THE FECUNDITY OF HERRING IN THE NORTHERN BALTIC SEA

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1 International Council for the Exploration of the Sea C.M. 1990/J:32 Baltic Fish Committee Olbliothol, fj, F' l!c~hei. 11!'.r'," ",\\,t, THE FECUNDITY OF HERRING IN THE NORTHERN BALTIC SEA by R. Parmanne and E. Kuittinen Finnish Game and Fisheries Research Institute, Fisheries Division, P.O. Box 202, SF Helsinki, Finland Abstract The sampies for the study were collected from trap net catches in spring The mean egg diameter at maturity stage 4 is mm and at maturity stage 5 it is mm. Large herring have large eggs. In most cases there is a significant correlation between the total length and relative fecundity. The number of eggs per female in the same lengthl group is larger at maturity stage 4 than at stage 5. The relationship between the fecundity and the size of the fish is investigated with the aid of five equations. The squared correlation of the relationship is generally greatest with the linear equation between the fecundity and the weight of the herring. As an exception to the general trend, the fecundity is highest in the northernmost sampling area, in the Bothnian Bay.

2 2 1. Introduction Although studies of herring fecundity have been carried out in various parts of the Baltic Sea (KÄNDLER & DUTT 1958, RANNAK 1970, OJAVEER 1974, KOSIOR & STRZY'ZEWSKA 1979, and others), no fecundity data have been available from the northernmost waters of the Baltic. However, information on the number of eggs produced by a single female of a given size is needed, for. instance, in assessments of the spawning biomass based on the number of eggs on the spawning grounds. In stock identification, the fecundity and egg size are used for both Atlantic herring (FARRAN 1938, BAXTER 1959, HEMPEL & BLAXTER 1967, BURD & HOWLETT 1974, MOLLOY 1979, JOHNSON et al. 1987) and Baltic herring (KÄNDLER. & DUTT 1958, RANNAK 1970, OJAVEER 1974). This paper investigates egg diameter and possible areal differences in the fecundity of herring in the northern Baltic Sea. 2. Material and methods The samples were collected from trap net catches in spring The sampling sites are given in Figure 1. Fecundity was estimated only for fish with well-developed ovaries (maturity stages IV and V according to KESTEVEN 1960, Ref. BAGENAL & BRAUM 1970). Herring with completely mature ovaries (stage VI) were not included, because capture and handling may have induced the loss of some eggs. The fish were preserved in a 4 % formalin solution for some months. In the laboratory the fish were measured (total length) and weighed. Both ovaries were removed, weighed, split

3 3 longitudinally, placed in jars, and fixed in modified Gilson's fluid (BAGENAL & BRAUM 1970) for some weeks. The jars were shaked vigorously at intervals to help remove the ovarian tissue from the eggs. Before counting the ovarian tissue free from eggs was removed and clumps of eggs were broken up manually. Some eggs were very difficult to separate, evidently due to the first preservation in formalin. Due to difficulties in separating the ovaries, it was necessary to exclude some herring from the material. The subsampling of the preserved eggs was based on the volumetrie method. The eggs of a herring were mixed with water 4t to a volume of 1.5 litres. The mixture was stirred weil and a subsampie of 10 ml was taken rapidly with a measuring cup attached to a rod. The count of the eggs in the subsampie was made under a dissecting microscope. The subsampie was then returned to the total sampie. The number of subsampies per fish was 3-6. In a test of 50 subsampies the coefficient of variation was 8.3 %. The total number of eggs was estimated by rnultiplying the mean number of eggs in the subsampies by the ratio of the total sampie volume to the subsampie volume, i.e.by,150. The rnean diameter of the eggs of a herring specimen was calculated from measurernents of 30 eggs made under a rnicroscope with an ocular microrneter. dissecting The relationships of fecundity to length and weight were investigated with the following equations: F = a + bw F = aw b F = a + bl

4 4 F = alb F = a + bl 3, where F = feeundity, W weight of fish (g), L = total length of fish (ern), a and bare eonstants. Power funetions were derived by log transformations. The fitness of the equations was eompared using the squared eorrelations. Relative feeundity was estimated by dividing the total egg number by the total weight of the fish. A feeundity index (BURD & HOWLETT 1974) was ealeulated as 100 * (total egg number)/(length 3 (ern». The eomputations were made aeeording to the SAS system (SAS Institute Ine. 1985, 1987). 3. Results The mean egg diameter at maturity stage 4 is mm and at maturity stage 5 it is mm (Table 1). Large herring have large eggs (Table 2). The eorrelation between the total fish length and egg diameter is in most eases statistieally signifieant (Table 3). The relative feeundity of a small herring is lower than that of a larger fish (Table 4). In most eases there is a statistieally signifieant eorrelation between the total length and relative feeundity (Table 5).

