© John Lehmann/The Globe and MailA male sockeye salmon attacks another male as they make their way up the Adams River at Roderick Haig-Brown Provincial Park north of Chase B.C. October 12, 2010.
Large numbers of sockeye salmon are dying in the Fraser River, before spawning, because of a mysterious virus, new research suggests.
Historical records show that some fish always die en route to their spawning beds, but since the early 1990s the problem has become increasingly acute - with more than two million fish dying in some years. Researchers have long puzzled over what was causing the seemingly healthy fish to suddenly stop swimming and turn belly up.
A large team of researchers from the federal Department of Fisheries and Oceans and three Canadian universities has now found most of the fish that die before spawning have a common "genomic signature" - or a pattern that shows changes have taken place in an array of genes activated to fight infection.
"Our hypothesis is that the genomic signal associated with elevated mortality is in response to a virus infecting fish before river entry and that persists to the spawning areas," says the report published in the journal
Science on Thursday.
Studies on the spawning grounds show more than 70 per cent of the salmon that died before spawning had the genomic signature.
