Science Advisory Report 2014/039
Stock Assessment and Harvest Advice for Rock Sole (Lepidopsetta spp.) in British Columbia
Summary
- Rock Sole (Lepidopsetta spp.) is a commercially important flatfish that occurs along the entire coast of British Columbia, Canada. Abundance is highest in Queen Charlotte Sound (Area 5AB) and Hecate Strait (Area 5CD), which is where the majority of Rock Sole catch is taken. Catch is almost entirely taken by the groundfish trawl fishery.
- Rock Sole stocks in Areas 5AB and 5CD are assessed as two independent stocks using a female-only, catch-at-age model, implemented in a Bayesian framework to quantify uncertainty of estimated quantities. Limited fishery and survey data from the other three management areas (3CD, 4B, 5E) preclude the provision of quantitative harvest advice for these areas.
- Female spawning biomass in Area 5AB at the start of 2014 (B2014) is estimated to be 0.37 (0.27 - 0.49) of unfished female spawning biomass (B0), where numbers denote median (and 5-95 percentiles) of the Bayesian results. B2014 is estimated to be 1.52 (0.98 - 2.26) of the female spawning biomass associated with maximum sustainable yield (BMSY). In Area 5CD, B2014 is estimated to be 0.80 (0.58 – 1.07) of B0 and 3.22 (2.10 – 4.64) of BMSY.
- Stock status is evaluated relative to reference points that are consistent with the provisional reference points contained in the DFO ‘Fishery Decision-making Framework Incorporating the Precautionary Approach’. These include a limit reference point (LRP = 0.4BMSY), an upper stock reference point (USR = 0.8BMSY), BMSY, and the harvest rate associated with maximum sustainable yield, uMSY. A set of historical reference points that were previously developed and applied to British Columbia Rock Sole stocks in 2006 are also used, which include a limit biomass (BLIM), a target biomass (BTAR), current biomass (B2014), and a target harvest rate (uTAR).
- In Area 5AB, the model estimates the probabilities that B2014 is greater than 0.4BMSY, 0.8BMSY, BMSY, BLIM and BTAR to be 100%, 99%, 94%, 100% and 41%, respectively. The model estimates the probabilities that the harvest rate in 2013 was less than uTAR) and less than uMSYto both be 100%.
- In Area 5CD, the model estimates the probabilities that B2014is greater than 0.4BMSY, 0.8BMSY, BMSY, BLIM and BTAR to be 100%, 100%, 100%, 100% and 95%, respectively. The model estimates the probabilities that the harvest rate in 2013 was less than uTAR) and less than uMSY to both be 100%.
- Advice to management is presented in the form of decision tables using five-year projections for a range of constant catches. In Area 5AB, a constant catch of 330 tonnes (males and females combined), which is just below the recent average annual catch, has a 98% probability of maintaining stock size above BMSY by 2019. Stock size is predicted to likely decrease at catch levels of 550 tonnes and higher.
- Harvest advice for Area 5CD shows that a constant catch of 670 tonnes (males and females combined), which is just above the recent average annual catch, has a 100% probability of maintaining stock size above BMSY by 2019. Stock size is predicted to likely decrease at catch levels of 900 tonnes and higher.
This Science Advisory Report is from the Regional Peer Review meeting on ‘Assessments of British Columbia Rock Sole and Silvergray Rockfish Stocks’, held on November 20-22, 2013. Additional publications from thismeeting (Proceedings and Research Documents) will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
