Regional patterns in prevalence of principal external diseases of dab Limanda limanda in the North Sea and adjacent areas 1992-1997

The prevalence and spatial distribution of major diseases of dab Limanda li manda in the North Sea and adjacent areas were studied in the summers 1992 to 1997. Areas covered were the North Sea, Irish Sea, northern and northeas tern British Waters and the English Channel. The diseases studied were lymp hocystis, epidermal hyperplasia/papilloma and skin ulceration. To standardi se data, results were analysed for females >15 cm (>3 yr old). Data were su bjected to median polish, and additive, extended and additive plus multipli cative models were applied to best account for effects of region and year. Annual differences in disease prevalence were low whilst differences betwee n areas were pronounced. For lymphocystis higher prevalence was observed in the northwestern sector of the North Sea, at the northern tip of Scotland and in an area south of Iceland. Prevalence was low in the Irish Sea, the E nglish Channel and the southern North Sea, and intermediate in the German E ight. For epidermal hyperplasia/papilloma, levels were low at Icelandic sta tions, in the northern Irish Sea, in the southern North Sea and the English Channel, whilst levels were high in the northwestern part of the North Sea and the German Eight. Elevated levels of skin ulceration were found on the Dogger, at 1 station in the Irish Sea (off Sellafield) and at 1 station to the south of Iceland. Lower levels were detected west of Iceland. Prevalen ce in all other areas was intermediate. It is concluded that a detailed ana lysis of available data on disease prevalence and putative causative factor s is desirable and, given the good availability of data, would be a promisi ng step forward toward elucidating possible cause and effect relationships between diseases and anthropogenic factors.