Fisheries Management Models Research Articles

A review of game-theoretic models of fishing

Game theory is a formal tool for analysing strategic interaction between a finite number of agents. The fact that usually more than one entity or agent has property rights to fishery resources, has led to an explosion in the use of game theory and applications thereof to analyse fishery management problems. This review shows that game-theoretic modelling has made significant contributions to our understanding of the problems of fishery resource management. However, many challenges still remain. For instance, models of straddling stocks are yet to be fully developed. In addition, fisheries economists have not yet fully exploited the opportunity provided by computational methods now available, and the ever increasing power of computers, to develop more empirical game-theoretic models for practical fisheries management.

Effect of size‐selective mortality on growth of coastal cod illustrated by tagging data and an individual‐based growth and mortality model

In a release experiment with cod in Norway, the apparent mean growth rates of 3+ cod, calculated by sampling the released cohorts at different ages, were very slow (<0·08 mm day−1). However, when individual growth rates of individual tagged cod of the same size range were measured, the mean growth rates were much faster (0·24 mm day−1). These observations were attributed to size‐selective fishing mortality and were illustrated by an individual based simulation model of a cohort of cod with variable individual growth rates. The effects on mean length at age of the surviving cohort of increasing fishing intensity were demonstrated. The model showed that size‐selective fishing with the observed individual growth variation, removed the fastest‐growing individuals at proportionally higher rates than the slower‐growing ones, leading to decreased apparent mean growth rate. The fishing pattern which gave the optimum yield, changed when individual variation was included, and when the apparent growth rate was used in the model the yield per recruit reduced dramatically. This study has shown that individual growth heterogeneity and size‐selective mortality are factors which should be considered in future fisheries management models.

Fisheries Management Models: Assumptions and Realities or, Why Shrimpers in Mississippi Are Not Firms

The Schaefer-Gordon model of fisheries management does not adequately predict the state of stocks or the behavior of fishermen. In any scientific discourse, this should call the basic assumptions into question. I review the challenges to the model's biological assumptions and argue that its economic assumptions are also flawed. I review the approach developed by A.V. Chayanov for studying peasant economies in conjunction with comparative data on other fisheries and data from Mississippi Shrimpers to show that Chayanov's model characterizes the shrimpers of Mississippi. From the comparative and ethnographic data, I conclude that fishermen do not operate as firms. This further calls into question the adequacy of the current fisheries management model and raises the question of how and why such an inadequate model is perpetuated.

Populations Indices of Reproduction and Recruitment in Loligo Forbesi (Cephalopoda: Loliginidae) in Scottish and Irish Waters

1. As a preliminary step towards a fishery management strategy for the squid Loligo forbesi, indices of reproduction, egg production and recruitment were derived for this species in Irish (1991-93) and Scottish (1990-95) waters to give a quantitative estimate of peaks in spawning and fishery recruitment. 2. The indices were derived by combining landings or catch per unit effort (CPUE) data with the estimated proportions of mature squid (reproducers) and immature squid (recruits) to give an index of the number of squid spawning in and recruiting to the fished population each month. 3. The reproductive index peaked between November and December in Irish waters and between December and January in Scottish waters, earlier than predicted by simply examining peaks in the proportion of mature squid. 4. The index of recruitment showed peaks in the autumn in both Irish and Scottish waters, but there was also an additional April peak in Scottish waters. The two periods of recruitment in Scottish waters, together with a decrease in the size of mature females during the spawning season, are not compatible with a single breeding season and possible explanations for this are discussed. 5. By helping to define the timing of the fishing season (to avoid overfishing) and by providing estimates of natural mortality (for assessment of population size), the indices provide important input for population models for fisheries management of squid and short-lived fish species. 6. A possible model for a directed fishery for L. forbesi is proposed. In the model, the start of the fishing season is delayed to prevent growth overfishing and the season curtailed during spawning to prevent recruitment overfishing. However, on the basis of the indices developed here, this leaves only a narrow time window in which such a fishery could operate.

Fishery management, environmental protection and trade liberalization

Discusses marine environment management and maximization of the sustainable use and non‐use values of the flow of goods and services generated by that environment. Expands on the traditional economic model of fishery management to include the protection of non‐use values. Assesses international agreements made to include the protection of non‐use values of the marine environment, and examines the conflict between GATT rules and unilateral attempts to protect existence values. Proposes solutions based on the full cost pricing principle.

A Multicohort Stock Production Model

An age-structured production model of multicohort fish population dynamics based on the mean metabolic state of individuals and the average abundance of year-classes is proposed. The model allows variations in life stage basal metabolic rates by parameterizing their effects on total population abundance through a mortality function which itself depends upon an individualˈs status relative to an optimal metabolic state. The metabolic equations are derived in terms of age-specific individual weight. The interaction of individual status and intraspecific competition is allowed by coupling the metabolic equations for growth to those for population abundance. This coupling yields a second-order nonlinear equation in abundance or biomass. In model simulations, (1) increased numbers of cohorts decreased the stability of population biomass, (2) numerically “strong” year-classes damped and sometimes caused collapse of proximal age-classes, (3) exploitation reduced competitive interactions and increased model stability, and (4) increases in natural mortality introduced greater recruitment variability. The transitional and steady state behaviors of the multicohort model are explored and compared to traditional fishery management models for a small pelagic species, northern anchovy Engraulis mordax.

