Research Document - 2012/150

Utilizing the Albion Test Fishery as an In season Predictor of Run Size of the Fraser River Spring and Summer Age 5₂ Chinook Aggregate

By M.W. Chamberlain and C.K. Parken

Abstract

The Albion test fishery provides a long continuous index for measuring Chinook (Oncorhynchus tshawytscha) abundance in British Columbia’s Fraser River (Figure 1). Following the recommendations of Dempson et al. (1998), Parken et al. (2008) demonstrated that population abundance indices developed from the test fishery were significantly associated with run size at the river mouth in 2000 and 2001. The investigation used cumulative weekly average Catch per Unit Effort (CPUE) from the Albion fishery coupled with genetic stock identification (GSI) data from captured Chinook salmon to develop abundance indices for populations and aggregates of populations by geographic stock structure and migration timing.

Using the same approach as Parken et al. (2008), but in the absence of GSI data, we have re-examined the relationship between the Albion test fishery abundance indices and the aggregate run size for spring- and summer-run age 5₂ populations of Fraser River Chinook (PSC 2008; English et al. 2007). The goal was to examine the feasibility of using the test fishery abundance indices to predict the in-season run size of the aggregate of the spring- and summer-run age 5₂ populations. These predictions could then be used as an in-season tool to design fisheries compatible with the abundance of the aggregated populations.

For the aggregate of the spring- and summer-run age 5₂ populations, we explored the relationship between the Albion test fishery abundance indices and spawning escapement and reconstructed terminal runs at the Fraser River mouth. Regression models were examined for each of ten periods (statistical week 05/3 to statistical week 07/3), where each period was represented by the cumulative weekly average CPUE’s from statistical week 05/1 to the end of the individual period. The periods were chosen as they were far enough along into the returning salmon migration to provide a clear signal of the potential run size and early enough to enable managers to use the information to modify fishing plans if necessary.

We found that years with high test fishery abundance indices generally had large terminal runs and spawning escapements. For both terminal run size and spawning escapement data sets, strong relationships were detected as early as period 05/2. Those relationships remained strong until period 07/3. The performance of regression models declines after week 07/2 when the abundance of populations in the Fraser River summer-run age 4₁ stock group increases rapidly.

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