Report of the International Whaling Commission (1995)


Published data on concentrations of organochlorine compounds and heavy metals in tissues of harbour porpoises from the eastern North Atlantic are reviewed. The dynamics of pollutants in this population are poorly known because of lack of consistency and coordination between surveys. tDDT concentrations were of the same order of magnitude, or somewhat lower, than in conspecifics from other regions, but those of PCBs were usually higher. Therefore, tDDT/PCB ratios in eastern North Atlantic harbour porpoises were substantially lower than values estimated for other regions. Within the whole area surveyed, specimens from the Baltic Sea were different from the rest because they had proportionally more tDDT and less PCBs. During the period 1970-88, the overall tDDT/PCB ratio significantly decreased with time, indicating that tDDT decreased while PCBs remained constant or increased in the area. Levels of mercury, lead, copper, zinc and cadmium were not significantly higher in this population than in others from the same species or than those detected in other small odontocetes of similar body size and food habits from northern waters. Concentrations of other metals in North Atlantic harbour porpoises have seldom been reported but do not appear to be a matter of concern for the population. For reasons not yet clarified, overall levels of cadmium were substantially lower than reported for any other cetacean species. It was not possible to ascertain the current impact, if any, of pollutants on eastern North Atlantic harbour porpoises, but the levels of organochlorines especially PCBs were found to be high enough to cause concern about their possible effects on the maintenance of the population.