 Dungeness crabs (Cancer magister)
 Distribution of Dungeness crabs in San
Francisco Bay
Cancer magister, the Dungeness crab, ranges from the Aleutian Islands to Pt. Conception . C. magister are important as both a predator and prey species in nearshore coastal and estuarine habitats. Estuaries have been documented to be important nursery areas throughout much of their range.
C. magister supports a large commercial fishery from northern California to British Columbia. Landings from the San Francisco area reached a peak of almost 9 million pounds during the 1956-57 season but declined to under 1.5 million pounds each season since 1961-62 except for 1987-88, when landings were 3.1 million pounds.
Mating occurs from March through May in the ocean and peak hatching occurs from late December to mid-January in the Gulf of the Farallones. C. magister pass through six larval stages over 105 to 125 days. The last larval stage (megalopa) is carried by currents to the nearshore area and newly settled crabs move into the Bay from March to June. Most early instar crabs are collected in the channels north of the Golden Gate and by July C. magister are widely distributed in San Pablo and lower Suisun bays. By the spring of the next year, most 1+ crabs have emigrated to the ocean.
A tagging study conducted by CDFG showed that crabs reared in San Francisco Bay grew about twice the rate of ocean-reared crabs, with an average carapace width of approximately 100 mm one year after hatching. It has been hypothesized that increased food availability, particularly crustaceans, and warmer Bay temperatures is responsible for this rapid growth. Bay-reared crabs probably are recruited to the fishery three years after hatching, while ocean-reared crabs enter the fishery four to five years after hatching. Estimates of the number of juvenile crabs in the Bay as a percentage of the total number of juveniles in the Bay and Gulf ranged from 38% to 82% for 1975 to 1978.
C. magister are omnivores, feeding upon bivalves, crustaceans, and fishes. A variety of fishes, including brown smoothhound, big skate, white sturgeon, green sturgeon, pile perch, staghorn sculpin, white croaker, and starry flounder have been reported to prey on C. magister in the Bay.
Annual abundance of 0+ Cancer magister has been highly variable since 1980. The strongest year classes were in 1984, 1985, and 1988, while the weakest year classes were in 1983, 1986, 1990, 1992, and 1993. Poor recruitment of C. magister to the Bay occurred in years with warm-water ocean events or frequent storms. Warm water events are detrimental to spawning and hatching success, while frequent storms create currents that transport larvae offshore and northward, away from the Gulf of the Farallones and the mouth of the Bay.
Annual abundance indices for C. magister are generated from the San Francisco Bay Monitoring Program using otter trawl and ringnet data.
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