Researchers test effects of conditioning on hatchery-cultured red king crabs

Experimental mesocosm containing substrate (hydroid mimics) and halibut. The substrate provides refuge for the crabs. The tank is about 1 meter in diameter.

Hatchery-cultured red king crabs have no experience with predators and may succumb to high rates of mortality due to predation if released into the wild. Conditioning techniques, such as exposure to predators during hatchery rearing, may be critical for increasing post-release survival.

Ben Daly conducted behavioral experiments on juvenile red king crab at the Hatfield Marine Science Center in Newport, Oregon, as a part of his Ph.D. dissertation research at the University of Alaska Fairbanks. Daly collaborated with Dr. Al Stoner of NOAA to determine the effect of exposure to predators on survival and behavior of juvenile crabs. In separate experiments using Pacific halibut and Pacific cod, crabs were exposed to visual and chemical cues of the fish, with and without physical contact with the fish. Conditioned crabs were held either in cages within a tank containing fish, allowing the crabs to experience visual and chemical cues, or held in tanks without a barrier, allowing crabs to experience visual, chemical, and physical cues of the fish. Naïve crabs were not exposed to fish predators.

Experiments were designed to determine if behavioral responses of crabs were enhanced by prior predator exposure, and if exposure increased survival during later encounters with fish. After conditioning, crabs were held in mesocosms containing pairs of fish and artificial substrate. Replicated trials were video recorded to determine crab survival rates, attack rates by predators, activity levels of crabs and fish, and substrate use by crabs. Preliminary results suggest that prior exposure to halibut induces a behavioral modification in juvenile red king crabs. Conditioned crabs had higher survival and more cryptic behavior than crabs not exposed to halibut. The lower cryptic behavior of the naïve crabs was likely coupled with increased predation susceptibility.

This research will help modify hatchery-rearing procedures that will ultimately reduce post-release mortality rates for juvenile red king crabs. Similar benefits of conditioning artificially reared organisms with natural predators have been demonstrated in fish, lobster, and crab stock enhancement programs elsewhere.

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.