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Yellowtail Rockfish (Sebastes flavidus) Stock Assessment for British Columbia in 2024

Regional Peer Review - Pacific Region

September 9-10, 2024

Nanaimo, BC

Chairperson: Dana Haggarty

Context

Yellowtail Rockfish (YTR, Sebastes flavidus) is a key species caught in the British Columbia (BC) multi-species integrated groundfish fishery. This species is intercepted by midwater and bottom trawl gear directed at mixed rockfish (Sebastes spp.), and is also caught as a non-target species in the midwater trawl fishery directed at Pacific Hake (Merluccius productus).

The primary challenge to the assessment of YTR in both Canadian and United States (US) waters is the lack of reliable measures of stock abundance (DFO 2015). The species resides in the vicinity of the bottom but is often in the water column (Love et al. 2002) and, therefore, may not be consistently represented in the various bottom trawl surveys conducted coastwide. Survey sampling error for YTR relative biomass estimates is typically large, with coefficients of variation averaging 50%, with highs up to 90% (Starr et al. 2014). Alternative survey gears (e.g., longline hook and trap) are inefficient for catching YTR, and there is no available midwater trawl survey, or index series derived from acoustic measurements, that is suitable for indexing YTR abundance. In BC waters, YTR is caught concurrently with species such as Pacific Hake, Widow Rockfish (S. entomelas), Canary Rockfish (S. pinniger) and other Sebastes species, which makes target identification problematic for acoustic surveys (Kieser et al. 1993; Hand et al. 1995). Commercial trawl fishing relies on acoustic detection of rockfish schools prior to deployment of trawl gear; YTR tend to dive when fished by trawl so that a fishing master must decide to target by positioning the net opening in the expected path of the descending school (Brian Mose, Canadian Groundfish Research and Conservation Society, pers. comm.). Because of this targeting behaviour, commercial catch per unit effort (CPUE) is unlikely to be proportional to abundance.

A secondary challenge to the stock assessment of YTR is the unresolved issue over the relative absence of females at increasing ages in comparison to males (Starr et al. 2014). Competing hypotheses, including female senescence or different availability to trawl gear, have been proposed to explain the difference by sex in the observed age frequencies. Modelling solutions to date have been based on the preference of the analyst rather than strong biological evidence favouring one hypothesis.

Although there is no biological evidence for stock structure within BC waters, YTR is currently managed in two areas: a “boundary” management area that includes Groundfish Management Unit (GMU) area 3C and a “coastal” management area that includes areas 3D and 5A-E (DFO 2015). Management area 4B (the inside waters of Juan de Fuca Strait, Strait of Georgia, and Queen Charlotte Strait between Vancouver Island and the BC mainland) is not included and YTR are rarely reported from this area. Yellowtail Rockfish in Pacific Marine Fisheries Commission (PMFC) areas 3B (in the United States) and those in 3C (Canadian waters) likely mix. It is known that the species is capable of wide-ranging movement that can span several PMFC management areas based on tag release-recovery experiments (see discussion and references in Stanley and Haist 1997 and Stanley 1999). However, for the purposes of this assessment, a single closed population in the total BC waters (3CD + 5A-E) will be assumed, as was the case in the previous YTR stock assessment in 2014 (DFO 2015; Starr et al., unpublished working paperFootnote 1).

Fisheries and Oceans Canada (DFO) GMU has requested that DFO Science Branch provide advice regarding the assessment of a coastwide stock relative to reference points that are consistent with DFO’s Fishery Decision-Making Framework Incorporating the Precautionary Approach (PA; DFO 2009), including the implications of various harvest strategies on expected stock status. In 2019, Bill C-68 was enacted to amend the Fisheries Act (now ss. 6.1-6.3) with the Fish Stocks Provisions (FSP). The FSP came into force through amendments to the Fishery (General) Regulations (FGR) on April 4, 2022. The FSP established binding obligations on the Minister of Fisheries and Oceans to (a) maintain major fish stocks at levels necessary to promote sustainability (s. 6.1); and (b) develop and implement rebuilding plans for stocks that have declined to or are below their limit reference point (s. 6.2). A list of 30 major stocks (for all of Canada) has been identified (Batch 1) out of 62 proposed major stocks. Future batches will appear under FGR’s Schedule IX Major Fish Stocks. The YTR stock currently does not appear on the FSP/FGR lists.

The advice arising from a Canadian Science Advisory Secretariat (CSAS) Regional Peer Review (RPR) will be used to inform fisheries management decisions to establish catch levels for the species. This work may also inform and supplement decisions external to DFO, specifically for the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

Objectives

The following working paper will be reviewed to provide the basis for discussion and advice on the specific objectives outlined below.

The specific objectives of this working paper are to:

  1. Recommend reference points consistent with the DFO Precautionary Approach (PA), including the biological considerations and rationale used to make such a determination. If possible, these should include the DFO limit reference point (LRP) of 0.4 BMSY and the upper stock reference (USR) of 0.8 BMSY recommended in the PA for the stock. The following additional reference points will be presented: BMSY, uMSY, 0.2 B0, and 0.4 B0 for the stock.
  2. Assess the current status of YTR in BC waters coastwide (excluding area 4B), relative to the selected reference points.
  3. Using probabilistic decision tables, evaluate the consequences of a range of harvest policies on projected biomass (and exploitation rate) relative to the reference points and provide additional stock metrics for the stock.
  4. Conditional objective (to be addressed if a stock is assessed to be in the Critical Zone, i.e., a 50% or greater probability of being below the LRP): provide guidance for a rebuilding plan for YTR that satisfies rebuilding requirements under the “Guidelines for Writing Rebuilding Plans per the Fish Stocks Provisions and A Fishery Decision-making Framework Incorporating the Precautionary Approach”. Specifically, assess the probable causes of the stock’s decline and provide probabilistic decision tables that demonstrate a high probability (>75%) of the stock growing out of the Critical Zone (i.e., above the LRP) within a reasonable timeframe (1.5–2 generations or tmin under no fishing, DFO 2021).
  5. Describe sources of uncertainty related to the model (e.g., model parameter estimates, assumptions regarding catch, productivity, and population status).
  6. Recommend an appropriate interval between formal stock assessments, 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.
  7. Consider environmental covariates that may affect the stock as presented in the “Guidelines for Implementing the Fish Stocks provisions in the Fisheries Act”.

Expected Publications

Expected Participation

References

Notice

Participation to CSAS peer review meetings is by invitation only.

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