Fisheries and Oceans Pêches at Océans Canada Canad a Canadian Stock Assessment Secretariat Secrétariat canadien pour l'évaluation des stocks Research Document 98/8 8 Document de recherche 98/8 8 Not to be cited without Ne pas citer sans permission of the authors ' autorisation des auteurs ' A Review of the Biology and Fisheries of Horse Clams (Tresus capax and Tresus nuttallii) R. B . Lauzier, C . M. Hand, A. Campbell and S .Heizerz Fisheries and Oceans Canada Pacific Biological Station, Stock Assessment Division, Nanaimo, B.C. V9R 5K6 2 Fisheries and Oceans Canada South Coast Division, N anaimo, B.C. V9T 1K3 ' This series documents the scientific basis for the ' La présente série documente les bases scientifiques evaluation of fisheries resources in Canada . As des évaluations des ressources halieutiques du such, it addresses the issues of the day in the time Canada. Elle traite des problèmes courants selon les frames required and the documents it contains are échéanciers dictés. Les documents qu'elle contient not intended as definitive statements on the subjects ne doivent pas être considérés comme des énoncés addressed but rather as progress reports on ongoing définitifs sur les sujets traités, mais plutôt comme investigations . des rapports d'étape sur les études en cours . Research documents are produced in the official Les documents de recherche sont publiés dans la language in which they are provided to the langue officielle utilisée dans le manuscrit envoyé Secretariat. au secrétariat . ISSN 1480-4883 Ottawa, 199 8 Canada* Abstract A review of the biology and distribution of horse clams (Tresus capax and Tresus nuttallii)and a review of the fisheries of horse clams from British Columbia, Washington and Oregon is presented, based on previous surveys, scientific literature, and technical reports . Stock assessment strategies and management strategies are presented . Recommendations for additional information requirements for stock assessments and management plans are given . Résumé Un examen de la biologie et de la distribution de la fausse-mactre (Tresus capax et Tresus nuttalli) et un examen de la pêche de la fausse-mactre en Colombie- Britannique, à Washington et en Orégon, fondés sur des relevés antérieurs, des publications scientifiques et des rapports techniques, sont présentés. On y traite aussi des stratégies d'évaluation et de gestion . Des recommandations sont formulées relativement à l'obtention de renseignements supplémentaires pour les plans d'évaluation et de gestion des stocks . 1 Table of Contents 1 . INTRODUCTION........... ...... .... .. .. .... .. .. .. .. .. .. .... .. .... .. .... ...... .. .. .. .. .. .. .. ............................... .... 1 1 .1 . PLAN FOR THE DEVELOPMENT OF A DIRECTED FISHERY ON HORSE CLAMS . .1 1 .2 . BIOLOGICAL OBJECTIVES . .2 2. REVIEW OF CURRENT INFORMATION ON TRESUS CAPAX AND TRESUS NUTTALLII ........................... ...... .. .. .. .. ... .. .. .. .. .. .. .. .... .. .... ............ .. .. .. .. .. .. .. ............ ...... .. ..... .. ......2 2 .1 . DESCRIPTION . .2 2 .2. GEOGRAPHIC DISTRIBUTION . .3 2 .3 . HABITAT, ECOLOGICAL RELATIONSHIPS, CO-OCCURING SPECIES . .3 2 .4. PREDATORS, PARASITES AND DISEASE . .. .4 2 .5 . PHYSIOLOGY, FOOD AND FEEDING . .. .. .. .. .5 2 .(). REPRODUCTION . .. .. .. .. .. .. .. .. .. .. :. .. .5 2 .7. GROWTH AND AGE .. .. .. .. .. .. .. .7 2 . 8 . RECRUIT ME NT AND MORTALITY . .. .. .. .. .. .ô 2 .9. DENSITY AND BIOMASS . .. .. .. .. .. .9 3. FISHERIES ....................................... .... .. .. .. .. .. .. .... .. .. .. .. .. .................................. ..10 3.1 . REVIEW OF TRESUS FISHERIES IN BRITISH COLUMBIA . .. .. .. .. .. .. .. .. .. .. .. .1 0 3 .2. REVIEW OF TRESUS FISHERIES IN WASHINGTON AND OREGON . .. .. .. .. .. .. .I 1 4. DISCUSSION .................................. .... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .... ........................ .......12 4.1 . BIOLOGICAL CONSIDERATIONS . .. .. .. .13 4.2. STOCK ASSESSMENT CONSIDERATIONS . .. .. .. .. .. .14 4.3 . MANAGEMENT STRATEGIES .. .. .. .. .. .. .. .. .1 4 5. CONCLUSIONS ............................. .. .. .. .... .. .. .. .. .... .. .... .. .... .. .... .. .. .. ... .. .... .. ................ .. .. ... ....15 6. ACKNOWLEDGEMENTS ........... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .............................. ... ..15 7. REFERENCES.................................... .... .. .. .. .. .. .. .. ... .. .. .. .. .................................... .. ...16 2 List of Tables Page Table 1 . Von Bertanlanffy growth parameters for T. capax and T. nuttallü form British Columbia . 21 Table 2. Density Estimates of horse clams, Tresus sp. derived from geoduck (Panopea abrupta) dive surveys. 