Red King Crab Hatchery Culture And Ecological Requirements: Applications For Stock Enhancement

Abstract

The ecologically and commercially important red king crab (Paralithodes camtschaticus) is depleted throughout much of the North Pacific and thought to be recruitment limited, making it an appropriate candidate for stock enhancement efforts. This research addresses bottlenecks associated with hatchery production and lays the groundwork for developing release strategies. I investigated effects of diet, stocking density, and size grading on survival, growth, and shell coloration of recently-settled juvenile red king crabs in large-scale hatchery experiments. I also conducted laboratory experiments with fish predators to determine if red king crab predator responses could be enhanced with experience. Finally, I tethered hatchery-cultured red king crabs of two sizes in the field for 24 h trials and used underwater video cameras to identify predators and predation susceptibility. In hatchery experiments, dietary astaxanthin supplementation improved survival and shell coloration suggesting that red king crab coloration is plastic and that astaxanthin may provide nutritional or immune system benefits. Size grading strongly influenced survival and growth in the hatchery. Generally, small crabs had higher survival than large and ungraded crabs, but large and ungraded crabs had higher growth, likely from cannibalism. In laboratory experiments, halibut exposure enhanced red king crab crypsis and survival suggesting that cryptic behavior is plastic and may be enhanced with experience. In the field experiment, I identified specific predators of recently-settled red king crabs in a nearshore habitat and showed that survival did not vary with body size or deployment month during the first juvenile instar stages. My research provides an important step for developing a responsible red king crab stock enhancement program by demonstrating that hatchery production can be improved with specific advances in rearing technology, hatchery-cultured red king crabs are morphologically and behaviorally plastic, hatchery-cultured red king crabs tethered in the field show no obvious behavioral deficiencies that may exacerbate predation, and that differences in predation susceptibility during the first juvenile instar stages are subtle and may be ecologically inconsequential for post-release survival. As bottlenecks in hatchery production and survival of released juveniles are overcome, stock enhancement will become increasingly feasible for red king crabs in Alaska.