Kodiak is synonymous with giant bears, king crabs, and weathervane scallops. The weathervane, also known as the giant Pacific scallop, is the largest scallop in the world. Its beautiful orange shell makes it a treasure for beachcombers, and gourmet chefs prize its large adductor muscle for its taste and texture.
Weathervanes range from California to the Bering Sea and west to the Aleutian Islands. They prefer a mud, sand, or gravel substrate and live anywhere from the intertidal zone to depths of 984 ft. (300 m). They are more common in the deeper parts of their range. Adult scallops form dense, oblong beds that parallel the current.
The round valves of a weathervane can grow to 11.8 inches (30 cm) in diameter, and they differ slightly in color, ribbing, and shape. The upper valve appears reddish-pink and has approximately ten primary ribs alternating with smaller ribs. The bottom valve is lighter in color and has about twenty primary ribs separated by several smaller ribs. The top valve of a weathervane is relatively flat, and the organism rests on the rounder bottom valve.
Unlike most other bivalves, such as clams and mussels, scallops cannot burrow into the substrate to escape predation. Instead, they detect predators with their primitive “eyes” located on the front of their bodies, just inside the shell opening. These eyespots can detect movement, even in the dark depths where the scallops live. When a scallop detects a predator, it swims away from danger by rapidly opening and closing its shell. This movement requires a large adductor, or hinge, muscle. Processors remove this hinge muscle from the shell and market it as a “scallop.” They then dispose of the rest of the animal.
Scallops are either male or female, but gonad color is the only way to distinguish the sexes. Female gonads range in color from orange to red, while a male has creamy white gonads. Weathervanes become sexually mature when they are three to four years old and have a shell height of three inches. Scallops are broadcast spawners and reproduce by gathering in a large group and releasing clouds of eggs and sperm. When a sperm encounters an egg, it fertilizes it in the water column. Biologists think the increasing water temperature in May and June induces the scallops to spawn.
Fertilized scallop eggs sink to the bottom, where they remain for a few days until they develop into tiny larvae. The larvae swim and feed in the water column for a few weeks before sinking to the bottom and transforming into a benthic, filter-feeding scallop. Weathervane scallops can live for 28 years. Primary threats to weathervanes include predation by crabs, sea stars, and octopuses, diseases, habitat damage, and ocean acidification.
Consumers consider scallops a delicacy, and the commercial demand is high. Fishers use dredges to harvest scallops, though, and dredges can severely impact benthic organisms and their habitat. Concerns regarding the effects of dredging have prompted the Alaska Board of Fisheries to enact extensive closures of the scallop fishery and tightly regulate the scallop harvest. The commercial fleet of weathervane harvesters in Alaska is small, with a handful of vessels located in Kodiak. These boats dredge from beds located fifty to one-hundred meters deep, but their bounty does not meet commercial needs.
In the late 1980s, my husband and I volunteered to join an experimental mariculture venture for weathervane scallops sponsored by the Japanese government and several U.S. agencies, including the Alaska Department of Fish and Game. We suspended cages covered with fine mesh in the ocean and collected scallop larvae, as well as the larvae of several other invertebrate species. We then began growing the scallops to a marketable size. We didn’t gather many weathervanes, but we learned where to place the cages to collect the most scallop larvae. Unfortunately, the scallop project ended abruptly in 1989 when the Exxon Valdez oil spill occurred, and state and federal agencies focused their attention on cleaning up the oil and assessing the damage caused by the spill.
More than thirty years later, scientists still have not given up on raising scallops in a mariculture setting, but first, they realize they need to fill the gaps in their knowledge about weathervane biology. Researchers do not know how to determine the age of a weathervane properly, how fast they grow, or how abundant they are in Alaska’s waters. Biologists are also not sure about when weathervanes spawn or if they spawn several times a year. Once researchers can answer some of these questions, they hope to successfully induce weathervanes to grow and reproduce in captivity and make them a viable species to raise in a mariculture operation. Biologists think that farm-raised scallops and wild-caught weathervanes will someday complement each other in the worldwide marketplace.
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Robin Barefield is the author of four Alaska wilderness mystery novels: Big Game, Murder Over Kodiak, The Fisherman’s Daughter, and Karluk Bones. Sign up below to subscribe to her free, monthly newsletter on true crime and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.
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