Pacific salmon not affected by lice: study
Dec 13, 2010 (CBC) – The decline in wild Pacific salmon populations is not likely caused by sea lice acquired from farmed salmon, a study released Monday suggests. The findings of the study headed by Gary Marty, a professor at the University of California, suggest that the number of wild salmon that return to spawn in the fall can predict the number of sea lice that will be found on farmed salmon the following spring, which, in turn, predicts the extent of sea lice infestations in young wild salmon. However, the survival of wild salmon populations appears unrelated to the number of lice found on farmed fish or to farm fish production. Some experts have argued that separating farmed and wild salmon would help wild populations rebound, but this latest study suggests that is not the case. “Separating farm salmon from wild salmon — proposed through co-ordinated fallowing or closed containment — will not increase wild salmon productivity and that medical analysis can improve our understanding of complex issues related to aquaculture sustainability,” study researchers wrote in their report. They concluded that other factors, including environmental stress or bacterial and viral infections, might have contributed to the alarming decrease in salmon populations in 2002. “Productivity of wild salmon is not negatively associated with either farm lice numbers or farm fish production, and all published field and laboratory data support the conclusion that something other than sea lice caused the population decline in 2002,” they wrote in the report. … Data showed that the number of pink salmon returning to spawn in the fall predicts the number of female sea lice on farm fish the next spring. This, the researchers said, accounts for 98 per cent of the annual variability in the prevalence of sea lice on outmigrating wild juvenile salmon. The researchers suggested that “determination of the causes of salmon population decline requires investigation of other variables.” They noted that in 2001, sick juvenile pink salmon frequently had “bleeding at the base of the fins,” but, the lesions did not occur in pink salmon exposed to sea lice under controlled laboratory conditions. Instead, the reddening of the fins was “commonly associated with stressful environmental conditions or bacterial and viral infections.” However, none of these differentials were studied in 2001 and “their potential role in fish mortality that year remains unknown.” …
