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Researchers at NOAA Alaska Fisheries Science Center in Kodiak examine red king crab cannibalism


red king crabAn age-1 red king crab hunts for younger crabs in an experimental container. Photo courtesy of NOAA Fisheries.

Red king crabs are highly cannibalistic, which is a problem for mass culture and may reduce post-release survival. During the last two summers Jessica Popp and Laura Whitefleet-Smith, undergraduate recipients of the NOAA Hollings Scholarship, conducted experiments to reveal how predator size affects predation at different prey densities and in different habitats. They were mentored by Dr. Chris Long and Kathy Swiney at the NOAA AFSC Kodiak Lab.

Predators (age-1 and age-2 red king crabs) and prey (young-of-the-year red king crabs) at a range of densities (2, 5, 10, 18, 25, 35, 50 crabs per tank) were placed in containers with habitats of different structural complexities (bare sand, sand with shell hash, sand with shell, algal mimic). In low structure habitats (bare sand, sand with shell hash), proportional predation by age-1 crabs was greater at low prey densities, while age-2 crabs consumed almost all the prey at all densities. In high structure habitats (sand with shell, algal mimics) proportional predation by age-1 crabs was reduced at all prey densities, while predation rates by age-2 crabs increased with prey density.

Results indicate that habitat complexity reduces predation, and suggest that releases should target habitats with complex structure at low densities (i.e., fewer than 30 crabs per m2). Also, stocking in alternate years in a given area may minimize cannibalism among year classes.

News Flash is edited by Ben Daly. AKCRRAB is a research and rehabilitation project sponsored by the Alaska Sea Grant College Program, UAF School of Fisheries and Ocean Sciences, NOAA Fisheries, the Alutiiq Pride Shellfish Hatchery, community groups, and industry members. For more information go to http://seagrant.uaf.edu/research/projects/initiatives/king_crab/general.

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