VARIATIONS IN PARASITIC CALIGID INFESTATIONS ON FARMED SALMONIDS AND IMPLICATIONS FOR THEIR MANAGEMENT

In order to evaluate the performance of various sea lice management st rategies, data sets from a number of salmon farm sites on the west coa st of Ireland were examined. These data sets were collected as part of the ongoing National Sea Lice Monitoring Programme in Ireland. Tempor al and geographic variations in infestations of Lepeophtheirus salmoni s and Caligus elongatus are described from two species of farmed salmo nids, Salmo salar L. and Oncorhynchus 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, ar e identified between sites. Where infestation parameters are observed to change over successive seasons, these are linked to changing husban dry practices. (C) 1997 International Council for the Exploration of t he Sea.