Effort Dynamics of the Northern California Dungeness Crab (Cancer magister) Fishery

Knowledge of the dynamic response of fishing effort to abundance is essential to a complete understanding of the cycles in catch in the northern California Dungeness crab fishery. In this fishery there is a lagged response of harvest rate to changes in abundance that is caused either by a time lag in fishermen entering and leaving the fishery following changes in abundance, a lag in market expansion and contraction following changes in abundance, or a combination of both. The time lag in this response appears to have decreased over the past 30 yr. This lagged response is a potential cause of the cycles. However, neither of the two potential cyclic mechanisms examined here, a predator–prey mechanism (with man as the predator) and a price-dependent escapement mechanism (with price dependent on past catch), is a cause of these cycles. Although time-varying effort does not cause the cycles, it does have a substantial effect on the resulting catch record and population dynamics. If there is a density-dependent recruitment mechanism in this population as proposed earlier, the presence of this lagged response would cause the period of observed cycles to be longer than would be expected on the basis of population dynamics alone. Hence, previous estimates of the expected period of cycles from various population mechanisms are low. Removal of this response is a potential means of stabilizing this fishery.Key words: effort, Dungeness crab, harvest rate, predator–prey, price, stability, age, cycles

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Wind Stress and Cycles in Dungeness Crab (Cancer magister) Catch off California, Oregon, and Washington

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f86-103 ◽

1986 ◽

Vol 43 (4) ◽

pp. 838-845 ◽

Cited By ~ 38

Author(s):

David F. Johnson ◽

Louis W. Botsford ◽

Richard D. Methot Jr. ◽

Thomas C. Wainwright

Keyword(s):

Wind Stress ◽

Time Lag ◽

Northern California ◽

Dungeness Crab ◽

Cancer Magister ◽

Cyclic Pattern ◽

Environmental Forcing ◽

Larval Phase ◽

Crab Larvae ◽

Time Required

Dungeness crab (Cancer magister) catch records along the coasts of northern California, Oregon, and Washington covary in a cyclic pattern with a period of 9–10 yr. Both environmental forcing and density-dependent recruitment have been proposed as the mechanisms causing these cycles. Spring wind stress in a southward direction is correlated with crab catch along this coast at typical lags of 4 and 5 yr. This time lag corresponds to the time required for growth from the larval phase to the size caught in the fishery. Also, computed autocorrelations show that wind stress is itself cyclic. Since crab larvae appear to be transported offshore and northward during the early larval phase, the observed correlation may result from a dependence of subsequent successful settlement on wind-driven southward, onshore transport during the late larval phae in the spring. However, the exact mechanisms are not known. The computed correlations indicate that wind stress may contribute to the observed cycles.

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Effects of Environmental Forcing on Age-Structured Populations: Northern California Dungeness Crab (Cancer magister) as an Example

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f86-286 ◽

1986 ◽

Vol 43 (11) ◽

pp. 2345-2352 ◽

Cited By ~ 11

Author(s):

Louis W. Botsford

Keyword(s):

Time Series ◽

Size Distribution ◽

Dungeness Crab ◽

Cohort Size ◽

Cancer Magister ◽

Environmental Forcing ◽

Harvest Rate ◽

Density Dependent ◽

Constant Rate ◽

Recruitment Time

Evaluation of potential environmental effects on recruitment requires knowing how environmental forcing can affect recruitment and subsequent catch, and how these effects depend on life history. General relationships between a time series of an environmental forcing variable, the resulting time series of recruitment, and the subsequent time series of catch or abundance are described here for a fishery in which environmental forcing affects density-dependent recruitment and the population is fished at a constant rate. For a stable population with overcompensatory, density-dependent recruitment, the recruitment time series will resemble the environmental time series except that frequencies near 1/(2 × mean age in the population) will be emphasized. The amount of selective emphasis will depend on the degree of overcompensation, harvest rate, and width of the cohort size distribution (in a size-selective fishery). For a population harvested at constant rate, the catch time series will resemble the recruitment time series except that lower frequencies will be emphasized. The degree of selective emphasis will depend on harvest rate and width of the cohort size distribution. Application of these results to Dungeness crab (Cancer magister) research has allowed analysis of combined effects of density dependence and environmental forcing. They show (1) that criteria formerly used to evaluate density-dependent recruitment mechanisms were too strict, (2) that female harvest could reduce harvest variability due to environmental forcing, and (3) how a nonlinear influence of spring wind stress in combination with density-dependent recruitment could cause the observed catch record. Implications for other crustacean populations are discussed.

