Research Document 2017/058

Redbanded Rockfish (Sebastes babcocki) stock assessment for the Pacific coast of Canada in 2014

By Edwards, A.M., Haigh, R., and Starr, P.J.

Abstract

Redbanded Rockfish (Sebastes babcocki) is found along the entire outer coast of British Columbia. It is caught by both the trawl and the hook-and-line commercial fisheries. The average annual commercial catch over the last 10 years (2004-2013) is 407 t, and over the last five years (2009-2013) is 342 t. Catches peaked at an estimated 1,360 t in 1992. The stock of Redbanded Rockfish along the Pacific coast of Canada has never been assessed using a population model.

We attempted to assess the status of the coastwide stock using an annual two-sex catch-at-age model, implemented in a Bayesian framework. The model was tuned to the following data: seven fishery-independent trawl survey series (including a novel series constructed from the annual International Pacific Halibut Commission longline survey), one fishery-independent hook-and-line survey series, annual estimates of commercial catch since 1940 from the trawl and hook-and-line fisheries, and age-composition data from the commercial fishery and surveys. The same modelling approach has been successfully used to assess stocks of other species of rockfish in Canadian Pacific waters.

However, for Redbanded Rockfish the data proved insufficient to yield reliable results from the model, despite numerous attempts using different assumptions and exclusion of various components of the data. In the simplest configurations we removed all of the age data, somewhat analogous to a surplus production model, but the Markov Chain Monte Carlo algorithm proved unstable.

We are therefore unable to provide specific quantitative advice to fisheries management, such as decision tables involving evaluation of current and future stock status relevant to reference points. We document all available data, including information on the species' biology, catch, fisheries management and our calculations of indices of abundance for the eight fishery-independent surveys. Catches have remained steady over the past eight years. We also present results of linear regressions on the survey indices. None of the regressions show a significant increasing or decreasing trend.

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