Egg weight and fecundity in the North Sea herring (Clupea harengus)
Zijlstra, J. (1973). Egg weight and fecundity in the North Sea herring (Clupea harengus), in: Zijlstra, J. Het "rassen"-onderzoek bij de haring (Clupea harengus L.) en de interpretatie van veranderingen in de Noordzee-haring visserij. pp. 173-204
In: Zijlstra, J. (1973). Het "rassen"-onderzoek bij de haring (Clupea harengus L.) en de interpretatie van veranderingen in de Noordzee-haring visserij. PhD Thesis. E.J. Brill: Groningen. 204 pp., more
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| Abstract |
Changes in fecundity and egg weight in the course of the extended, about 5 months lasting, spawning period of the North Sea summer-autumn spawning herring appear to be discontinuous. As far as these parameters are concerned, the North Sea herring seems to comprise 2 distinct groups. A northern group, including spawners of the northern and central North Sea, spawning mainly between August and October, has a high fecundity and a relatively low egg weight, whereas the southern Downs group, spawning mainly in November-December around the Dover Straits, produces about half as many eggs as the northern herring which are about two times as heavy. In both herring groups egg weight increases slightly in the course of the spawning season. An irregularity in the fecundity pattern of the central North Sea spawners (Dogger herring)-the younger herring having fecundities comparable to the Downs stock and the older herring being similar to the northern North Sea spawners-is explained by admixtures of pre-spawning Downs herring which pass through this area on their migration to the spawning grounds in the southern North Sea and English Channel. The differences in egg weights and egg counts between the 2 North Sea herring groups are thought to be of genotypic origin, as changes in the spawning season are discontinuous and the herring of the 2 groups mix in nursery areas and on feeding grounds, thus growing up under similar environmental conditions. Apart of spawning group and to a lesser extent spawning time egg weight seems dependent on the age of the mother; recruit-spawners having in some cases eggs with a slightly reduced weight. In the case of the North Sea herring there are no indications, that feeding or other environmental conditions affect the weight of the eggs, as egg weights did not vary between years and were not correlated to the condition the mother. Fecundity, apart of being determined by spawning group, is strongly related to the length of the mother and also to her age. As with egg weight, fecundity of North Sea herring does not vary greatly between years and is not related to the condition of the mother. |
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