The harbour porpoise: fishing and pesticides

Once common, the harbour porpoise has declined sharply because of fishing and poisoning from PCBs and other substances. Recently, however, the species has been increasing again.

Current situation

Around 1960 the harbour porpoise was a common species in Dutch coastal waters. It then went into sharp decline. The probable causes are drowning in trawler nets and the accumulation of PCBs ingested in its food, which damaged the reproductive organs and reduced reproduction. Contributory factors were changes in the occurrence of prey species, such as the herring.

Since the late 1980s, numbers of harbour porpoise observed off the Dutch coast have been rising sharply, to a maximum of 0.15 harbour porpoises per monitoring hour in February 2001. The increase in the coastal zone seems to be particularly of juveniles.

It is also possible that the observed increase in harbour porpoise numbers along the coast is not the result of population increase but is because the species is coming closer inshore. The harbour porpoise is on the Red List of mammals.