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Presumably the decline in these seabirds is
contributed to (as much or more) by the decline in fish populations, as well as
increased predation on them by skuas.
Philip
-----Original Message-----
From:
knightl <>
To:
Birding Aus <>
Date:
Thursday, 19 February 2004 18:17
Subject: [BIRDING-AUS] North
Sea Skua Ecology
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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