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Movements of Adult Female Dungeness Crabs (Cancer magister) In Northern California Based on Tag Recoveries

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f85-116 ◽

1985 ◽

Vol 42 (5) ◽

pp. 919-926 ◽

Cited By ~ 16

Author(s):

Nancy Diamond ◽

David G. Hankin

Keyword(s):

Adult Female ◽

Fishing Effort ◽

Nonparametric Tests ◽

Northern California ◽

Cancer Magister ◽

Directed Movement ◽

Location Data ◽

Movement Data ◽

Large Numbers ◽

Dungeness Crabs

Of 11072 adult female Dungeness crabs (Cancer magister) tagged and released in northern California, 463 were recovered with useful location data that could be used for analyses of crab movement patterns. Although qualitative analyses of movement data suggested possible directed northward movement during winter months, application of two nonparametric tests of movement directionality (the Rayleigh test and Moore's test) failed to support significant directed movement during winter. Large numbers of tagged crabs were recovered inshore of release in shallow sandy areas during spring months, but valid statistical analyses of spring movement data were ruled out by concentration of fishing effort in shallow waters during spring. Nevertheless, recovery of large numbers of tagged females in inshore areas during spring is entirely consistent with an hypothesis of spring inshore movement of females for molting, mating, and later extrusion of egg masses. This hypothesis can be constructed on the basis of information independent of tag recovery data. The most striking finding was that 46% of all recovered crabs were recaptured within 2 km of original release sites; many of these crabs had been at large more than 1 yr. Adult female Dungeness crabs appear to constitute extremely localized stocks in northern California.

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Estimated Preseason Abundance in the California Dungeness Crab (Cancer magister) Fisheries

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f82-145 ◽

1982 ◽

Vol 39 (8) ◽

pp. 1077-1083 ◽

Cited By ~ 15

Author(s):

Richard D. Methot Jr. ◽

Louis W. Botsford

Keyword(s):

Large Fraction ◽

Northern California ◽

Dungeness Crab ◽

Cancer Magister ◽

Common Assumption ◽

Central California ◽

Large Size ◽

Exploitation Rate ◽

The Common ◽

High Catch

Annual preseason abundance for the central and northern California Dungeness crab (Cancer magister) fisheries is estimated from the decline in catch per unit of effort (CPUE) within each fishing season. The results support the common assumption that a large fraction of the available, legal size, male crabs are harvested each year; however, we noted regular changes in this fraction and also that it is rarely as high as previously assumed. In central California, annual exploitation rate was 92% during 1951–56 and declined to 72% following the collapse of the fishery. In northern California the annual exploitation rate varies with the 10-yr cycle of catch: 69% during the last few high catch years of each cycle, 84% in the first low catch year, and 54% during remaining low catch years and the first high catch year. The second high catch years are exceptions to a high exploitation rate. CPUE was saturated (i.e. did not decline) throughout the 1957 and 1977 fishing seasons. The large size of male crabs in the third and fourth high catch years also indicates high escapement in the second high catch years. Individual year-classes apparently may dominate the fishery for several years. This indicates that the time series of population abundance and recruitment is not as smoothly cyclic as the catch record.Key words: dungeness crab, Cancer magister, abundance, recruitment, catch per unit of effort

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Stable Cycles in Multistage Recruitment Models: An Application to the Northern California Dungeness Crab (Cancer magister) Fishery

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f80-279 ◽

1980 ◽

Vol 37 (12) ◽

pp. 2323-2345 ◽

Cited By ~ 29

Author(s):

R. McKelvey ◽

D. Hankin ◽

K. Yanosko ◽

C. Snygg

Keyword(s):

