Blue king crab rearing experiment shows low cannibalistic mortality in first juvenile stages

Juvenile blue king crab (2.0 mm carapace width) used in hatchery experiment. Photo courtesy of Ben Daly.

Researchers at the Alutiiq Pride Shellfish Hatchery conducted a large-scale blue king crab rearing experiment, looking at effects of high stocking densities during the first juvenile instar stages. The experiment was initiated after the crabs transitioned from the semi-benthic post-larval (glaucothoe) stage to the first benthic juvenile instar stage (C1). The crabs were stocked at 500, 1000, 2000, 4000, and 6000 crabs per m³ and reared for 42 days at 10°C. Survival was above 89% for all stocking densities. A similar study with red king crabs lasting 42 days at 8°C, in 2008, yielded survivals of 59, 55, and 45% at densities of 500, 1000, and 2000 crabs per m³.

Though cannibalism is problematic for red king crab nursery rearing, it is unknown if blue king crabs exhibit similar cannibalistic mortality. The lower mortality suggests cannibalism may be less problematic for blue king crabs than red king crabs, at least during the first juvenile instar stages. Even at a warmer temperature, the blue king crabs grew slower than red king crabs. By the end of 42 days, blue king crabs reached the C2 stage (1 molt), while red king crabs reached the C2 and C3 stages (1–2 molts). Crabs are more vulnerable to cannibalism during molting because of a lack of defensive armor. The additional molting of red king crabs may partially explain their lower survival. The higher blue king crab survival shows that individuals can be stocked at high densities during the first juvenile instar stages without compromising hatchery production, which has important implications for economic cost of large-scale stock enhancement programs.

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.