Nutrition and Condition of Red King Crab Larvae: Enhancement of King Crabs to Improve Sustainability of Alaskan Coastal Communities
School of Fisheries and Ocean Sciences, University of Alaska Fairbanks
- Asia M Beder, MS program
Alaska king crabs are iconic, historically important species in many regions for sport, subsistence, and community harvest. Almost all of the historical king crab fisheries in Alaska crashed and are now closed. The lack of recovery in stocks, such as Kodiak red king crab and Pribilof Islands blue king crab, which have not recovered in the absence of fishing for decades, suggests that alternative approaches are needed to rebuild king crab stocks in Alaska. King crab enhancement has the potential to restore king crab stocks, which would economically benefit the fishing industry and coastal communities throughout Alaska. The recent success of king crab culture in Alaska suggests that enhancement with hatchery animals is possible, yet mortality during the last larval rearing stage is a bottleneck in hatchery production of juveniles. In this project researchers will test whether a larval nutritional deficiency is the source of the bottleneck.
The lack of recovery in Alaska king crab stocks including Kodiak red king crab and Pribilof Islands blue king crab, despite the absence of fishing for decades, suggests that alternative approaches are needed to rebuild king crab stocks in Alaska. Stock enhancement is one alternative. A team of federal, state, and University of Alaska scientists under the auspices of the Alaska King Crab Research and Rehabilitation Program (AKCRRAB), have worked since 2006 to develop the knowledge to hatch and raise wild red and blue king crab as a way to reinvigorate collapsed stocks in places like Kodiak Island and the Pribilof Islands. They’ve made significant progress, increasing the number of crab reaching the juvenile stage from almost zero in 2007 to 50 percent in 2010. A wild restocking program would likely release hatchery crab raised to the juvenile stage. But researchers don’t know why many of these crab die in the hatchery soon after reaching the juvenile stage. Researchers in this study will test whether a nutritional deficiency explains the source of the apparent bottleneck in development and survival.
Why is this an Alaska Sea Grant project?
This project supports stock enhancement research goals of the Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) program. One of Alaska Sea Grant's six key goals outlined in the 2009–2013 Strategic Plan is sustained, well-managed, and healthy marine, coastal, and watershed ecosystems in Alaska. The program pursues this goal through support of research that provides decision-makers with science-based information that can be used to craft well-informed policies governing the use and conservation of Alaska's marine and coastal resources.
How will researchers conduct their study?
To achieve our specific objectives we will (1) determine a lipid profile of hatchery-cultured and wild-collected red king crab glaucothoe and juveniles to compare their bioenergetics and nutritional profile, (2) determine a lipid profile of hatchery-cultured blue king crab glaucothoe and juveniles, (3) perform live-feed dietary experiments to determine the EFA requirements for red king crab during the larval stages along with hatchery health indices and salinity stress tests, and (4) inform interested industry, fishery managers, and other stakeholders of advancements in king crab aquaculture through outreach.
Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) Program, Alaska Sea Grant
Alutiiq Pride Shellfish Hatchery, Seward, Alaska
Chugach Regional Resources Commission
Alaska Department of Fish and Game
NOAA National Marine Fisheries Service, Behavioral Ecology Laboratory, Hatfield Marine Science Center, Newport, Oregon
What researchers learned
The goal of this research project is to improve larval survival through improved nutrition, and therefore increase hatchery larval production. We raised larvae from eight ovigerous red king crab females in twelve 190 L tanks at the Alutiiq Pride Shellfish Hatchery in Seward, Alaska. We varied the nutritional content of the larval diet by feeding larvae Artemia nauplii enriched with lipid emulsions with various essential fatty acids: (1) high docosahexaenoic acid (DHA); (2) high DHA and eicosapentaenoic acid (EPA); (3) high DHA and amino acids (AA); and (4) a control lipid. We found similar larval survival to the glaucothoe stage among the diet treatments. Larval condition during the four zoeal stages (assessed by viewing size and number of lipid droplets) varied at the glaucothoe stage. The glaucothoe fed diets enriched with high DHA and EPA and high DHA and AA had more and larger lipid droplets than those fed DHA and control lipid diets. During a stress test that measured response time after exposure to freshwater, glaucothoe that were fed the diet enriched with the control lipid recovered significantly more slowly than the other diets, suggesting that diet can improve performance during stress. Biochemical analyses showed that proportions of EPAs were significantly different in crabs from all dietary treatments during the fourth zoeal, glaucothoe, and first juvenile stages. During the glaucothoe stage the total fatty acids standardized by larval wet weight were significantly lower in crabs fed the control diet. Results from this study will be used to improve diets of hatchery-reared king crab to increase larval production.
King crab enhancement has the potential to restore king crab stocks, which would have economic benefits for the fishing industry and coastal communities throughout Alaska. The knowledge gained through the proposed research will aid in the development of successful release strategies for hatchery-cultured king crabs. The ability to maintain a sustainable crab fishery by augmenting natural stocks would provide employment opportunities for fishermen and their children. Enhancing depressed stocks may also replenish depleted stocks to the degree necessary to reopen areas currently closed to fishing, further increasing job opportunities. Impacts of this research can be applied to other crustacean stock enhancement programs, as many components of red king crab rearing may be applied to other species.
Overall, researchers believe a better understanding of the nutritional requirements of late-stage larval and juvenile stage king crab born in hatcheries will lead to improved feeding of hatchery crab and development of aquaculture feed specifically formulated for Alaska king crab.
The results of this project will be included in a master’s thesis and will be prepared as peer-reviewed manuscripts. Researchers anticipate producing two manuscripts, one on the lipid comparison to hatchery health indices titled, “The effect of live food with variable ratios of essential fatty acids on the hatchery health index, stress resistance, growth, survival, and lipid composition of larval red king crab,” and one on the hatchery-wild comparison titled, “A comparison of the lipid classes and fatty acid composition of hatchery-reared and wild juvenile red king crab: toward developing appropriate hatchery live-food enrichments." Potential target journals for these publications include Marine Ecology Progress Series, Aquaculture, Fisheries Bulletin, Aquaculture Research, Journal of Experimental Marine Biology and Ecology, or Canadian Journal of Fisheries and Aquatic Sciences.
Copeman, L.A., B. Daly, G.L. Eckert, and J.S. Swingle. 2014. Storage and utilization of lipid classes and fatty acids during the early ontogeny of blue king crab, Paralithodes platypus. Aquaculture 424-425:86–94. http://doi.org/10.1016/j.aquaculture.2013.12.025
Copeman, L.A., A.W. Stoner, M.L. Ottmar, B. Daly, C.C. Parrish, and G.L. Eckert. 2012. Total lipids, lipid classes, and fatty acids of newly settled red king crab (Paralithodes camtschaticus): Comparison of hatchery-cultured and wild crabs. Journal of Shellfish Research 31(1):153–165. http://doi.org/10.2983/035.031.0119
Please visit the AKCRRAB website for links to progress reports, scientific publications, and presentations.