Research Document - 2016/013

Stock Assessment for Lingcod (Ophiodon elongatus) in the Strait of Georgia, British Columbia in 2014

By Kendra R. Holt, Jacquelynne R. King, and Brian A. Krishka

Abstract

This stock assessment updates stock status for the inside Lingcod stock in the Strait of Georgia, British Columbia based on a range of hypotheses about uncertainties in Lingcod data and biology. Harvest advice for Strait of Georgia has not been requested at this time. Instead, this assessment focuses on characterizing how stock status has changed since the current management regime was introduced in 2006, as well as how current spawning biomass compares to biomass-based reference points. A two-sex statistical catch-at-age model in a Bayesian estimation framework was used to reconstruct abundance. The model was fit to catch data and two indices of abundance based on fishery catch-per-unit effort (CPUE). Nine stock assessment scenarios were used to characterize a range of stock status estimates in 2014. For each scenario, two sets of reference points were used to characterize stock status: the reference points developed by the 2005 Lingcod Management Framework Committee and provisional reference points identified by the more recent DFO Decision-making Framework Incorporating the Precautionary Approach (DFO PA Framework).

In all scenarios, spawning biomass in 2014 was predicted with 100% certainty to be greater than spawning biomass at the start of the current management regime in 2006. The estimated magnitude of recovery however, was dependent on both the treatment of historical catch from the DBS District 1 (1927-1946) and the assumption made about density-dependent catchability. When the 2005 Lingcod Management Framework reference points were used to classify stock status, two scenarios predicted B₂₀₁₄ was most likely above the short-term recovery target of 0.25B₀ but below the target of 0.40B₀. The remaining seven scenarios predicted that B₂₀₁₄ was most likely above the limit reference point of 0.10B₀, but below 0.25B₀. A scenario-averaging approach to status estimation, in which the Bayesian posterior distributions from all nine scenarios were combined with equal weights, estimated a 71% probability that B₂₀₁₄ was between 0.10B₀ and 0.25B₀. When the B_MSY-based reference points from the DFO PA Framework were used to classify stock status, six scenarios predicted that B₂₀₁₄ was most likely in the cautious zone (between 0.4 B_MSY and 0.8 B_MSY) and three scenarios predicted that B₂₀₁₄ was most likely in the critical zone (B₂₀₁₄ > 0.4 B_MSY). The scenario-averaging approach estimated that B₂₀₁₄ had a 58% probability of being in the cautious zone, a 37% probability of being in the critical zone, and a 5% probability of being in the healthy zone (above 0.8 B_MSY ).

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