IS FISHING COMPATIBLE WITH ENVIRONMENTAL CONSERVATION: A STOCHASTIC MODEL WITH AN ELEMENT OF SELF‐PROTECTION

Abstract The purpose of this paper is to introduce the impact of fishing activity on a marine ecosystem. The fishing activity is considered not only through annual harvest but also through a second component, called the degree of protection of the fishery environment. This characterizes the environmental impact of fishing. A stochastic dynamic programming problem is presented in infinite horizon, where a sole owner seeks to maximize a discounted expected profit. The main hypothesis states that the stock–recruitment relationship is stochastic and that both components of the fishing activity have an impact on the probability law of the state of the fishery environment. The optimal fishing policy is obtained and compared with standard models. This optimal policy has the following properties: is not a constant escapement policy and indicates an element of self‐protection by the fishery manager. The paper ends with a discussion on the existence of degrees of protection of the fishery environment that take into account the environmental conservation and preservation of economic activity.     

Distributed decision making––a unified approach

The paper gives an overview over the broad area of distributed decision making (DDM). In achieving a systematic procedure a general framework is developed that allows to describe the numerous approaches in DDM in a unified way. Focusing on application areas the paper is not only considering various fields in the management sciences, like hierarchical production planning, supply chain management, or managerial accounting, but is regarding other disciplines as well. Particularly, economics and computer sciences are investigated as to their specific contributions to DDM. It turns out that each field and discipline elaborate different aspects of DDM which particularly for OR could be used to solve concrete highly involved DDM problems.     

IMPACTS OF RECREATIONAL FISHING ON THE COMMERCIAL SECTOR: AN EMPIRICAL ANALYSIS OF ATLANTIC MACKEREL

There are often tensions between recreational and commercial uses of marine fisheries. The Atlantic mackerel along the coast of the United States and Canada is one such fishery. Although recreational catch is only a small percent of total catch, it has been suggested that recreational use be incorporated into a broad management scheme for the fishery. This paper measures the costs domestic commercial fishermen incur from the recreational harvest of Atlantic mackerel. The results indicate that the domestic commercial fishery, which takes only a small portion of total commercial catch, would see no significant gain from limiting recreational fishing. An earlier version of this paper was presented at the AERE Workshop on Sport and Commercial Fisheries. Participants at that conference, anonymous referees, and Peter Berck offered valuable suggestions which improved this paper. Any errors are my own.     

Information,Incentives and Decentralized Decision-Making in a Bayesian Framework

This paper examines the problem of choosing an organization structure for decision-making for two-level organizations under various information conditions. Decentralized decision-making (DDM), centralized decision-making with reporting by division (CDRD), and centralized decision-making (CDM) are considered. The information conditions pertain to the observability of states and actions. It is shown that if the party not making the decisions can infer the choice of action from the ex post knowledge of the state, then DDM and CDRD are essentially equivalent in that it is possible to devise optimal incentive schemes in both cases. If, however, the action choice cannot be inferred, then CDRD is at least as preferred as DDM by the centre (regulator). If ex post observation (or inference) of the state can be made only by the party making the decision, we show that the centre (regulator) prefers CDRD to DDM. For this case, we derive an incentive scheme which elicits truthful information from the division (regulated entity). Finally, the incentive schemes are applied to the problem of regulating an industry that pollutes the environment.     

Multiple criterion management of a sequential fishery

A static stochastic simulation was used to assess the performance of alternative management strategies in the satisfaction of multiple objective criteria in the context of a sequentially exploited transboundary resource. The model was applied to the Yukon River chum salmon (Oncorhynchus keta) fishery. Four strategies were evaluated using three criteria: probability of satisfying escapement objectives; probability of jointly satisfying escapement and subsistence harvest objectives; and probability of simultaneously reaching escapement, subsistence and commercial harvest objectives. The modeled strategies were also compared with the actual performance of the fishery for 1980–1995. The results indicate that satisfaction of escapement and subsistence harvest goals in the middle Yukon depends on imposing restrictive limits on commercial harvests in the lower Yukon. However, even with full information, escapement objectives in the upper drainage are only satisfied 65–70% and 75–80% of the time for summer and fall chum, respectively. The model was also used to explore the effects of increased average run strength that could arise from reduced bycatch of Yukon origin chum in marine fisheries. The results suggest that reduced marine interceptions are unlikely to substantially increase the probability of satisfying catch and escapement goals for the middle and upper Yukon.     

