Terms of Reference

Update Stock Assessment for Arrowtooth Flounder (Atheresthes stomias) in British Columbia

Regional Peer Review - Pacific Region

October 2, 2024

Nanaimo, BC

Chairperson: Dana Haggarty

Context

Arrowtooth Flounder (Atheresthes stomias) stock status for British Columbia (BC) was assessed using data from 1996–2021 and examined at a CSAS review meeting on October 19 and 20, 2022^{Footnote 1}.

The model used to assess this stock was the Integrated Statistical Catch-at-Age Model (ISCAM) and was tuned to five fishery-independent trawl survey series covering 1996–2021. In addition, a Discard Catch Per Unit Effort (CPUE) series was used as an index of abundance. This series was created using discards from fishery trawl catch as a proxy for CPUE. A two-sex base model was selected and implemented in a Bayesian context using Markov chain Monte Carlo (MCMC) methods.

The 2022 assessment estimated a median stock size at the beginning of 2022 of 67.95 kilotonnes (kt) with a 95% credible interval of 56.14–83.83 kt. When divided by the estimated initial or virgin biomass (B₀), the median relative biomass for 2022 was estimated to be 0.37 with a credible interval of 0.26–0.51. The estimated median relative biomass for 2011 (10 years prior), was estimated to be 0.77 with a credible interval of 0.53–1.09. The estimated biomass has declined each year from 2011–2021.

Updated stock status and harvest advice would assist in determining whether current harvest levels are sustainable and compliant with the Sustainable Fisheries Framework (SFF). The SFF policy, A Fishery Decision-making Framework Incorporating the Precautionary Approach (PA Framework; DFO 2009), outlines the methods for applying the Precautionary Approach (PA) in the management of Canadian fisheries. Application of the PA usually implies estimation of fishery reference points and evaluation of current stock status relative to those reference points. Estimation of these quantities requires development of quantitative models conditioned on available fishery, survey, and biological data.

Fisheries and Oceans Canada (DFO) Fisheries Management Branch has requested DFO Science Branch provide an update to the 2022 stock assessment including commercial fishery catch data, Synoptic survey index estimates, and new Discard CPUE indices for 2022 and 2023. The update will include estimates of stock status relative to reference points that are consistent with DFO’s Fishery Decision-Making Framework Incorporating the Precautionary Approach (DFO 2009), including the implications of various harvest strategies on expected stock status.

The assessment, and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR), will be used to inform fisheries managers on stock status.

Objectives

The objectives of this Science Response are to:

1. Assess the current status of coastwide Arrowtooth Flounder in BC waters relative to the reference points used in the 2022 stock assessment;
2. Using probabilistic decision tables, evaluate the consequences of a range of harvest policies on projected biomass relative to the reference points;
3. If stock status is estimated to be below the Limit Reference Point (LRP), provide guidance to be used by a management rebuilding plan under the Precautionary Approach Framework. Specifically, provide probabilistic decision tables that demonstrate a high probability of the stock growing out of the Critical Zone (i.e., above the LRP) within a reasonable timeframe (usually 1.5-2 generations under no fishing);
4. Explore how environmental conditions and aspects of the species biology may affect the stock consistent with the Guidelines for Implementing the Fish Stocks provisions in the Fisheries Act;
5. Describe sources of uncertainty related to the assessment model (e.g., model parameter estimates, assumptions regarding catch, productivity, carrying capacity, and population status); and
6. Recommend an appropriate timeframe for the next formal stock assessment, indicators used to characterize stock status in the intervening years and/or triggers of an earlier than scheduled assessment (DFO 2016). Provide a rationale if indicators and triggers cannot be identified.

Expected Publications

• Science Response

Expected Participation

• Fisheries and Oceans Canada (Science and Fisheries Management sectors)

References

• DFO. 2009. A fishery decision-making framework incorporating the precautionary approach.
• DFO. 2016. Guidelines for providing interim-year updates and science advice for multi-year assessments. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2016/020.
• Grandin, C., and Forrest, R. 2017. Arrowtooth Flounder (Atheresthes stomias) Stock Assessment for the West Coast of British Columbia. DFO Can. Sci. Advis. Sec. Res. Doc. 2017/025. v + 87 p.