For another year out-migrating wild juvenile salmon in Clayoquot Sound have been put at risk by sea lice infestations. Juvenile salmon in Clayoquot Sound migrate from their natal streams beginning in the early spring. In May at our continual juvenile salmon monitoring sites, we found that there was a major spike in sea lice prevalence and abundance on smolts. We observed 70-100% prevalence of infected salmon and we were seeing a weekly average of 3 and 12 lice per fish during May at these locations, with some individuals having 20, 30 and 50 lice on them.
Research conducted on sea lice induced mortality found approximately 1 louse per gram of fish can be lethal. Studies in BC found 1-3 lice correlated to 60-98% lice induced mortality on salmon fry. Lower levels of sea lice can impact predator avoidance and the ability to feed effectively, reducing chance of survival and ultimately leading to decreased population productivity.