Published
February 6 at 5:31 AM Updated February 6 at 10:09 AM
The
federal government killed thousands of double-crested cormorants living on a
Columbia River island between 2015 and 2017 in an effort to help young salmon
make it to the Pacific Ocean alive. But Oregon state biologists say the birds
just moved upriver—possibly tripling the number of salmon each bird ate.
The U.S. Army Corps of
Engineers killed 5,576 cormorants and destroyed 6,181 nests in
an effort to prevent the birds from eating an estimated 12 million young salmon
each year as they swim past East Sand Island, just east of the mouth of the
Columbia as it flows into the Pacific.
Biologists
say the mass slaughter may have caused the collapse of the birds' largest
breeding colony. It also may have been for nothing.
James
Lawonn, biologist in charge of avian predation for the Oregon Department of
Fish & Wildlife, is preparing a new study on the effects of the
birds' redistribution along the river. (His study was first
reported by Courthouse News Service.) Lawonn says his agency
"expects little to no gain in survival" from the corps' actions for
young salmon swimming through the Columbia River estuary.
That's
because cormorants are now living farther upriver—still in huge numbers. And
where they live makes a difference. Cormorants that live closer to the ocean
choose from an extensive menu of ocean fish that form huge schools in the
Columbia estuary, like anchovies, herring and smelt. Upriver, they eat a far
higher proportion of salmon and other freshwater fish.
In 2017,
during the bird kill, most of the colony on East Sand Island fled, in an event
the Audubon Society called a "catastrophic collapse" of the largest
population of double-crested cormorants in the world. The corps says there's no
direct evidence to link the two events. But the mass exodus came during the
corps' third year of shooting thousands of birds out of the air, destroying
their nests and setting off explosives on the island.
