Environmental influences on the availability of smooth pink shrimp, Pandalus jordani, to commercial fishing gear off Vancouver Island, Canada

Short time scale (less than seasonal) variability in commercial catch rates of smooth pink shrimp, Pandalus jordani, off the west coast of Vancouver I sland, Canada, was examined in relation to changes in environmental conditi ons. Catch per unit of effort (CPUE) data were used as a proxy for catchabi lity to identify environmental conditions affecting the availability of shr imp to the two main gear types in this fishery: otter trawls and beam trawl s. Correlogram analyses of the 1996 CPUE (log-transformed) data from each g ear type, and autocorrelation analyses of wind stress, tidal current speed, sea surface temperature and salinity, and hours of bright sunshine (the la tter three as residuals from their seasonal trends) for 1996 indicated a me an decorrelation time scale of 7.7 days. This was used to construct smoothe d time series of these CPUE and environmental data for 1996. Multiple regre ssion analyses with CPUE as the dependent variable and the environmental da ta as independent variables were significant, explaining 44% of the variabi lity in otter-trawl data and 35% of the beam-trawl variability. Three hypot heses are proposed to explain these results, involving interactions between the shrimp's behaviour and environmental conditions. A significant proport ion of the within-season variability in CPUE (and therefore in the availabi lity of shrimp to fishing gear) for P. jordani off Vancouver Island can res ult from variations in environmental conditions which, if included in stock analyses, should reduce the variability of population abundance estimates.