Terms of Reference

Widow Rockfish (Sebastes entomelas) stock assessment for British Columbia in 2019

Regional Peer Review Process – Pacific Region

June 18-19, 2019
Nanaimo, BC

Chairperson: Greg Workman

Context

Widow Rockfish (Sebastes entomelas) ranges from the Gulf of Alaska to Baja California and is most abundant in waters from British Columbia (BC) to northern California. Widow Rockfish is a key species caught in the BC multi-species integrated groundfish fishery. This species is primarily intercepted by midwater trawl gear directed at mixed rockfish (Sebastes spp.), with less than 20% of catch coming from bottom trawl gear. The species is also caught as a non-target species in the midwater trawl fishery directed at Pacific Hake (Merluccius productus). Annual coastwide landings of Widow Rockfish over the last 23 years (1996-2018) account for about 10% of the total weight of rockfish landed by trawl.

Conventional stock assessments typically use fishery time series data to estimate current stock size and productivity. Although good catch and biological data series are available for Widow Rockfish in BC, the lack of reliable fishery-independent indices of relative abundance has hampered stock reconstruction. Existing abundance indices derived from modern surveys conducted in collaboration with industry use bottom trawl gear, which is not ideal for species like Widow Rockfish that exhibit pelagic behaviour. The survey indices for widow rockfish are imprecise and display large inter-annual shifts in index values suggesting survey catchability varies widely making bottom trawl survey indices unsuitable for tracking widow rockfish abundance. Targeted commercial catch rates using midwater gear are also unsuitable as a basis for indexing abundance because pelagic species are searched for acoustically. Indices derived from bycatch in the bottom trawl commercial fishery have been successfully used in recent stock assessments for species which also show pelagic behaviour. Examples include Redstripe Rockfish (S. proriger) and Walleye Pollock (Theragra chalcogramma), making this approach a possible source of abundance indices to be used with the available survey indices.

There are no published studies that have examined the genetic population structure of Widow Rockfish in northeastern Pacific waters. After an evaluation of available data by a technical working group, it was agreed that this species should be treated as one coastwide BC stock.

In the absence of updated science advice, there is uncertainty about the risks posed to the BC stock by current levels of catch. DFO Fisheries Management has requested that DFO Science provide advice regarding the assessment of the Widow Rockfish stock relative to reference points that are consistent with the DFO’s Fishery Decision-Making Framework Incorporating the Precautionary Approach (DFO 2009), including the implications of various harvest strategies on expected stock status. The advice arising from this 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, including Marine Stewardship Council certification of the Pacific Hake fishery.

Objective

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

Widow Rockfish (Sebastes entomelas) stock assessment for British Columbia in 2019. Paul J. Starr and Rowan Haigh. 2019. CSAP Working Paper 2018GRF01

The specific objectives of this review 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.
2. Assess the current status of Widow Rockfish in BC waters relative to the recommended reference points. If necessary, provide evidence to support the separation of this species into spatially distinct stocks, and if required, provide advice on the status of these stocks.
3. Using probabilistic decision tables, evaluate the consequences of a range of constant catch harvest policies to projected biomass relative to the reference points and additional stock metrics, including projected biomass relative to current biomass. If the data are insufficient to quantitatively evaluate BC Widow Rockfish in terms of PA reference points and decision tables, summarise what is known about the status of this species, and discuss the implications for harvest advice.
4. Describe sources of uncertainty related to the model (e.g. model parameter estimates, assumptions regarding catch, productivity, carrying capacity and population status).
5. 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.  Provide a rationale if indicators and triggers cannot be identified.

Expected Publications

• Science Advisory Report
• Proceedings
• Research Document

Expected Participation

• Fisheries and Oceans Canada (DFO) (Science and Fisheries Management)
• Commercial and Recreational Fishing Representatives
• Environmental Non-government Organizations
• First Nations
• Province of BC
• USA Government Agencies (NOAA, Alaska Fish & Game)

References

DFO 2009. A Fishery Decision-Making Framework Incorporating the Precautionary Approach.