CM_1977_H_37.pdf (651.1Kb)

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ABSTRACT

ON THE INTERPRETATION OF THE CENTRAL ZONE IN OTOLITHS OF CAPELIN FROM THE BARENTS SEA

by

Johannes Hamre

Institute of Marine Research

P.O.Box 1870-72 N-5011 Bergen, Norway

The present paper deals with biological aspects assooiated to the width of the central zone in oapelin otoliths. It is found that the central zone represent the O-group growth even in cases when the radius of the zone is as small as 0.05 mm. The investigation shows that the capelin with central zones less than 0.20 mm are mainly distributed in the south-eastern part of the 8arsnts Sea during their first year of life. The component of this small O-group capelin constitutes a major part of the strong yearolasses recruited after 1970. The bwlk of the small O-group Oqpelin,

which may be recrui ted from summer spawners, matures as spring

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spawners at S years of age. whereas the recruits of the spring spawners. which is far the dominating spawning group. normally mature at 4 years. The increased strength of the small Q-group capelin has thus changed the age composition of the spawning stock and added a new cohort to the immature part of the popu- lation. This has to a large extent effected the Norwegian capelin fishery.

INTRODUCTION

Scales of capelin do not develop during the first year of life.

otoliths has therefore been prefered in age readings. The ~ones

in capelin otolith are relative well pronounsed. except for the first one which may be difficult to detect particularly in older 8epcimens.

Various ways of reading and interpreting the central ~one in capelin otoliths are described in the literature. Some workers have omitted the central zone in their age reading(RAKHMANO~A

1928. PITT 1958). others have counted the central zone as the

first winter ring (HANSEN 1943. KANNEWORFF 1968. VILHJALMSSQN

1968. PROKHOROV 1968). and some workers have counted the central

zone in special cases only. according to size and structure of the otolith center (TEMPLEMAN 1948, 1968. WINTER 1974).

Norwegian scientists have previously used the method described by PROKHOROV (1968). PROKHOROV. who worked on Barents Sea capelin suggested that even the smallest sign of an inner center should be counted as the first winter ring.

In recent years, when abundance eastimates of capelin by the acoustic method became available. it turned out that using the age reading suggested by PROKHOROV the density distribution of the 1-ringers in early summer did not correspond to that observ8d in late autumn. On the other hand the abundanc8 estimates of

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1-L'.inger coinside well when the zone is interpretod as d8s[ri~:t':r.::

by TEMPLEMAN (1948, 1968). Based on these evidences we decidsd to change our age reading accordingly.

The present paper deals with recent research carried out to check the validety of thel;lmethods used in our age reading.

Templeman's method of age determination

An outline of the method of age re~diHg described by TEMPLEMAN

(1948) 1968) is necessary for the understanding of the problems

involved in the present study. TEMPLEMAN's work refers to New- foundland capelin which spawn during summer and autumn.

In reflected light the center of the capelin otoliths does

normally appear as a broad tranclusent nucleus) without the inner limit which makffia typical winter zone look like a narrow tranclusent ring. In the cases of small sentral zones) the otolith center of capelin appears to be somewhat similar to the otolith center of an autumn spawning herring. TEMPLEMAN interpreted

this center to be assosiated to the larval growth up to some 3 cm in body length) i.e. that the tranclusent structure of the cent8+

WaS independent of the time of the year the cente~ was formed.

TEMPLEMAN assumed that the O-group capelin was a fast growing fish which in case of summer spawned fry could obtaine a modal

length of some 7 cm at the end of the year. The tranclusent center was therefore regarded as an extended otolith nucleus which he termed the larval chech ring. These central zones were omitted in his age reading.

The Newfoundland capelin stock has however also components which spawn in late summer and autumn. The O-group capelin f+om these late spawning components should therefore be considerably smaller

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at the end of the year. In such cases it was reasonable to assumed that no visible opaque otolith material was laid down between the tranclusent center and the first tranclusent winter ring. The otoliths of these smallest O-group capelin would therefore be characterized by an extended center including bouth the larval check ring and the first winter ring.

TEMPLEMAN observed that the alternate opaque summer zone and the tranclusent winter band corredponded to ridges and grooves on the otolith surface. TEMPLEMAN used this observation to identify the small size O-group fish, in which the otolith center also included the first winter ring. The specimens which had a broad tranclusent zone and a groove in the center were aged according to the number of tranclusent zones (winter rings), whereas the otoliths lacking the central groove were aged one year younger.

