Organochlorines and Marine Mammal Reproduction

Abstract

Reproductive failures in four populations of marine mammals (Californian sea lions (Zalophus californianus), Bothnian Bay ringed seals (Pusa hispida), Dutch Waddensee harbour seals (Phoca vitulina), and most recently, Gulf of St. Lawrence beluga whales (Delphinapterus leucas)) have been attributed to the effects of contamination by organochlorine (OC) residues. In this article, I review the evidence for these effects. I conclude that since (a) crucial biological information in the light of which OC residue data can be interpreted is often missing, (b) the nature of the supposed reproductive effect is variable, and (c) the OC residues to which these effects are attributed vary qualitatively and quantitatively, correlations between observed residue concentrations and apparent reproductive changes do not provide any firm evidence for a cause – effect relationship. In a single experimental study, a diet with a higher OC content than that used as a control impaired reproduction in harbour seals; however, dietary components other than OC content also differed. Although there appears to be no firm correlative evidence sinking residue concentrations in marine mammals with reproductive effects, there is enough concern about possible links to justify more experimental studies, with the aim of identifying the possible biochemical mechanisms involved.