Science Advisory Report 2017/047
Assessment of the Arctic Surfclam (Mactromeris polynyma) Stock of Banquereau for 2016
- The framework for Arctic Surfclam on Banquereau (DFO 2016) recommended the use of a surplus production model fit to a time series of Catch Per Unit Effort (CPUE) data from five spatial assessment areas where areal expansion of Surfclam density was limited to an estimation of suitable clam habitat.
- Vessel Monitoring System (VMS) location data was used to construct a proxy for suitable clam habitat by assuming that fishing effort is related to Surfclam density and has targeted all areas with commercial concentrations over the past 13 years. The resulting polygons of fished area showed a high degree of overlap with areas of high habitat suitability estimated from an independent analysis using predictors derived from multibeam sonar data.
- The distribution of Surfclam is a key factor to consider in the management of the resource. The previous bank-wide estimate of Surfclam biomass from the 2010 survey did not include uncertainties related to dredge efficiency, gear selectivity, or the patchy distribution and density of clams across the Bank.
- The production model permits the uncertainties in CPUE and the estimates of dredge efficiency to be quantified and propagated into the biomass estimates.
- The annual CPUE index has generally declined in most assessment areas since the 2010 assessment, with an increase in 2016.
- Exploitation rates have varied between 0 and 0.15 as the fishery shifted focus among areas. Spikes in exploitation are generally followed by reduced exploitation in subsequent years and do not typically occur in multiple areas in the same year.
- The Banquereau Arctic Surfclam stock is considered to be in the Healthy Zone, with the median modelled biomass estimates above all of the biomass reference levels (limit reference point, upper stock reference and CPUE of 70 g/m2) for all of the assessment areas.
- Setting potential harvest levels based on the estimated biomass in the fished areas would increase the likelihood that the areas that have supported a commercial fishery since 1986 are not depleted. Setting potential harvest levels based on an estimated biomass for the full Bank could increase the likelihood that these historically fished areas might be depleted.
- The proposed fishing mortality level of 0.5 FMSY would result in a Total Allowable Catch (TAC) of 20,943 t for Banquereau, which is comparable to the current TAC (24,000 t).
This Science Advisory Report is from the April 20-21, 2017, Arctic Surfclam Assessment. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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