(COPEPODA: CALIGIDAE) ON PINK (ONCORHYNCHUS GORBUSCHA) AND CHUM (O. KETA) SALMON IN COASTAL BRITISH COLUMBIA

In total, 23,750 specimens of the salmon louse, Lepeophtheirus salmonis, were collected from 3,907 juvenile pink and 3,941 chum salmon caught within the Broughton Archipelago during a 2-yr survey. The prevalence on pink salmon was significantly higher than on chum salmon in 2004 (62.3% and 58.6%, respectively) and in 2005 (26.4% and 23.1%, respectively). The mean abundance on chum salmon was significantly higher than on pink salmon in 2004 (7.0 ± 0.3 and 2.8 ± 0.2, respec- tively), whereas in 2005 the mean abundance did not differ between species (0.6 ±0.1 and 0.5 ± 0.0, respectively). The mean intensity on chum salmon was significantly higher than on pink salmon in 2004 (12.0 ± 0.4 and 4.5 ± 0.2, respectively) and in 2005 (2.5 ± 0.2 and 1.7 ± 0.1, respectively). The prevalence, intensity, and abundance of L. salmonis were significantly higher on salmon belonging to both host species in 2004 compared with 2005. In both years, a majority of pink and chum salmon had 2 or fewer lice. In general, a decline in abundance of L. salmonis over the 3 collection periods in each year coincided with an increased percentage of motile developmental stages. The abundance was lowest on fish collected from zones in which the seawater surface salinity was also lowest. Seawater surface temperature was higher and salinity was lower in 2004 compared with 2005. The spatial and temporal trends in the abundance of L. salmonis in relation to host size, infestation rates, and seawater salinity and temperature, evident in both years, must be considered in future studies assessing the role of farmed salmon in the epizootiology of this parasite on juvenile salmon in this area. The marine ecosystem of the Broughton Archipelago in coastal British Columbia, Canada (Fig. 1), is hydrographically and biologically complex. The area supports numerous popu- lations of Pacific salmon (Oncorhynchus spp.), and there are 28 sites for the production of farmed Atlantic salmon (Salmo sa- lar), of which 15 to 18 are typically active at any time. There are few studies of the relationships among the physical and biological components of this region (e.g., see Brooks, 2005; Foreman et al., 2006). The Broughton Archipelago has been the focus of recent scientific debate because of concerns that ju- venile pink (O. gorbuscha) and chum (O. keta) salmon migrat- ing from natal streams in the area toward the open ocean are vulnerable to infestations with the salmon louse, Lepeophthei- rus salmonis (Morton et al., 2004; Krkosek et al., 2005, 2006). These studies concluded that the spatial and temporal patterns of mixed infestations with L. salmonis and a related parasite, Caligus clemensi, are consistent with proximity of the pink and chum salmon to salmon farms. Furthermore, the studies con- cluded that the farmed salmon serve as reservoirs of the salmon

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