http://www.nature.com/nsu/040216/040216-16.html
Bird eat bird world
Great skua scavengers snack on seabirds as fisheries decline.
19 February 2004
LAURA NELSON
Attempts to save ravaged fish stocks in the North Sea seem to have had
a perverse effect on the area's ecology. A reduction in fishing has
ended up putting seabirds in danger.
The problem is caused by great skuas, vicious scavenging seabirds that
usually feast on a diet of fish and small birds. At the height of
fishing activity in the North Sea, great skuas learned to feed on
discarded undersized fish and fish guts thrown out by fishing boats.
These free lunches have helped to increase the population of great
skuas in the North Sea - it is now 200 times the size it was a hundred
years ago.
But the North Sea has now been severely overfished. In an attempt to
allow fish stocks to recover, policies have been put in place to close
down some fisheries or reduce their activity. This has resulted in
fewer fish discards, leaving the great skuas hungry.
With few fish in the ocean for them to catch, the birds have turned to
feasting on other seabirds, such as puffins, guillemots, kittiwakes and
fulmars. None of these bird species are seriously threatened by
predation, but their populations have declined markedly over the years.
Stock solution
Now Stephen Votier, an ornithologist at the University of Glasgow, UK,
and his colleagues have shown there is a direct relationship between
the decline in fish discards and the increased predation of seabirds 1.
In a 30-year-long study, Votier and colleagues collected information on
discard amounts from North Sea fisheries and compared this with the
birds' diets. They determined what the birds were eating by looking at
the pellets of feathers, scales, bones and other indigestible bits that
the birds regurgitate after a meal.
As expected, they found that the birds ate more discards when they were
more readily available. And the less discards they ate, the more birds
they consumed instead.
Votier worries that his results might turn people against the skuas,
prompting them to ask for a cull of the birds. Great skuas have already
suffered from some bad press - they have been known to steal sick lambs
from farms, for example.
But there are other ways to protect the seabirds. Euan Dunn, senior
marine policy officer at the Royal Society for the Protection of Birds
(RSPB), says the best way would be to focus on allowing natural fish
stocks to recover, giving the skuas a better menu option.
Some steps may have been taken towards this goal already. Last year the
European Union reformed its common fisheries policy, which dictates how
member states should manage fish stocks. The new rules emphasize that
the entire ecosystem should be taken into account when setting
fisheries guidelines.
"We're looking for a balanced ecosystem," says Dunn. Then, he says, the
birds should be able to take care of themselves.
References
Votier, S. C. et al . Changes in fisheries discard rates and
seabird communities. Nature ,427, 727 -730 , doi:10.1038/nature02315
(2004)
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