Research Document - 2011/124
Lingcod (Ophiodon elongatus) stock assessment and yield advice for outside stocks in British Columbia
By J.R. King, M. McAllister, K.R. Holt, and P.J. Starr
Abstract
Lingcod (Ophiodon elongatus) are unique to the west coast of North America. They are distributed in nearshore waters from California to Alaska, with the centre of abundance off the coast of British Columbia. Lingcod are found on the bottom at depths of 3-400 m, with most individuals occupying rocky areas at depths of 10-100 m. Tagging studies have shown lingcod to be largely non-migratory; however, stock delineation has not been clearly defined in British Columbia. Lingcod populations in British Columbia are assessed and managed as five separate units based on DFO Statistical Areas. These units include one inside stock in the Strait of Georgia (Area 4B) and four outside stocks: southwest Vancouver Island (Area 3C), northwest Vancouver Island (Area 3D), Queen Charlotte Sound (Areas 5A and 5B), and Hecate Strait and the west coast of Haida Gwaii (Areas 5C, 5D, and 5E). This assessment provides advice for the four outside assessment areas only (Area 3C, Area 3D, Area 5AB, and Area 5CDE).
Lingcod are an important component of both the commercial and recreational groundfish fishery off British Columbia. They are exploited primarily by trawl gear, but also by hook and line gear, including handline, longline, and troll. For the 2009-2010 fishing year, a 65 cm size limit was in place for lingcod retained in commercial fisheries. The size limits also applied to recreational fisheries in Areas 3C, 3D and 5A only. A coastwide winter closure (November 16 to March 31) was in effect for the hook and line commercial fishery, and for recreational fisheries conducted in 3C, 3D and 5A. All commercial fisheries are managed with an Individual Vessel Quota system. The total lingcod commercial catch for the outside management areas in 2009 was 2,014 tonnes. The total lingcod recreational catch in 2009 was estimated as 44 tonnes (27, 275 pieces).
We applied a Bayesian surplus production model to assess lingcod stock status within each of the four assessment areas. Data inputs for area-specific models included total annual catch since 1927, three or more abundance indices (with CV’s), and prior probability distributions for estimated parameters. Area-specific parameter estimates for intrinsic rate of increase (r) and carrying capacity (K) were used to calculate management parameters such as maximum sustainable yield (MSY), the optimum fishing mortality rate at MSY (FMSY), and the optimal stock size at MSY (BMSY). The assessment model was projected 5 years into the future under a range of alternative constant harvest policies (e.g., total allowable catch levels) to create decision tables for each assessment area. Sensitivity analyses were used to evaluate the effect of stock assessment assumptions on the results.
Current lingcod stock status is assessed in the context of the DFO Fishery Decision-making Framework Incorporating the Precautionary Approach, which requires the definition of three stock status zones (Healthy, Cautious and Critical). Delineation between these zones is based on an Upper Stock Reference (USR) set at 80% of BMSY that delineates the boundary between Healthy and Cautious zones and a Limit Reference Point (LRP) set at 40% of BMSY that delineates the boundary between Cautious and Critical zones. For each assessment area, we present the probability that current biomass levels are within Healthy and Critical zones. In addition, we quantify stock status relative to commonly used management parameters, including: current biomass relative to BMSY, current biomass relative to unfished biomass, and current fishing mortality relative to FMSY. Additional management parameters reported include MSY and the replacement yield for 2010, which is the amount of yield that can be removed without leading to biomass increase or decline in 2011.
Based on the medians of the estimated posterior distributions for current biomass, the lingcod stocks in all four assessment areas are most likely in the Healthy Zone (i.e. current biomass is greater than 80% of BMSY). Considerable uncertainty exists in the stock status estimates for Areas 3C and 5AB. There is high confidence in classifying stocks in both Area 3D Area 5CDE as in the Healthy Zone.
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