Science Response 2024/003
Status Update of Pacific Cod (Gadus macrocephalus) off the West Coast of Vancouver Island in 2023
Context
The 2020 assessment for Pacific Cod (Gadus macrocephalus) in British Columbia (BC) found the Area 3CD stock (West Coast Vancouver Island: WCVI; Figure 1) to be in the Cautious Zone with 97–98% probability, with 2–10% probability of being in the Critical Zone, over all catch scenarios considered (DFO 2021). This followed a notable reduction in the 2018 WCVI synoptic bottom trawl survey index (approximately 26–27% of the 2014 and 2016 observations (Table 1; Figure 2)). Given the low index point in 2018, the 2020 Science Response recommended updating the assessment following the 2020 WCVI synoptic bottom trawl survey. However, due to the COVID-19 pandemic, the scheduled 2020 WCVI survey was postponed to 2021, returning to its regular biennial schedule in 2022. Both the 2021 and 2022 index points were lower than the 2018 observation (Table 1). Catches since 2018 have also been lower than in previous years (Table 2; Figure 3). The commercial catch-per-unit-effort (CPUE) index decreased substantially in 2018 but has since increased, following increases in commercial catch (Figure 4).
A Request for Science Information and Advice (RSIA) for Pacific Cod was issued in 2022 for both the 3CD and 5ABCD (Hecate Strait and Queen Charlotte Sound) stocks. The stock assessment model (see Analysis and Response) is fitted to commercial and survey indices of abundance, commercial catch, and an index of mean weight, derived from commercial length samples (Forrest et al. 2020). However, due to the COVID-19 pandemic and a subsequent shift towards at-sea electronic monitoring, there has been no at-sea biological sampling on commercial trawl vessels since 2019. This change follows a trend of reduced biological length sampling of Pacific Cod on commercial vessels that began around 2015 (Appendix A).
The 2022 RSIA therefore had two steps: 1) an assessment of the potential sensitivity of the stock assessment to missing length data from the commercial fishery; and 2) a stock status update with updated catch advice for both stocks. The RSIA advised to only proceed to Step 2 if the missing length data were “deemed to not be of significance to the quality and rigour of the scientific advice”. Using the 2020 assessment model, the authors presented several sensitivity analyses to the Pacific Cod Technical Working Group (TWG) to evaluate alternative methods for updating the commercial mean weight index. This included a generalized linear model (GLM) for predicting the commercial mean weight index from a survey mean weight index derived from WCVI survey samples. The TWG found that the GLM provided acceptable predictions of the commercial mean weight index for the Area 3CD stock. However, the TWG decided that a similar GLM applied to the 5ABCD stock did not produce predictions consistent enough with the commercial mean weight index in overlapping years to be used in an assessment. Because of this issue with the 5ABCD commercial mean weight index and limited staff resources, Step 2 did not proceed.
The Pacific Groundfish Management Unit has not requested updated catch advice for 2023. However, given the three low index points in 2018, 2021, and 2022, Fisheries and Oceans Canada (DFO) Science Branch has issued a abbr RSIA requesting a stock status update for the Area 3CD stock to ensure all three of these index points are considered in a timely evaluation of stock status. While the last assessment found that there was low probability (2%–10%) of the stock falling below its limit reference point (LRP) in 2022 under all considered catch scenarios (DFO 2021), the stock has failed to rebound under low estimated fishing mortality rates.
The Fish Stocks provisions (FSP) of Canada’s Fisheries Act require that a rebuilding plan be developed for major fish stocks that have declined to or below their LRP. While the FSP only apply to major stocks prescribed in the Fishery (General) Regulations, guidance has been provided that states that, for stocks not subject to the FSP (such as Pacific Cod), DFO’s Precautionary Approach (PA) Policy (DFO 2009) still applies:
“[. . . ] under the [PA] policy, the requirement to develop a rebuilding plan is triggered once the stock declines to, or below, its LRP. However, in keeping with the 2009 PA Policy, if a fish stock is decreasing and approaching the LRP, management measures must encourage stock growth and arrest preventable declines, and the development of a rebuilding plan should be initiated sufficiently in advance to ensure that the plan is ready to be implemented if a stock declines to its LRP.”
For the purpose of triggering a rebuilding plan, the guidance provides the following definitions of whether a stock is at or below its LRP:
“[A stock] is considered to be at or below its LRP if the terminal year stock status indicator is estimated to be at or below the LRP with a greater than 50% probability or if the projected stock status indicator falls below the abbr LRP with a greater than 50% probability under a zero catch scenario in a 1-year projection, unless an alternative method or probability is defined in a stockspecific precautionary approach framework.”
This Science Response reports results from the regional peer review of October 20, 2023, on the Status Update of Pacific Cod (Gadus macrocephalus) for West Coast Vancouver Island in 2023. Since there has been no request for catch advice, this is a stock status update only. The update uses the same model configurations as the 2018 and 2020 assessments (Forrest et al. 2020; DFO 2021), including model-averaged stock status based on the same seven sensitivity scenarios as in 2018 and 2020. Due to the ongoing absence of commercial length samples, this update uses the GLM developed in 2022 to update the last five years of the annual commercial mean weight index, based on values from a new survey mean weight index. The survey mean weight index and the GLM are described in Appendices B and C.
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