OPTIMAL-SUSTAINABLE MANAGEMENT OF MULTI-SPECIES FISHERIES: LESSONS FROM A PREDATOR-PREY MODEL

ABSTRACT. In this paper we consider the meaning of sustainable resource management in multi-dimensional resources. Based on the principle of intergenerational fairness, we define fisheries management as sustainable if it does not lead to a decline in the net present value of the fishery. If sustainability, or intergenerational fairness, were held as an obligation by fishery managers, then the traditional present-value maximization objective would be constrained. Using numerical solutions to a simple predator-prey model, we explore how the optimal-sustainable management of this fishery would differ from management that seeks to maximize the present value of the benefits. General lessons regarding the meaning of sustainable fishery management are discussed.     

Game theoretical treatment of material accountability problems Part II

In a previous paper, the optimal strategy for an inspection authority which has to safeguard material on the basis of material accountability principles has been determined with game theoretical methods: Sets of reasonable inspection and diversion strategies have been defined, and a saddlepoint of the overall probability of detection forn inventory periods during the reference time under consideration has been determined. In this paper it is shown that, with respect to the probability of detection, performing a single inventory is superior to performing a multiple inventory. A justification is given for the use of multiple inventories when the detection time is also concerned.     

INTEGRATING MARINE PROTECTED AREAS INTO MODELS FOR FISHERY ASSESSMENT AND MANAGEMENT

ABSTRACT. Marine protected areas (MPAs) have been proposed as an insurance policy against fishery management failures and as an integral part of an optimal management system for some fisheries. However, an incorrectly designed MPA can increase the risk of depletion of some species, and can reduce the value of the system of fisheries it impacts. MPAs may alter structural processes that relate fishery outcomes to management variables and thereby compromise the models that are used to guide decisions. New models and data gathering programs are needed to use MPAs effectively. This paper discusses the motivations and methods for incorporating explicitly spatial dynamics of both fish and fishermen into fishery models so that they can be used to assess spatial policies such as MPAs. Some important characteristics and capabilities which these models should have are outlined, and a topical review of some relevant modeling methodologies is provided.     

IN-SEASON FISHERY MANAGEMENT: A BAYESIAN MODEL

A Bayesian model is presented for optimizing harvest rates on an uncertain resource stock during the course of a fishing season. Pre-season stock status information, in the form of a “prior” probability distribution, is updated using new data obtained through the operation of the fishery, and harvest rates are chosen to achieve a balance between conservation concerns and fishing interests. A series of fishery scenarios are considered, determined by the stock size distribution and the timing distribution; the uncertainty in the fish stock is seen to have a rather complex influence on optimal harvest rates. The model is applied to a specific example, the Skeena River sockeye salmon fishery.     

A MODEL OF TROPICAL MARINE RESERVE‐FISHERY LINKAGES

ABSTRACT. The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. In this paper we examine the contribution of fully protected tropical marine reserves to fishery enhancement by modeling marine reserve‐fishery linkages. The consequences of reserve establishment on the long‐run equilibrium fish biomass and fishery catch levels are evaluated. In contrast to earlier models this study highlights the roles of both adult (and juvenile) fish migration and larval dispersal between the reserve and fishing grounds by employing a spawner‐recruit model. Uniform larval dispersal, uniform larval retention and complete larval retention combined with zero, moderate and high fish migration scenarios are analyzed in turn. The numerical simulations are based on Mombasa Marine National Park, Kenya, a fully protected coral reef marine reserve comprising approximately 30% of former fishing grounds. Simulation results suggest that the establishment of a fully protected marine reserve will always lead to an increase in total fish biomass. If the fishery is moderately to heavily exploited, total fishery catch will be greater with the reserve in all scenarios of fish and larval movement. If the fishery faces low levels of exploitation, catches can be optimized without a reserve but with controlled fishing effort. With high fish migration from the reserve, catches are optimized with the reserve. The optimal area of the marine reserve depends on the exploitation rate in the neighboring fishing grounds. For example, if exploitation is maintained at 40%, the ‘optimal’ reserve size would be 10%. If the rate increases to 50%, then the reserve needs to be 30% of the management area in order to maximize catches. However, even in lower exploitation fisheries (below 40%), a small reserve (up to 20%) provides significantly higher gains in fish biomass than losses in catch. Marine reserves are a valuable fisheries management tool. To achieve maximum fishery benefits they should be complemented by fishing effort controls.     

