Scientists look to fourth year of crab hatchery research
- Ben Daly, Research Biologist, Alaska Sea Grant, 907-224-4311, firstname.lastname@example.org • staff profile
Adult female blue king crab with eggs that are expected to hatch in spring 2010. Photo courtesy Kurt Byers, Alaska Sea Grant. (Click on image for larger version, 2.1 MB)
Seward, Alaska—Scientists studying how to hatch and raise large numbers of larval king crab recently received wild adult king crab broodstock for another year of research. The scientists say three years of research have helped them clear many of the technological and biological hurdles to hatching and raising large numbers of larval crab to the juvenile stage in a hatchery setting.
Understanding the details of hatching and raising king crab in a hatchery is considered by commercial fishermen and researchers as a key step toward providing state fishery managers with the information they need to decide whether hatchery enhancement can help rebuild depleted king crab stocks in waters around the Pribilof Islands and Kodiak Island. Both areas have not had king crab fisheries in many years. State fishery managers have not yet approved the release of hatchery crab into the wild.
“We have learned a lot in the past three years, and we now believe the technology is there, and that we have a good understanding of rearing requirements,” said Ben Daly, research biologist with Alaska Sea Grant.
Daly is a member of a research team that includes university and federal scientists, and researchers at the Alutiiq Pride Shellfish Hatchery in Seward. Together, they are conducting studies as part of the Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) program.
Created in 2006, AKCRRAB is an Alaska Sea Grant partnership with regional fishermen's groups, coastal communities, National Marine Fisheries Service (NMFS), the Alutiiq Pride Shellfish Hatchery and Chugach Regional Resources Commission, and the University of Alaska Fairbanks (UAF) School of Fisheries and Ocean Sciences. Their goal is to conduct a research program aimed at hatching and rearing wild red and blue king crab in a large-scale hatchery setting.
Under a special state permit, fishermen aboard the FV Zone Five collected 19 egg-bearing, or ovigerous, female blue king crab during the November commercial season in waters near St. Matthew Island in the Bering Sea. These crab joined three blue king crab collected in July by scientists who conducted trawl surveys in the Bering Sea. In addition, fishermen aboard the FV Stormbird collected 18 ovigerous red king crab during the recent commercial opening in Bristol Bay. All of the blue king crab and most of the red king crab were delivered to Alutiiq Pride Shellfish Hatchery in Seward. Nine red king crab were delivered to federal scientists in Kodiak.
“All of the eggs have eye spots and we expect them to hatch in the spring,” Daly said. “The reds are further along and will likely hatch in March, while we expect the blues will hatch in April, or possibly May.”
At the Alutiiq Pride Shellfish Hatchery, scientists and hatchery staff are studying what it takes to hatch king crab eggs and culture large numbers of larvae to the juvenile stage. UAF researchers in Seward and NMFS scientists in Kodiak are conducting studies on the dietary needs of larval and juvenile king crab. NMFS scientists in Newport, Oregon, are examining the role of predation on juvenile king crab, while UAF and University of Alaska Southeast researchers in Juneau are conducting additional research on such things as genetics, growth physiology of crab in the wild, and habitat requirements.
Since 2006, local fishermen eager to assist the AKCRRAB program have provided researchers with wild adult red and blue king crab. Scientists care for the adult crab until their eggs mature and hatch millions of tiny larvae. The researchers have developed the technology and scientific understanding to raise food for the larvae, as well as to maintain the correct water temperature and quality needed to ensure the maximum number of larvae survive to the juvenile stage.
Scientists say the juvenile stage is the stage in which crab would be released into the wild, if a hatchery restocking program were to take place.
The road to success has not been easy. In 2007, the program’s first year of production, most of the larvae did not reach the juvenile stage, due largely to gaps in understanding of diet and water temperature needs.
After a disappointing first year, Daly said they took steps to improve water quality and the larval diet. In the second year, scientists had better luck, producing 35,000 juvenile-stage crab. Scientists also tackled a bacteria problem that seemed to be holding back growth and survival of the larvae.
“The bacteria produce tiny hair-like structures that grow on the crab,” explained Daly. “They can prevent the animal from feeding, breathing and swimming properly. We solved the problem by warming up the water a bit, which causes the crab to molt, or lose their shell, a little more frequently, before the bacteria become a problem. We have had much better survival since then.”
Combining their hard-earned knowledge from two intensive years of research, Daly said scientists in 2009 succeeded in culturing more than 100,000 larvae to the juvenile stage.
“That was significant improvement, so we were happy. In this fourth year, we’ll continue to refine our techniques and protocols and try to get at least as many larvae to the juvenile stage, hopefully a lot more,” said Daly.