Review of methods for developing catch limits for Greenland cockle (Serripes groenlandicus) and northern propeller clam (Cyrtodaria siliqua) in the Banquereau and Grand Bank offshore clam fisheries

Abstract

The Arctic Surfclam fishery began on Banquereau in 1986 and on Grand Bank in 1989. The directed Surfclam fishery allows for the retention of Greenland Cockle and Northern Propeller Clam. Greenland Cockle have been landed in the Banquereau fishery since 1999 and from Grand Bank since 1994. Northern Propeller Clam have been landed in the Banquereau fishery since 1996 and from Grand Bank since 1994. The amount and frequency of landings have varied over the time series for both species. A complete time series of actual catch (discards plus landings) is unavailable for Greenland Cockle and Northern Propeller Clam. Changes in landings over time is a function of economics and fishery behaviour as much as species densities or biomass. Landings-based approaches do not account for discards and should be used with caution until more discard information can be collected. Approaches based on biomass estimates, from survey or from landings per unit effort, are sensitive to the catchability coefficient, the area used to calculate the biomass, and the removal rate applied to the biomass. Length-based indicators provide information on size distribution of the stock and are a simple means for monitoring.