OPTIMAL AUSTRALIAN AND JAPANESE HARVESTING OF SOUTHERN BLUEFIN TUNA

A 19-cohort bioeconomic model is developed for the southern bluefin tuna fishery. The fish are long-lived and highly migratory. They are harvested as juveniles by Australia and Japan in Australian waters, and as adults by Japan on the high seas. The potential for conflict between Australian and Japanese fleets therefore exists in the exploitation of the fishery. The model is used to compare Japanese and Australian social rents and harvest levels through time under joint maximization, and under duopoly.     

INFLUENCES OF AVAILABILITY ON PARAMETER ESTIMATES FROM SITE OCCUPANCY MODELS WITH APPLICATION TO SUBMERSED AQUATIC VEGETATION

Site occupancy models are commonly used by ecologists to estimate the probabilities of species site occupancy and of species detection. This study addresses the influence on site occupancy and detection estimates of variation in species availability among surveys within sites. Such variation in availability may result from temporary emigration, nonavailability of the species for detection, and sampling sites spatially when species presence is not uniform within sites. We demonstrate, using Monte Carlo simulations and aquatic vegetation data, that variation in availability and heterogeneity in the probability of availability may yield biases in the expected values of the site occupancy and detection estimates that have traditionally been associated with low‐detection probabilities and heterogeneity in those probabilities. These findings confirm that the effects of availability may be important for ecologists and managers, and that where such effects are expected, modification of sampling designs and/or analytical methods should be considered. Failure to limit the effects of availability may preclude reliable estimation of the probability of site occupancy.     

EXOGENOUS SHOCKS AND MARINE RESERVES

Abstract The impact on the value of a fishery from exogenous shocks is investigated. Part of the habitat is protected by a marine reserve, while the remaining fishery is managed by optimal, total allowable catch quotas. Shocks of different, spatial nature and with different probability distributions are investigated. The results suggest that reserves are of minor interest as a management tool when shocks affect the stock uniformly. Reserves may substantially enhance the value of the fishery when shocks are nonuniformly spatially distributed.     

INFERRING A BIOPOLITICAL CONSENSUS VIEW OF STOCHASTIC DYNAMICS FOR MANAGEMENT OF A TRANSBOUNDARY FISHERY

ABSTRACT. Management of trans‐boundary fisheries is a complicated problem with biological, legal, economic and political implications. We propose a simple stochastic differential‐equation model to describe a biopolitical consensus view of fish stock dynamics. Estimates of the drift and diffusion terms of three stochastic differential equations are obtained using data from the southern bluefin tuna (SBT) fishery with a method based on the Kolmogorov‐Smirnov statistic. We refer to these estimated equations as alternative biopolitical consensus views of SBT stock dynamics. Each of these is used to generate a time series of optimal harvest that achieves the objective of maximizing the present value of expected fishery returns. These time series of optimal harvests are then compared to actual harvests for the period 1981 1997.     

An infinite horizon mathematical programming model of a multicohort single species fishery

Fishery policy evaluation should take account of the initial state of the fishery and the population dynamics of the fish stock. Although multicohort bioeconomic fishery policy evaluation models have been developed, the results from these models depend on the choice of planning period and the desired state of the stock at the end of this period. In this paper it is noted that these limitations can be overcome by evaluating fishery policy over an infinite time horizon, and a mixed integer programming (MIP) model is developed for carrying out this form of analysis in a multicohort single species fishery. This new MIP model allows policies to be evaluated over an infinite horizon by incorporating results from a steady state fishery model into a multiperiod framework. The use of this MIP model in determining policies for reaching and maintaining a steady state is illustrated.     

