50 DECEMBER 2017 • WORLD AQUACULTURE • WWW.WAS.ORG aspects of farm production and harvest operations. The principal elements of Chuckanut farm production practice are: 1) Seeding clams in meter-wide rows to facilitate mechanization, 2) Culture in a sand substrate versus a mixed sand-gravel, 3) Mechanized installation of predator nets using a tractor and a modified terrestrial agriculture implement, 4) Using a tractor-mounted street sweeper to clean predator nets, 5) Mechanized net removal and rolling for storage, 6) Mechanized clam harvesting using a modified tulip bulb harvester, and 7) Vessel-assisted retrieval of harvested clams unitized on pallets. Production Methods at Chuckanut Shellfish Farm Chuckanut farm is located on a 2.6-ha, intertidal, gently sloping tidal flat isolated from the adjoining shoreline by several deeper channels and broad tidal flats (Fig. 1). The bottom elevation ranges from -0.3 m to 0.0 m Mean Lower Low Water. It has a mixed fine to medium sand substrate and very flat topography. Approximately 70 percent of the area is used for Manila clam culture and the remaining 30 percent forms aisles between cultivated rows. The surrounding bottom has a slightly lower elevation with a light to moderate cover of seagrass (Zostera marina and Zostera japonica) mixed with the green algae Ulva spp. and scattered patches of nonvegetated substrate. The site is accessed by boat from a staging area located about 4 km west of the farm. Usually a small outboard engine-powered landing craft is used to transport personnel, a work tractor and other farm equipment (Fig. 2). This vessel also tows a barge or scow holding the harvest machine, spools of plastic mesh, and packing supplies (Fig. 3). Typically, two to five workers conduct farm operations during the period of tidal exposure. FIGURE 3. A work barge towed by the landing craft and used to carry the mechanical harvest machine, clam bins, netting and other supplies. FIGURE 4. Installation of predator netting. Clam netting is spooled out from the tractor in long generally north to south rows. Tension is maintained on the net to ensure it lies close to the ground and the edges are driven into the sediment and sealed with planting tools mounted on the tractor. Large metal staples are pushed into the bottom along the length of the netted rows at approximately 50-ft intervals. Once sufficient netting is installed, seed clams are dropped onto the net surface during an incoming tide. These clams drop through the netting and remain in place, covered by the predator net until harvest. FIGURE 5. Regular net maintenance is a critical part of clam farm operations. During late spring to early fall, a variety of macroalgae settle and grow on the surface of the net. Much of this algae consists of the green sea lettuce (Ulva), along with the brown algae Fucus and Sargassum.
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