Effect of variable fishing strategy on fisheries under changing effort and pressure: An agent-based model application

An agent-based model was used to evaluate the response of a two-species fish community to fishing boat exploration strategies, namely: boats following high-yield boats (Cartesian); boats fishing at random sites (stochast-random); and boats fishing at least exploited sites (stochast-pressure). At low fishing pressure, the stochast-random mode yielded a high average catch per boat while sustaining fish biomass. At high fishing pressure, the Cartesian mode was more effective. For the Cartesian strategy, fish biomass exhibited four distinct behaviors with increasing number of boats. In the first phase, the fish biomass dropped with increasing number of boats due to a corresponding rise in biomass extraction. Rapid exploitation occurred in the second phase, when two or more boats occupied the same initial area, that led to the faster abandonment of those sites which then underwent biomass recovery. In the third phase, adding more boats resulted in a fluctuating stock biomass, where the combined effects of initial spatial distribution of boats and rapid localization led to either full stock recovery when boats were eventually confined to a single location due to spillovers, or stock extirpation when the entire area became fully occupied. Beyond the third phase, stock extirpation was assured. In order to break the pattern of localization (bandwagon effect), we introduced stochast-random intruders in a Cartesian-dominated fishery. Adding a single intruder changed the patchy-structured stock biomass pattern of a purely Cartesian fishery to a uniformly explored stock biomass pattern because of the additional spatial information provided by the intruder. Consequently, the average catch per boat increased but at the expense of a disproportionate decline in equilibrium biomass.     

A simulation model to explore the relative value of stock enhancement versus harvest regulations for fishery sustainability

Harvest restrictions and stock enhancement are commonly proposed management responses for sustaining degraded fisheries, but comparisons of their relative effectiveness have seldom been considered prior to making policy choices. We built a population model that incorporated both size-dependent harvest restrictions and stock enhancement contributions to explore trade-offs between minimum length limits and stock enhancement for improving population sustainability and fishery metrics (e.g., catch). We used a Murray cod Maccullochella peelii peelii population as a test case, and the model incorporated density-dependent recruitment processes for both hatchery and wild fish. We estimated the spawning potential ratio (SPR) and fishery metrics (e.g., angler catch) across a range of minimum length limits and stocking rates. Model estimates showed that increased minimum length limits were much more effective than stock enhancement for increasing SPR and angler catches in exploited populations, but length limits resulted in reduced harvest. Stocking was predicted to significantly increase total recruitment, population sustainability, and fishery metrics only in systems where natural reproduction had been greatly reduced via habitat loss, fishing mortality was high, or both. If angler fishing effort increased with increased fish abundance from stocking efforts, fishing mortality was predicted to increase and reduce the benefits realized from stocking. The model also indicated that benefits from stock enhancement would be reduced if reproductive efficiency of hatchery-origin fish was compromised. The simulations indicated that stock enhancement was a less effective method to improve fishery sustainability than measures designed to reduce fishing mortality (e.g., length limits).     

Spatial effects and strategic behavior in a multiregional transboundary pollution dynamic game

We analyze a transboundary pollution differential game where pollution control is spatially distributed among a number of agents with predetermined spatial relationships. The analysis emphasizes, first, the effects of the different geographical relationships among decision makers; and second, the strategic behaviour of the agents. The dynamic game considers a pollution stock (the state variable) distributed among one large region divided in subregions which control their own emissions of pollutants. The emissions are also represented as distributed variables. The dynamics of the pollution stock is defined by a parabolic partial differential equation. We numerically characterize the feedback Nash equilibrium of a discrete-space model that still captures the spatial interactions among agents. We evaluate the impact of the strategic and spatially dynamic behaviour of the agents on the design of equilibrium environmental policies.     

