Trace metals in the harbour porpoise from the North Sea and adjacent areas: relationship with stable isotope measurements, the nutritional status, lesions of the respiratory system and parasitism.

Abstract

Growing concern has been raised about the status and the long-term viability of the harbour porpoise (Phocoena phocoena) in the North Sea and adjacent areas. Sources of trace metal variations were investigated using a multidisciplinary approach. Porpoises from the Belgian coasts were compared to individuals from the German North Sea and Baltic coasts, Denmark, Norway and Iceland. Toxicological results (Hg, Zn, Cu, Cd and Se) were confronted to most common pathological findings, namely emaciation, lesions of the respiratory system or parasitism. Influence of diet through stable carbon and nitrogen analysis (d13C and d15N), age and sex have also been considered. As expected, the nutritional status of stranded harbour porpoise from the Southern North Sea is poor compared to by-caught individuals from Norway and Iceland, as reflected by their blubber thickness, weight to length ratio and hepatic to total body mass ratio. The porpoises collected along the Southern North Sea coast display higher Zn and Hg concentrations compared to individuals collected in more preserved areas from the North Atlantic. Moreover, significant Zn, Hg and Se levels were observed with increasing emaciation severity. Porpoises displaying severe bronchopneumonia also have higher Zn concentrations probably due to the association previously described of emaciation and bronchopneumonia. Hg is clearly linked to parasitism. These increasing concentrations are not related to a shrinking of liver mass as it remains unchanged during the emaciation. As a result, hepatic trace metal load increases also. These observations tend to indicate a general redistribution of heavy metals within the organs (muscles to livers), which results from protein catabolism. Such a re-distribution could well be an additional stress for porpoises already experiencing stressful conditions (organochlorines, etc…). In contrast, Cu and Cd were never associated to emaciation. Other parameters such as age class or diet are more likely to be involved