A new angle on fish stocks
20 October 2006
If fish stocks keep plummeting, cod and chips won't be on the menu for much longer. So in an attempt to avoid tragedy, scientists have been trawling decades worth of fish data - but have they found a solution? Antenna takes the bait...
This story was published in Nature on 19 October 2006.
Image: Stock.XCHNG
Fish aren't like cows in a field; we can't count exactly how many there are because they're hidden deep in the sea. Giant trawling nets and huge industrial fishing vessels add to this problem, making it easy for fishermen to catch far more than they should.
Three-quarters of the ocean's fisheries are at risk, and closer to home the North Sea cod community is on the brink of collapse. Concerned European scientists are warning that no-one should be allowed to catch any cod in 2007.
Fishing tradition is to throw back the smaller fish and keep the bigger, older fish for the freezer. Because the tiddlers have long lives ahead of them and will lay lots of eggs, it's been thought that leaving them alone was the best way to keep fish figures up.
It seems to make sense, but several decades, thousands of hours at sea and lots of hard work later, scientists now have a completely different take on this theory. They've discovered how fishing affects fish populations and think the rules need to be updated.
Scientific volunteers look overboard during a data-gathering mission.
Image: CalCOFI
The dedicated researchers have been getting the lowdown on fish families living off the coast of California. They've counted the eggs and newly hatched larval fish from a range of species to figure out how many individuals there are and how this has varied over the years.
'What is so unique about this study is that it involves sampling of the unfished species as well as the fished species,' says George Sugihara, an ecologist at the Scripps Institution of Oceanography. The unfished species give scientists a 'baseline' to measure the effects of fishing against.
George Sugihara, ecologist, Scripps Institution of Oceanography, USA
Image: Gary Payne
Watch the scientists launch one of the nets, known as a bongo, over the side of the boat.
Video: NOAA
Specially designed nets sieve the eggs and larvae out of the sea so that scientists on board can classify and count them. There are different pieces of kit - some which catch fish that live near the surface and others which scoop up those that swim further down. |
The eggs and larvae can be identified on board immediately, and details are sent back to the main lab on dry land. By tallying up baby fish numbers, scientists have been able to estimate how many there have been of each species over 50 years. |
Because the ocean environment is unstable, fish numbers always go up and down. Pollution or lack of food can kill off lots of fish, and hooking the ones who've survived only causes more problems.
'We found that as fish populations are fished, not only do they get smaller, but they fluctuate in size far more than before they were fished, and far more than those species in the same ecosystem that are left alone.'John Beddington, fisheries expert, Imperial College.
John Beddington, fisheries expert, Imperial College
Why does fishing make things worse?
The scientists think it's because the biggest and oldest fish are caught first, with the little ones slipping out of the net or being thrown back by the fishermen. The problem is, these youngsters aren't as tough as mature fish, and are less able to cope with troublesome environmental changes.
Huge numbers of fish can be killed by sudden changes in their environment, like pollution.
But fish quotas don't take account of this. For years, fishermen have had to weigh in their catch as a way of limiting how many fish they take. The scientists think these rules should change in light of their new findings.
'These results suggest that some attention should also be given not just to "how much is fished" but also to "who is fished". Don't pick on the big guys!'George Sugihara
So would these tips help manage the number of cod in local waters? UK scientists say that some of the findings from the US research match up with what's happening to European cod.
'We agree that the population structure is an important feature of fish populations. Cod can live for 15 - 20 years but there's a scarcity of older fish in the catches.'Gerd Hubold, fish expert, International Council for the Exploration of the Sea.
Gerd Hubold, fish expert, International Council for the Exploration of the Sea
Image: ICES
They think the best action to take will be trying to create fish communities well balanced in all ages. Protecting older cod would be a good idea too.
Newly hatched fish look very different from the adults.
Image: U.S Fish and Wildlife Service
'You get more offspring from older cod than from younger cod. Also, spawning times and health of eggs and larvae differs between younger and older fish parents. Therefore it is useful to maintain a population which is composed of many age classes, including the very old.'Gerd Hubold
Even so, experts are recommending that cod stays off the menu in 2007.