Putting free-riding to work: A Partnership Solution to the common-property problem

The common-property problem results in excessive mining, hunting, and extraction of oil and water. The same phenomenon is also responsible for excessive investment in R&D and excessive outlays in rent-seeking contests. We propose a “Partnership Solution” to eliminate or at least mitigate these excesses. Each of N players joins a partnership in the first stage and chooses his effort in the second stage. Under the rules of a partnership, each member must pay his own cost of effort but receives an equal share of the partnership's revenue. The incentive to free-ride created by such partnerships turns out to be beneficial since it naturally offsets the excessive effort inherent in such problems. In our two-stage game, this institutional arrangement can, under specified circumstances, induce the social optimum in a subgame-perfect equilibrium: no one has a unilateral incentive (1) to switch to another partnership (or create a new partnership) in the first stage or (2) to deviate from socially optimal actions in the second stage. The game may have other subgame-perfect equilibria, but the one associated with the “Partnership Solution” is strictly preferred by every player. We also propose a modification of the first stage which generates a unique subgame-perfect equilibrium. Antitrust authorities should recognize that partnerships can have a less benign use. By organizing as competing partnerships, an industry can reduce the “excessive” output of Cournot oligopoly to the monopoly level. Since no partner has any incentive to overproduce in the current period, there is no need to deter cheating with threats of future punishments.     

Fishing as a Supergame

This paper considers how cooperative solutions to games of sharing fish resources can be supported by threat strategies. With highly mobile fish stocks, the number of agents compatible with a cooperative self-enforcing solution is not very high for reasonable values of the discount rate, but sensitive to changes in the discount rate and costs and to cost heterogeneity. With migrating stocks, where growth and reproduction depend on how much all agents leave behind after harvesting, the likelihood of a cooperative, self-enforcing equilibrium is increased. With a dominant player and a competitive fringe the rents and optimum stock level of the dominant player fall quickly as the share of the competitive fringe increases.     

Catch equations: restoring the missing terms in the nominally generalized Baranov catch equation

Observational models for the catch of fish at age a (or size) at time t are fundamental equations in fisheries science, linking a population model with data. The well known Baranov catch equation (which assumes that fishing and natural mortalities are constant over both age and time) is a nominal basis of those most commonly used in fish stock assessment and fish population models (which assume that fishing and natural mortalities vary with both age and time). But, what should a catch equation look like, if the instantaneous rates of fishing and natural mortalities of fish of age a at time t vary with age a and time t? Without answering this question, use of those catch equations in fish stock assessment and population models renders their results uncertain. In this paper, I derive a general catch in number or in biomass equation as observational models of an age- and time-dependent model for a fish population by Taylor series expansion of, and by directly manipulating, a general catch integral, reduce it to commonly used catch equations, and compare the performance of 11 of them using data on the western king prawn Penaeus latisulcatus. I show that the nominal generalization of the Baranov catch equation misses several terms. In so doing, I derive the catch equations more accurately and restore these missing terms. Although almost all approximations overestimate the catch per recruit for older prawns, all commonly used catch equations and their extensions perform worse than theoretically sound representations of the general catch equation and their approximations. The age-specific bias of all models is <2.5, <18 and <90% for a time interval of sampling of 1, 7 and 30 days, respectively. Such large biases even for moderate values of the length of the time interval of sampling highlight a need for assessing the utility of commonly used catch equations for individual species.     

A dynamic programming implemented resource competition game theoretic model

Resource competition is commonly occurred in animal populations and studied intensively by researchers. Previous studies have applied game theoretic model by finding Nash equilibrium to investigate this phenomenon. However computation of the Nash equilibrium requires an understanding of the payoff matrix that allocates the rewards received by players when they adopt each of the strategies in the game. In our study we present a dynamic programming implemented framework to compute 2 × 2 intraspecific finite resource allocation game's payoff matrix explicitly. We assume that two distinct types of individuals, aggressive and non-aggressive, are in the population. Then we divide the entire animal development period into three different stages: initialization, quasilinear growth and termination. Each stage for each type of players is specified with their own development coefficient, which determines how resource consumption could convert into strength as reward. Each player has equal and finite resource at the beginning of their development and fights against other players in the population to maximize its own potential reward. Based on these assumptions it is reasonable to use backward induction dynamic programming to compute payoff matrix. We present numerical examples for three different types of aggressive individuals and compute the payoff matrices correspondingly. Then we use the derived payoff matrices to determine the Nash equilibrium and Evolutionary Stable Strategy. Our research provide a framework for future quantitative studies on animal resource competition problems and could be expanded to n-players interspecific stochastic asymmetric resource allocation problem by changing some settings of dynamic programming formulation.     

