From Environmental News Service
SIDNEY, British Columbia, Canada, February 8, 2011 (ENS) – The
first link between salmon farms on the British Columbia coast and
elevated levels of sea lice on juvenile Fraser River sockeye salmon has
been demonstrated by new research published today.
While there has been speculation that lice from captive salmon has been
transferred to wild salmon, the new study is the first to show a
potential role of salmon farms in sea lice transmission to juvenile
sockeye salmon during their critical early migration to the sea.
The research by scientists from Raincoast Conservation Foundation,
Watershed Watch Salmon Society, and the Universities of Victoria and
Simon Fraser is published in the journal “Public Library of Science
ONE.”
The authors conclude that their work “demonstrates a major migration
corridor past farms for sockeye that originated in the Fraser River, a
complex of populations that are the subject of conservation concern.”
The rapid growth of marine salmon farms over the past two decades has
increased host abundance for pathogenic sea lice in coastal waters, and
wild juvenile salmon swimming past farms are frequently infected with
lice, the authors say.
“Given the high intensities of lice observed on some juveniles in this
study – up to 28 lice on a single fish – there’s an urgent need to
understand the extent of threat posed by sea lice to juvenile Fraser
River sockeye,” said co-author Dr. Craig Orr of the Watershed Watch
Salmon Society.
The scientists examined sea lice on migrating sockeye in an area of
Canada’s west coast between Vancouver Island and the mainland known as
the Discovery Islands, taking samples in 2007. This region hosts the
northeast Pacific’s largest salmon farm industry, 18 active salmon
farms, and also hosts one of the largest migrations of salmon in the
world, primarily to and from the Fraser River.
The scientists genetically identified 30 distinct stocks of infected
Fraser sockeye that pass by open net-pen salmon farms in the Strait of
Georgia, including the endangered Cultus Lake stock.
The study found that “parasitism of Fraser sockeye increased significantly after the juvenile fish passed by fish farms.”
These same species of lice were found in substantial numbers on the salmon farms.
Not only did juvenile Fraser sockeye host higher lice levels in the
Georgia Strait after they passed salmon farms, the researchers found
that these fish hosted “an order of magnitude more sea lice” than Skeena
and Nass River sockeye that migrated along the north coast where there
are no farms.
The new study contradicts the Canadian fisheries agency’s statement
that, “Juvenile sockeye that migrate past salmon farms in the Discovery
Islands are significantly larger than pink salmon … when they migrate
into the ocean, well beyond the threshold for susceptibility to sea
lice.”
Read full article