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Data Set #062


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About the Data

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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