Entry Deterrence and Signaling in a Nonrenewable Resource Model

We analyze a nonrenewable resource model in which an incumbent firm faces potential entry from a rival firm. The incumbent has private information about its stock size but the rival can observe extraction. With observable extraction and unobservable stock, the rival can use extraction as a signal about stock, from which it can infer whether entry is likely to be profitable. We characterize the necessary conditions for pooling and separating perfect Bayesian equilibria in a signaling game of resource extraction and provide examples of each. We show that the incumbent will often prefer pooling to separating even though welfare is higher in separating equilibrium.     

Fishing the line near marine reserves in single and multispecies fisheries.

Throughout the world "fishing the line" is a frequent harvesting tactic in communities where no-take marine reserves are designated. This practice of concentrating fishing effort at the boundary of a marine reserve is predicated upon the principle of spillover, the net export of stock from the marine reserve to the surrounding unprotected waters. We explore the consequences and optimality of fishing the line using a spatially explicit theoretical model. We show that fishing the line: (1) is part of the optimal effort distribution near no-take marine reserves with mobile species regardless of the cooperation level among harvesters; (2) has a significant impact on the spatial patterns of catch per unit effort (CPUE) and fish density both within and outside of the reserve; and (3) can enhance total population size and catch simultaneously under a limited set of conditions for overexploited populations. Additionally, we explore the consequences of basing the spatial distribution of fishing effort for a multispecies fishery upon the optimality of the most mobile species that exhibits the greatest spillover. Our results show that the intensity of effort allocated to fishing the line should instead be based upon more intermediate rates of mobility within the targeted community. We conclude with a comparison between model predictions and empirical findings from a density gradient study of two important game fish in the vicinity of a no-take marine-life refuge on Santa Catalina Island, California (USA). These results reveal the need for empirical studies to account for harvester behavior and suggest that the implications of spatial discontinuities such as fishing the line should be incorporated into marine-reserve design.     

Pastoralists' responses to variation of rangeland resources in time and space.

We explore the response of pastoralists to rangeland resource variation in time and space, focusing on regions where high variation makes it unlikely that an economically viable herd can be maintained on a single management unit. In such regions, the need to move stock to find forage in at least some years has led to the evolution of nomadism and transhumance, and reciprocal grazing agreements among the holders of common-property rangeland. The role of such informal institutions in buffering resource variation is well documented in some Asian and African rangelands, but in societies with formally established private-property regimes, where we focus, such institutions have received little attention. We examine agistment networks, which play an important role in buffering resource variation in modern-day Australia. Agistment is a commercial arrangement between pastoralists who have less forage than they believe they require and pastoralists who believe they have more. Agistment facilitates the movement of livestock via a network based largely on trust. We are concerned exclusively with the link between the characteristics of biophysical variation and human aspects of agistment networks, and we developed a model to test the hypothesis that such a link could exist. Our model builds on game theory literature, which explains cooperation between strangers based on the ability of players to learn whom they can trust. Our game is played on a highly stylized landscape that allows us to control and isolate the degree of spatial variation and spatial covariation. We found that agistment networks are more effective where spatial variation in resource availability is high, and generally more effective when spatial covariation is low. Policy design that seeks to work with existing social networks in rangelands has potential, but this potential varies depending on localized characteristics of the biophysical variability.     

