Study: Sea Lice Killing Off Wild Salmon
Pastor Dale Morgan
Dec 13, 10:13 PM EST
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Study: Sea Lice Killing Off Wild Salmon*
By JEFF BARNARD
AP Environmental Writer
GRANTS PASS, Ore. (AP) -- The more salmon that growers pack into farms
near rivers and streams, the greater the harm done to wild salmon
populations, new research suggests.
The problem is sea lice, natural parasites that normally attach to adult
salmon with little ill effect and have little contact with vulnerable
juvenile salmon.
That changes when the fish farms move in, according to a study to be
published Friday in the journal Science.
In natural conditions, the adult salmon that carry the sea lice aren't
in the migration channels and rivers at the same time as young pink and
chum salmon, so the little fish are rarely exposed.
When fish farms move in, hundreds of thousands of adults are raised in
floating net pens anchored year-round in the channels where the young
wild fish migrate. The study suggested that the density of fish farms
reached a tipping point in 2001 that triggered a killer sea lice
infestation.
Principally funded by the Canadian Natural Sciences and Engineering
Research Council, the peer-reviewed study is the latest in a series by a
group of scientists trying to push the Canadian government to place more
strict regulations on salmon farms to control sea lice.
When West Coast salmon catches in the United States crashed in the
1990s, farmed salmon filled the gap in supermarket coolers. Global
production has been growing ever since.
Canada trails Chile, Norway and Scotland in farmed salmon production.
British Columbia reports 120 salmon farms in the province produced
78,000 tons in 2006, the bulk of it going to nearby U.S. markets.
Based on government stream surveys, the study used a computer model to
analyze pink salmon returns in 64 rivers without exposure to salmon
farms and seven rivers where young fish must migrate past at least one
salmon farm. The study considered returns before and after sea lice
infestations were noticed in wild fish in 2001.
The study found that sea lice infestations around salmon farms in
British Columbia's Broughton Archipelago, north of Vancouver Island,
have reached a density so high they are killing juvenile wild pink
salmon at a rate fast enough to drive local runs to extinction within
another four years.
"This is the first time scientists have had enough detailed data to
actually measure the impact of sea lice on wild salmon populations,"
said Martin Krkosek, lead author of the study and a doctoral candidate
at the Center for Mathematical Biology at the University of Alberta.
The Canadian Department of Fisheries and Oceans, which regulates salmon
farms and is responsible for protecting wild salmon, said the study
overstates the risks, which are not consistent with figures for pink
salmon returns since 2002, when populations collapsed.
"They are asking us to believe 80 percent mortality is from one source,"
said Brian Riddell, head of the salmon science branch of the
department's Pacific Biological Station in Nanaimo, B.C. "That's simply
unrealistic."
The authors suggested that the simple solution is to move fish farms out
of salmon migration corridors, but Riddell said that was impractical
given the prevalence of wild salmon.
Alexandra Morton, a co-author and director of the Salmon Coast Field
Station in the archipelago, said wild salmon are surviving commercial
fishing but not sea lice.
"The trajectory is much steeper than we expected," she said.
Ray Hilborn, a professor of fisheries at the University of Washington
who was not associated with the study, said he replicated the analysis
and agreed with the conclusions. But the stream surveys are far from
exact, he said.
"It is a very localized effect," not likely to threaten pink salmon
populations in general, he said.
Wild pink salmon are not a commercially important species, but they are
an important food source for orcas and other salmon in the ocean. They
also provide food for bears and other wildlife and nutrients for trees.