Infestations of Motile Salmon Lice on Pacific Salmon along the West Coast of North America
Marc Trudel, Simon R. M. Jones, Mary E. Thiess, John F. T. Morris, David W. Welch, Ruston M. Sweeting, Jamal H. Moss, Bruce L. Wing, Edward V. Farley, Jr., James M. Murphy, Rebecca E. Baldwin, and Kym C. Jacobson
Abstract.—We report patterns of infestation with motile salmon lice, Lepeophtheirus salmonis, on Pacific salmon collected with a surface trawl in coastal waters of Oregon, Washington, British Columbia, and Alaska during 2002 and 2003. Salmon lice were observed on all salmon species examined and in all areas surveyed. The prevalence and abundance of lice infestation varied significantly among species, size-classes, seasons, regions, and years, with larger salmon being consistently more heavily infested than small salmon. The number of lice infesting the small size-class (100–400 mm) of salmon rarely exceeded 5 lice per fish with a mean abundance generally below 0.2 lice per fish. Lice prevalence and, to a lesser extent, lice abundance increased over time in small fish, with lower values during spring and higher values in the following winter, and continued to increase in larger and older fish. There were no apparent effects of water temperature on lice infestation in Pacific salmon. This study suggested that salmon infested with lice remained in coastal waters throughout the year. We suggest that lice on salmon that overwinter in coastal waters will contribute to a pool of infective copepodids in these habitats.