Strategic investment in reputation

Although collective efforts are common in both animal and human societies, many human and probably animal social dilemmas have no obvious cooperative solution, which is a challenge for evolutionary biologists. In public goods games, i.e. the experimental paradigm for studying the sustainability of a public resource with human subjects, initial cooperation usually declines quickly. Recently, it has been shown that the interaction with another social game in which good reputation attracts help, can maintain a high level of cooperation in the public goods game. Here we show experimentally that humans use different strategies in the public goods game conditional on whether the player knows that his decisions will be either known or unknown in another social game. The knowledge of being recognized as the same individual in both scenarios motivates players to invest in their reputation and thus sustain the public resource. However, cooperation declines immediately when individual identities switch from being recognizable to being unrecognizable between the two interacting games.Communicated by M. Borgerhoff-Mulder     

Instrument Choice When Regulators and Firms Bargain

We compare outcomes with an emissions tax and an emissions standard when a firm and regulator engage in cooperative bargaining over the stringency of the regulation. Bargaining is motivated by giving the firm a choice of abatement technologies. If the firm's preferred technology differs from the regulator's, the first-best outcome is not an equilibrium of the traditional noncooperative game in which the regulator is a Stackelberg leader. The regulator may therefore choose to offer the firm a more lenient regulation if it agrees to switch technologies. We find that the resulting bargaining outcomes differ for a tax and a standard even though information is symmetric, and we identify conditions under which each instrument yields lower social costs.     

Flattening the carbon extraction path in unilateral cost-effective action

Internalizing the global negative externality of carbon emissions requires the flattening of the extraction path of world fossil energy resources (=world carbon emissions). We consider governments with sign-unconstrained emission taxes at their disposal and seeking to prevent world emissions from exceeding some binding aggregate emission ceiling in the medium term. Such a ceiling policy can be carried out either in full cooperation or by a sub-global climate coalition. Unilateral action has to cope with carbon leakage and high costs, which makes a strong case for choosing a policy that implements the ceiling in a cost-effective way. In a two-country, two-period general equilibrium model with a non-renewable fossil-energy resource, we characterize the unilateral cost-effective ceiling policy and compare it with its fully cooperative counterpart. We show that with full cooperation there exists a cost-effective ceiling policy in which only first-period emissions are taxed at a rate that is uniform across countries. In contrast, the cost-effective ceiling policy of a sub-global climate coalition is characterized by emission regulation in both periods. The share of the total stock of energy resources owned by the sub-global climate coalition turns out to be a decisive determinant of the sign and magnitude of unilateral cost-effective taxes.     

Dynamic resource management under the risk of regime shifts

This paper provides a framework through which a dynamic resource management problem with potential regime shifts can be analyzed both in a strategic environment and from a social planner?s perspective. Based on a fairly general model, a condition for a precautionary policy is discussed. By applying the framework to a common-property resource problem with a linear production technology, we illustrate how the qualitative as well as quantitative nature of equilibrium is altered due to the possibility of regime shifts. In particular, when the risk is endogenously affected by the players? behavior, potential regime shifts can facilitate the precautionary management of resources as long as the resource stock is in good shape. As the stock of resource becomes scarce, however, the precautionary effect vanishes and more aggressive resource exploitation emerges. The impacts of irreversibility on the equilibrium behavior are highlighted. It is also shown that there can exist a resource-depletion trap in which a regime shift, once it happens, triggers a continuous decline of resource stock no matter which regime materializes in the subsequent periods.     

Evaluating impacts of forage fish abundance on marine predators

Forage fish—small, low trophic level, pelagic fish such as herrings, sardines, and anchovies—are important prey species in marine ecosystems and also support large commercial fisheries. In many parts of the world, forage fish fisheries are managed using precautionary principles that target catch limits below the maximum sustainable yield. However, there are increasing calls to further limit forage fish catch to safeguard their fish, seabird, and marine mammal predators. The effectiveness of these extra-precautionary regulations, which assume that increasing prey abundance increases predator productivity, are under debate. In this study, we used prey-linked population models to measure the influence of forage fish abundance on the population growth rates of 45 marine predator populations representing 32 fish, seabird, and mammal species from 5 regions around the world. We used simulated data to confirm the ability of the statistical model to accurately detect prey influences under varying levels of influence strength and process variability. Our results indicate that predator productivity was rarely influenced by the abundance of their forage fish prey. Only 6 predator populations (13% of the total) were positively influenced by increasing prey abundance and the model exhibited high power to detect prey influences when they existed. These results suggest that additional limitation of forage fish harvest to levels well below sustainable yields would rarely result in detectable increases in marine predator populations.     

