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Sea Lice from Salmon Farms Threaten Wild Stocks
12/17/2007
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Study affirms findings of prior research; pink salmon at risk from British Columbian fish farms

by Craig Weatherby


Evidence has been growing that wild Salmon stocks are threatened by sea lice spawned in Salmon farm pens.


And the startling results of a new study, published in the journal Science, indicate that the farm-spawned pests could wipe out Canada’s wild Pink Salmon population within 10 years.


We’ve reported on this problem before: See “Sea Lice Grow Drug Resistant,” “Court Vindicates Claim that Fish-Farm Lice Kill Wild Salmon,” and “Farmed Salmon Seen Spreading Sea Lice.


Farm-raised Salmon are prone to infestations of fish-killing parasites called sea lice, and their pens can become breeding ground for the pests, which are particularly deadly to young fish.


Young wild Salmon encounter sea lice when they swim down river to the sea. The parasites bite the fish, creating open wounds and killing many of the juvenile fish.


This is a natural phenomenon, and usually leaves most of the baby fish unharmed.


The problem becomes much more serious when young wild Salmon have to swim past Salmon farms, and are exposed to thick swarms of the blood-sucking pests before they are large enough to endure the ordeal.


Absent the presence of Salmon farms near their migration from river to seas, young Salmon would not normally encounter sea lice until they are large enough to survive a typical infestation.


But these insidious oceanic insects proliferate in fish pens, which are typically anchored at the mouths of spawning rivers, directly in the path of juvenile fish swimming toward the sea.


Young wild Salmon can become so heavily infested that they turn into “carriers” before succumbing to the lice, thereby spreading the problem to other juvenile Salmon.


The new study is the first to predict that sea lice from western Canada’s Salmon farms could lead to virtual extinction of a wild Salmon population.


Farm-spawned lice could eliminate Canada’s Pink Salmon

Canadian researchers from the University of Alberta and elsewhere reported last week that sea lice from fish farms kill so many young wild Pink Salmon that they threaten the survival of its populations in some rivers and streams.


The study focused on Pink Salmon north of Vancouver Island, British Columbia, but when combined with the results of earlier studies, suggest that Salmon farming as practiced in the Pacific Canadian province poses an existential threat to some wild Salmon.


The new study shows that repeated louse infestations of wild juvenile Pink Salmon, all associated with Salmon farms, have devastated Pink Salmon populations.


As the scientists said, “The louse-induced mortality of pink salmon is commonly over 80% … If outbreaks continue, then local extinction is certain, and a 99% collapse in Pink Salmon population abundance is expected in four salmon generations. These results suggest that salmon farms can cause parasite outbreaks that erode the capacity of a coastal ecosystem to support wild Salmon populations” (Krkosek M et al 2007).


Canadian agencies and salmon farmers dispute findings

The government agency responsible for developing aquaculture and safeguarding wild fish stocks declared that they found no direct cause and effect between sea lice and wild Salmon deaths in the study. The agency says sea lice prevalence is “a complex ecosystem puzzle” in need of further study.


Fisheries and Oceans Canada asserts that other factorsincluding fishing practices, logging and climate changecould affect salmon abundance.


In response, the study’s authors noted that while death rates among young salmon from sea lice infestations varied, a staggering four in five were being killed.


As Martin Krkosek, the University of Alberta fisheries ecologist at who led the work told The New York Times, “If nothing changes, we are going to lose these fish” (Dean C 2007).


Ray Hilborn, a fisheries biologist from the University of Washington told The New York Times that he found the study persuasive, and said that it raised “…serious concerns about proposed aquaculture for other species, such as cod, halibut and sablefish. These high-density fish farms are natural breeding grounds for pathogens” (Dean C 2007).


The authors of the new report said that it might take 10 salmon generations to accumulate large sets of data on the effects of farm-related parasite infestations, they said in the report, and that “greatly exceeds the predicted time to extinction.”



Sources

  • Krkosek M, Ford JS, Morton A, Lele S, Myers RA, Lewis MA. Declining Wild Salmon Populations in Relation to Parasites from Farm Salmon. Science 318 (5857), 1772, 14 December 2007. [DOI: 10.1126/science.1148744]
  • Dean C. Lice in Fish Farms Endanger Wild Salmon, Study Says. The New York Times, December 14, 2007. Accessed online December 16, 2007 at http://www.nytimes.com/2007/12/14/science/earth/14salmon.html.

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