Diagnostic Procedures ◽

Field Studies ◽

Control Mechanisms ◽

Northern California ◽

Dungeness Crab ◽

Least Squares Regression ◽

Cancer Magister ◽

Feedback Controls ◽

Animal Populations ◽

Numerical Experimentation

This study illustrates, through the modeling of the Northern California Dungeness crab fishery, a diagnostic approach to the inference of multistage density-dependent recruitment mechanisms operating in animal populations. Northern California Dungeness crab landings have exhibited a strikingly regular cycling pattern since the early 1940s, but with increasing amplitude swings as the fishery has expanded suggesting the possibility of an eventual crash. A variety of mechanisms have been proposed, involving either biological feedback controls or exogeneous environmental effects, to account for the regular cycling and its possible destabilization by fishing. This study examines the plausibility of various alternative biological control mechanisms by incorporating them, one by one, into a multistage dynamic recruitment model, of nonlinear renewal type, based on general qualitative features of the crustacean's life history. A total of 48 plausible model variants are examined, reflecting differences in intensity and timing of possible feedback controls and uncertainty about exploitation and survival rates.Model analysis incorporates two complementary approaches to test out the range of alternative hypotheses incorporated in these variants. The first approach is based on examination of qualitative features of model dynamics: period and amplitude of stable cycles, and the model's response to varying levels of exploitation. The second is based upon extracted estimates of probable historic year-class strength and assesses the fit of model variants by least-squares regression techniques. These twin diagnostic procedures allow elimination of most model variants, and support the hypothesis that recruitment must be determined in the very early life stages, egg, or larval.The last phase of analysis is to further probe the model by numerical experimentation, including a simulation of the institution of female harvest. Finally, the implications of the modeling exercise are drawn, for future field studies and for second generation modelling.Key words: bifurcations, Dungeness crab, Cancer magister, stable cycles, multistage recruitment models, stock-recruitment

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Effect of Individual Growth Rates on Expected Behavior of the Northern California Dungeness Crab (Cancer magister) Fishery

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f84-009 ◽

1984 ◽

Vol 41 (1) ◽

pp. 99-107 ◽

Cited By ~ 12

Author(s):

Louis W. Botsford

Keyword(s):

Age Structure ◽

Growth Pattern ◽

Specific Model ◽

Individual Growth ◽

Time Lags ◽

Northern California ◽

Dungeness Crab ◽

Cancer Magister ◽

Density Dependent ◽

The Mean

Cycles in the northern California Dungeness crab (Cancer magister) fishery may be caused by density-dependent recruitment or a cyclic environmental variable. Investigation of these potential causes requires knowledge of the age(s) at which crabs enter the fishery. Behavior of this fishery has previously been analyzed using mathematical models that include density-dependent recruitment and describe changes in age structure with time. From data available on the northern California crab population and a review of previous studies elsewhere it appears that a single year-class of crabs enters this fishery over several years rather than in one year as described by models with only age structure. The realism of models of this fishery can therefore be increased by including size structure. Behavior of size-specific models is in general different from that of age-specific models. However, it is shown here that an effective survival rate can be derived from a size-specific model that enables interpretation as an age-specific model. This is used to demonstrate that inclusion of size dispersion in a population model increases stability, but if the mean age of the population is not changed, it will not substantially change the period of cycles. Because the growth pattern developed here changes the mean age of entry into the fishery it results in cycles with a longer period than determined in previous analyses. With regard to environmental causes, this growth pattern implies time lags of 4 and 5 yr between an environmental factor affecting recruitment and its effect on the catch record.

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Behavior of Age-Specific, Density-Dependent Models and the Northern California Dungeness Crab (Cancer magister) Fishery

Journal of the Fisheries Research Board of Canada ◽

10.1139/f78-134 ◽

1978 ◽

Vol 35 (6) ◽

pp. 833-843 ◽

Cited By ~ 60

Author(s):

Louis W. Botsford ◽

Daniel E. Wickham

Keyword(s):

Age Groups ◽

Cyclic Behavior ◽

Northern California ◽

Dungeness Crab ◽

Cancer Magister ◽

Specific Density ◽

Model Stability ◽

Density Dependent ◽

Stock Recruitment ◽

Fishery Model

A continuous time and age model which reflects the effect of older age-groups on mortality in young is presented. The conditions under which this model is unstable and the characteristics of solutions under various conditions are examined. Results obtained are related to results obtained by others from stock–recruitment models. Analytical expressions for the period of oscillations, the effect of fishing all age-classes, and the effect of the slope of the stock–recruitment curve at the replacement point support earlier simulation results. The effect on the model of size-selective fishing is shown to be a decrease in the stability of the population in some cases. These results are demonstrated with a model that approximately reflects the Dungeness crab (Cancer magister) population in northern California. The cyclic behavior of this population is similar to an unstable mode of the model. Conditions under which this mode arises are derived and potential causes of decreased stability, among which is fishing, are examined. Key words: fishery, model, stability, Dungeness crab, age-specific, density-dependent, stock–recruitment, cannibalism, Carcinonemertes

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