Variations in parasitic caligid infestations on farmed salmonids and implications for their management

Abstract

In order to evaluate the performance of various sea lice management strategies, data sets from a number of salmon farm sites on the west coast of Ireland were examined. These data sets were collected as part of the ongoing National Sea Lice Monitoring Programme in Ireland. Temporal and geographic variations in infestations of Lepeophtheirus salmonis and Caligus elongatus are described from two species of farmed salmonids, Saimo salar L. and Uncorhynchus mykiss Walbaum. Patterns of lice transmission, both within and between fish populations, are discussed and environmental and biotic influences considered. Clear differences in infestation parameters, which persist over a number of seasons, are identified between sites. Where infestation parameters are observed to change over successive seasons, these are linked to changing husbandry practices.