Stochastic Bio-economic Model of Northern Atlantic and Mediterranean Bluefin Tuna

The purpose of this paper is to study the implications of introducing a stochastic stock in a multi-gear and age structured bio-economic model for the Northern Atlantic Bluefin tuna. In order to account for variations on the recruitment, uncertainty is introduced on a bilinear recruitment function, and it is represented by an exponential random error term leading the stock to be, on average, higher than in the deterministic case. Both the bionomic equilibrium and the optimal management of this species are examined. In the latter, two alternative instruments are studied: the constant total allowable catch and the constant effort and the purpose is to maximize the expected total net present value. The conclusions enhance that the results do not differ significantly from those in the eterministic model, that is, the fishing effort should be the policy instrument to adopt, both in the East and the West Atlantic. Despite the previous reasoning, the shock on recruitment should be taken into account, as certain realizations of the random variable may lead to different results. In particular, for low Bluefin tuna stock levels, it is optimal to regulate the caches instead of the fishing effort, to ensure the stock recovery.Stochastic Bio-economic model, Bluefin tuna, Optimal management.

Management of Southern Atlantic bluefin tuna: the time consistency of the cooperative management solution

The purpose of this paper is to examine the stability of the cooperative management agreement of the North Atlantic Bluefin tuna fisheries over time,as the stock recovers, assuming that the players were engaged in previous cooperation for a certain period of time. This analysis is focused on the sharing of the total net returns from cooperation using the concept of Shapley value. It is based on simulation and optimization results from a multi-gear age structured bio-economic model both for the East and the West Atlantic and assumes that the nations were initially in cooperation for either 5 or 15 years. In general terms, the results show, as expected, that the net present values from both cooperation and non-cooperation increase as the stock recovers. Nevertheless, the latter increases more than the former and consequently, the net gains from cooperation decrease. More specific results are obtained for the East and West Atlantic. In the former, it is proved that, the net bargaining power decrease and, as a result, the shares of the net gains from cooperation based on the Shapley Value tend to be equalized, that is, we tend to the Nash bargaining solution. In the latter, the bargaining power may increase and the trend for the equality is not clear. In both, cases there are situations in which the cooperative solution is in the core of the game, meaning that no other strategy yields better outcomes for the players.Shapley value, time consistency, Bluefin tuna, cooperative games

The East Atlantic Bluefin Tuna Fisheries: Stock Collapse or Recovery?

A discrete time, multi-gear, and age structured bio-economic model is developed for the East Atlantic bluefin tuna fisheries, a paradigmatic example of the difficulties faced in managing highly migratory fish stocks. The model is used to analyse alternative management strategies for the Regional Fisheries Management Organisation (RFMO) managing this fishery, and to investigate some of the policy implications. For the various scenarios, the optimal stock level varies between 500–800,000 tonnes, which compares with a stock level of 150,000 tonnes in 1995. In other words, there is a very strong case for rebuilding the stock. Moreover, the sustainability of the stock is threatened unless a recovery programme is implemented; indeed, the alternative may be stock collapse. Second, to rebuild the stock, Draconian measures are called for: either outright moratoria over fairly lengthy periods, or possibly a more gradual approach to steady state given by a Total Allowable Catch (TAC) at a low level for an extended period of time. Third, the cost of inefficient gear structure is very high indeed.Bioeconomic model, bluefin tuna, optimal management., Resource /Energy Economics and Policy, Q22,

Management of Northern a Atlantic Bluefin Tuna: the Time Consistency of the Cooperative Management Solution

The purpose of this paper is to examine the stability of the cooperative management agreement of the North Atlantic Bluefin tuna fisheries over time, as the stock recovers, assuming that the players were engaged in previous cooperation for a certain period of time. This analysis is focused on the sharing of the total net returns from cooperation using the concept of Shapley value. It is based on simulation and optimization results from a multi-gear age structured bio-economic model both for the East and the West Atlantic and assumes that the nations were initially in cooperation for either 5 or 15 years. In general terms, the results show, as expected, that the net present values from both cooperation and non-cooperation increase as the stock recovers. Nevertheless, the latter increases more than the former and consequently, the net gains from cooperation decrease. More specific results are obtained for the East and West Atlantic. In the former, it is proved that, the net bargaining power decrease and, as a result, the shares of the net gains from cooperation based on the Shapley Value tend to be equalized, that is, we tend to the Nash bargaining solution. In the latter, the bargaining power may increase and the trend for the equality is not clear. In both, cases there are situations in which the cooperative solution is in the core of the game, meaning that no other strategy yields better outcomes for the players.N/

