Occurrence of 0-group sprat ( Sprattus sprattus) in the littoral zone along the Norwegian Skagerrak coast 1945–1992, compared with the occurrence of 0-group herring ( Clupea harengus)

Abstract

A long time series of abundance indices of 0-group sprat ( Sprattus sprattus) and herring ( Clupea harengus) from beach seine hauls, consisting of 6074 hauls, representing 120 sites taken annually in September–October in 1945–1992, is analysed. Species composition and length measurements of sprat and herring are based on 138 samples from 1974 to 1992. Considerable annual variation in abundance indices in both sprat and herring is shown, but no trends over the period are detectable. There was a positive correlation between the abundance of 0-group herring and 0-group sprat both within years and within stations. No trend in mean length of the two species over the period was observed. When co-occurring in schools, a positive correlation was found between the mean lengths of sprat and herring, but no correlation between mean lengths of sprat and proportion of herring in the shoals is indicated. There are no indications that abundance of cod, 0-group and older, is a major regulator of abundance of young sprat in the littoral zone on the Norwegian Skagerrak coast. A positive correlation was found between abundance indices based on the beach seine samples and those based on the International Council for the Exploration of the Sea (ICES) Bottom Trawl Surveys in the Skagerrak (Div. IIIa) the following year.