Changes between 1931 and 1990 in by-catches of 27 animal species from the southern North Sea

By-catches of commercial fishing vessels from the southern North Sea have been registered since 1930. The present paper presents these long-term by-catch data for 27 species of (mainly non-commercial) fish and invertebrates. We argue that the by-catch data series possibly represents long-term trends in the actual population numbers of these species. Most species showed a decline that started already around 1950. Far-reaching speculations on the causes of this decline are beyond the scope of the paper.