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Genes Contribute To Sockeye Salmon Mortality

CANADA - Fraser River sockeye salmon with a certain genomic profile are more likely to die before spawning, contributing to the recent declines in British Columbian salmon, says a new study by researchers at the University of British Columbia (UBC) and Fisheries and Oceans Canada (DFO).

For the study, researchers biopsied and then tracked adult salmon in the ocean and river to determine if successful and unsuccessful spawners were physiologically distinguishable prior to reaching the Fraser River. The study, published today in the journal Science, used gene expression profiling to assess physiological differences among fish. It found that ocean-tagged salmon showing a certain gene expression signature were 13.5 times more likely to die before spawning, and river-tagged salmon showing the same expression signature were 50 per cent more likely to die before spawning.

“We demonstrated that the survivorship of salmon can be predicted based on gene expression, over 200 kilometers before salmon enter the river,” said Scott Hinch, a professor at UBC’s Faculty of Forestry and Institute for Resources, Environment and Sustainability, who was a co-author on this study.

Since the early 1990s sockeye salmon have been in decline, and in 2009 the Fraser River sockeye salmon run was significantly lower than pre-season estimates. Previous research suggests that massive premature mortalities, where anywhere between 40 – 95 per cent of spawning salmon have died en route to spawning and in spawning areas, contributed to this.

The researchers embarked on this study to find a way to better predict the fate of salmon in the river.

“The gene expression profile in fish that died before spawning showed escalation of an immune response typically used to kill pathogens and viruses infecting cells,” said Tony Farrell, a professor in the Department of Zoology and in the Faculty of Land and Food Systems at UBC, and a co-author of this study.

Elements of the immune response led the researchers to hypothesize that the genomic profile related to salmon mortality may reflect a viral infection.

“This study indicates that disease present in the fish before they enter the river may be impacting spawning success,” said Mr Hinch.

To do this study, researchers tracked the fate of more than 150 individual salmon using biotelemetry. The researchers also took non-lethal biopsies to assess physiological and genomic status of the salmon at the time of tagging. This is the first large-scale ecological genomics study to combine biotelemetry, non-lethal biopsies and genomics in an effort to understand poor performance of wild populations.

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