Deep-sea fish species decimated in a generation

At least five species of deepwater exotic fish – only caught since the 1970s – are now on the critically endangered list, according to Canadian scientists. The researchers say many other species are likely to be similarly endangered and, worse, there seems little hope of saving them.

Most commercial fish, such as cod, live on the continental shelves. But overfishing in the 1970s led fishing vessels to move on to a hitherto-unexploited wealth of strange-looking fish on the slopes of the continental shelves, down to 1600 metres.

The bonanza was short-lived. Most of these fisheries peaked after five years and collapsed after 15, says Jennifer Devine, a fisheries scientist at Memorial University in St. John’s, Newfoundland. The deep-sea species reproduce slowly, often not until their late teens, so they do not recover readily from excessive fishing.

Scientists have always feared they would be easy to deplete – and those fears have now been realised. In the first analysis of its kind, Devine looked at data on five species of deep-water fish from surveys by the Canadian government’s fisheries department between 1978 and 1994.

Roundnose and onion-eye grenadier were once commercially fished, but are now taken almost entirely as accidental by-catch alongside Greenland halibut, another deep-water fish that has also begun to decline. The other three species analysed – blue hake, spiny eel and spinytail skate – have only ever been taken as by-catch.

But that was enough. Between 1978 and 1994 the five lost between 87% and 98% of their initial abundance. Further data from 1995 to 2004 for the grenadiers showed they declined still further – 93.3% for the onion-eye and an astonishing 99.6% for the roundnose over 26 years. Their average size has also halved, showing that few fish are getting a chance to mature and breed.


Political horizons
"This happened in a single generation of these species," Devine notes. The danger of extinction depends on the rate of decline per generation. The International Union for the Conservation of Nature calls any species that declines 80% or more within three generations due to a continuing cause 'critically endangered'.

The data on the five species show that in three generations they will decline by 99% to 100% – i.e. they will go extinct. And they are unlikely to be the only species at risk, notes Richard Haedrich, who heads the lab at Memorial University where the research was done.

"The way forward is to close some areas to fishing entirely," Haedrich told New Scientist. But these fisheries are mainly in international or shared waters and are controlled by international groups such as the Northwest Atlantic Fisheries Organisation and the European Union, which face massive political pressure against limiting fisheries. "The decades we would need to close these areas to get recovery far exceeds the political horizons of these agencies," Haedrich notes.

The EU has just provided an example. Independent scientific advice recommended that "fishing pressure should be reduced considerably" for all deepwater species. But the European Commission recommended a cut in deepwater fishing effort of only 20%, and EU fisheries ministers meeting in Brussels, Belgium, in late December 2005 reduced that to just 10%.

They did set quotas of zero for roundnose grenadier. But most of those are caught by accident alongside Greenland halibut – and the Greenland halibut quota was virtually unchanged.

Source: www.newscientist.com