PURPLE HINGED ROCK SCALLOP (CRASSADOMA GIGANTEA)
Life History
Purple Hinged Rock Scallops (Crassadoma gigantea) have a large geographical range. They can be found from the coast of northern Mexico to northern Alaska. Rock scallops use external fertilization to spawn. After the egg is fertilized, it goes through multiple planktonic stages and then metamorphosizes into its benthic life stage as a juvenile. Once a scallop reaches its juvenile stage, it can use its abyssal threads to attach to hard substrate. At this stage, it can still detach and swim to new locations but once it reaches the end of its juvenile stage it permanently cements itself to a rock or other hard substrate. The rock scallop will spend the remainder of its life in that once location unless physically removed by an external force (i.e. storm or predator).
Mariculture
The Purple Hinged Rock Scallop is a prized harvest for commercial and recreational divers in southeast Alaska. In an effort to diversify shellfish mariculture in Alaska APMI has been developing hatchery techniques to produce juveniles for trial grow out for perspective famers. PHRS have a large abductor muscle considered a delicacy which commands a high price in white table cloth restaurants. Very few hatcheries have enjoyed the success of APMI in culturing the juveniles and because of the high costs of production and uncertainty of grow out success PHRS have not been widely tested by Aquatic Farmers.
One of the challenges of PHRS is their capacity to adhere by "cementing" to substrates for their final stage of growing to maturity and harvest. This requires an extra step in culture by "freeing them" when this occurs or alternatively sacrificing culture gear for grow out. Other unique observations at APMI is the protracting of larvae culture over several months for portions of a cohort making hatchery processes cumbersome. PHRS as a mariculture product needs additional work into maximizing hatchery production and developing grow out technologies.
APMI will continue to work on PHRS culture techniques as funding and interest from the aquatic farm industry allow.
ALUTIIQ PRIDE MARINE INSTITUTE PURPLE HINGED ROCK SCALLOP PROJECT
Nursery/Growout
This project was a continuation of the Western Regional Aquaculture Center’s “Profitable and Biosecure Rock Scallop Culture for the West Coast”. The Alutiiq Pride Marine Institute successfully completed its portion of the grant by producing 100,000 juvenile rock scallops (1mm and 5mm). The second component of the grant was to produce seed up to 30mm for the final growout phase. Tom Henderson of Pearl of Alaska conducted the nursery component of the project. In August 2015, 10,000 5+mm rock scallop seed were shipped to Kake and placed in 1.5mm and 3mm pearl nets at a density of 500 per net (20 nets). Mr. Henderson hung the pearl nets on his farm site and sampled bi-monthly for growth and mortality. When the scallops were close to 30mm (past the cementing stage) they were transferred to lantern nets for final grow out.
