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