February 2016

NOAA researchers complete second release experiment

Diver examining seafloorNOAA researcher Pete Cummiskey monitors red king crab densities by searching a quadrat. Click image for larger version [1.3 MB].

In a second experimental-scale release of hatchery-reared red king crabs in Trident Basin in Kodiak, Alaska, NOAA biologists Chris Long, Pete Cummiskey, and Ben Daly released over 12,000 juvenile crabs during summer-fall 2015 and tracked them for six months. Crabs were cultured at the Alutiiq Pride Shellfish Hatchery in Seward from larvae hatched from ovigerous females (broodstock) captured in Alitak Bay at the southern end of Kodiak Island. The 2015 experiment built on a 2014 release in Trident Basin, which examined effects of stocking density on post-release survival. It was demonstrated in 2014 that crabs could be released at a high density (up to 75 per square meter) without substantial increases in mortality. In 2015, researchers were encouraged by occasionally finding crabs from the 2014 experiment.

The 2015 experiment examined how release time and crab size affect the success of releases with a goal of determining how to maximize the survival of crabs at release. The 2015 experiment has been completed, but a full analysis of results is not yet available. Red king crab juveniles are highly cannibalistic in a laboratory or hatchery, so the longer they are held before release the fewer crabs survive to be released. However, the 2015 study suggests that predation rates in the field are higher in summer than in fall. Researchers released crabs in June, August, and September, to understand effects of release timing. In addition to tracking crab densities, researchers performed tethering experiments to determine relative predation rates and monitored the predator assemblage around the release area.

a small crab and kelpA tethered crab (see arrow) hides from predators under a piece of kelp. Click image for larger version [1.2 MB].

Using optimal release strategies, such as releasing at a density and season that maximizes survival, is key to responsible stock enhancement. By conducting small-scale experimental releases, researchers develop strategies for red king crabs in Alaska. The experiments represent a significant step forward for the AKCRRAB project, which has brought together collaborators from the fishing industry, native groups, coastal Alaska communities, the University of Alaska, and state and federal agencies. Researchers have worked closely with the Alaska Department of Fish and Game throughout the broodstock collection and outstocking experiment through collection and transport permits.

News Flash is edited by Ginny Eckert. AKCRRAB, the Alaska King Crab Research, Rehabilitation and Biology Program, is sponsored by Alaska Sea Grant, UAF School of Fisheries and Ocean Sciences, NOAA Fisheries, the Alutiiq Pride Shellfish Hatchery, community groups, and industry members.

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