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Newport Laboratory: Fisheries Behavioral Ecology Program

Laboratory and Field Experiments to Support the Culture and Release of Hatchery-Reared Juvenile Red King Crab

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Figure 11. A hatchery-reared red king crab, approximately 5 mm in carapace length, approaching the highly preferred hydroid habitat in a laboratory trial.
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Figure 12. Survival of juvenile red king crab in nine different experimental substrata with age-1 Pacific halibut as predators. The treatments range in complexity from bare sand habitat, to several forms of algae (AM) and algal islands (4 x 42 and 1 x 168), to a complex habitat of algae, shells, and stones, plus a homogeneous gravel bottom. Values represent the mean percent survival of crab (±SE) for six replicate runs.

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Figure 13 (right). Diagram showing the apparatus used to observe predation events on tethered red king crab in the field. Underwater cameras with infra-red lighting are mounted above crabs positioned in different substratum types. A cable carries the live video image from each camera to a digital recorder on the adjacent shore. To date, tethered crabs and cameras have been placed in subtidal and intertidal locations with three different types of substratum, and more than 30 animal species have been observed in the video records. Several fishes and invertebrates have been identified as likely predators on red king crab juveniles in nearshore Juneau.

The Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) Program is a coalition of partners from the Alaska Fisheries Science Center, Alaska Sea Grant, the University of Alaska Fairbanks (UAF), the Alutiiq Pride Shellfish Hatchery in Seward, and fishermen’s groups and coastal communities in the Gulf of Alaska and Bering Sea. The program was initiated in 2006 with the goal of investigating the feasibility of stock enhancement of Alaskan king crab species for the purpose of stock rehabilitation.

While larval culture in Alaska began at the Kodiak Laboratory after the collapse of red king crab (RKC) in the mid-1980s, large-scale culture at the Alutiiq Pride Shellfish Hatchery has produced over 100,000 first-stage juvenile during the last 2 years. The program now faces the challenging tasks of determining the best practices for culture of juveniles to a stage appropriate for release, evaluating the best possible habitats for releases of juveniles, and understanding recruitment processes such as growth and mortality.

Laboratory studies conducted at the AFSC’s Newport Laboratory and by the UAF in Juneau have shown that early-stage juvenile RKC prefer complex biogenic habitats formed by sessile invertebrates and macroalgae (Fig. 11) that provide both food and shelter. The strengths of the associations increase in the presence of both fish predators and larger cannibalistic RKC. The behavioral adaptation gives young crabs a significant survival advantage, particularly in the presence of a visual predator such as Pacific halibut (Fig. 12).

Pacific cod were less effective predators than halibut, but the presence of structurally complex habitat increases the survival of RKC juveniles in both laboratory and field experiments, regardless of the predator type.

Remote field video with tethered crabs (Fig. 13) has been critical in identifying the host of fishes and invertebrates that may be important predators on young king crabs and will be a useful tool in exploring release strategies for hatchery-reared juveniles.

The results of these studies are guiding choices of release sites for hatchery-reared juveniles, but many questions are yet to be answered. For example, it will be important to determine the optimal size for release, and whether season or time of day might affect the subsequent survival of crabs in the field.

Other experiments recently completed in Newport include analyses of the effects of seawater temperature on growth rate and lipid storage and the effects of temperature on rates of cannibalism by age-1 RKC on age-0 crabs. These studies are useful in two ways – for maximizing hatchery production of juvenile crabs intended for release and for evaluating the likely impacts of warming climate on crab recruitment to the fishery.



By Allan Stoner

 

 


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