Growth Studies on North Sea Herring: II. 0-Group Growth of East Anglian Herring

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Abstract
The analysis of the variation in l1 estimates between successive samples, that is as a year-class re-appears each year in the seasonal East Anglian fishery, besides making possible the estimation of the degree of recruitment results in precise comparative estimates of first-year growth. The marked changes and fluctuations in 0-group growth do not necessarily parallel those found for I-group (and older) fish when the same years of growth are compared; it must be assumed that this reflects the discontinuity which occurs in habitat preference, behaviour and ecology between the inshore juvenile stages and the subsequent phases of the life history. A significant decline in 0-group growth during the early 1940s, when the unfished adult stock increased in abundance, suggests that density-dependent factors were operating. This hypothesis receives some quantitative support from data on larval abundance and on the relative abundance of sprat year-classes over the latter part of the period under review, and implies that density dependence is an integral feature of 0-group growth. A hypothesis such as this is difficult to prove because of the problem of separating the effects of density dependence and of environmental factors, but a link between growth rate and survival of very young fish could be generated in a density-dependent relationship.

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