Fraser River Sockeye Fisheries and Fisheries Management - Cohen ...

Alternative escapement estimation MethodsVirtually every type of enumeration method used to estimate escapement for salmon hasbeen used in the Fraser watershed for Fraser sockeye. A wide variety of hydroacousticsystems and test fisheries have been tested and used in the lower Fraser River to estimatethe escapement from marine fisheries (Appendix J). The advances in hydroacoustictechnology in the 1990s led to substantial changes and significant improvements in themethods used at the Mission hydroacoustic site between 2004 and 2010. The PSCSouthern Endowment Fund has supported studies to evaluate new hydroacoustic systemsand other methods for estimating sockeye escapement to the lower Fraser River.The 2007-2010 Fraser fishwheels and telemetry studies (Robichaud et al. 2008; 2010;Smith et al. 2009) tested several methods similar to those used successfully on the lowerNass River to enumerate escapements of sockeye, Chinook, coho and steelhead (Link andEnglish 1996; Alexander et al. 2002). Fishwheels were tested at the two best sitesdownstream of Mission throughout the sockeye migration period under a widely varyingriver flow and abundances of other co-migrating salmon species. Conventional externaltags (spaghetti tags) were applied to all sockeye and Chinook salmon caught by thefishwheels in 2007 and 2008 and upstream fisheries were sampled for mark-rateinformation. These assessments clearly indicated the portion of the run that could becaptured by fishwheels and sampled for mark-rates by in-river fisheries was too low toprovide reliable estimates of lower river escapement for Fraser sockeye (Robichaud et al.2008; Smith et al. 2009). In 2009, the focus of the fishwheel studies shifted towardsobtaining near-shore samples of species composition and providing sockeye for radiotelemetrystudies designed to assess the magnitude and location of en-route losses. ThePSC Mission hydroacoustic estimates were split into near-shore (within 50 m of eachriver bank) and off-shore strata (>50 meters from each river bank). The speciescomposition of the Crescent Island fishwheels and the Whonnock gillnets were applied tothe near-shore and off-shore counts, respectively, to derive daily estimates of the numberof sockeye passing Mission; results were consistent with the PSC’s ‘best judgement’ inseasonsockeye abundance estimates. This method, combined with DIDSONhydroacoustic estimates for near-shore areas in September 2009, provided daily estimatesof the number of Chinook and pink salmon passing Mission that were consistent with thepre-season expectations and post-season escapement estimates for these species(Robichaud et al. 2010).Capture and assessment methods for other fish such as fences, traps and tower counts arenot feasible or suitable for the lower Fraser River. The lower Fraser River is more than500 m at the majority of sites below Mission and river discharges can exceed 10,00096