- Marine biologists are puzzled by a series
of abnormal conditions which have affected the Bering Sea, between Alaska
and Siberia, during the last two summers.
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- The changes observed include extreme
die-offs of seabirds, rare algal blooms, abnormally warm water temperatures,
and very low numbers of salmon.
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- Almost half the USA's fish comes from
the Bering Sea, and the commercial value of the catch is more than a billion
dollars a year.
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- The US National Oceanic and Atmospheric
Administration (NOAA) has published the conclusions of an international
workshop on the problems of the Bering Sea.
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- James Balsiger, head of NOAA's Alaska
Fisheries Science Center, said: "People whose livelihood depends on
the Bering Sea need to know if these are fleeting anomalies or persistent
large-scale changes.
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- "Scientists want to determine the
cause of these unusual conditions and their portent for the future of this
national resource."
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- An important migration route
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- Most of the fish and shellfish caught
in the Bering Sea come from the continental shelf, a broad, shallow area
that runs down Alaska's west coast.
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- The shelf is also used by large numbers
of resident and migratory seabirds and marine mammals.
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- The sea has the largest international
aggregation of seabirds in the world, and represents 43% of all breeding
seabirds in the USA.
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- NOAA says that some of the changes observed
in the 1997 and 1998 summers - warmer than usual ocean temperatures, and
altered currents and atmospheric conditions - might have been caused by
El Nino.
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- But the area has been undergoing change
on a much longer timescale, going back several decades.
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- Over that period one species of sea lion,
for example, has declined by between 50% and 80%.
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- And northern fur seal pups on the Pribilof
islands - the major Bering Sea breeding grounds - have declined by half
between the 1950s and the 1980s.
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- In parts of the Gulf of Alaska harbour
seal numbers are as much as 90% below what they were in the 1970s.
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- Growth as well as decline
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- There have been significant declines
in the populations of some seabird species, including common murres, thick-billed
murres, and red- and black-legged kittiwakes.
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- There have also been big variations in
the abundance of some fish and shellfish species over the past 30 years.
Some have registered large increases.
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- One of the most striking changes observed
involved the appearance in 1997 of large areas of milky, aquamarine water
over most of the continental shelf.
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- This was caused by changes in water temperature
and atmospheric pressure, which led to a massive bloom of coccolithophores,
a type of non-toxic, microscopic marine plant.
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- The coccolithophores replaced the normal
summer plankton community, and had what NOAA calls "profound, but
not well-understood effects on the rest of the food chain".
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- Blooms of this sort have never been seen
in the Bering Sea for extended periods.
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- Despite different atmospheric conditions
in 1998, the bloom returned.
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- Altered migration patterns
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- Other changes recorded included unprecedented
mortality in one seabird species, the short-tailed shearwater, and unsuccessful
reproduction rates for another, the kittiwake.
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- The number of salmon was far below expected
levels, the fish were smaller than average, and their traditional migratory
patterns seemed to have been altered.
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- There was also an unusual sighting of
Pacific white-sided dolphins in one area, and large numbers of baleen whales
(species without teeth) appeared on the shelf.
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- NOAA says all the changes observed, "taken
together, show how responsive the ecosystem is to climate and suggest that
climate change would have a strong effect on the ecosystem".
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