Stochastic Bio-economic Model of Northern Atlantic and Mediterranean Bluefin Tuna

The purpose of this paper is to study the implications of introducing a stochastic stock in a multi-gear and age structured bio-economic model for the Northern Atlantic Bluefin tuna. In order to account for variations on the recruitment, uncertainty is introduced on a bilinear recruitment function, and it is represented by an exponential random error term leading the stock to be, on average, higher than in the deterministic case. Both the bionomic equilibrium and the optimal management of this species are examined. In the latter, two alternative instruments are studied: the constant total allowable catch and the constant effort and the purpose is to maximize the expected total net present value. The conclusions enhance that the results do not differ significantly from those in the deterministic model, that is, the fishing effort should be the policy instrument to adopt, both in the East and the West Atlantic. Despite the previous reasoning, the shock on recruitment should be taken into account, as certain realizations of the random variable may lead to different results. In particular, for low Bluefin tuna stock levels, it is optimal to regulate the caches instead of the fishing effort, to ensure the stock recovery.N/

MANAGEMENT OF THE NORTHERN ATLANTIC BLUEFIN TUNA: AN APPLICATION OF C-GAMES

This paper considers the prospects for cooperative multilateral management of the North Atlantic bluefin tuna fisheries in accordance with the United Nations (UN) Agreement on Straddling Fish Stocks and Highly Migratory Fish Stocks signed in December 1995. A three-players characteristic function game (c-game) is used to analyze the cooperative agreements. The analysis focuses on the sharing of total net returns from cooperation. Three sharing rules are calculated; namely, the Nucleolus, the Shapley value, and the Nash bargaining solution. The analysis is based on simulation and optimization results from a multi-gear, age-structured, bioeconomic model developed for the North Atlantic bluefin tuna fisheries, East and West stocks. The results show, as expected, that significant gains can be attained from cooperation. The different sharing rules for the distribution of gains provide different returns to each player. Nonetheless, the basic transfer payments structure is rather stable. This case study points out some particular situations where these solutions are not enough to guarantee cooperation between all the coastal states.Resource /Energy Economics and Policy,

Ensaios em economia dos recursos naturais

The problem of overexploitation of resources, either renewable or exhaustible, is a fundamental issue in Natural Resource Economics. The present dissertation is composed of four chapters in Natural Resource Economics. Chapter 1 addresses the preservation of environmental assets under uncertain future preferences, while Chapters 2, 3 and 4 focus on Fisheries Economics, in particular, on the management of highly migratory species. Irreversibility associated with the consumption and destruction of exhaustible resources imposes a severe externality across different generations: future generations will suffer from the destruction of a unique asset and it is not clear how such a loss could be compensated in terms of other goods. Moreover, future generations may value natural resources differently from us. This has important implications for current decisions about environmental preservation. In the first chapter, the impact of resource amenity values on the optimal growth of an economy that depends upon those resources for the production of goods and services is examined. In particular, in the context of a capital -resource growth model, we examine the conditions under which it is optimal to preserve the environmental asset when there are two sources of uncertainty about future preferences: (i) uncertainty about the time of change in preferences and (ii) uncertainty about the change in preferences itself. We show that, under mild assumptions, in the presence of uncertain future preferences, the chances for optimal preservation increase. These results depend on the characteristics of the distribution that governs the time at which preferences change. Focusing now on renewable resources, the last few decades have been characterised by the collapse of several valuable resources, namely fish stocks in the high seas. Several species are clearly overexploited and many fishery activities are characterized by overcapacity. The main challenge of Fisheries Economics is to avoid depletion by encouraging fishing nations to manage the resources in a sustainable way. The stock of the Northern Atlantic Bluefin tuna has decreased substantially in the last decades and has reached levels of great concern. The last three chapters of this dissertation concentrate on the analysis of this species. In the second chapter, a brief description of the fishery studied is presented as well as the United Nations' legal framework for the management of high seas fisheries. In the third chapter, the optimal management of the Northern Atlantic Bluefin tuna in the presence of uncertain recruitment is examined. The purpose of this chapter is to study the implications of introducing a stochastic recruitment function on the optimal management of this fishery, as historical evidence points out to occasionally huge recruitment. To this end, a multi -gear and age structured bio-economic model was developed for this species, in order to compare the deterministic and stochastic results. Specifically, the goal is to examine whether the deterministic optimal policy remains robust to the presence of uncertainty in the recruitment, in particular, in limit cases such as situations of low recruitment. These are the most relevant situations, as they endanger stock preservation. In the East Atlantic, the results show that uncertainty on the recruitment should be taken into account in order to satisfy the recommended precautionary approach. If uncertainty is disregarded, the probability of having low recruitment is ignored and, thus, the Bluefin tuna stock may not be able to recover. In fact, there would be a short run effect, as the stock recovers initially due to the moratorium, but in the medium and long run the intervention would produce no impact. The case of the West Atlantic is of less concern, since the fishery was severely restricted in the past and the stock stabilised. The optimal management of the Bluefin tuna turns out to be a problem, since this species is targeted by several nations using different gears. In these cases, international agreements between nations are required. The main question that arises concerns the stability of these agreements. Chapter 4 examines the stability of the agreement solution for the management of the Northern Atlantic Bluefin tuna defined by the United Nations Agreement on straddling and highly migratory fish stocks, within a Regional Fisheries Management Organisation. The purpose is to compare the agreement solution with two alternative non-cooperative solutions: the myopic open access and the time consistent feedback Nash equilibrium. The agreement solution is shown to be preferred to both noncooperative solutions (open access and feedback Nash), but it may be unstable both with and without side payments, as there are free riding incentives by some of the players. In contrast to the open access case, in the feedback Nash case, the only source of instability comes from the distant water fishing nations, which, however, can be eliminated. In fact, in its legal framework, the United Nations Agreement eliminates all nations from the Bluefin tuna harvest unless they are members of a Regional Fisheries Management Organisation and abide by its rules. If this legal constraint is enforced, we show that the feedback Nash solution, based on non-linear Markov strategies, with side payments distributed according to the Shapley value rule almost replicates the agreement solution

