Egg weight and fecundity in the north sea herring (clupea harengus)

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