MATERIAL AND METHODS

The Barents Sea capelin stock consist of spring spawners mainly, but some components spawn also in summer and autumn (PROKHDRDV 196B). In recent years, the stock has been assessed by acoustic method twice a year, in the summer (June-July) and in the autumn

(September-October). When TEMPLEMAN's age readings is applied to the Barents Sea stock one should exp8ct to find:

1. a relative low abundance of I-ringers in the summer survey,

2. a considerably increase in the abundance of I-ringers in the autumn survey, and a decrease in the average width of the otolith central zones,

3. a considerably number of post larvae in July with a modal length corresponding to the body

length when the larval rings are completed

(3-4 cm).

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The results of the previous summer surveys comparad to tho2Q obtained in the autumn are in agreement with the expectations with respect to 1 and 2 whereas the post larvae of the Bxpsctsd size in July has not yet been observed or reported. The low abundance of I-ringers recorded during the summer survey CQuld be explained by an underestimate of the I-group fish. becaUSE these are often found near the surface and above the range ~f

the echo sounder transducer (DDMMASNES and NAKKEN 19751. Ho~av8r,

the corresponding decrease in the width of the otolith certsr

indicated that a new component of I-ringers enters the stock in the autumn. If TEMPLEMAN's method of age readings was not valid

for the Barents Sea stock, i.e. that the central zone always re- flect the O-group growth, a component of small I-ringers should be found somewhere in July, presumably in the south-eastern p~rt

of the Barents Sea.

In order to obtain data for a study of the larval grqwth and

the size and distribution of I-group capelin, a relevant sampling programme was incorporated in the summer survey in 1976, lasting from 6 June to 10 July. The survey was carried out by the R/V

"G,D. Sars", the survey routes and stations are shown in Figure 1.

The larvaes were caught by a Bongo 60 net, mesh size 500 ~,

towed in 15 min. in 2-15 meters depth. The I-group capelin Were

c~ught by the pelagic trawl used in the international O-group surveys. The trawl was towed in the surface layers (0-20 m) by the use of additional floats on the headline. The trawl was

lowered to deeper layer when echo traces of capelin were observed.

In the area south of 71 degrees north no capelin was recorded on the echo-sounder and the trawl stations here are surface hauls only.

Data on density, back-calculated 11 and distribution of the I-ringers obtained during the autumn survey in 1976 ars given for comparison (Figures 4 an~ 5). In order to show the effect of the first year growth on the maturing capelin stock, bac~

calculated 11 distirbutions of the yearclasses 1970 to 1972 as mature fish are included in the present study (Table 1, Figure 7).

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With respect to the sampling prugrammes and prosessing of the data, reference is made to OOMMASNES (1977).

RESULTS

Figure 2 shows the mean lenght of I-ringers by stations in JunB- July 1976. It is seen that the size of the l-ringars in the sDuth-eastern area is considerably smaller than in the north- western one, although no well pronounced boundery between size.

groups does appear from Fig. 2. The· largest concentration of 1-ringers (trawl catches above 10.000 individuals) was found in the central area (73 to 74 degrees north, 32 to 36 degrees east) and in the south-eastern area (70.30 degrees north, 45 degrees east). In the latter area the capelin were not detect- able by our acoustic equipment and the trawl stations were taken at random. The density distribution of the small size I-group capelin was therefore difficult to estimate, but the observation indicate that this was probably the area from which the small I-ringers, entering the stock in the autumn, Were ret::ruited.

In Figure 3 are shown length frequency distributions of the radius (R) of the central zone. The samples are grouped in 0.05 mm

groups by two areas, east and west of 37 degrees east respectively.

The corresponding back-calculated body length (1

1), was obtained according to the equation given by GJ0S~TER 8nd MONSTAO (1977).

The curve of the western area is more or less identical to the observation made in previous summer cruises~ The length distribution of R is nearly symmetrical, with a peak corresponding to a back-calculated body length of 5.6 cm. Most of these capelin have a 11 above 4.5 cm. The curve of the eastern area demonstrate larger range in R, and containe a considerably amount of 'papBlin having a 1

1, below 4.5 cm, i.e. within the range of th8~larval

G h e c k ri n g !'

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The investigation during the summer cruise indicated the ^8Ylstanc8 of two different size groups of I-ringers, but it was difficult to separate the groups because the smallest fish could not be detectsd by the available acoustic equipment. Being aware of this possi- bility, special attention was paid to the problem during the following autumn survey.

