The Survival of Larval Fish in the Northern North sea According to the Quality of the sea Water

Extract

The numbers of fish eggs and planktonic stages of fish taken during a 5-year period by the Scottish research vessels in the northern North Sea have been associated with the presence of Sagitta elegans and S. setosa in the same collections and over an 11-year period with the presence or absence of S. elegans. The results confirm Russell's findings in the English Channel that fish larvae are more abundant when S. elegans is present than when S. setosa is present.

The total numbers of fish eggs do not show these differences; spawning does not appear to be any more productive in water associated with S. elegans, rather the reverse, and this is shown to be so for the eggs of those species separately examined. Numbers of the larvae were distinctly greater in the ‘mixed’ conditions indicated by the presence of S. elegans and a more abundant food supply is a possible cause. That the differences may signify a more fundamental effect, however, is suggested by the figures for cod and haddock eggs, which show the earliest stages to be more abundant where S. elegans was absent although later stages were more abundant when S. elegans was present.