Whale researchers say landing as bycatch in fishnets is one of the leading causes of death for marine mammals.

A study by French researchers showed that only 8 per cent of the animals killed as bycatch were actually detected, according to Harald Benke, the head of the German Marine Museum. Benke said bycatch is apparently a bigger problem than previously assumed. Benke alluded to a study in which the researchers marked 100 dolphins and porpoises caught in fishnets along the French coast and returned them to the Atlantic Ocean from the fishing vessels. Only 8 per cent of the cadavers were later found on the coast.

Porpoises in the Baltic Sea are also threatened by the fishing industry. Researchers along the German coast have found an increasing number of dead animals in recent years. There were 23 porpoises found dead on the coastlines in 2004. In 2009 that number had increased to 52. A study last year of the preserved cadavers identified 30 to 60 per cent of them as bycatch.