Terms of Reference

Stock Assessment Update of Bocaccio Rockfish (Sebastes paucispinis) for British Columbia in 2021

Regional Science Response Process – Pacific Region

October 15, 2021
Virtual Meeting

Chairperson: Rowan Haigh

Context

Bocaccio rockfish (BOR) was last assessed in 2019 (DFO 2021, Starr and Haigh, in press). The results of the 2019 stock assessment showed that the coastwide BOR stock in British Columbia (BC) experienced a nearly continuous decline from the start of the population reconstruction in 1935, interrupted only by a relatively level plateau spanning the years 1970-86 due to a few good recruitment events in 1969, 1976, and 1978. However, the decline continued from 1987 onwards until a very large recruitment event occurred in 2016, estimated to be 44 times the long-term average recruitment.

Using the Awatea catch-at-age model, the 2019 assessment included data from six fishery-independent trawl survey series (1967-2019), a standardised commercial bottom trawl catch per unit effort (CPUE) series (1996-2012)^{Footnote 1}, annual estimates of commercial catch from two fisheries, and age composition data from the combined commercial trawl fishery and four of the six surveys.  A summary of the 2019 stock assessment as well as descriptions of earlier Bocaccio stock assessments (including the Committee on the Status of Endangered Wildlife in Canada [COSEWIC] reviews of this species) can be found in the Science Advisory Report 2020/025.

The 2019 stock assessment predicted that there would be a quick rebound in the spawning biomass starting in 2021 because, even though only a small proportion of the 5-year old fish would become mature, the large size of the 2016 cohort would contribute a detectable increase in the spawning population. By the beginning of 2022, assuming a constant catch of 200 tonnes/year or a harvest rate of 0.04/year, the stock assessment projected that the BOR stock would move into the Cautious zone (i.e., the median was near the upper stock reference [USR] of 0.8BMSY). The stock assessment further projected that the probability of the spawning biomass exceeding the limit reference point (LRP), i.e. P(Bt > 0.4BMSY), was greater than 95% in one more year (i.e. at the beginning of 2023). These projections were repeated based on the lowest 5% of the posterior distribution of the composite base case, resulting in rebuild predictions that were only delayed by 2-3 years. Finally, the 2019 stock assessment noted that both the Queen Charlotte Sound (QCS) and west coast Vancouver Island (WCVI) synoptic surveys showed good monitoring capability for this species and suggested that corroboration of the size of the rebuild would be available when these surveys were repeated in 2020^{Footnote 2}and 2021.

Because of the demonstrated capacity of the synoptic surveys to monitor Bocaccio, it was considered feasible to check the progress of the rebuild through an update of the 2019 stock assessment once the 2020 and 2021 information from the synoptic surveys^{Footnote 3}used in the model became available. Although no new age data will be available in 2021, it is likely that the 2016 cohort will be identifiable from the length frequency data in the three surveys, given the large size of this cohort. It is also possible that new recruitment, if significant in size, will also be identifiable in these data.

On June 21, 2019, Bill C-68 received Royal Assent resulting in amendments to the Fisheries Act, which includes the Fish Stock provisions (FSP) and the authority to create regulations regarding the requirements for rebuilding plans for stocks prescribed in regulation that are below their LRP. In January 2021, Bocaccio was one of nine stocks in the Pacific Region included in the pre-publication in Canada Gazette Part 1 of regulatory amendments under the FSPs. It is anticipated Bocaccio will be prescribed in the fall of 2021.

The assessment, and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR), will be used to inform fisheries management of changes in stock abundance and to determine if current harvest levels are sustainable and consistent with the Precautionary Approach, the current Rebuilding Plan for Bocaccio and any new regulatory rebuilding requirements under the FSPs.

Objectives

The specific objectives of this science response are to:

1. Assess the current status of the coastwide Bocaccio stock in BC waters relative to the reference points used in the 2019 stock assessment.
2. Using probabilistic decision tables, evaluate the consequences of a range of harvest policies, including a no harvest policy, on projected biomass (and exploitation rate) out to 10 years relative to the reference points.
3. Provide guidance to be used by a management rebuilding plan under the PA framework for Bocaccio to satisfy recent legislation (Fisheries Act). 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).
4. Describe sources of uncertainty related to the model (e.g. model parameter estimates, assumptions regarding catch, productivity, carrying capacity, and population status).

Expected Publication

• Science Response

Expected Participation

• Fisheries and Oceans Canada (DFO) (Science and Fisheries Management)
• Canadian Groundfish Conservation Society

References

• DFO. 2009. A fishery decision-making framework incorporating the Precautionary Approach.
• DFO, 2020. Bocaccio (Sebastes paucispinis) stock assessment for British Columbia in 2019, including guidance for rebuilding plans. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2020/025.
• Starr, P.J. and Haigh, R. 2021. Bocaccio (Sebastes paucispinis) stock assessment for British Columbia in 2019, including guidance for rebuilding plans. DFO Can. Sci. Advis. Sec. Res. Doc. In press.