Wind-induced transport of plaice (Pleuronectes platessa) early life-history stages in the Skagerrak-Kattegat

Identifying mechanisms of exchange between adjacent fish populations is important to understanding causes of fluctuations in abundance. This study addresses the hypothesis that the abundance of settled 0-group plaice along the Danish coast of the Kattegat depends on transport from the Skagerrak. Abundance data are derived from annual (1957–1994; 10–15 years missing depending on sample site) juvenile fish surveys conducted at four sites by the Danish Institute for Fisheries Research. The 0-group abundance measured in July-August is significantly higher in years when wind conditions during the larval development period (March-April) were moderate to strong. Meristic variation (number of anal fin rays) depends on wind conditions in a manner consistent with the role of wind on abundance. In years with strong winds, meristic variation along the coast is low due to influx of progeny from the Skagerrak; in years with weak winds (when influx of Skagerrak progeny is low), regional variation in meristic counts is larger. These abundance and meristic patterns are consistent with historical observations of stock distribution and mixing in the area, and demonstrate the potential for physical processes to mediate exchange of eggs and larvae between areas. Abundances showed no evidence of long-term changes, even after allowing for the significant role of wind on abundance, and despite eutrophication of the Kattegat.