Figure 4 shows the density distribution of I-ringers obtained by acoustic technique in September-October 1976 (OOMMASNES and R0TTINGEN 1977). Two main concentration of I-ringers appear from this chart, one centered at 7~d~grees north, 35 degrees east, the other at 74 degrees north, 36 degrees east. Figure 5 shows the length- and back-calculated I1-distributions CA and B) of the two components, the samples grouped according to the area north and south of 75 degrees and 15 min. north. The

Figures show two different groups of I-ringers, both with regard to distribution area, and length distribution pattern. The 1

1- distribution of the northern one is identical to the l1-distribution of the largest I-ringers in Figure 3 whereas the component containing the small sized fish is better pronounced as a

separate group in the autumn survey, when the two groups could be located by the acoustic method. The modal 11~ 4.2 cm correspond to the 11 interpeted as the larval ring.

Figure 4 shows the density distribution in volum. The area integrated total volum, converted to number are 11.8 . 1010 and 13.6 . 1010 for the southern and north8rn on8 r8sp8ctiv8ly.

i.8. th8 two components are approximately of equal abundance in number.

The compon8nt of I-ringer found in the southern part of the surveyed ar8a in th8 autumn is obviously th8 small l-ring8rs found in th8 summ8r which have migrat8d north and westward during the p8riods betwe8n th8 cruis8s. The interpretation of

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tile central zun8S in the otolith has thus beCC.I:10': cl c;u:;:,,,ti'.::r,

of the age of the small I-ringers. which have a modal 11 of 4.2 cm. In the samples collected in the first week ^o~July.

a 11 of 4.2 cm (R '" 0.15 mm) correspond to a bDdy lengt.h ^{( I f}

5.8 cm.

Figure 6 shows the catch in number and mean length of the capalin larvae by stations. It is seen that even at the boarder of the larval drift towards north and east th,e mean length ef the larvass is less than 2 cm (range 0.9 - 2.4 cm). This observation and the small increament in larvae length ih the direction of the larval drift provide evidence to conclude that the capelin larvaes do not grow fast enough to reach a model length of 5.8 cm in early July. even in the case of th8 most early hatched fry. Conse- qUently. the central zone in the capelin otolith with a radius of 0.05 mm or more reflects the first year growth and should thus be counted as the first winter rings.

In Figure 7 are shown the 11-distribution of the yearclasses 1970, 1971 and 1972 by age of spawning. The data are collected in the winters 1974 to 1976. and consist of capelin in maturity stages 3 or above (DDMMASNES 1977). Details of the plots are shown in Table 1.

The capelin normally spawns only ones (PRDKHDRDV 1968) and the figure shows a close relationship between the 11-distribution and the age at which the capelin is maturing. The 3 year old

spawners consist of the largest I-ringers. and those who spawns as 5 year old the smallest one. It may also be noted that the 11-distriburion of the 4 years old spawners are similar for the 3 yearclasses and coinside to the 11-distribution o~ the northern component of I-ringers found during the 1976 cruises, whereas the I1-distribution of the 1971-yearclass which spawned as 5 year old fish is similar to the 11-distribution of the

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small I-ringers which were found in the southern part of ths Barents Sea in 1976 (Fig. 58).

DISCUSSION AND CONCLUSIONS

The hatching of the capelin larvae in 1976 started in the first week of May, and the front of the larval drift found in June corresponde with the drift of the larvuesas observed during a larvae survey in May. The Bongo net used was tested in August and caught larvaes up to 31 mm in length. Gear selectively should therefore not constitute ·any serious source of error in the

observation on the distribution and growth of the larvae popu- lation. Although the area off the Murmansk coast is not properly covered with respect to the larval drift. it seems reasonable to conclude that the southern component of I-ringers with a mean length of 6 cm in July can not o~jginate from the larvae

produced that year.

These findings confirm the method of age reaching for capelin proposed by PROKHOROV (196B). Even the smallest central zones should be counted as the first winter ring and the first ring may be overseen unless special attention is paid to the ^~roblem.

particularly in reading otoliths of older capelin. The 1₁- distribution of the 5 year old spawners of the yearclass 1971 compared to that of the yearclass 1975 indicate that rings less than 0.15 mm may have been lost in readings of the old ones

(Figures 7 and 5). Such an error should however result in a corresponding "transfer" of individuals to the yearclass 1972.

