WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2017 49 The Manila clam Venerupis philippinarum (synonymous with Tapes semidecussata, T. philippinarium, and T. japonicas) is a significant aquaculture crop in China, Japan, France and Italy and other shellfish farming regions. Manila clams were accidentally introduced during the 1920s and 1930s to the Pacific coast of North America in oyster seed shipments from Japan. The clam quickly naturalized and spread to become common from southern British Columbia to northern California. It is now an important commercial clam species on the Pacific coast, with nearly all harvest from Washington State, USA (4,300 t in 2015) and British Columbia, Canada. While historically much of the production resulted from natural recruitment and limited husbandry, extensive and intensive aquaculture production methods are currently employed in many locations. Most are grown in sand or mixed gravel/sand/shell sediments with or without a protective groundcover of predator netting and harvested manually using short-handled rakes. These labor-intensive husbandry and harvest methods require a large work force and account for 15 to 25 percent of the total production cost of market-sized clams. About 15 years ago, Chuckanut Shellfish in Samish Bay (Washington State, USA), which is an embayment of Puget Sound, in the Salish Sea (Figs. 1 and 2), began experiments to adapt landbased agricultural practices to Manila clam production, applying results from several years of small-scale trial clam plantings and a long history of successful oyster production in adjacent areas of Innovative Farming Methods for Production and Harvest of Manila Clams in Washington State, USA Andrew D. Suhrbier, Daniel P. Cheney, Jeffery R. Cordell, William F. Dewey, Jonathan P. Davis and João G. Ferreira Samish Bay. The production method combined predator netting, mechanical net deployment and sweeping, and a modified tulip-bulb harvester to intensively cultivate and harvest Manila clams. This has allowed effective predator protection, biofouling control, and efficient harvest. With a perperson harvest rate of 1,100 to 1,300 kg/h, total harvest costs are now reduced to 3 to 5 percent of the farm gate value. In this article, we describe various aspects of bivalve cultivation and harvest studied at the Chuckanut Shellfish farm. Specific objectives were to assess aspects of planting bed preparation, predator net maintenance and clam harvest with respect to water quality, macroalgae, benthic communities, and mobile macrofauna; and to examine and contrast benthic and epibenthic speciation and abundance between manually and mechanically harvested clams, swept and non-swept predator nets, and farmed or non-farmed substrata. Details of changes in benthic and epibenthic fauna and other site-specific farm site and harvest effects were described in a recent thesis paper (Kralj 2017). In a companion paper, we assessed yield in terms of clam growth, mortality and quality and incorporated the results into a Farm Aquaculture Resource Management (FARM) model to simulate potential harvest, sustainable carrying capacity, and positive and negative aspects of production (Saurel et al. 2014). This article focuses on general (CONTINUED ON PAGE 50) FIGURE 1. Samish Bay, North Puget Sound, with the location circled of the Chuckanut Shellfish farm location (left). Layout of the farm showing the locations and lengths of individual planted rows (right). Source: National Geographic Society (left) and Google Earth satellite photo 7-14-2014 (right). FIGURE 2. The Chuckanut Shellfish farm is located in the middle of Samish Bay and several miles from the nearest land. A landing craft is used to access the growing beds and to carry a small tractor, bed maintenance equipment and people across the bay. The day begins and ends with the fall and rise of the tide and at high tide water six feet deep or greater covers the farm.
RkJQdWJsaXNoZXIy MjExNDY=