- A classic conservation dispute, fuelled by stark images
and emotive arguments, may be challenged by the findings of a new study.
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- Fishers accuse whales and seals of eating their precious,
diminishing fish stocks, leading to renewed calls that these mammals be
culled to safeguard the future of a beleaguered industry.
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- Conservationists and animal welfare advocates retort
that it is the other way round. They see the notion that whales and seals
eat too much fish as unwarranted propaganda intended solely to justify
archaic and inhumane whale and seal hunts.
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- What is more, they say, overfishing is taking food from
the mouths of some of the world's most endangered animals, stifling their
recovery.
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- Surprisingly, it now appears that for most marine animals
and most fisheries there is nothing to argue about.
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- The first global study of its kind, released earlier
in May 2004, shows that marine mammals and fishing fleets rarely prey heavily
on the same fish stocks. The findings are provisional, but they suggest
that scientists and policy makers should only rarely need to make a wrenching
choice between the economic needs of fishers and their desire to protect
threatened marine mammals.
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- Commercial whaling
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- This week, Norwegian ships set sail to resume their country's
hunt of minke whales, and Canadian hunters are continuing their cull of
harp seals, the largest for 50 years.
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- Debates over whether such animals degrade fish stocks
have raged for years. Japan and Iceland, for example, continue to press
the International Whaling Commission (IWC) to allow a resumption of commercial
whaling, partly on the grounds that this will allow fish populations to
grow, says IWC secretary Nicky Grandy.
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- And fishers in North America routinely claim that seals
and sea lions eat so many cod and salmon that they reduce the fishers'
take.
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- Conversely, environmental groups such as Greenpeace contend
that overfishing has destroyed the food sources of whales and seals off
the Atlantic coast of Canada. In Alaska, Greenpeace and other conservation
groups took the US government to court to force it to curtail fishing of
Alaskan pollock, an important food source for the endangered Steller sea
lion.
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- These claims have generated enormous controversy and
not a little research on particular species and ecosystems. Until now,
however, no one has known how important conflicts between marine mammals
and fisheries might be on a global scale.
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- Reported sightings
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- At first glance, the potential for competition seems
enormous. Estimates put the amount of fish eaten by marine mammals worldwide
at more than 800 million tonnes annually, or roughly 10 times the worldwide
ocean fish harvest, says Kristin Kaschner, a marine biologist at the University
of British Columbia (UBC) in Vancouver.
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- However, the picture changes dramatically when you take
into account where marine mammals and fishing boats spend their time.
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- Kaschner scoured reported sightings of 115 species of
marine mammals. For each sighting, she noted ocean depth, water temperature,
and distance from the ice edge. This gave her a crude picture of where
each species prefers to live with respect to these three variables.
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- Then she divided the world's oceans into a grid of around
180,000 approximately rectangular cells, measuring one-half a degree in
each direction, and assigned to each one a relative suitability for each
species.
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- The distributions of marine mammals predicted by this
method were a fairly closely match to those observed on transect surveys
taken by the IWC and other research groups.
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- Little overlap
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- Kaschner included what is known about marine mammals'
food habits to derive a global picture of how much they are eating and
where. She then compared this with the global distribution of fisheries
harvests taken from a database maintained by the Sea Around Us Project,
a research group led by Daniel Pauly, a fisheries biologist at UBC.
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- "Last Sunday I ran the full model for the first
time, and it was like, Oh my God," Kaschner said at the World Fisheries
Congress in Vancouver earlier in May, where she presented her results.
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- About 80 per cent of the world's fish catch comes from
regions where there is very little overlap with marine mammals, she found,
and 99 per cent of marine mammal feeding takes place where very little
fishing occurs.
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- "Marine mammals are not likely to have a large impact
on large fisheries," concludes Kaschner. "And the other way around
large fisheries are not likely to have a large impact on wide-ranging marine
mammals."
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- Local conflicts
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- Kaschner admits her analysis is fairly crude and abstract.
"These are like weather maps," she says. "It's a best guess."
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- More to the point, she notes, a global analysis of this
sort does not rule out the possibility of local conflicts.
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- She found substantial overlap between marine mammal consumption
and fisheries in a few places, such as near Iceland, in the Bering Sea,
and in the Yellow Sea west of Korea all areas where claims of conflict
have been especially heated in the past. Each of these potential problem
areas will need to be studied in more detail, she says.
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- For example, Steller sea lions on the Alaska coast may
indeed be under pressure from fishing. When sea lion mothers are nursing
pups, they cannot range far in search of a meal, so overfishing near their
rookeries can leave them hungry, says Naomi Rose, a marine mammal scientist
with the Humane Society of the US in Washington DC.
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- International policies
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- Fisheries also have other impacts. For example, trawler
nets can churn up the seafloor, disrupt food chains, and linger for years
entangling sea mammals, she notes.
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- The new results suggest that international policies will
not resolve the conflicts over who is taking all the fish.
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- "If there are going to be problems, they are not
at a global level. They are at a local level, of local fisheries affecting
local populations of marine mammals," says Phil Hammond, a marine
mammal biologist at the Sea Mammals Research Unit of the University of
St Andrews, Scotland.
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- "It would be nice if this could pour water on the
fervour that says we need to take measures all over the place to deal with
this."
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