Status of marine mammals in the North sea

Abstract

Information on the population status of marine mammals in the North Sea is rather scarce. For Grey Seals and Common Seals, which regularly come ashore, fairly accurate population estimates exist. However for whale species, even the more commonly observed dolphins and Harbour porpoise, no reliable data on stock areas or stock sizes can be provided. Nevertheless, it is assumed that most whale populations have decreased in numbers. And only after cessation of hunting, seal stocks have been increasing in most areas. Major recent and potential threats to marine mammals are interactions with fisheries and pollution. Several aspects of interactions considered are: drowning in nets, damage to nets or catch, ‘competition’ for fish and marine mammals as hosts for parasites. Most of these issues can only be answered by more intense population studies combined with multispecies fisheries assessments. Observer netwoeks and stranding data can provide useful indices for qualitative occurrence of marine mammals, but are of limited use for proper population analyses. Adequate management of an ecosystem requires understanding of interspecies relationships and the vulnerability of its components to changes in environmental conditions. Data on the status of marine mammals are urgently required to evaluate their role in the marine ecosystem.