Dolphin Mortality Rising in English Channel

File image courtesy Cornwall Wildlife Trust Marine Stranding Network / Jeff Loveridge

Published Jul 19, 2017 2:14 PM by The Maritime Executive

Researchers in France and Britain are raising the alarm about a spike in dolphins washing up on beaches along the English Channel. The levels are the highest in a decade, and marine biologists suspect that they are linked to an increase in pair trawling. 

In Cornwall, environmental activists say that 125 dolphins washed up in January and February alone, a threefold increase relative to the same period the year before. The numbers are comparable, though, to the period in 2003 when pair-trawling was permitted in the UK fisheries industry. 

The issue may be even more severe on the French coastline. Deutsche Welle reports that 800 dead dolphins were found along the Bay of Biscay's beaches in the span of less than one month. Marine biologist Helen Peltier told DW that 80 percent showed signs of injury from trawl nets, and that the number killed and lost at sea is likely much higher than the number found on shore. 

Pair trawling involves the use of a net suspended between two boats at a distance of thousands of feet apart, allowing the vessels to sweep up a large volume of fish all at once. UK-flagged trawlers are not allowed to use this method within Britain's 12-mile line, but it is still commonly used by other nationalities in the English Channel sea bass fishery. Researchers say that dolphins are attracted to the mass of fish that forms at the mouth of the net, and are not aware of the impending danger until it's too late. 

Sonic pingers are a reliable way to keep dolphins out of the nets, and the latest models cost only $100 dollars each (plus a bit more for replaceable batteries). They are typically spaced every 300 feet along the net to warn the cetaceans away, and research results from around the world show that they are effective. Subsurface microphone monitoring in studies conducted by the Cornwall Wildlife Trust showed that porpoise vocalizing (porpoise clicks) fell off by about 80 percent near nets with pingers, relative to nets without, suggesting that porpoises stayed away from the pingers. However effective they may be, though, the use of pingers is voluntary, and getting the international fishing fleet to adopt them may be difficult.