2 1 Table 3. Mean density of horse clams derived from transect surveys conducted in the Yellow Bank/Elbo w Bank area of the west coast on Vancouver Island, Sept .-Oct. 1995 . 22 Table 4. Results of census data for horse clams (T. capax) at Seal Island from surveys performed 1952-1992 . 23 Table 5. History of management actions for the horse clam fishery in the Pacific Region . 23 Table 6. Summary of horse clam landings (tonnes) by management area from South Coast to North Coast areas, 1979 to 1996, as reported by sales slips or harvest logs . 2 4 Table 7. Horse clam landings (tonnes) and effort for Bristish Columbia, 1979to 1996, as reported on sales slips and harvest logs . 2 5 Table 8. Horse clam landings (kg) from Area 24 rotational harvest areas, from harvest log reports, 1988 to 1994 . 26 Table 9 . Catch per unit effort (CPUE kg/diver hr) for horse clam directed fisheries and geoduck fishe ries 26 List of Figures Page Figure 1 . Wet weight-length relationship for Tresus spp. dug intertidally from Seal Island in 1995 . • 27 Figure 2 . Annual horse clam landings (all Tresus spp.) in British Columbia and whole landed value ($/t) in British Columbia . 2 7 Figure 3 . Total annual reported landings (all Tresus spp.) from major producing beds in Statistical Area 14 . 28 3 1 . Introduction Two species of horse clams (Tresus nuttallii an d T. capax) have been harvested incidentally in the geoduck (Panopea abrupta) fishery since 1979 . Harvest is restricted to G licence holders and to subtidal areas deeper than 10 feet below chart datum . There has never been an assessment of horse clam stocks in British Columbia, or a specific recommended or allocated quota. Current management includes time/area openings co-incident with the geoduck fishery and, in recent years, arbitrary catch caps . There is a building desire on the part of G licence holders to develop the markets for this potentially high value product and to expand the fishery from an incidental one to a targetted or directed fishery . Fisheries and Oceans Canada (DFO) placed a moratorium on new invertebrate fisheries in the Pacific Region in 1992, as the department lacked the resources to collect and analyze the biological information necessary to develop a sound management strategy . Since then, DFO and the Ministry of Agriculture, Fisheries and Food (MAFF) proposed several new invertebrate stocks for potential exploitation, including the neon flying squid (Ommastrephes bartrami), Pacific milky venus clam (Compsomyax subdiaphana), and the deepwater or grooved Tanner crab (Chionoecetes tanneri). In addition, octopus (Octopus dofleini) and horse clams (Tresus capax and Tresus nuttallii) were identified as high priorities for expansion from incidental fisheries to targetted fisheries . There are ongoing discussions between DFO and MAFF to develop policy and guidelines for the development of new fisheries, with a phased precautionary approach, to ensure an orderly development of a sustainable, viable fishery . 1.1 . Plan for the Development of a Directed Fishery on Horse Clams Within the Stock Assessment Division of DFO, a framework was developed for the provision of scientific advice for the management of new and developing invertebrate fisheries, including established fisheries whose expansion is limited due to a lack of information of the species distribution or abundance (Perry et.al. in prep). This framework included three phases for the precautionary development of a fishery : Phase 0 : Collection of all available information on the target species, and from similar species elsewhere, to provide a baseline with which to advise on the alternative management options and to identify areas where information is lacking ; Phase 1 : Involves surveys and experimental fishing where the objective is the collection of data required to fill in the information gaps identified in the first phase and to explore the fishery potential. Phase 2 : Fishing for Commerce . A fishery is developed at the commercial level, while stocks are monitored and management strategies are evaluated. This paper presents the Phase 0 review of known and derived information on the two species of horse clams found in British Columbia, Tresus capax and T. nuttalii. It includes a 1 review of horse clam distribution, life history and biology, population dynamics, abundance and a summary of horse clam fisheries in B .C and elsewhere . 1.2. Biological Objectives The biological objective for a fishery on horse clams is to maintain a viable, healthy, and productive stock throughout their natural range in British Columbia . Three basic biological objectives were provided for the management of Pacific Region fish and invertebrate stocks by Rice et.al. (1995) . These provided the framework for the specific biological