cod. Coun. Meet. into Coun. Explor. Sea, 1959

(19): 1-15. E1imeo ~

1970a. Factors in fluencing year-class strength of Nor- ,,,egian spring spawning herring. (C1upea j:,arengus Linne) FiskDi-r • SkI'. Ser. HavUnders., 15: 381-450.

1970b. Distribution, abundance and mortality of young and adolescent Norvlegian spring spawning l.'lerring (Clupea lc.arengus Linne) in relation to subsequent year-class strength.

FiskDLr" Skr. Ser. HavUnders., 15: 451-556.

Dragesund, O.~and Olsen, S. 1965. On the possibility of estimating year- class strength by measuring echo-abundance of' O-group f'ish.

FiskDir. Skr. Ser. HavUnders., 13 (3): 48:62.

Dragesund, 0., Hidttun, L. and Olsen, S. 1970. Hethods for estimating distribution and abundance of O-group :fish.

Coop. Res. Rep. Ser. A, into Coun. EJplor. Sea,18 : 25-34.

Garrod, D.J. 1966. Stock and recruitment data f'or Arcto-Norwegian cod.

Coun. Meet. in!. Coun. Explor. Sea, 1966 (G:8): 1-5, 1 table and 4 f'igs.

i

I1imeo

-:J

' - - ~

1967. Population dynamics of the Arcto-Norwegian cod.

J.. Fish. Res. Bd. Canada, 24: 145-190.

1968. Stock and recruitment relationship in four north Atlantic cod stocks. Coun. Heet. into Coun. Explor. Sea, 1968 (F:14): 1-6, 1 table and 3 figs. ~limeo~

Gull and , J.ll. 1964. The abundance of fish stocks in the Barents Sea.

Hjort, J.

Hylen, A.

Rapp. P.-v. Reun. Cons. perm. into Explor. Mer, 155:

126-137.

1914. Fluctuations in the great fisheries o:f northern Europe view-ed in the light of biological research.

Rapp. P.-v. Reun. Cons. perm. into Explor. Mer, 20: 1-228.

1962. Notfisket i Lofoten. Fiskets Gang, 48: 581-587.

1967. On the estimation of cod ~~d haddock discarded by trawlers using different chapers. Coop. Res. Rep. Ser. B:

1966: 65-76.

1969. Discarding of fish in North-East Atlantic. Coop.

Res. Rep. Sero B, 1968: 56-58.

Hylen, A. and Eide, Po 1969. Yield curves for Arctic cod and haddock.

Coun. Heet. into Coun. Explor. Sea, 1969 (F:19): 1, 2 figs.

-i]1imeo ;~

'-'- --.i

Meyer, A. 1969. German investigations of Arcto-Nonvegian haddock.

Jrr.mls biol., CopewL., 25: 125-126.

Nizovtsev, G.P. 196L1-. Results of determining the abundance of young cod in the Barents Sea in the autmnn-1'linter period of 1963/64.

Hater. ryb. Issled. Sever. bass., 4: 14-17 •. [En Russian]

1966. Soviet Researches on the 0, I, II and III age-groups of young cod in the Barents Sea. Annls bio1., Copenh., 2l:

78-79.

1967. Soviet investigations on young cod of 0, I, II and III age-groups in the fishing areas I and IIa. Aru~s biol., CopeID2., 22: 76,77.

(14)

Barents Sea during autu.nn.1.--.;-;inter 1966/67. Mater. ryb.

Issled. Sever. bass., 12: 13-19. [En Russian~

1968b. Soviet investigations of young cod of the 0, I, II a..."J.d III age-groups in the Barents Sea in 1966.

Annls bioI., Copenh. ^% 23: 102-10h.

1963c. The result of young cod registration in the Barents Sea during autuTIm-vlinter 1966/67. Mater. ryb.

Issled. Sever. bass., 12: 13-19. f!n Russian,..:!

1969. Soviet investigations on young cod of the 0, I, II and III age-groups in the Barents Sea. Ann1s bioI., Copenh., 25: l12-114.

Nizovtsev, G.P. and Trambachev, H.F. 1969. Soviet investigations on young cod of the O·r I, II and III age-groups in the Barents Sea. Coun. Meet. into Coun. Explor. Sea, 1969

(F:13): 1-3. "(I4imeo::J

Ponomarenko, I .. Ja. 1961. On possible influence on feeding of cod fry

Ro11ef'sen, G.

Sund, O.

Sc;etersdal, G.

upon their abun~ance. Trudy.Sovesnch. iYJltio1. Kom.,

12:

^301-306. fln Rus sian.:J

1930. Observation on cod eggs. Rapp. P.-v. Reun. Cons.

perm. into Explor. Mer, 150: 31-34.

