Research Document 2017/069

Data Review and Assessment Framework of the Arctic Surfclam (Mactromeris polynyma) on Banquereau and Grand Bank

By Hubley, B., and Heaslip, S.G.

Abstract

A review of life-history characteristics, impacts of dredging, habitat suitability, and survey and fishery information for Arctic Surfclam (Mactromeris polynyma) in Atlantic Canada was performed to provide a basis for a risk assessment framework to assess management options.

Since the last survey in 2010, fishing has occurred almost entirely on Banquereau with little effort directed towards Grand Bank, thus this review is focused on an analysis of fishery data from Banquereau. Issues associated with using the Catch Per Unit Effort (CPUE) data included changing efficiency, spatial variability, and a short time lag in the reporting of catch. Changes in efficiency over time was not accounted for; however, the time lag and spatial variability was partially mitigated through censoring and spatial aggregation of the data and the use of Vessel Monitoring System (VMS) positional data which provided more accurate and frequent information to identify areas of exploitation during 2004–2015.

Density estimates from the 2010 survey were similar to the 2010 CPUE density estimates for overlapping locations. When these density estimates were expanded to the fished area, as  identified from the VMS footprint, the resulting biomass estimates for 2010 were also similar between the survey (209,261 t) and CPUE (217,604 t). Biomass estimates from the last assessment were corrected for dredge efficiency, which was estimated to be 0.45 with considerable uncertainty. A Bayesian surplus production model incorporated and quantified the uncertainties associated with dredge efficiency, the resulting estimates of biomass, and provided estimates of process and observation error.

In order to facilitate the discussion of a spatial management approach, five example areas were constructed considering the following criteria: easily navigable, encompass large scale contiguous clam beds, approximately equal in total biomass, and inclusion of both high and low density areas. The production model was fit to the CPUE index for each area with some parameters (e.g., dredge efficiency) estimated across areas. Model results show a trend of declining catch rates across all areas for the last five years. Maximum Sustainable Yield (MSY) reference points were calculated from the surplus production model with F_MSY estimates near 0.1; however, phase plots indicate that catch rates tend to decline when F (fishing mortality) is greater than 0.05. A qualitative risk assessment indicated that despite how the spatial management areas are divided, there is considerably more risk associated with setting Total Allowable Catch (TAC) recommendations based on biomass estimates that result from areal expansion to areas that have not previously been fished. In addition, exploitation rates near the estimates of F_MSY are more risky than alternative F reference levels that are below F_MSY.

Complete document (PDF, 1,660 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.