The prevalence, density and impact of Lepeophtheirus salmonis (Krøyer) infestation on juvenile pink salmon (Oncorhynchus gorbuscha) from the central coast of British Columbia, Canada

Juvenile Pacific pink salmon (Oncorhynchus gorbuscha) were captured by beach seine in two adjacent channels leading from headwaters to coastal marine areas in 2004 and examined for sea lice. The sample sites represented the key areas of potential wild/farmed interaction by sea lice (Lepeophtheirus salmonis and Caligus clemensi) in the Finlayson and Mathieson Channels. The mean prevalence of infestation was 18.4% with a mean density of 0.28–0.64 lice g−1. The ratio of L. salmonis life stages was 26%:35%:39% for copepodid/chalimus:pre-adult:adult life stages respectively. There was no significant effect of sample site on sea lice prevalence. There was a significant increase in sea lice density between headwater and seaward sample sites. Significantly higher condition indices were recorded for pink salmon from the Finlayson Channel compared to the Mathieson Channel. There was no significant effect of sample site on condition indices within each channel between sample sites towards the headwaters, adjacent to and seaward from commercial salmon farms. There was no effect of sea lice density on the condition indices of juvenile pink salmon sampled at each site.