Eradication programme threatens Basking shark

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The world's second largest fish species is close to disappearing from Canadian waters because of a program the federal government started to eradicate the species.

The Basking shark, Cetorhinus maximus, has a tendency to get caught in salmon nets, causing severe damage, so an eradication programme was started in an attempt to protect the salmon fishery.

The programme ended in 1970, but experts now believe that it caused the Canadian Basking shark population to drop so much that the species is now under threat in the area.

According to a report from Canada's News1130, Jeffrey Hutchings, the chairman of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), said that Basking shark numbers had dropped by more than 90%.

"In retrospect it's almost unbelievable", Hutchings told News1130. "And even at the time one would think it would have been a radical thing to do, but there were lots of eradication programs on at the time and this was one of them.

"It's Canada's longest fish, has the longest gestation period of any vertebrate, has an extremely slow rate of growth and it's in big trouble around the world.

"Why we took the shark out the way that we did? I can only think it was simply just as basic as taking the primacy of industry's concerns over its fishing gear over the primacy of the animals' right to exist."

During the 1950s, fisheries vessels equipped with a sharped ram were used to impale and kill Basking sharks, to prevent them from damaging salmon nets.

The Basking shark is second only to the Whale shark in size and has been recorded at sizes of up to 12.27m/40ft and a weight of 16 tons. However, very large specimens have become rare due to fishing pressures, and now the largest specimens seen measure around 6-8m/20-26ft.

Basking sharks are not man-eaters, or even predatory. They are filter-feeders that eat tiny plankton, just as Whale sharks do.

The species is vulnerable to population declines because it takes the females up to 18-20 years to reach sexual maturity, and then females are pregnant for 3.5 years. The sharks give birth to pups measuring 1.5-1.7m long.

COSEWIC said that populations on the British Columbia coast had plummeted and only six specimens have been seen there in the past ten years.

Basking sharks are found in temperate seas worldwide (Fish Mapper map for Cetorhinus maximus) and are sometimes seen around the UK coast, particularly during the summer months.