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Researchers
were surprised to find wild salmon were more fit than farmed
salmon.
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The
last wild Atlantic salmon in the US are confined to eight Maine
rivers, and all eight stocks are officially endangered. The numbers
are incredibly low. In 2001, fewer than 150 adult wild fish returned
to all eight rivers combined. What's going on? In "Down East - The
Extinction Vortex," biologists such as John
Kocik, race to save the species.
Like
their west coast cousins, the Atlantic salmon - once abundant -
have had to contend with large scale fishing, dams, logging and
agriculture. But even 15 years after fishing on the salmon's Greenland
feeding grounds ended, and with biologists working to restore the
species, the numbers continue to decline.
Implanting
acoustic transmitters into smolts -- young salmon ready to go to
sea -- biologists can track the young fish as they head downstream
and into the Gulf of Maine. After tracking 400 smolts, researchers
found only half survived the trip. The acoustic transmitters reveal
that the smolts get into trouble just where they first encounter
salt water. Research in Norway suggests that young salmon from acidified
rivers have trouble regulating salt. Is New England's notorious
acid rain the smoking gun?
Maybe.
But wild salmon also face a threat posed by their farmed cousins.
Research also in Norway has found that salmon smolts can pick up
a lethal dose of parasites from nearby salmon farm cages. What's
more, just as in the Pacific Northwest, each stock of wild Atlantic
salmon has evolved particular adaptations to its home stream, while
farmed fish have had their genes all mixed up. So when farm fish
escape - as some inevitably do - they may interbreed with wild fish
and produce offspring that are no longer adapted to their habitat.
Even
if biologists can pinpoint exactly what is causing the wild fish
numbers to fall, it may still be too late. There aren't enough breeding
adults to make up for all the losses. It's what biologists call
an "extinction vortex." As a last desperate measure, scientists
are capturing smolts to be raised in captivity. It's a start, but
it's still unclear if humans will be able to restock Maine's rivers
with wild salmon.
For
more on this topic, see the web feature:
Fishy Figures
Livin'
in the Sea
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