Optimal exploitation of a fishery employing a non-linear harvesting function

A harvesting function is developed to described the rate of removal of fish from a fish population. The function incorporates the effects of both the handling or processing time of the catch and the competition, between boats in the fleet, for the fish.We will assume that the growth rate of the fish population can be modelled with a concave, dome shaped growth curve. With this assumption, it has been shown that if the rate of harvesting the fish is linearly related to both effort (which can be thought of as some measure of the number of boats in the fleet) and the population size, then the population will tend towards a single equilibrium level which is globally stable. This paper shows that the saturation effects due to the handling time may generate two equilibrium levels (one stable, one unstable) rather than a single globally stable equilibrium. The results of competition between boats are economically undesirable because of the decrease in efficiency. However, this competition may be beneficial to the exploited fish population.Using the harvesting model derived earlier, the steady state or long term optimal harvesting policies as well as the transition paths to these states are developed. The only constraint is on the maximum allowable effort which is effectively an upper limitation on the fleet size or number of man-hours of fishing.     

Impact of a once-through cooling system on the yellow perch stock in the western basin of lake erie

The surplus production model, a conventional fishery stock assessment model, is applied to assess the entrainment and impingement impact of the Monroe Power Plant on the yellow perch standing stock and fishery in the western basni of Lake Erie. Biological parameters of the model are estimated from commercial catch and effort data and entrainment and impingement coefficients are estimated from power plant data. The model is applied to estimate stock biomass, egg production, and larva production; the proportions entrained and impinged are then estimated. The impact of water withdrawal on the equilibrium standing stock and maximum sustainable yield from the fishery is estimated and the impact of increased water withdrawal on the equilibrium standing maximum sustainable yield are larger than the proportion of the standing stock entrained and impinged, but the impact of the Monroe Power Plant is relatively small; it decreases biomass and the maximum sustainable yield of the yellow perch stock by only a few percent. However, there are several power plants impacting the yellow perch stock of the western basin of Lake Erie and the combined impact should be examined.     

The social and ecological determinants of common pool resource sustainability

We study a dynamic common pool resource game in which current resource stock depends on resource extraction in the previous period. Our model shows that for a sufficiently high regrowth rate, there is no commons dilemma: the resource will be preserved indefinitely in equilibrium. Lower growth rates lead to depletion. Laboratory tests of the model indicate that favorable ecological characteristics are necessary but insufficient to encourage effective CPR governance. Before the game, we elicit individual willingness to follow a costly rule. Only the presence of enough rule-followers preserves the resource given favorable ecological conditions.     

Subgame-perfect cooperative agreements in a dynamic game of climate change

We model climate change as a dynamic game and prove existence of a unique subgame-perfect Nash equilibrium (SPNE) that is also Markov perfect. We interpret this unique SPNE as the business-as-usual (BAU) equilibrium and show that if the countries are not sufficiently symmetric then the familiar trigger strategy equilibria may not be Pareto improvements over the BAU equilibrium and may even lack efficiency properties. We then motivate and introduce a subgame-perfect cooperative agreement as an improvement over the BAU equilibrium in the sense that every country or coalition of countries is better off in every subgame, irrespective of the extent of heterogeneity of the countries. We characterize subgame-perfect cooperative agreements and identify sufficient conditions for their existence. We show that (direct or indirect) transfers between countries to balance the costs and benefits of controlling climate change are a necessity and not a matter of approach.     

Nash Implementation of a Proportional Solution to International Pollution Control Problems

For a very general class of pollution control models involving strictly quasi-concave utility functions over consumption and environmental quality and strictly convex emission abatement cost functions, a proportional cost sharing mechanism is presented inspired by the ratio equilibrium introduced by7. It is shown that the proportional solution yields a cost efficient allocation of abatement efforts and that the resulting utility imputation always lies in the stand alone core of the cost sharing game. In order to decentralize the proportional cost sharing equilibrium, a financial compensation mechanism implementing the proportional solution in complete information Nash equilibrium is presented.