King Crab Life History Paralithodes camtschatica

Fig. 2.3 Schematic of king crab life history. (From Hayes, 1983.)

During the first year of growth, juveniles are solitary in relatively shallow water; during the first two to four years they are often in shallow water in dense "pods." King crabs, even adults, tend to segregate by size, sex, and molt condition.

Growth is discontinuous at times of molts. In the absence of a method for direct aging, growth is studied by determining the frequency of molts and the increment of growth per molt. Animals reach about 78 mm in four years and can then be tagged without loss during molt. King crabs enter the fishery at age eight. They grow to about 200 mm in 11 years and there is some molt skipping by males from 145 mm in size.

King crab are bottom-foraging omnivores; there appear to be no significant differences in diets between sexes and sizes of adults. Major food includes starfish, clams, and other mollusks, as well as small crabs, shrimps, other crustaceans, worms, fish, and algae. Predators on king crab include yellowfin sole, Pacific cod, walleye pollock, and halibut (Fukuhara, 1985; Larkin et al., 1990).

In view of this life history, ocean conditions on the inner shelf of the eastern Bering Sea, eastern Aleutians, and Kodiak Island in the winter and spring probably influence, and perhaps determine, the success of recruitment.

The eastern Bering Sea is divided into three domains separated by fronts (Fig. 2.4a,b) which are a function of depth and differ in circulation and vertical mixing (Schumacher & Reed, 1983). Crab eggs, larvae, and juveniles appear to be mostly within the coastal domain where tidal mixing exceeds buoyancy input, where water away from river mouths is mixed vertically, and where the average flow is to the northeast along the Alaska Peninsula and northward along isobaths east of the inner front (Fig. 2.5a,b). Flow is affected by wind events but is principally geostrophic and is driven by interaction of the tides with bathymetry. There is important interannual variability in wind stress, especially in the winter, and in its effects on temperature and ice coverage (up to 80% coverage in March).

In the Gulf of Alaska, the prevailing circulation is westward along the Alaska Peninsula (the Alaska Stream offshore, the Alaska Coastal or Kenai Current inshore) with some flow through Uni-mak Pass into the Bering Sea (Fig. 2.5b). The coastal circulation is wind driven, coupled with freshwater input along the coast. There is interannual variability in winds and rainfall and runoff with effects on currents, temperature, and salinity. Larval development, hence recruitment success, can be affected by interannual changes in transport of larvae to favorable grounds for settling, in temperature which determines the duration of larval periods, and in food supply, for example as determined by the timing and location of the spring plankton bloom (Larkin et al., 1990).

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