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Dungeness crab (Cancer magister) is an important commercial fishery along the northeastern Pacific coast (California to Alaska). The data show the commercial harvest of Dungeness crabs, excluding sport fishery and non-treaty landings, from 1950 to 1999 off the coast of Washington State. The harvest season typically runs from December through February. The mean catch is about 8.7 million pounds per year, however the time series seems to be composed of two parts, before 1986 (when the catch was lower on average) and after 1986.

There are dramatic variations in harvest size with time, which could be explained in a number of ways. First, organisms often go through natural "boom and bust" cycles; for example, a boom in crabs might create a boom in crab predators, which would then induce a bust in crabs. Second, the crab population might be affected by changes in its environment, "forcing" the crab population to grow or decline. Third, the crab population may be perfectly stable, but the catch may vary due to changes in prices (overharvesting during times of high prices is common) or changes in catch limits or fleet size regulated by governmental agencies.

According to Johnson et al (1986), one of the most important factors in decreasing the crab population is southward-directed winds in the late spring, that drive crab larvae onshore. There is an approximate 5 year lag time between these anomalous winds and the crab bust, corresponding to the 5 years from larvae to maturity. The southward directed winds (and crab cycles) have a period about 8-10 years, as can be seen in the graph.

Students can determine the mean and standard deviation from the mean for these widely varying data. A more challenging exercise would be to model the apparent 8-10 year cycles using trigonometric functions.

Sources: Washington State Department of Fish and Wildlife, Program Fish Management, and the Pacific States Marine Fisheries Commission.

For further information:   Johnson et al (1986), Wind stress and cycles in Dungeness crab catch off CA, OR and WA; Can. J. Fish Aquat. Sci., v. 43, pp 838-845.

http://wfcb.ucdavis.edu/www/PopData/Crab/crab.htm

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 Washington State coastal commercial Dungeness crab harvest excludes sport crabbing, etc. Data courtesy of the Washington State Department of Fish and Wildlife Program Fish Management season harvest (Mlbs) harvest (lbs) 1950 3.3 3,255,826 1951 3.4 3,364,112 1952 5.3 5,295,677 1953 6.4 6,418,057 1954 5.8 5,801,123 1955 8.5 8,547,876 1956 10.9 10,876,236 1957 11.0 10,961,119 1958 7.7 7,685,525 1959 6.9 6,911,299 1960 5.9 5,865,415 1961 4.4 4,384,234 1962 4.1 4,112,664 1963 3.3 3,342,341 1964 6.3 6,296,500 1965 10.2 10,165,395 1966 8.4 8,422,551 1967 10.8 10,789,893 1968 18.4 18,433,896 1969 17.7 17,745,642 1970 12.6 12,552,037 1971 9.2 9,199,701 1972 4.3 4,339,221 1973 3.6 3,633,958 1974 5.2 5,199,105 1975 8.5 8,516,055 1976 11.7 11,673,995 1977 7.4 7,368,660 1978 8.0 7,979,403 1979 6.5 6,546,544 1980 2.7 2,689,142 1981 2.6 2,564,766 1982 4.0 3,972,555 1983 4.7 4,696,701 1984 2.9 2,921,078 1985 3.9 3,946,552 1986 3.2 3,183,112 1987 16.2 16,247,300 1988 21.9 21,886,400 1989 6.7 6,705,764 1990 6.8 6,760,143 1991 7.5 7,460,962 1992 13.5 13,461,000 1993 19.7 19,714,288 1994 19.6 19,611,000 1995 17.5 17,492,266 1996 9.3 9,275,760 1997 8.6 8,559,709 1998 9.5 9,513,803 1999 17.0 16,998,535 mean 8.7 8,666,898
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