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

1982 ◽  
Vol 39 (8) ◽  
pp. 1077-1083 ◽  
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

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

1983 ◽  
Vol 40 (3) ◽  
pp. 337-346 ◽  
Author(s):  
Louis W. Botsford ◽  
Richard D. Methot Jr. ◽  
Warren E. Johnston
Keyword(s):  
Population Dynamics ◽  
Time Lag ◽  
Substantial Effect ◽  
Fishing Effort ◽  
Northern California ◽  
Dungeness Crab ◽  
Cancer Magister ◽  
Harvest Rate ◽  
Predator Prey ◽  
Market Expansion

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

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

1986 ◽  
Vol 43 (4) ◽  
pp. 838-845 ◽  
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.

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

1980 ◽  
Vol 37 (12) ◽  
pp. 2323-2345 ◽  
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

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

1984 ◽  
Vol 41 (1) ◽  
pp. 99-107 ◽  
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.

Use of length-based models to estimate biological parameters and conduct yield analyses for male Dungeness crab (Cancer magister)

2004 ◽  
Vol 61 (11) ◽  
pp. 2126-2134 ◽  
Author(s):  
Z Zhang ◽  
W Hajas ◽  
A Phillips ◽  
J A Boutillier
Keyword(s):  
Carapace Width ◽  
Natural Mortality ◽  
Biological Parameters ◽  
Dungeness Crab ◽  
Cancer Magister ◽  
Model Yield ◽  
Exploitation Rate ◽  
Threshold Ratio ◽  
Yield Per Recruit

Length-based models were developed for the male Dungeness crab (Cancer magister) population on the Fraser delta near Vancouver, British Columbia. The models incorporate the probability of moulting, moult increments, natural mortality during moulting and non-moulting periods, direct fishing mortality, and handling mortality that occurs when sublegal-sized crabs are caught and released. The models were used to investigate how long-term yield might be affected by the combination of handling mortality and an intensive fishery. The models were calibrated to survey data, and key biological parameters were estimated. The probability of moulting is near one for male crabs in the 130- to 150-mm carapace width range and decreases as crabs get larger. There is a 70.1% probability a crab will survive the 1-month period beginning with a moult. The non-moulting natural mortality rate is 0.97 year–1. When handling mortality is incorporated into the model, yield per recruit increases with the exploitation rate until it reaches approximately 94%. F0.1 is equivalent to 70%. An approach was developed to calculate the threshold ratio of discarded to retained crabs beyond which fishing would reduce the long-term yield.

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

1978 ◽  
Vol 35 (6) ◽  
pp. 833-843 ◽  
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

Student Perceptions of Community: A Different Perspective

NASPA Journal ◽  
1998 ◽  
Vol 35 (4) ◽  
Author(s):  
Jackie Clark ◽  
Joan Hirt
Keyword(s):  
Student Perceptions ◽  
Large Scale ◽  
Research University ◽  
Small Scale ◽  
Social Environments ◽  
Common Assumption ◽  
Small Communities ◽  
Public Research University ◽  
The Common ◽  
Using Data

The creation of small communities has been proposed as a way of enhancing the educational experience of students at large institutions. Using data from a survey of students living in large and small residences at a public research university, this study does not support the common assumption that small-scale social environments are more conducive to positive community life than large-scale social environments.

scholarly journals Contributions to Management Strategies in the NE Atlantic Regarding the Life History and Population Structure of a Key Deep-Sea Fish (Mora moro)

Biology ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 522
Author(s):  
Régis Santos ◽  
Wendell Medeiros-Leal ◽  
Osman Crespo ◽  
Ana Novoa-Pabon ◽  
Mário Pinho
Keyword(s):  
Population Structure ◽  
Life History ◽  
Deep Sea ◽  
Management Strategies ◽  
Size Composition ◽  
Large Size ◽  
The Common ◽  
Fishing Impacts ◽  
Sea Fish

With the commercial fishery expansion to deeper waters, some vulnerable deep-sea species have been increasingly captured. To reduce the fishing impacts on these species, exploitation and management must be based on detailed and precise information about their biology. The common mora Mora moro has become the main deep-sea species caught by longliners in the Northeast Atlantic at depths between 600 and 1200 m. In the Azores, landings have more than doubled from the early 2000s to recent years. Despite its growing importance, its life history and population structure are poorly understood, and the current stock status has not been assessed. To better determine its distribution, biology, and long-term changes in abundance and size composition, this study analyzed a fishery-dependent and survey time series from the Azores. M. moro was found on mud and rock bottoms at depths below 300 m. A larger–deeper trend was observed, and females were larger and more abundant than males. The reproductive season took place from August to February. Abundance indices and mean sizes in the catch were marked by changes in fishing fleet operational behavior. M. moro is considered vulnerable to overfishing because it exhibits a long life span, a large size, slow growth, and a low natural mortality.

scholarly journals Śaivism after the Śaiva Age: Continuities in the Scriptural Corpus of the Vīramāheśvaras

Religions ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 222
Author(s):  
Elaine M. Fisher
Keyword(s):  
Thirteenth Century ◽  
Common Assumption ◽  
Academic Practice ◽  
The Common ◽  
Popular Work ◽  
First Time

This article makes the case that Vīraśaivism emerged in direct textual continuity with the tantric traditions of the Śaiva Age. In academic practice up through the present day, the study of Śaivism, through Sanskrit sources, and bhakti Hinduism, through the vernacular, are generally treated as distinct disciplines and objects of study. As a result, Vīraśaivism has yet to be systematically approached through a philological analysis of its precursors from earlier Śaiva traditions. With this aim in mind, I begin by documenting for the first time that a thirteenth-century Sanskrit work of what I have called the Vīramāheśvara textual corpus, the Somanāthabhāṣya or Vīramāheśvarācārasāroddhārabhāṣya, was most likely authored by Pālkurikĕ Somanātha, best known for his vernacular Telugu Vīraśaiva literature. Second, I outline the indebtedness of the early Sanskrit and Telugu Vīramāheśvara corpus to a popular work of early lay Śaivism, the Śivadharmaśāstra, with particular attention to the concepts of the jaṅgama and the iṣṭaliṅga. That the Vīramāheśvaras borrowed many of their formative concepts and practices directly from the Śivadharmaśāstra and other works of the Śaiva Age, I argue, belies the common assumption that Vīraśaivism originated as a social and religious revolution.

scholarly journals Adverse Selection, Heterogeneous Beliefs, and Evolutionary Learning

2021 ◽  
Author(s):  
Clemens Buchen ◽  
Alberto Palermo
Keyword(s):  
Adverse Selection ◽  
Relative Size ◽  
Nonlinear Dynamic System ◽  
Heterogeneous Beliefs ◽  
Evolutionary Learning ◽  
Common Assumption ◽  
Cobweb Model ◽  
The Common ◽  
Learning Set ◽  
Set Up

AbstractWe relax the common assumption of homogeneous beliefs in principal-agent relationships with adverse selection. Principals are competitors in the product market and write contracts also on the base of an expected aggregate. The model is a version of a cobweb model. In an evolutionary learning set-up, which is imitative, principals can have different beliefs about the distribution of agents’ types in the population. The resulting nonlinear dynamic system is studied. Convergence to a uniform belief depends on the relative size of the bias in beliefs.

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