MULTISPECIES EXPLOITATION WITH EVOLUTIONARY SWITCHING OF HARVESTING STRATEGIES

In this paper, we propose a bioeconomic model which describes a fishery in which each of two noninteracting species is harvested by a given group of fishers during a defined time period. Then the Fishing Regulatory Authority allows each fisher to reconsider the harvesting decision at fixed (discrete) periods of time. The model derives from an Italian fisheries management experience in the Northern Adriatic Sea, where this kind of “self‐adjusting” fishing policy has been proposed to regulate harvesting of two shellfish species. The proposed dynamic model assumes the form of a hybrid system, as the natural growth functions of the two species (in continuous time) are coupled with a discrete time adaptive system that regulates how agents switch from one harvesting strategy to the other period by period according to an evolutionary mechanism based on profit comparison. In order to obtain some insights into the basic mechanisms of the system, some relevant benchmark cases are analyzed before tackling (mainly numerically) the complete hybrid model. Our results suggest that, for proper sets of parameters, this kind of myopic and adaptive self‐regulation may ensure a virtuous trade‐off between profit maximization and resource conservation, driven by cost externalities and market pressure.     

THE EFFECTS OF ITQ IMPLEMENTATION: A DYNAMIC APPROACH

ABSTRACT. This paper investigates the intertemporal effects of introducing Individual Transferable Quota, ITQ, fishery management programs on stock size, fleet size and composition, and returns to quota holders and to vessel operators. Theoretical analysis is conducted using a specific version of a general dynamic model of a regulated fishery. It is demonstrated that the effects will differ depending upon the prevailing regulation program, current stock size, and existing fleet size, composition and mobility and upon how the stock and fleet change over time after the switch to ITQs. The paper expands upon previous works by modeling the dynamics of change in fleet and stock size and by allowing for changes in the TAC as stock size changes, by comparing ITQs to different regulations, and by allowing the status quo before ITQ implementation to be something other than a bioeconomic equilibrium. Specific cases are analyzed using a simulation model. The analysis shows that the annual return per unit harvest to quota owners can increase or decrease over the transition period due to counteracting effects of changes in stock and fleet size. With ITQs denominated as a percentage of the TAC, the current annual value of a quota share depends upon the annual return per unit of harvest and the annual amount of harvest rights. Because the per unit value can increase or decrease over time, it is also possible that the total value can do the same. Distribution effects are also studied and it is shown that while the gains from quota share received are the present value of a potentially infinite stream of returns, potential losses are the present value of a finite stream, the length of which depends upon the remaining life of the vessel and the expected time it will continue to operate.     

NONCOOPERATIVE MANAGEMENT OF THE NORTHEAST ATLANTIC COD FISHERY: A FIRST MOVER ADVANTAGE

The point of departure for this analysis is Bjørndal and Lindroos [2012], who developed an empirical bioeconomic model to analyze cooperative and noncooperative management of Northeast Atlantic cod. In their analysis, only constant strategies were analyzed for noncooperative games. In this paper, nonconstant strategies are considered. Moreover, the fishery in question is characterized by cooperative management. What may happen in the real world is that one nation breaks the cooperative agreement by fishing in excess of its quota. Often, it takes time for the other agent to detect this and respond. In this paper, we allow this kind of delayed response into a two‐agent noncooperative game so that, if country 2 exceeds its quota, there will be a time lag before this is detected by country 1; moreover, there may also be a delay until country 1 is able to respond. Results show that the outcome critically depends on the length of these two lags as well as initial conditions.     

EFFECTS OF INDIVIDUAL HETEROGENEITY IN ESTIMATING THE PERSISTENCE OF SMALL POPULATIONS

ABSTRACT. Population viability models are commonly used to estimate the probability of persistence of small, threatened, or endangered populations. Demographic, temporal, spatial, and individual heterogeneity are important factors affecting the probability of persistence of small populations. Because stochastic process are intractable analytically (Lud-wig [1996]), computer simulation models are often used for estimating population viability via numerical techniques. Although demographic, spatial, and temporal stochasticity have been incorporated into some population viability models, individual heterogeneity has not been included. In this paper we include individual heterogeneity in a simulation model and examine probabilities of population persistence at different levels of heterogeneity and population size. Individual heterogeneity may increase the probability of persistence of small populations. The mechanism for the extension in persistence may be explained by natural selection. Genotypes persisting through a decline may be those that survive better under the conditions causing the decline. These individuals that survive and reproduce in the face of adverse conditions may extend the probability that a small population persists.     

添加捷径对环状DEDS的影响分析

研究具有环性拓扑的离散事件动态系统添加捷径后的时序性能变化问题.分析了添加捷径对周期长度和周期时间的影响.发现添加少量捷径即可使周期长度为1的概率有显著提高.