Fishery biology and biological reference points for management of ocean quahogs (Arctica islandica) off Iceland

Ocean quahogs off Iceland are large, slow growing clams distributed on the continental shelf around the north Atlantic. The Icelandic stock is most northern and found in the shallowest water. Maximum age may exceed 200 y. Commercial fishing and biological research for ocean quahogs started in 1995 but relatively little biological information is available. We used published information, estimated key parameters, and calculated biological reference points for the Icelandic stock based on per recruit models. Commercial catches varied during 1995-2000 and increased to 14,200 t in 2003. The growth model was L = 99.9(1−e−0.0223(a+22.5)), where L is shell length (SL, mm) and a is age (y). Fifty-percent of ocean quahogs reach sexual maturity by 64 mm SL (23 y) and 50% are fully selected by commercial fishing dredges by 72 mm SL (55 y). Based on a length-based per recruit model, FMAX = 0.0694, F0.1 = 0.0312 and F50% = 0.032 y−1. Managers should consider precautionary management approaches in view of ocean quahog life history, uncertainties about recruitment, and likely low stock productivity. The current 2.5% harvest rate approach seems reasonable in the near term because 2.5% is less than F50% and F0.1 from a per recruit model. However, based on simulation analyses in the literature, approaches that maintain high levels of spawning biomass (e.g., 60-80% of virgin) might perform better in the long term. More accurate approaches to measuring stock size, simulation studies to determine optimum harvest strategies, estimation of current (near virgin) stock size, recruitment studies, and biological parameters are key areas for future research.