5 5 The fecundity is higher at maturity stage 4 than at stage 5 (Table 6). In many length groups, the herring fecundity is highest in the northernmost area, in Kalajoki. The squared correlation of the fecundity/weight relationship is generally greatest with the linear equation F = a + bw (Tables 7 and 8, Fig. 2). However, in two cases the correlation is greatest with the power function F = aw b. In the fecundity/length relationship, the squared correlation is in four cases greatest with the equation F = a + bl 3 (Tables7 4t and 8) and in three cases with the power function F = alb. According to the analysis of covariance, there are statistically significant differences in the fecundity of Baltic herring, especially between the southern and northern sampling sites (Table 9). 4. Discussion The sampies investigated are all from one single year. The fecundity may differ between years (KELLY & STEVENSON 1985, BAILEY & ALMATAR 1987) due to variation in the temperature of. the sea (TANASICHUK & WARE 1987) or the feeding conditions (HAY & BRETT 1988), though such differences were not observed in North Sea herring (JOHNSON et al. 1987) or Baltic herring (OJAVEER 1974). In the northern Baltic Sea large herring produce large eggs (Table 2). The same size dependence has been observed in Atlantic herring (HEMPEL & BLAXTER 1967) and Pacific herring (KINGSTON 1982, Ref. HAY & BRETT 1988). The oldest individuals,

6 6 however, may have small eggs (NIKOLSKII 1969). The fact that small herring have a low relative fecundity (Table 4) has been observed in other areas as weil (KÄNDLER & DUTT 1958, RANNAK 1970). According to Table 6, the number of eggs per female in the same length group is larger at maturity stage 4 than at stage 5. A reduction in the number of maturing oocytes may occur naturally (BOWERS & HOLLIDAY 1961) and reflect a mechanism that allows herring to adjust their egg size and egg number to the energetic resources and environmental conditions (HAY & BRETT 1988). Capture and handling mayaiso have induced the loss of some eggs. Some eggs were found at the bottom of the containers, though most of them were probably from fish at maturity stage VI, which were excluded from the material. In most cases the linearequation between fecundity and weight (Tables 7 and 8) gives the closest approximation to the numbers of eggs. This agrees with the observations made by KÄNDLER & DUTT (1958), RANNAK (1970) and KOSIOR & STRZY'ZEWSKA (1979) on Baltic herring, by BURD & HOWLETT (1974) on North Sea herring and by HAY & BRETT (1988) on Pacific herring. In two cases (Kalajoki and Inga, Table 7) there is a curvilinear relationship between fecundity and weight, as observed in. herring in Newfoundland coastal waters (HODDER 1972) The linear relationship between the cubed length and fecundity noted in four cases in the northern Baltic Sea, has been observed in herring in the southern and central parts of the Baltic by KÄNDLER & DUTT (1958), and in Atlantic herring by BURD & HOWLETT (1974), MOLLOY (1979) and JOHNSON et al. (1987). In Pacific herring RABIN & BARNHART (1977) found a linear relation-

