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

econstruction-based model developed by Bill Gazey was employed. This modelincorporated features of the cumulative-normal and cumulative-passage-to-date models,and implemented an objective method for combining the estimates from its componentmodels based on the relative uncertainty of these models. This model has since beenreplaced by a Bayesian time and density model using Winbugs software, similar inconcept to the Cumulative Normal model. This model incorporates historical informationon run-size, timing, spread of the migration and test fishing expansion line (inverse ofcatchability, see below) in the form of prior probability distributions or “Priors” as wellas in-season reconstructions of daily abundance and test fishing CPUE. Previously, aCumulative Passage model had also been employed but this model has been discontinuedas priors on timing and historical distributions make its use redundant in the currentmodel. The models described previously (PSC 1995) that used exclusively commercialcatch and effort data have also been discontinued, due primarily to the major changes infishing pattern, levels of effort and irregularity of the fisheries which provide the sourcedata for these models.The Pacific Salmon Commission conducts “Panel Approved Test Fisheries” in the marineareas “inside” Vancouver Island and in the Fraser River below Mission to collect CPUEdata and biological information on stock identification and species composition. DailyCPUE data in combination with the stock composition information and historicalestimates of catchability (q) are used to project stock abundances from the marine testfisheries. Catchability or “q” is defined as the proportion of a population removed by adefined unit of effort and the “Expansion line” is the inverse of catchability (1/q). DailyCPUE data are multiplied by expansion lines to generate estimates of abundance inmarine areas from test fisheries. The CPUE-based estimates are used until the stockspass the Mission Hydroacoustics site 6 days later in the case of Early Stuart, EarlySummer-run and Summer-run sockeye. During some years, Late-run sockeye (WeaverCreek and Harrison River sockeye) pass directly upstream, a phenomenon known as“Early Upstream Migration” (http://www.psc.org/pubs/LateRun/R-69_LateRunSockeyeConf_2009_final.pdf). In these situations the projected abundancesfrom marine test fisheries are replaced with estimates from the Mission Hydroacousticsprogram 6-8 days later. However on the 2010 and 2011 cycle years, Late-run sockeyeare dominated by Late Shuswap sockeye, the majority of which continue to delay in theStrait of Georgia. Therefore the assessment of run-size, timing and escapement to theStrait of Georgia are derived from the marine test fisheries. During these years, most ofthe escapement of Late-run stocks passes Mission too late to be used in assessments forthe management of most fisheries although these data still form the best estimate ofpotential spawning escapement.I-2