This would be specimens with an extraordinary large inner ring (above 0.30 mm), and the number with large R would be higher.

Since this is not observed it may be assumed that such an error is negligible in our readings.

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PROKHOROV (19G3) assumed that the small inner zones indicated recruits of summer and autumn spawning capelin, but found no reason to separate the stock in different populations. The 1

1-

distribution of the 1971 yearclass which spawned as 5 years old fish during the spring 1976 confirm this view.

According to PROKHOROV (1968), summer and autumn spawning

capelin have been observed in various areas on the Murmansk coast, but the contribution from these late spawning components to the stock was assumed to be relative small. According to our obser- vcations some increase in the abundan.ce .. of summer spawning

capelin has taken place since the summer 1975. Although

abundance estimate of summer spawning capelin is lacking this component is obviously very small compared to the spring spawning stock.

DOMMASNES and NAKKEN (1977) give abundance estimates of the spawning stocks in the years 1974 to 1976. These estimates

have been grouped according to the age composition of the spawning stock and the resulting figures are included in the last column

(B) of Table 1. It is seen from the table that the component of the 1971 yearclass spawning as 5-year old fish is of the same

order of magnitude as the component spawning at an age of 4 years, Subjected to mortality in one year more than the latter group, including a record catch in the summer fishery of 1975, the oom- ponent recruited from the summer spawners must therefore have been the dominating group of the 1971 yearclass. This may also be the case with respect to the yearclass 1975. The abundance of the small I-ringers in the south were probably underestimated in the autumn survey in 1976, due to their frequent occurrence in the surface layers and also due to lacking coverage of their

distribution area to the south (Figure 4).

The composition of the yearclasses 1972-1974 are not yet assesst with respect to the relative abundance of the two groups of

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I-ringers. Prt!lirninary analysis of samples based on imn:atun=:

fish indicate however that the contributions of the small 1- ringers are considerable, particularly in the yearclass 1973.

In case the small I-ringers are recruited from the summer spawners only, this imply that the parent stock/recruitment relationship must be quite different for the two groups. Other factors as late hatching of spring spawned eggs and slower growth r.;:lte of the larvaesin the south-easter~ Barents Sea may however play an important role to this relationship. Further research is

therefore nee de d to provi de con c 1 us-i-ve' 'evi den ce to the ori gi n of the small size O-group capelin.

The capelin yearclasses 1971 to 1973 are extraordinary strong.

The increased recruitment has resulted in a corresponding in-

crease in the immature stock, with respect to number, but in terms of biomass the immature stock has more or less remained on the same size level as in 1971 (OOMMASNES and NAKKEN 1975). This imply that the average weight of the fish has decre.;:lsed. This is partly assosiated to decreased average length, but the

weight/length relationship (the condition factor) of the immature capelin has decreased considerably since 1973 (OOMMASNES and

NAKKEN (1975). Taking into- account that the feeding area of capelin is strictly limited by the ice boarder to the north anq east, and by the warm atlantic water current to the south and west, it seems fair to associate this finding to .;:l density- depending phenomenon.

The yearclasses 1974 and 1975 are we.;:lker than the previous ones.

The biomass of the immature stock remains however on the same high level, and also in terms of numbers the stock level remains high. The reason to the high number [although recruitment has decreased) is the delay in age of spawning which add a new cohort to the immature stock consisting of 4 years old fish.

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Taklrlg into accDunt that the yearly catch8S of capelin in the years under study have increased by 3 to 5 times compared to the catches in the 1960-ies. it may be assumed that the survival of capelin larvaeshas increased considerably in recent years.

One may speculate whether this is associated to the disappea- rence of the herring from the Barents Sea in the late 1960-iea.

The delay in maturing of the 1971-yearclass had a serious effect on the Norwegian' capelin fishery durin~ the winter 1975. Although the yearclass was the most aboondant year61ass so far reGorded

(DOMMASNES and NAKKEN 1977) the winter'fishery became the poorest since 1969. However. this was to some extent compensated by a record catch in the capelin fishery of the following summer and autumn. The summer fishery is mainly based on capelin above 11 cm. and the

imm~ture

capelin of the 1971-yearclass constituted an additional cohort to the catchable stock in the summer fishery in 1975. More over this cohort. probably recruited from the south eastern Barents Sea. had a more eastern distribution pattern than the remaining juvenile stock. In late June 1975 they were found in large concentrations north of the Skolpen Bank. and formed the main bases for the Norwegian capelin fishery in July-August. This eastern area of the Barents Sea had not previously been fished by the Norwegian cape1in seinars during summer. The winter

fishery in 1976 became very good and 38 % of the catch consisted of the 1971 yearclass.

