The era of ”heroic” fish — rod-busting marlin, great white sharks and mighty tuna, which inspired legends and novels — is well and truly over, according to the most complete study ever compiled of these species.
The world’s numbers of large predatory fish have plummeted by 90% in less than half a century, thanks to unbridled pillaging by industrial trawlers, its authors report on Thursday.
In an effort spanning 10 years, Canadian marine biologists assembled catch data from four major fisheries on continental shelves and in nine ocean fishery systems from 1952 to 1999.
The figures were for tuna, swordfish, marlin and sharks and large groundfish such as cod, halibut, skate and founder. Catches dramatically declined over this period, reflecting a similar fall in species populations.
”Our analysis suggests that the global ocean has lost more than 90% of large predatory fishes,” they write in Thursday’s issue of Nature, the British science weekly.
”Although it is now widely accepted that single populations can be fished to low levels, this is the first analysis to show general, pronounced declines of entire communities across widely varying ecosystems.”
Most surveys on fish populations compare relatively recent data and focus on a specific, important species and fishery — for instance, cod in the North Atlantic.
Such a narrow snapshot may lull fisheries managers into thinking that over-fishing may be a short-term and local problem, the authors say.
This study, however, has a much longer time scale and wider picture, and suggests the advent of large factory ships has inflicted catastrophic and global damage.
It is not just the large fish that are scooped up, but the smaller fish, the ”biomass,” that sustain them, it says.
In some fisheries, industrial techniques have taken as little as a decade to reduce fish populations to 10% of what they were previously, it warns.
The study is written by Ransom Myers and Boris Worm of Dalhousie University in Halifax, Nova Scotia.
”Where detailed data are available, we see that the average size of these top predators is only one-fith to one-half of what it used to be,” Myers said in a press release.
”The few blue marlin today reach one-fifth of the weight they once had. In many cases, the fish caught today are under such intense fishing pressure, they never even have the chance to reproduce… we have to understand how close to extinction some of these populations really are.”
The worst-hit species need ”a minimum reduction” of 50% in mortality in order to have a chance of recovery, says Myers.
”We have forgotten what we used to have,” said Jeremy Jackson, a biologist at the US Scripps Institution of Oceanography.
”We had oceans full of heroic fish — literally sea monsters.
People used to harpoon three-metre-long swordfish in rowboats. Hemingway’s ‘Old Man and the Sea’ was for real.” – Sapa-AFP