7 7. ship between body length and the numbers of eggs produced. The power function equation F = alb noted in three cases in this study has been observed in the Gulf of Finland (RANNAK 1970), in Atlantic herring (BURO & HOWLETT 1974, KELLY & STEVENSON 1985) and in Pacific herring (NAGASAKI 1958). In the northern Baltic Sea, the coefficient b in the equation F = a + bw (Tables 7 and 8) is , which is less than for spring spawning herring in the western and central Baltic ( , KÄNDLER & DUTT 1958), but in most cases higher than in the southern Baltic Sea (391, KOSIOR & STRZY'ZEWSKA 1979). However,.... differences in the values of b between the maturity stages (Tables 7 and 8) affect the comparison between the areas. Along the Pacific coast of North America, the size-specific fecundity of herring is inversely related to latitude (PAULSON & SMITH 1977, HAY 1985). The tendency for herring fecundity to decrease from south to north is not as pronounced in the Atlantic (NIKOLSKII 1969). The weight-specific fecundity decreases from the summer spawning herring of the central North Sea (BURO & HOWLETT 1974) to the spring spawning herring of the central Baltic (KÄNDLER & DUTT 1958) and further to the northern Baltic Sea. An exception to this decreasing trend is the northernmost sampling area, Kalajoki (Fig. 2, Tables 5-8), where the fecundity of herring is greater than in other parts of the northern Baltic Sea. In the Bothnian Bay some morphological characters also differ from the general trends (PARMANNE 1990). The high fecundity of herring in the Bothniari Bay may be connected with the low salinity in that area.

8 8 Referenees BAGENAL, T.B., & BRAUM, E. In: Rieker, W.E.: production in fresh 18l Eggs and early life history. Methods for assessment of fish waters. IBP Handbook No. 3, p BAILEY, R.S. & ALMATAR, S Hypothesis on the stability of marine fish populations with particular reference to variation in the feeundity of herring. ICES C.M. 1987/Mini No 7. BAXTER, I.G Feeundities of winter-spring and summerautumn herring spawners. J. Cons. int. Explor. Mer 25(1), p BOWERS, A.B. & HOLLIDAY, F.G.T Histologieal ehanges in the gonad assoeiated with the reproduetive eyele of the herring (Clupea harengus L.). Mar. Res. Seot. 5, 16 p. BURD, A.C. & HOWLETT, G.J. 1974: Feeundity studies on North Sea herring. J. Cons. int. Explor. Mer 35(2), p FARRAN, G.P On the size and number of the ova of Irish herrings. J. Cons. int. Explor. Mer 13(1), p HAY, D.E Reproductive biology of Paeifie herring (Clupea harengus pallasi). Can. J. Fish. Aquat. Sei. 42 (Suppl. 1), p HAY, D.E. & BRETT, J.R Maturation and feeundity of Paeific herring (Clupea harengus pallasi): an experimental study with comparisons to natural populations. Can. J. Fish. Aquat'. Sei. 45, p HEMPEL, G. & BLAXTER, J.H.S Egg weight in Atlantie herring. J. Cons. int. Explor Mer 31(2), p HODDER, V.M.,1972. The feeundity of herring in some parts of the Newfoundland area. ICNAF Res. Bull. 9, p JOHNSON, P.O., WATSON, A.M. & THOMPSON, A Reeent fecundity observations on North Sea 'Banks' herring. ICES 'C.M. 1987/H:39, 12 p. KELLY, K.H. & STEVENSON, D.K Feeundity of Atlantie herring (Clupea harengus) from three spawning areas in the western Gulf of Maine, 1969 and J. Northw. Atl. Fish~ Sei. 6, p KOSIOR, M. & STRZY'ZEWSKA, K The feeundity of Baltie herring. ICES C.M. 1979/J:11, 17 p. KÄNDLER, R. & DUTT, S Fecundity of Baltie herring.' Rapp. et Proe.-Verb. 143(II), p MOLLOY, J Feeundities of Celtie Sea autumn and winter spawning herring. ICES C.M. 1979/H:47. NAGASAKI, F The fecundity of Paeifie herring (Clupea pallasi) in British Columbia coastal waters. J ~ Fish. Res. Bd. Canada 15, p NIKOLSKII, G.V Theory of fish population dynamies as the biologieal background for rational exploitation and management of fishery resourees. Edinburgh. Oliver & Boyd. 323 p.