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REFERENCES

BELTESTAD, -A., NAKKEN, O. and SMEOSTAD, O. 1977. Investigations on diel vertical migration of Opgroup fish in the Barents Sea. FiskDir.Skr.Ser.HavUnders.,~

(I n pri n t) .

DOMMASNES, A. 1977. The Norwegian research program on the Barents Sea capelin stopk. Coun.Meet.int.Coun.

~lor.Sea,1977 CH:36): 1-8. 3 figs. MimeD.

DOMMASNES, A. and R0TTINGEN, I. 1977. Capelin investigation in the Barents Sea in September-October 1977. (In pres s) .

ORAGESUND, D., GJ0S~TER, J. and MDNSTAD, T. 1973. Estimates of stock size and reproduction of the Barents Sea capelin in 1970-1972. FiskDir,Skr.Ser.HavUnders., 16: 105-139.

GJ0S~TER, J. and MDNSTAD, T. 1977. Growth of the Barents Sea capelin of the yearclasses 1967-70. Coun.Meet.

int.Coun.Explor.Sea, 1977 (H.37): 1~15. MimeD.

HANSEN, P.M. 1943. Capelin CMal10tus villosus)' Greenland.

Annls.biol., Copenh.,

1:

121-124.

KANNEWORFF, P., 1968. Preliminary results and some problems concerning capelin investigation in Greenlanp,

Rapp.P.-v.R~eun.Cons.~erm.int.Explor.Mer,158:

30-40.

MONSTAD, T. 1971. Alder, vekst og utbredelse av lodde

C.lvlallotus vill.£ .. § .. ~.!~) i Barentshavet og ve~ysten

av Nord-Norge i 1968-1970. Thesis (cand,real), Univ. Bergen, 80 p. Mimeo.

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. ^" ^", - 14 -.

NAKKEN, D. and DOMMASNES. A. 1975. The application of an echo integration system in investigations on the stock strength of the Barents Sea capelin (Mallotus vil1osus. Muller) 1971-1974. Int.Coun.Explor.SeB Coun.Meet. 1975(B:25): 1-9. Mimeo.

NAKKEN, D. ~nd DDMMASNES, A. 1977. Acoustic estimates of the Barents Sea capelin stock 1971-76. Int.Coun.

Exp1or.Sea Coun.Meet. 1977 (H:36) Mimeo.

OLSEN, S. 1968. Some results of t~~'Ndrweigan Capelin investigations, 1960-1965. Raep.P.-v.R8un.Cons~Perm.Int.

Explor.Mer, 158: 18-23.

PITT, T.K. 1958. Distribution. spawning and racial studies of the capelin Mal10tus villosus (MUller) in the offshore Newfoundland area. J.Fish.Res.Bd.Can. 15(3): 275- 293.

PRDKHDRDV, V.S. 1968. Materials on the ecology of capslin in the Barents Sea. Rapp.P.-v.Reun.Cons.Perm.Int.Explor.

Mer, 158: 23-31.

RAKHMANDVA, S.I. 1928. Reference is mads to Prokhorov 1968.

TEMPLEMAN, W. 1948. The life history of the capelin (Mal1otus villosus D.F. MUller) in Newfoundland waters.

Nfld. Government Lab.Res.Ser.Bull. 17: 1-151.

TEMPLEMAN, W. 1968. Review of some aspects of capelin biology in the Canadian area of the Northwest Atlantic.

Rapp.P.-v.R8un.Cons.Perm.Int.Explor.Mer, 158:

41-53.

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VILHJALMSSON, H. 1968. A contribution to th8 knowledg8 of the Icelandic cap8lin. ~aPe.P.-v.R~uQ.Cons.Perm.lnt.

Ex,plor.Mel> 158: 32-38.

WINlttRS, G. 1974. Back-calculation of the growth of capelin (Mallotus villosusl in , , th~ Newfoundland area.

ICNAF Res.ooe. 74/7. Serial No. 3150.Ann.Meeting June 1974.

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Year of spawning

1974

1975

1976

i \

,.. 1. 6 ^~

Table 1. Measurements of the radius of the ^c8nt~alzone (R) in capelill otpliths. The f ;i.g\Jres show frequency (in %) by 0.05 mm groups~ by' age and years of spawning (n) number measured 8) spawning

component in mil1.tons . -

R1 ^{in mm}

.

