An evaluation of environmental and other factors in some recent marine mammal mortalities in Europe: implications for conservation and management

Major mortality events in marine mammal populations have become a feature of recent years and their causes have been much debated. Here we review the investigations that have been made to date into the 1988 seal epizootic in the North Sea region, the 1990-1992 striped dolphin epizootic in the Mediterranean Sea, and the recent spate of sperm whale strandings in the northeastern Atlantic. We consider the evidence for multifactorial causality in these events and the problems inherent in determining causes. The patterns of disease seen in both the phocine distemper virus and the dolphin morbillivirus precipitated events suggest complex underlying aetiologies with changes in hosts and (or) marine environment, with significant implications for the conservation and management of marine mammal populations. The sperm whale strandings are used to illustrate the difficulty of investigating or even detecting such events in marine mammal populations.