North Atlantic and Mediterranean Bluefin Tuna: Biological and Economics Issues

The Northern Atlantic and Mediterranean Bluefin Tuna (Thionnus Thynnus) is a highly migratory species that faces a serious risk of extinction. In the most recent years, there has been a clear decrease in the Bluefin tuna stock, most noticeable in the Western Atlantic, caused by an increase and technological improvement in the fishing effort directed at the Bluefin Tuna. This has been stimulated by the high value placed on this fish, especially in the Japanese market. Some regulations have been studied and adopted in order to prevent this stock from being depleted. In this report, we intend to describe important aspects of this fish-ery, including the biology of the species and its migratory pattern, the stock evolution. the catches and landings, the regulations and management recommendations and the economic issues, namely the price evolution of Bluefin Tuna and information on costs and revenues broken down by gear. These elements are essential to an understanding and modelling of the dynamics of the species and its exploitation.N/

Bio-Economic Modelling of Northern Atlantic Bluefin Tuna

This paper presents a discrete-time bio-economic model of Northern Atlantic bluefin tuna. The bluefin tuna is caught by several gears, targeting different age classes in different areas. To properly capture the dynamics of this species, an age-structured and multi-gear model was used. The model captures the dynamic interrelations between gears. In this way, the migrations are implicitly modelled, as gears can be associated with age classes and locations. Three cases are simulated and analysed: open-access, total allowable catch (TAC) and constant fishing effort. Two alternative links between the economic and biological parts of the model were used and it is shown that the simulation results are very sensitive io the functional form of the production function. For both functional relations there are substantial gains to be had by departing from a situation of open access to a regulated one.N/

Management of Nothern Atlantic Bluefin Tuna An Application of the Shapley Value

In this paper a game theoretic setting is applied to the management of North Atlantic Bluefin tuna fisheries. The aim is to explore possible solutions for multilateral management by a regional conservation organization in accordance with the UN Convention on Straddling Fish Stocks and Highly Migratory Fish Stocks. The analysis is based on simulation results from a multi-gear age structured bioeconomic model developed for the North Atlantic Bluefin tuna fisheries, both for the East and for the West Stock. A characteristic function game approach (c-game) is used to analyse cooperative aggreements. The analysis is focused on the sharing of the total net returns from the fishery. In particular, Shapley values are calculated assuming three players for the East Stock: EU (European Union), OCS (Other Coastal States) and DWFN (Distant Water Fishing Nations) and three players for the West Stock: USA (United States), CAN (Canada) and DWFN (Distant Water Fishing Nations). Moreover, the cooperative solution as well as coalition solutions assume that the possible strategies are fixed strategies (either constant level of effort or constant level of catch). The simulation results show, as expected, that significant gains can be attained from cooperation. A distribution of the gains according to the Shapley values, could guarantee cooperation in many situations. However, this case study points out some particular cases where this solution is not enough to guarantee cooperation namely, from all coastal states.N/