Malformations in North Sea pelagic fish embryos during the period 1984-1995

Malformation rates in embryos of dab, whiting, cod, flounder, and plaice in the southern North Sea have been monitored between 1984 and 1995 by quantitative investigations of developmental defects in eggs immediately after capture. Incidences were highest in near-coastal waters known to receive high pollution loads. For all species and all areas investigated, synchronous trends were found with intermediate incidences in 1984, maxima in 1987 and significant decreases thereafter. The variations are compared with trends in organochlorine residues in dab and plaice from the German Eight collected over the same period. Trends vary for different organochlorine substances, but the overall picture indicates elevated levels in the period 1984-1987 and decreasing concentrations thereafter. Although the general pattern is consistent with the trend in incidences, significant correlations were only found for malformations of dab and concentrations of p,p'-DDE. Trends in concentrations of nutrients and hydrographic factors were also investigated, indicating a significant negative linear correlation between surface water temperature and incidence of malformed embryos of dab. The hypothesis is put forward that low temperature may predispose developing fish embryos to the impact of organochlorines. (C) 1996 International Council for the Exploration of the Sea