1954. Observations on the cod and cod fisheries of Lo- f'oten. Rapp. P.-v. Reun. Cons. perm. into Explore Mer, 136: 40-47.

1956. Introduction. Rapp. P.-v. Cons. perm. into E~ylor.

Her, 140 (Part I): 5-6.

1924. Snow aJ.1.d survival of cod fry. Nature 113: 163-16l.j·.

1936. The fluctuations in the European stocks of cod •

• P.-v. Reun. Cons. perm. into Explor. :Her. 101

Some investigations 011. the Arcto-Norwegian haddock.

Coun. l1eet. into Coun. Explor. Sea, 1954 (47): 1-9, 12

~. PM· '<

XlgS.

l:

^lmeo^~l

TvToodhead, P.M.J. 1964. Diurnal cha.'11.ges in trawl catches of fish.

Rapp. P. -v. Cons. perm. int. Exp1or. M:er, 155: 35-L~4.

(15)

0-GROUP COD p.,;. ~ ~ ® ... A

" •

5 0 0 6

•

0 8 Fig. 1. Distribution of O-group cod in the autumn of 1963, (1) scattered, (2) dense consentration, (3) O-group cod caught by midwater trawl with cover net, (4) O-group cod not observed in midwater trawl catches, (5) 0 -group cod caught by purse seine catches, (7) O-group cod caught by bottom trawl with cover net, (8) O-group cod not observed in bottom trawl catches.

0-GROUP COD

,

AA A A ~

A A A 0 A A A (I) A <) A A A A AAA A A A A A

o

5' 10 Fig. 2. "Distribution of O-group cod in the autumn 1964. Legend as in Fig, 1.

(16)

"

76'

"

" "

" " " " " "

" "

"

75'

" " "

"

0.

""

" 8

" " "

75' "

"

0

" " "

" Q

" " " "

"

"00

"

7~'

"

",,"

"

" " " 0'bQ

" " "

~

A 1965

A 3-17SEPT 69' A 1966 68' 27 AUG. -10 SE PT 68' 67 5' 10' IS' 20' 25' 30' 35' 40' 45' 50' 67 5' 10' IS' 20' 25' 30' 35' 40' 45' Fig. 3. Distribution of a-group cod in the autumn 1965. Fig. 4. Distribution of a-group cod in the autumn 1966. Legend as in Fig. 1. Legend as in Fig. 1.

(17)

80' O-GROUP COD 19' 6 6 ~ 18' 71' ;., 6 6 A 6A A6 A A 6 16' 6, A 6 6 A 6 6 6 75' A A A A A 6 6 Q A 6A6 A 6 A A 6 A D 74' A 6 A 6 A A ~ A6 6 73' A A 6 6 6 '}. A A 6 A A A A A

..

72' 6 A A A A 6 A A 6 A A A A 71' 6 6 6 A A A A A A A A A A A A A 70' A A A A A 6 69' 1967 A 24AU.G.-8SEPL 68 , 67 5' 10' 15' 20' 25' 30' 35' 40' 45' Fig, 5. Distribution of 0-group cod in the autumn 1967, Legend as in Fig. 1.

A AA, A A A 6 A

0

50'

80' )

0

0-GROUP COD 19' ~

~

"1

6 6

~)

6 71' 6 6 6 AA A Iv: I 6 A A 6A A A A A 6 A 16' AA6 6 A A A A A A A A AA A A A • A A A A D A A A A 15' A A D A AD AA' A At/:> A A A A 6A A t!' A QA A A A D A A 6 6 A A 14' D A A A A A A A A A A A A A A 13' 6 6 A A A 6 A A A 6 A A 72' A A& A A 6 A A A 6 11' A A A 10' A 69' 1968 25 AUG.-9 SEPT. 5' 10' 15' 20' 2~' 30' 35' Fig, 6. Distribution of O-group cod in the autumn 1968, Legend as in Fig, 1.

A

A A 6A A A A AA

(18)

o O-GROUP COD o -G ROU P /1 /1 /1 /1 /1/1 /1 /1 /1 /1 /1 /1 /1 ~ /1 /1 /1 /1 /1 /1 /1 /1 /1 /1 5' 10' Fig. 7. Distribution of O-group cod in the autu:mn 1969. Legend as in Fig. 1.

Fig. 8. Distribution of O-group haddock in the autu:mn Legend as in Fig. 1.

(19)

80T---r~,_---,---~

'" '" '" '" '" '"

66 6

@

66 6 6 6

'" '"

6

'"

6 Q 6

'"

666

'" '"

6 6 6 66 s' 10'

6

I 6 6 6

'"

6 66 1964 19 JULY -IL AUG 28AUG -50Cl

6 6t.

