Research Document - 2016/009

Stock Assessment and Harvest Advice for Rock Sole (Lepidopsetta spp.) in British Columbia

By Holt, K.R., Starr, P.J., Haigh, R., and Krishka, B.

Rock Sole (Lepidopsetta spp.) occur along the entire coast of British Columbia (BC), Canada, with abundance highest in Hecate Strait and Queen Charlotte Sound. The majority of Rock Sole catch is taken by the groundfish trawl fishery. Two species of Rock Sole occur in BC: Southern Rock Sole (L. bilineata) and Northern Rock Sole (L. polyxystra). Rock Sole encountered in BC fisheries and research surveys are almost exclusively Southern Rock Sole. Rock Sole stocks in BC are assessed and managed as five separate areas based on DFO Statistical Areas. This assessment provides harvest advice for Areas 5AB (Queen Charlotte Sound) and 5CD (Hecate Strait). Limited fishery and survey data from the other three management areas (3CD, 4B, 5E) preclude the provision of quantitative harvest advice. Summaries of available data for these areas are provided.

A female-only statistical catch-at-age model in a Bayesian estimation framework was used to assess Rock Sole in Areas 5AB and 5CD. The model was fit to catch data, two or more indices of abundance, and age composition data from commercial trawl fisheries and research surveys. Indices of abundance included fishery-dependent catch-per-unit effort time series as well as fishery-independent trawl survey indices. Stock status in Areas 5AB and 5CD is evaluated relative to two types of reference points: MSY-based and historical. The MSY-based reference points 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 = 0.4B_MSY, where B_MSYis the female spawning biomass associated with maximum sustainable yield), an upper stock reference point (USR = 0.8B_MSY), B_MSY, and the harvest rate associated with MSY (u_MSY). The historical reference points were previously developed and applied to BC Rock Sole stocks in 2006, and include a limit biomass (B_LIM), a target biomass (B_TAR), current biomass (B₂₀₁₄), and a target harvest rate (u_TAR).

Results show that in Area 5AB, female spawning biomass in 2014, B₂₀₁₄, is estimated to be 0.37 (0.27 - 0.49) of unfished female spawning biomass, B₀(where numbers are given as posterior medians with 5^th and 95^th percentiles shown in brackets), and at 1.52B_MSY (0.98 - 2.26). There is a high probability that B₂₀₁₄ in Area 5AB is above B_MSY, 0.8B_MSY, 0.4B_MSY, and B_LIM, with B₂₀₁₄ most likely just below B_TAR. In Area 5CD, B₂₀₁₄ is estimated to be at 0.80B₀ (0.58 - 1.07) and 3.22B_MSY (2.10 - 4.64). There is a high probability that B₂₀₁₄ in Area 5CD is above all biomass-based reference points. Exploitation rates in 2013 are estimated to be below u_TAR and u_MSY in both management areas. In Area 5AB, the ratio of u₂₀₁₃ / u_TARis 0.59 (0.46-0.75) and the ratio of u₂₀₁₃ / u_MSY is 0.46 (0.30-0.72). In 5CD, the ratio of u₂₀₁₃ / u_TAR is 0.32 (0.24-0.42) and the ratio of u₂₀₁₃ / u_MSY is 0.08 (0.04 -0.16). In both areas, there is a 100% percent probability that the exploitation rate in 2013 is less than u_TAR and u_MSY.

Advice to management is presented in the form of decision tables using five-year projections for a range of constant catches. For each level of constant harvest, decision tables show the probability that projected stock status in each year will be greater than specified reference points.

Complete document (PDF, 14,209 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.