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 percent of the animals killed as bycatch were actually detected, according to Harald Benke, the head of the German Marine Museum. “These results are alarming,” Benke told the German Press Agency dpa.

During a congress of European whale researchers in Cadiz, Spain, Benke said bycatch is apparently a bigger problem than previously assumed. And he hopes similar investigations are carried out for the endangered Baltic Sea Harbour Porpoise. Bycatch figures often include a number of unreported cases, Benke added.

Benke alluded to a study by French scientists who were speaking in Cadiz. 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.

The scientists also say that 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. According to the German Marine Museum, there were 23 porpoises found dead on the coastlines of Mecklenburg-West Pomerania 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.

“In all countries which report important examination results, bycatch was the leading cause of death of the examined animals,” Benke said at the congress. The French study shows that only a fraction of the animals which die in this manner are reported.