'"

6 25 • 30'

0-GROUP HADDOCK o 6

'"

6

'" '" '"

3 S' Fig. 9. Distribution of a-group haddock in the autumn 1964. Legend as in Fig. 1.

80·r---~~~~~---;_---~ 79' o -GROUP HADDOCK 18' 11' 7S' 15' 14' 73' 72' 11' 10' 6 69' 6

~

6 1965 3-11SEPT

o

68'

"\-,

i 67 \ 5' 10' 15' 20' 2S' 30' 35-40' 4S' 50' Fig. 10. Distribution of a-group haddock in the autumn 1965. Legend as in Fig. 1.

(20)

0 A A 71,' 6 6

'" '"

0 6 A 6

'" '"

'"

1969 H AUG -7 SEPT. 67 5' 10' IS' 20' 25' 30' 35' 40' 45' 50' 10' IS' 20' Fig. 13, Distribution of 0 -group haddock in the autumn 1968, Legend as in Fig. 1. Fig. 14. Distribution of 0 -group haddock in the autumn 1969. Legend as in Fig. 1.

(22)

A IS SI ~-r---r---'r---'--_ 8 @ ® 10 15 20 10 15 20 ECHO ABUNDANCE INDEX OF O-GROUI' COD, 10" Fig. 15. Relationship between echo abundance index for 0 ~group cod and (A) at 0+ year of age for the year-classes 1963-1968, (B) at 1+ year of age for the year-classes 1963-1967, (C) at 2+ years of age for the year-classes 1963-1966 and (n) the absolute numerical strenght at 3 years of age for the year- classes 1963-1968. The respective year-classes are indicated inside the circles. Arrow show the O-group echo abundanc e index for the 1969 year -clas s.

@ @

A B 20

@ ® 1 30

® ,I 40

@ 1 50

z UJ U D: UJ 60 ~. ~ Fig. 17.

/ ./

./ 2 4 6 8 10 12 14 . AGE Maturation ogives for Arcto-Norwegian cod, (1) for the period 1941-1953 (Rollefsen 1953, Garrod 1967), (2) for recent years and (3) for Arcto- Norwegian haddock in 1953 (Saetersda11954). Fig. 18. Age compositions of spawning Arcto-Norwegian cod in the period 1963-1969, (1) long line catches from Lofoten during spawning season, (2) calculated from estimated -absolute numerical stock size.

40 20 40 20 I- Z UJ U a: UJ Q. 40 ~ z 0

...

Vi 20 0 Q. ::E 0 u 40

1963 1964 1965 1966 6 8 10 12 14 16

~

o

2 AOE

...,

fil

6

1967

rflr.fl-n~

1968

~ ~ rIl _ _

1969

~ Jl ~

8 10 12 14

(24)

": 250 o

..

c o u200 Cl. :::l o er: t!) b 150 u.. o >< w c 100 z w u z ~ 50 z :::l III « o W

@ 30 60 90 120 150 180 210 PARENT STOCK. SIZE IN METRIC TONS'x 10-J Fig. 19. Relationship between parent stock size of cod and the 0-group abundance index. The respective year- classes are indicated inside the circles. Fig. 20. Age compositions of spawning Arcto-Norwegian haddock in the period 1963-1969, (1) German trawl landings from Rcpst-Ma1angen during January-April 1963-1968 and Norwegian long line landings from Scpr- cpya area during January-February 1969, (2) calculated from estimated absolute numerical stock size.

I- Z w u 0:: w a. :!: z 0 I- Vi 0 a. :l: 0 u

40 20 1963 40 20 1964 1967 40 20 1965 1968 40 20 1966 1969 4 6 8 10 12 14 4 6 8 AGE

(25)

l

LOG", SURV'VAl J!>JDEX

f '--",

~_,,---L \ \ \

I

I.

-_

... ---.,-.,,-~~,---.... ----,-~ ..

:,-

~- ro -n u; ;:c z (,.., :;:: o ' :JJ

I

. ..,

; !

'JJ I 1> f',) -, i~l

,

'1'1 '

. I ~ ~ I ^(:0

^/t.;^...^ri.,=:) ^~

\\

(,':') \::,:'.1

\ \ @

\ \ 0~'1

~~\~

'\.~\

\ \ ®

\

\ \ \

("Q,) \.,!/

CID \\ \ ©

\ \

e, C' C' ,,'" "

'"

LOGe 51,JRVI,{/~l INDEX

"J (---\\--~---:--- I '\

~

!

I I i

j I I

:

j

I

® ®

\ \ \ \, (E)

'\ \\ @) (;y

/""1 \.:'~I

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\

\ \

>,

_.

_" N ~ o 0 i® ~ It

~~ I ~1 : ~1iJ

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@) @ (~ Fig. 21. Relationship between parent stock size of haddock and the O-group abundance index. The respective year-classes are indicated inside the circles.