Swiney et al. presented a portion of this research comparing spatial and temporal variability in red king crab fecundity. Bristol Bay 2007 and 2008 fecundities did not differ; however, those years were significantly more fecund than Bristol Bay in the 1980s, and Bristol Bay 2008 was significantly more fecund than southeastern Alaska in 2008 (Fig. 12). Thus, variability in fecundity should be considered in development of biological reference points, stock assessment, and management models. Red king crab reproductive dynamics are also impacted by environmental variability caused by decadal and climate influences.
Figure 12. Fecundity with regression lines of 105–145 mm carapace length Alaskan red king crab (Paralithodes camtschaticus). BB07 = Bristol Bay 2007 summer collections (R2 = 0.51), BB08 = Bristol Bay 2008 summer collections (R2 = 0.75), BB80s = Bristol Bay 1982, 1983, 1985 summer collections (R2 = 0.49), SEAK08 = southeastern Alaska 2008 summer collections (R2 = 0.29).
Figure 13. Ratio of eyed to uneyed embryos in female Bristol Bay red king crab (Paralithodes camtschaticus) with respect to bottom temperatures collected in early June on the eastern Bering Sea bottom trawl survey from 1998 to 2008.
Chilton et al. looked at the impact of temperature variability on female Bristol Bay red king crab distribution and reproductive cycles from 1998 to 2008. Mature females were distributed in nearshore areas that were relatively warmer (3°-4°C) than the cold pool (<2.0°C) that extended onto the Bristol Bay shelf in “cold” years. The ratio of mature females with eyed embryos compared to females with uneyed embryos increased dramatically in early June for the five cold years since 1998 (Fig. 13). The distribution of mature females in colder years coupled with delayed embryo development and subsequent larval hatching could affect larval survival and dispersion as well as the mating potential between mature male and female red king crab. Lastly, basic life history studies are still needed to adequately manage crab stocks in Alaska.
Urban and Swiney collaborated with ADF&G to establish whether the commercial size limit of Dungeness crabs (Cancer magister) in Alaska is appropriate based upon their size of physiological and functional maturity. Determining accurate size at maturity of crabs is a management need as legal catch size limits are typically set to ensure that males have an opportunity to mate at least once before recruiting to a fishery. Worton et al. reported a smaller size of male functional maturity than was previously reported, but cautioned that the noncompetitive laboratory studies employed in this study do not account for the complexities of mating dynamics and recommended that the size limit not be changed until laboratory results are validated with in situ studies.
KL researchers are also interested in trophic interactions between groundfish and crab stocks in Alaska. Urban presented the results of a study examining the predator/prey relationship between Pacific cod (Gadus macrocephalus) and Tanner crab to better understand crab stock recruitment and fluctuations. Analysis of data from a joint NOAA Fisheries and ADF&G study conducted in Marmot Bay off Kodiak June 1998 through June 1999 revealed that cod consumed over 365 million Tanner crabs from three separate cohorts, removing 81% of the 1997 cohort. The relationship between predation rates and crab population was shown to be density-
dependent, indicating that cod may work to stabilize local Tanner crab populations.
The KL remains instrumental in king crab culture and enhancement research in Alaska. Eckert et al. provided an overview of the Alaska King Crab Research, Rehabilitation, and Biology (AKCRRAB) program which the KL researchers have a large involvement in. To date, researchers in that program have demonstrated that king crab can be cultured in a hatchery on a large scale. Persselin and Daly also examined ways to improve red king crab larval survival in culture by assessing diets and water sources in two separate experiments. Mean survival to the glaucothoe stage was significantly higher, and mean larval duration was significantly shorter on a diet enhanced with natural cold water diatoms (Thalassiosira nordenskioeldii) than without. Also, it was found that using artificial seawater was not any better for culturing larvae than using natural seawater.
Van Sant et al. compared the survival, larval duration, and density of golden king crab (Lithodes aequispina) larvae reared at 4° and 6°C. Decreased temperature was found to delay molting and larval duration but did not reduce survival to the glaucothoe or crab 1 instars. Density did not significantly affect survival in this study. Cultivation techniques reported are useful for future research on settlement behavior and habitat preference which are dependent on the production of an adequate number of glaucothoe and juveniles.
The program remains highly involved in assessment and management of crab stocks, especially in the development and implementation of the 2008 U.S. federal fishery management plan (FMP) for Bering Sea king and Tanner crabs. Foy and Rugolo worked in collaboration with ADF&G and other NOAA Fisheries scientists on crab management projects which were presented at the symposium. Siddeek et al. highlighted the primary differences between the new and old FMPs, such as the change in reported biomass currency from total mature biomass to mature male biomass and a change in the overfishing limit to include total removal from all fisheries instead of retained catch removals from the directed fishery. Jie et al. evaluated the stock assessment model for St. Matthew Island blue king crab. A catch-survey analysis was developed to include trawl survey, pot survey, and commercial catch data from 1978 to present. Multiple scenarios changing natural mortality and survey catchability were presented and evaluated.
In addition to the contributions of Shellfish Assessment Program to the symposium, other AFSC biologists were involved with eight presentations and posters ranging from density-dependent and independent factors controlling snow crab distributions in the EBS, estimating unobserved mortality rates of Bering Sea crabs due to encounters with trawls on the seafloor, historical perspective of Bristol Bay red king crab habitat and behavior, climate change and disease in marine ecosystems, bitter crab disease in Tanner and snow crabs, optimal nursery habitat for red king crab, and co-authoring the keynote address. The crab symposium was a great addition to the prestigious time series of Wakefield Symposiums and provided an opportunity for AFSC staff to interact and share research with colleagues throughout the world.