10- 2

Age 10 15 20 25 30 35 40 45 R1 ⁿ ^B

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

3 6 20 29 25 12 5 3 27.2 65 0.12

4 1 11 26 29 _;2,3 8 2 0 25.2 332 0.63

5 ⁴ 21 31 26 14 2 26.7 133 0.25

3 3 13 22 25 21 12 4 30.0 106 0.08 4 2 10 26 29 21 9 2 1 24.8 794 0.65 5 B 18 23 23 15 8 2 2 23.1 92 0.07

3 5 28 33 23 9 2 25.5 43 0.11

4 11 30 34 18 5 2 24.1 389 1. 01

5 7 38 33 17 4 1 18.8 260 0.68

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Back-calculated 11-distribution (in cm) of

I-group .capelin in June-July 1976.

[1) The Barents Sea west of E 37 0•

2) Barents Sea ea'sf of E 37 0 ~ R)

of the otolith central zone in mm radius -2, . 10 J' 1 2 R I,

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- 20 -

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Figure 4. Estimated density distribution sf l-group Gapelin in September-Octsbep 1976 [hI pep (nautical mi1e)2] •

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Figure S. Length frequency curves CA) and back-calculated 11 -

qistribution CB) of I-group capelin (1 in cm) in September-

October 1976. [1) Barents Sea north of N7So1S', 2) Barents

Sea south of N7So1S'. R) radius of the otolith central zone

-2) .

n mm • 10 •

(22)

- ,22 -

73~---

o o

Figure 6.

'16.0 1

o 4 , '14.5 o

o o '18.9 12 '18.0 21 11 '16.1

'h5

o o '18.9 10

o 1

'17.0

.10 5

19.9 13 '1'7.8

• s .3 18.9 13 19.2 17. 7' 0 . • 1 Z 9 '18.6 35 0

27 6

'15.2 • 190 22 .

·18.7 '16.9 86

12 11

,2 '16.3 ·17.4

15.0 .43 33

185 • 1St.

.47 . 10

5

Q 17.6 'IB.3 3 1,)19.8 30 . 17 (» 3 .1~b8.2 16.7 5

13.0 ,2.50 .151

63 52 16.4 16 . 15.S· • 14.2 '14.8

• 16B 17.4

.149 e1fJ'l·2 ·17.4 (i

13 1'7.2.87 017.8

.. 9016.5

~d5.B

.432 251 ...

14.5 '16.6 • 14.5 18.1 .3

.63 .16 17.3

17

'17.8 '14.2

• 350 15.1;i

150'5.4 '175.1 051 18.7

'15.2 .56 17.8

.100 29 18.3

'18.4

16.0 39 40

• 2800 .27'17.2 "9.1

13.4 .1~0 1 7 . 9 2 2

350. 17.5 '19.8

16.3 13 38. 3

.200 13 62.53'185'18.518.7

41

07.7 44.56 .21754~7.619.0 18,3 '16.9 17.6 18.1 .

35¹¹

Larvae stations lO~25 June 1976. Number of capelin larvae and the.mean length of the larvae in mm by station.

: ... 1

" "

~., .

(23)

% 30

20

10

% 40

30

20 10

% 40

30

20

10

, ... ,

A

...

^....

, " " 2

I. ...• .... , . . "

.' ,/' . '. \ \ 3

..

^'

,

.'

, '

" .... \

/ ". \

/ '.~

" ,.

_~'.

,

^~.

/ -:.

"

^~,

.' '" ""-... ^,..

'd f - - ~' ! I ' -- - - , • I I I • " , . .

."-

...

3

B

c

, ,

,

:' '.

I

,

I

"

,

I

,

I I

,

.

,

/

19/

4

I

J j I

I

'.

,

I

I I

I

I I

'.

_'.

;s ...

" .

I '

... ,

...

^.... ^\

I

20 25

5

,

\

,

\

, ,

'\

\

30 3; ... "[10 _ _

6 7 8

R

9

I;

Figure 7. Back-calculated 11-distribution of the capslin yearclasses 1970(A), 1971(B) and 1972(C).

(1) 3 years old spawners, 2) 4 years old spawnerS, 3) 5 years old spawners, R) radius of the otolith

-2

J

central zone in mm . 10 ..