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

Forecasts for Bowron, Pitt, Chilko, and Stellako have been particularly poor, havingexplained only 8.7%, 0.4%, 9.1%, and 9.3% of return variation in the past 30 years. Thisis especially alarming for Chilko because this group contributes (on average) about 24%of the total Fraser return.The recent error in Fraser sockeye forecasts and recognized challenges with forecastingsalmon returns have led most managers to rely on in-season information to managesockeye fisheries. Fishermen and processors want reliable forecasts so they can makebetter business decisions, but most recognize that they should not make majorinvestments based on annual run size forecasts.Review of Pre-season Forecasting MethodsThe data sources and alternative methods (models) used to derive pre-season forecasts foreach of the 19 indicator stocks are fairly complex and described in detail in Cass et al.(2006). The suite of alternative models tested for each indicator stock depends on thetypes of data available for that group.Table 19 provides a list of the various models from Cass et al. (2006) that have been usedin the pre-season forecasting process from 2007 to 2010 (CSAS, 2006; 2007; 2009;2010). Most of the models use estimates of total returns, brood year spawners, or returnsper spawner available for each of the 19 indicator stocks; however, some models requiredata on fry or smolt abundance that are only available for a few stocks (e.g., Chilko,Cultus, Nadina, Weaver).The models range in complexity from simple, such as naïve models (i.e., simple timeseries models without explicitly modeled mechanisms), to the more complex, such asRicker stock-recruitment models that include environmental factors in their calculations.Cass et al. (2006) provides details on data sources, model equations, the retrospectiveanalysis approach, and measures used to assess the performance of the 14 models usedprior to 2008. Brief descriptions of the five additional models tested in 2009-2010 areprovided in (CSAS 2009, 2010). Most of the data required for these models are fromPSC databases.Four of the five models added in recent years use estimates of stock productivity, definedin terms of recruits per spawner (R/S), where recruits are the number of adults returning(catch plus escapement and “en-route losses”) for a specific stock and spawners are thenumber of “effective female spawners” in the brood year for that stock (i.e., female64