April 2012- The Alaska scallop fishery is based upon the weathervane scallop, also called the giant Pacific scallop, Patinopecten caurinus. Scallops are not only tasty, but quite an interesting and unusual bivalve species as well. Unlike most bivalves (clams and mussels), scallops cannot burrow to escape predation, but instead they detect predators with primitive ‘eyes’ and have limited ability to swim away by rapid opening and closing of their shells. Scallops require a very large adductor, ‘hinge’ muscle, to maintain this ability. This muscle is what we think of as a “scallop,” although it is only one part of the animal.
Life History
Scallops are dioecious (have two sexes), are broadcast spawners, and reproduce by assembling and releasing clouds of gametes (eggs and sperm) which are fertilized in the water column. The signal for scallops to assemble and spawn is thought to be increasing water temperature and in Alaska spawning occurs in May and early June. Fertilized eggs settle to the bottom where they develop after a few days into a tiny transparent-shelled veliger larvae. The veliger larvae swims into the water column where it feeds on microplankton (small free-floating plants) for a period of about three weeks before settling to the bottom to begin its life as a benthic (bottom-dwelling) filter feeder.
Weathervane scallops begin reproducing at three or four years of age at a shell height of about three inches, and are commercially harvestable at about four inches shell height and six to eight years of age. Scallops can live about 28 years in Alaska. Like other bivalve mollusks, scallops are aged by counting the rings on their shell, which are formed by alternating periods of slow and fast growth associated with seasonal changes in temperature and food availability. The two valves of scallop shells are not identical, and the scallop body lies on the bottom valve, which is more rounded in shape, while the top valve is flatter. Adult scallops assemble in dense ‘beds’; these have a characteristic oblong shape, with the longer axis parallel with the direction of the prevailing current.
Fishery
Weathervane scallop beds in Alaska are located on mud, clay, sand or gravel substrate at depths of 120 to 390 feet in the Gulf of Alaska and Bering Sea. Scallops are captured using standard New Bedford style scallop dredges that are on average 15 feet wide and weigh about 2,600 pounds. The frame provides a rigid, fixed dredge opening to which a steel ring bag (consisting of 4-inch rings linked together) is attached to collect the scallops as the dredge is towed. In response to an influx of vessels from the east coast, a vessel moratorium was implemented in state waters in 1997; eight vessels currently hold vessel-based entry permits. In a further effort to increase economic efficiency, permit holders created a scallop fishing cooperative in 2000. Some cooperative members opted to remove their boats from the fishery and arranged for their shares to be caught by other members of the cooperative, providing the remaining vessels with additional fishing opportunity. In recent seasons, only four vessels on average have participated in the fishery. This fleet of 70 to 120-ft vessels each has a crew of eight to twelve, who shuck and freeze the scallops onboard the vessels. Most of the scallops produced are marketed directly by the cooperative. Except in the Cook Inlet area, all commercial scallop fishing vessels are required to carry trained observers.
Read the full article at Alaska Fish and Wildlife News.