. The Canadian field-naturalist. Natural history; Sciences naturelles. 2(X)6 Morton and Williams: Sea Louse Inftjstation Levels 201 Wakeman River. Figure 1. Study area, the Broughton Archipelago, showing major Pinic Salmon rivers, salmon farm sites and status, and study site. The adult salmon caught in this study were lifted from the water without a net and kept free from con- tact with any surface in order to reduce loss of lice. They were examined immediately for Sea Louse counts, stages and species identification using a hand lens. We estimated the infective capability of the return- ing ad
. The Canadian field-naturalist. Natural history; Sciences naturelles. 2(X)6 Morton and Williams: Sea Louse Inftjstation Levels 201 Wakeman River. Figure 1. Study area, the Broughton Archipelago, showing major Pinic Salmon rivers, salmon farm sites and status, and study site. The adult salmon caught in this study were lifted from the water without a net and kept free from con- tact with any surface in order to reduce loss of lice. They were examined immediately for Sea Louse counts, stages and species identification using a hand lens. We estimated the infective capability of the return- ing adult salmon by counting gravid female sea lice per fish: a standard measure used to trigger de-lousing treatment of farm salmon to reduce infective capabil- ity and lower sea lice numbers on adjacent juvenile wild salmon (Heuch and Mo 2001). Louse counts were not expected to follow a nor- mal distribution. Rather than transforming the data, we made comparisons using Mann-Whitney U tests (MWU; the non-parametric equivalent of a two-sample t-test) in GraphPad version by InStat (GraphPad Software Inc., 5575 Oberlin Drive, #110. San Diego. California 92121 USA). We used the following standard measures of louse infestation rates (Margolis et al. 1982): prevalence = the proportion of fish infested with lice: intensity = the mean number of lice on each infected fish: and abun- dance = the mean number of lice on the entire sample. Results We fished for 47 "hook-hours" 4 June through July, without catching one adult Pink Salmon. We fished for 119 hook-hours in August until 19 Septem- ber, and beginning on 4 August, caught 50 adult Pink Salmon at an average of Pink Salmon hook-hour (SE = , n = 17 fishing sessions, range Pink Salmon/ hook-hour). Given that there was no variance in the 12 June/July fishing sessions (all 12 failed ses- sions to catch a fish), a W'ilcoxon signed-rank test was conducted to assess w hether the mediiui catch-per-unit- effort in Augu
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