The Nordic Fisheries Management Model: Description and Experience.

The Nordic Fisheries Management Model: Description and Experience.

Uncertainty and Information in Fishery Management Models: A Bayesian Updating Algorithm

SYNOPTIC ABSTRACTThis paper presents a Bayesian updating algorithm which can be incorporated into fishery management simulation models in order to examine the effects of imperfect knowledge, parameter uncertainty and the role of learning processes in fishery systems. In particular, the algorithm is utilized here to explore the effects of uncertainty on the performance of fishery management and the dynamics of capacity planning. Monte Carlo results indicate that, on average, the algorithm produces parameter estimates which eventually approximate the true values. However, initial uncertainty can affect significantly the economic performance of the fishery, through excessive investment and suboptimal harvesting policies.

Evaluating Fisheries Management Models by Simulated Adaptive Control — Introducing the Composite Model

This paper uses the technique of simulated adaptive control to provide a method for comparing the performance of different fisheries management models. The management model is evaluated not in isolation, but rather as part of an integrated fisheries management system which includes the simulated population dynamics of the exploited fish, the simulated fishery, the fishery management policy formulation process, and the analysis of the simulated fisheries data. The technique is used to compare a simple biomass dynamic based model introduced by Ludwig and Hilborn with a more complicated length-based model developed by Fournier and Doonan. A composite model which combines the biomass dynamic based model with the length-based model was also evaluated. The composite model performed better than either of its component models.

Estimation of population parameters and their application to the development of fishery management models in two African rivers

The dynamics of fish populations in two African rivers are being investigated with a view to developing fishery management models for tropical non‐floodplain rivers. Preliminary work was carried out in the Rufiji River, East Africa, to establish growth and mortality rates along with L∞ and K for six species in a river where fishing mortality is zero. These parameters, derived from scale‐reading and length frequency analysis, also allowed the development of phased management plans for the fishery resulting from impoundment.A subsequent investigation has begun on a West African river, the Taia in Sierra Leone, to pursue observations over four seasons, two of which are now complete. A systematic daily sampling programme is being carried out of the whole community, to accumulate similar but more extensive data to those obtained previously. In the Taia, however, fishing mortality must also be estimated from catch surveys, and analysis is carried out using the recently developed ELEFAN programs which can be compared with results obtained by other methods such as scale‐reading.

Resource Management of Precious Corals:

Abstract. Precious corals as a group consist of a variety of species which belong to several classes of Anthozoan corals. In general, all are long lived, slow growing and are characterized by slow rates of annual recruitment and adult mortality. In favorable environments, where large beds of commercial quantity exist, their life history parameters often approximate steady state. In such instances, fishery management models in which the assumption of steady state is explicit, can be applied to their management. In this paper, the history and ecology of precious corals are reviewed in light of modern attempts of resource management using fishery models. In Hawaii, the BEVERTON and HOLT model has been adapted for the management of black, pink and gold coral species. The application of this model as it applies to precious corals is described and an example is given illustrating that it can also be used for shallow water reef building corals which form discrete colonies.

Models for fisheries management

Realization of the massive potential harvests from the oceans, coupled with disastrous collapses of substantial fisheries has seen the development over the last 25 years of a quantitative fisheries management science. As an aid to management, models are used to represent fish populations and the effects of exploitation on them. Basic models currently used for fisheries management are reviewed. The models discussed range from the simple surplus production model through to the analytical model of Beverton and Holt incorporating age structure and finally to Kicker's stock-recruitment model. The models are used to examine the dynamics and stability of fish stock when subjected to different exploitation policies. Some of the problems for management in interfacing real fisheries data with the mathematical models are discussed. The goals of management, including catch, fishing effort and economics (e.g. price, cost and inflation) are quantified to produce an objective function which may be used to determine optimal strategies. The optimal harvesting strategies are examined for each model, with a view to developing a general workable robust harvesting policy, independent of the model used.

Some Applications of Optimal Control Theory to Fisheries Management

Abstract A review is made of some optimization techniques appiled to fisheries and related problems. Explanations of optimal control theory as applied to the Schaefer or logistic model and to the Beverton and Holt model are provided. An optimal policy for a fishery management model based on the Brody growth function is developed. The control variable in each of the above examples is the rate of fishing and the objective function is the maximum biomass yield. A method for estimating the parameters of the Brody growth function is illustrated for the albacore tuna.

Computer Simulation Models for Fisheries Research, Management, and Teaching

Recent and current activities involving large-scale computer simulation models in fisheries science and related areas of applied ecology are reviewed. Selected general references to computer modeling and simulation as well as specific references in resource management and ecology are given. Two types of existing models are described—those developed for investigating benefits and cost of fishery management policies and those for studying fundamental properties of natural animal communities. Use of simulated resource management games as Link trainers to provide students with the type of learning experience that now requires several years in responsible management positions is discussed. It is predicted that the resource management agency of the future will maintain a hierarchy of simulation models to serve as basic planning tools for studying total system response to natural and artificial change.