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

parents of the recruits). Effective female spawners are the female sockeye that contributeto the eggs deposited in the gravel, which is a necessary distinction from female recruitssince not all females that return to the Fraser River successfully deposit eggs at theirspawning site. Spawning ground surveys provide the sex ratios, egg retention and prespawnmortality estimates needed to estimate the number of effective female spawners.The primary reason for adding these R/S models into the 2010 forecasting process wasthe long-term trend of declining productivity for several Fraser sockeye stocks and theexceptionally low returns per spawner observed in 2009.The typical approach used in recent years has been to test the performance of the variousmodels for each of the 19 indicator stocks in retrospective analyses and use the resultsfrom the best performing model for the annual pre-season forecasts (Cass et al. 2006).Table 20 shows the best performing model for each of the 19 indicator stocks in each ofthe past four years (CSAS 2006; 2007; 2009; 2010). There are several stocks where thesame model has been the selected for multiple years but no instances where a singlemodel has been considered to be the best available in each of the past four years.Model descriptionsFor some stocks, 14 possible models were parameterized as candidates for forecasting.DFO separates the models into three groups—Naïve, Biological, and Biological-Environmental. For most Fraser stocks, current returns tend to be correlated with returnsfrom four years earlier due to spending one year in freshwater and three years in theocean, thus creating a four year life cycle. Naïve models simply average the previouscycle line returns (returns that occurred 4, 8, 12 years, etc. ago) and vary only by howmany cycles they include in the average.Biological models are further separated into escapement, juvenile, and sibling models.Returns are related to broodyear escapements by way of Ricker and power curves—Biological Escapement models. Juvenile data (fry and/or smolts) are available for eightof the 19 stocks and are used to predict returns in a power model—Biological Juvenilemodels. Smolt and jack (number returning as small three year olds) data are used incombination with survival and age composition estimates to forecast age-4 and age-5returns—Biological Sibling models.Biological-Environmental models use Fraser River discharge measured at Hope andspring sea surface temperature (SST) measured in the year of smoltification as covariates65