Over-fishing behind collapse of bluefin tuna population off northern Europe

A burst of over-fishing from the 1900-1950s led to a depletion in the blue fin tuna population off the coast of northern Europe, according to a new study by ocean historians affiliated with the Census of Marine Life.

Washington, Aug 7 : A burst of over-fishing from the 1900-1950s led to a depletion in the blue fin tuna population off the coast of northern Europe, according to a new study by ocean historians affiliated with the Census of Marine Life.

Researchers Brian R. MacKenzie of the Technical University of Denmark and the late Ransom Myers of Canada's Dalhousie University found in their research that majestic bluefins teemed the waters off northern Europe (North Sea, Norwegian Sea, Skaggerak, Kattegat, and Oresund) for a few months each summer until an industrialized fishery geared up in the 1920s, filling the floors of European market halls with them.

Generations ago Atlantic bluefins typically arrived in the northern waters by the thousands in late June and departed by October at the latest, their foraging travels likely related to seasonal warming. Danish fishers from the mid-1800s welcomed the bluefin tuna as a partner in the catch of the garfish species. The bluefins pursued garfish into nets that fishers set close to shore, the researchers said.

But the situation changed after WW1. Better know-how and equipment, including harpoon rifles and hydraulic net lifts, helped northern European fishers land burgeoning quantities of tuna, they said.

In 1915 nearly 8,000 bluefin (690 tons) were landed in Gothenburg, Sweden alone. Then in the 1920s, the catch peaked at Boulogne, France, homeport for the French bluefin fishers in the North Sea, the study said, adding, that finally the setting up of the first tuna cannery in Denmark in 1929, industrialized the tuna fishing process.

Landings of bluefin tuna by northern European boats in record numbers soared through the 1940s and by decade's end approached the catch levels of traditional Mediterranean fisheries, In 1949, Norway had 43 boats in pursuit of the bluefin; the next year it had 200. Norwegian catches briefly exceeded 10,000 tons per year in the early 1950s, the study further said.

The researchers said recreational fishing also took a toll on the bluefin tuna.

The species virtually disappeared from the region in the early 1960s and continues to be rare today, the study said.

Dr. MacKenzie said though it can't be said with certainty that over-exploitation is the smoking gun in the bluefin tuna's disappearance - "but clearly there has been a murder".

"We've shown bluefin tuna were here for a long time in high numbers. High fishing pressure preceded the species' virtual disappearance from the area and apparently played a key role, but other factors under study might have compounded the fishery's demise -the catch of juvenile tuna in subsequent years, for example," he said.

"As well, it's important to note that fishers from many other countries in Europe as well as Japan, the U.S. and Canada, contributed to the soaring increase in North Atlantic bluefin tuna fishing throughout the last century. We hope our work will inspire a more precautionary approach to the management of bluefin tuna in the Atlantic, with more concern about re-establishing and maintaining the historical range of the species," he added.

The study is set to appear in a special edition of the peer-reviewed journal Fisheries Research.

ANI