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Research Document - 2004/105

Pink Salmon Action Plan: Sea Lice on Juvenile Salmon and on Some Non-Salmonid Species in the Broughton Archipelago in 2003

By Jones, S., A. Nemec.

Abstract

Copepods of the family Caligidae (Siphonostomatoidea: Copepoda) are parasitic on the skin, fins, gills and in the buccal cavity of marine fishes. In British Columbia coastal waters these niches have been exploited by 11 species belonging to the genus Lepeophtheirus and two species of Caligus. There is little historic data on sea lice infection rates of juvenile salmonids in the Broughton Archipelago. In addition, prior to 2001, juvenile pink and chum salmon in the Broughton Archipelago had received virtually no scientific attention. Annual variations in the number and condition of out-migrating smolts from specific streams had been relatively poorly documented and their migratory routes through this region were speculative. The present study, one component of Fisheries and Oceans Canada’s Pink Salmon Action Plan (PSAP), was an effort to systematically survey juvenile Oncorhynchus spp. for caligid copepods throughout their nearshore marine migratory phase following seawater entry. The overall objective of the study was to describe patterns of spatial and temporal variations in the prevalence and intensity (or abundance) of sea lice infections on juvenile pink and chum salmon in a limited area of coastal BC: the Broughton Archipelago and Knight Inlet. For the purpose of this study, it was hypothesized that the prevalence and intensity (or abundance) of infections on salmonid and non-salmonid fishes would be uniformly distributed temporally and spatially throughout the study.

In the present study, approximately 25% of juvenile pink and chum salmon were infected with two species of sea lice: Lepeophtheirus salmonis and Caligus clemensi. On both salmon species most infections consisted of a single sea louse and most of these were chalimus stages of C. clemensi. The prevalence of motile L. salmonis on pink salmon increased towards the end of the study, coincident with a decline in the proportion of L. salmonis chalimus stages. Significant variability over space and time was observed for sea lice infections on juvenile salmon, size of the juvenile salmon and seawater surface salinity and temperature. A logistic regression model developed and fit with data collected in this study demonstrated that increased probability of infection with non-motile or motile sea lice stages was related to increases in salmon fork length, seawater temperature and seawater salinity. There was no evidence that infection with sea lice adversely affected the size or condition factor of juvenile pink and chum salmon during the time that was monitored. Caligus clemensi and an unidentified Lepeophtheirus sp. were found on approximately 60% of sticklebacks. Lepeophtheirus hospitalis and C. clemensi were also found on herring.

A second component of the PSAP is reported in Hargreaves et al. (2004), the main objective of which was to regularly monitor the abundance of juvenile pink salmon at many locations during the early sea life period, to obtain additional information about the migration routes of juvenile pink salmon in the Broughton. Hargreaves et al. (2004) concluded that juvenile pink and chum salmon were widely distributed throughout the Broughton and Knight Inlet, and that their data did not confirm or even strongly support the existence of a “main juvenile salmon migration corridor” in the Broughton.

Three recommendations derived from this work: 1, to initiate and coordinate field and laboratory studies to better understand the impact of sea lice and other infectious diseases on wild juvenile salmon; 2, to establish mechanisms for sharing relevant disease information between industry and DFO for example by initiating collaborative research programs to better understand local factors influencing prevalence, distribution and sources of sea lice infections on juvenile salmon and 3, to initiate studies to improve knowledge of the morphological characteristics of the chalimus stages of Lepeophtheirus species.

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