The use of catch statistics to monitor the abundance of escaped farmed Atlantic salmon and rainbow trout in the sea

Catch statistics and scale samples were collected from a gillnet fishery targeting escaped fanned salmonids between I October and 28 February each year from 2001 to 2004 in Hordaland County, western Norway. Fish were classified into different groups, or escape incidents, using catch per unit effort (cpue) and size distribution of the catch from different geographical subregions. Reported escape incidents of both rainbow trout and salmon appeared to be followed by peaks in the cpue lasting four to six weeks, but a large proportion of the catch of escaped salmon appeared to stem from unreported, small-scale escape events. The wide size-range of fish caught suggests that the escapees originated from different escape incidents, and the variability between regions suggests that most catches were of local origin. Genetic comparisons among three groups of escapees indicated that DNA profiling may facilitate identification in monitoring programmes of escapees originating in different genetic groups. A low incidence of wild fish was found in the catches. Provided the conservation status of local wild salmonid stocks is taken into account, a fishery targeting escaped farmed salmonids may reduce the numbers of escapees, thus lowering the risk of introgression with wild salmon populations and removing potential sources of sea lice. Information on the relative abundance of escapees in the sea would also be provided by a fishery targeting escapees. (c) 2006 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.