Record Wild Salmon Return - Despite Sea Lice
A record 34 percent of pink salmon fry from rivers flowing into Kingcome and Knight Inlets in British Columbia survived at sea and returned to spawn in 2004. Ocean survival rates for these salmon stocks have normally ranged from 1.2 to 6.6 percent since 1990.
Salmon survival was exceptional even though the juvenile fish became exposed to sea lice as they swam past salmon farms on their way to open sea the previous year. One-quarter of these wild pink salmon picked up sea lice in the Broughton Archipelago, typically hosting one or two lice per fish. At the 16 active fish farms in the area, sea lice infested two-thirds of Atlantic salmon, averaging up to 21 lice per fish.
The record return rate contrasts starkly with the dreadful marine survival of 0.1% for the parents of the 2004 run. A key influence on pink salmon mortality may be the volume of freshwater flowing from snow and glacier-fed rivers, like the Klinaklini, which due to climate have fluctuated considerably. High river flows in 2003 could have lowered ocean salinity enough to make conditions less favourable for sea lice.
Richard J. Beamish, Simon Jones, Chrys-Ellen Neville, Ruston Sweeting, Grace Karreman, Sonja Saksida and Elysha Gordon. 2006. Exceptional marine survival of pink salmon that entered the marine environment in 2003 suggests that farmed Atlantic salmon and Pacific salmon can coexist successfully in a marine ecosystem on the Pacific coast of Canada. ICES Journal of Marine Science. 63(7): 1326-1337.