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Studies Clash over Threat to Salmon Numbers

CANADA - Research on the Broughton Archipelago, British Columbia watersheds predicts that sea lice infections originating on Atlantic salmon (Salmo salar)farms will cause the extinction of pink salmon (Oncorhynchus gorbuscha) in the archipelago by 2010.

The research by Martin Krkosek from the University of Alberta said the impact on wild salmon was severe and it was only a question of when they would be extinct.

The Krkosek study was published in the journal Science and compared salmon populations numbers between 1970 and the present depending whether they had been exposed to salmon farms or not.

However, another study examined the issue in the context of all of the escapement data available for the archipelago and reviewed additional scientific reports and information not discussed by Martin Krkosekv of the university of Alberta in a 2007.

The researchers Kenneth M Brooks from Aquatic Environmental Sciences in Washington and Simon R M Jones of the Pacific Biological Station, said that additional research during the last five years is not consistent with the Krkosek et al. (2007a) conclusion that sea lice routinely cause in excess of 80 per cent mortality of fry.

They say the literature they reviewed indicates that pink salmon fry mount an effective immune response at sizes as small as 0.7 g, resulting in the rapid shedding of lice within two weeks.

Pink salmon returns are shown to be highly variable throughout the Northeast Pacific in areas without salmon farms.

Following periods of high abundance, pink salmon populations typically fall to low levels, and they may remain depressed for several generations.

However, in most cases, the populations then gradually increase to begin the cycle anew.

An examination of returns to all of the documented Broughton Archipelago watersheds indicates that following exceptionally high returns in 2000 and 2001, the populations declined to very low numbers in 2002 and 2003.

"Contrary to the conclusions reached by Krkosek et al. (2007a), Broughton pink salmon returns have steadily increased since then, with no indication that they are threatened with extinction. Other unsubstantiated assumptions used in Krkosek et al. (2007a) are also discussed in light of additional scientific reports and theoretical considerations," Brooks and Jones say.

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Ellen Hardy

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