9 OJAVEER, E The fecundity of autumn Baltic herring (Clupea harengus membras) populations in the northeastern Baltic. J. Ichtyol. 14, p PAULSON, A.C. & SMITH, R.L Latitudinal variation of Pacific herring fecundity. Trans. Am. Fish. Soc. 106, p PARMANNE, R Growth, morphological variation and migrations of herring (Clupea harengus L.) in the northern Baltic Sea. Finnish Fish. Res. 10, p RABIN, D.J. & BARNHART, R.A Fecundity of Pacific herring, Clupea harengus pallasi, in Humboldt Bay. Calif. Fish Game 63, p RANNAK, L (The fecundity of Baltic herring in the Gulf of Finland). Tr. Balt.n.-i. in-ta rybn. khva 4, (Russian). SAS Institute Inc SAS procedures guide for personal computers, version 6 edition. Gary, NC: SAS Institute Inc., 373 p. SAS Institute Inc SAS/STAT guide for personal computers, version 6 edition. Gary, NC: SAS Institute Inc., 1028 p. TANASICHUK, R.W. & WARE, D.M Influence of interannual variations in winter sea temperature on fecundity and egg size in Pacific herring (Clupea harengus pallasi). Can. J. Fish. Aquat. Sci. 44,

10 Figure 1". Sampling sites far the study af Bal~ic herring fecundity.

11 11 Fecundity I'laturity stage 4 /".',.' / I' /.',..'/... /..' /..' /.. ' /.',..' /.',.'..., /.'.',/.....,,... //., / o Maturity stage Kalajoki Korsnäs _. - - Taivassalo Inga O-L , ,r------r----, :1eight, g Figure 2. Relationship between fecundity and herring \veight ln the northern parts of the Baltic Sea.

12 Table 1. Mean values (upper figure) and the standard deviations (lower figure) of the variables in the herring fecundity material in Taivas- Kala- Sampling place salo Korsnäs joki Ingä Date Maturity stage 4, N = Fish length, cm Fish weight, g Weight of gonads, g Fecundity Egg diameter, mm Relative fecundity Fecundity index Maturity stage 5, N = Fish length, cm Fish weight, g Weight of gonads, g Fecundity Egg diameter, mm Relative fecundity Fecundity index

13 13 Table 2. Mean egg diameter of herring at maturity stages 4 and 5 in the different areas of the northern Baltic Sea(mm). Maturity stage 4 Maturity stage 5 Length Kalagroup, cm Korsnäs joki Ingä Length Taivas- Kalagroup, cm salo Korsnäs joki Ingä

14 Table 3. The correlations between the total fish length and egg diameter of herring in the northern Baltic Sea, and the significant probability of the correlation under the null hypothesis that the correlation is zero. 14 Maturity Area stage Correlation Probability Taivassalo Korsnäs Kalajoki Ingä All areas

15 15 Table 4. Relative fecundity of herring at maturity stages 4 and 5 in the different areas of the northern Baltic Sea. Maturity stage 4 Maturity stage 5 Length Kalagroup, cm Korsnäs joki Ingä Length Taivas- Kalagroup, cm salo Korsnäs joki Ingä

16 Table 5. The correlations between the total length and relative fecundity of herring in the northern Baltic Sea, and the significant probability of the correlation under the null hypothesis that the correlation is zero. 16 Maturity Area stage Correlation Probability Taivassalo Korsnäs Kalajoki Ingä

17 Table 6. Mean fecundity of herring at rnaturity stages 4 and 5 in the different areas of the northern Baltic Sea. 17 Maturity stage 4 Length Kalagroup, cm Korsnäs joki Inga Maturity stage Length Taivas- Kalagroup, cm salo Korsnäs joki Inga

18 r 18 Table 7. Regressions of fecundity on weight and length of Baltic herring at maturity stage 4. Area Equation R 2 F Taivassalo Korsnäs F = W F = *W F = L F = o.187*l F = L Kalajoki F = W F = *W F = L F = o.229*l F = L Ingä F = W F = 100.3*W F = L F = 0.044*L F = L

19 Table 8. Regressions of fecundity on weight and length of Baltic herring at maturity stage Area Equation R 2 F Taivassalo F= W F=64. 8*W F= L F=0.085*L F= L Korsnäs F= W F=70.3*W F= L F=O. 044 *L F= L Kalajoki F= W F=395.3*W 1. OO F= L F=0.905*L F= L Ingä F= W F= *W F= L F=O.286*L F= L

20 Table 9. Results of analysis of covariance of fecundity-weight relationships (F = a" + bw) between herring from different sampling areas in the northern Baltic Sea. Upper figure gives F-values and lower figure probabilities that the regressions are independent of the area. 20 Maturity stage 4 Korsnäs Taivas- Kalasalo Korsnäs joki Maturity stage 5 Kalajoki Ingä Korsnäs Kalajoki Ingä