the commons as a natural barrier to entry why there are so few fish farms a competitive industry which overuses a common access resource may create a barrier to entry similar to spence s example of a cartel that uses excess capacity to prevent entry in most industries when a new firm enters existing firms find that their demand curves have fallen so they reduce their output to accommodate the new entrant in spence s model the cartel disintegrates upon entry so that the output of existing firms increases which may make entry unprofitable in an open access fishery the supply curve bends backward thus a fall in price created by the entry of a fish farm increases rather than decreases supply in the backwardbending portion of the supply curve an important implication of this theory is that fish farms are more likely to be unprofitable the more heavily overharvested is a species in a common property competitive market this natural barrier to entry may explain why true mariculture is barely in its infancy bardach ryther and mclarney

environmental policy and international trade when governments and producers act strategically some environmentalists express concern that trade liberalization may damage the environment by giving governments incentives to relax environmental policies to give domestic producers a competitive advantage support for such concern may be given by models of imperfectly competitive trade where there may be rent shifting incentives for governments to relax environmental policies but there are also incentives for producers to act strategically e g through their investment in rd ii allowing governments to act strategically increases the incentive for producers to act strategically iii welfare is lower when both parties act strategically and iv strategic behavior by producers and governments is greater when governments use emission taxes than when they use emission standards

inventories rational expectations and the business cycle abstract the simplest macroeconomic models in which markets clear instantaneously and expectations are rational preclude the existence of business cycles that is of serially correlated deviations of output from trend this paper studies one of several mechanisms that can be used to make these so called new classical models produce business cycles the mechanism is the gradual adjustment of inventory stocks two macroeconomic models of inventory holdings are formulated both imply first that current output should be a decreasing function of the stock of inventories and second that inventories once perturbed from equilibrium levels should adjust only gradually these two features are then embedded into an otherwise standard macroeconomic model in which markets clear instantaneously and expectations are rational two principal conclusions are reached first disturbances such as unanticipated changes in money will set in motion serially correlated deviations of output from trend second if desired inventories are sensitive to the real interest rate then even fully anticipated changes in money can affect real variables

the economics of wildlife farming and endangered species conservation abstract there is growing concern that the traditional protectionist approach to conservation is expensive and insufficient to deliver the desired environmental outcomes supply side policies to conserve endangered species have drawn support by generating supplies from captive bred animals wildlife commodity prices are expected to fall thereby lowering the incentive to poach species in the wild supply side policies however often neglect the institutional framework within which the wildlife trade takes place and ignore the potential strategic responses of economic agents adopting a model that captures imperfect competition between traders and farmers we analyze the effect of supply side policies and conclude that under some circumstances these policies may contribute to further devastation of wild stocks we derive conditions under which captive breeding contributes to conservation and discuss implications for policy makers

optimal and open access harvesting of multi use species in a second best world expansion of human populations and activities has caused increased conflicts between wildlife and humans as a result the distinction between resource and pest species has become blurry we propose an economically based classification of species based on a multi use bioeconomic model the classification of the steady state population of a species is shown to depend on both species density and economic factors we extend earlier work on multi use resource pest species by applying the theoretical model to a developing country context where property rights to wildlife are imperfectly enforced so that second best trade measures are often applied by the international community to promote conservation upon calibrating the model using data for the african elephant we derive three further results first when comparing the optimal stock of a multi use species to the open access stock we find that the ranking in terms of abundance is ambiguous second and consistent with existing literature on resource management in a second best world our case study supports the idea that trade bans have ambiguous effectson wildlife abundance third due to a bifurcation effect characterizing the multi use model s solution strategic and temporary subsidizing by the north may enable them to free ride on conservation efforts of the south henceforth

the impact of agricultural biotechnology on yields risks and biodiversity in low income countries abstract this paper shows that the current generation of transgenic crop varieties has significant potential to improve economic welfare in low income countries these varieties might increase crop yields in low income countries in cases when pesticides have not been used they will reduce negative health effects of chemicals when they replace them with low transaction costs appropriate infrastructure and access to intellectual property multiple varieties of transgenics will be introduced the gain from transgenics will be reduced and crop biodiversity may be lost when only a small set of varieties is transgenetically modified the adoption of transgenics will also be affected by risk and credit considerations

a mechanism for booms and busts in housing prices the paper studies the dynamics of housing prices in a pure exchange overlapping generations framework a la samuelson 1958 and gale 1973 which is extended to include housing as a utility yielding durable good and a credit sector we completely characterize the equilibrium dynamics which alternates between an expansive regime where leveraged borrowing increases housing prices and a contractive regime where these variables decrease regime switches occur due to small but persistent income changes giving rise to boom bust cycles in housing prices price deviations from fundamentals are caused by leveraged borrowing and turn out to be fully welfare neutral

a qualitative dynamical modelling approach to capital accumulation in unregulated fisheries capital accumulation has been a major issue in fisheries economics over the last two decades whereby the interaction of the fish and capital stocks were of particular interest because bio economic systems are intrinsically complex previous efforts in this field have relied on a variety of simplifying assumptions the model presented here relaxes some of these simplifications problems of tractability are surmounted by using the methodology of qualitative differential equations qde the theory of qdes takes into account that scientific knowledge about particular fisheries is usually limited and facilitates an analysis of the global dynamics of systems with more than two ordinary differential equations the model is able to trace the evolution of capital and fish stock in good agreement with observed patterns and shows that over capitalization is unavoidable in unregulated fisheries r 2005 elsevier b v all rights reserved

storage and viability of a fishery with resource and market dephased seasonalities in this study we analyse the role of the storageregulation in a fishery s production process when theresource exploited and the market to which theproduction is exported are characterized by seasonaldephased oscillations for this purpose we built up adynamic model drawn from the french guyana shrimpfishery example the underlying objective of the modelis not the maximisation of a given criterion as wouldbe in the optimal control approach but merely themaintenance of the fishery s economical viability thefundamental principle is here to try to preserve asmany as possible viable control options theconditions to achieve and maintain this viability arecaptured in a certain number of constraints theanalysis points out periods and situations within theseason where the fishermen must anticipate theevolution of their storage to avoid violating thoseviability constraints the study also indicates howthe fishery s viability can be ensured even if theexploitation costs exceed the commercial value of thelandings for a finite part of the year however whenthe resource s and or market s oscillations are toolarge the fishery may be not viable any longer and itappears that the crisis can not be removed byinvesting in larger storage capacities

ecological and economic sustainability in fishery management a multi agent model for understanding competition and cooperation recent studies have shown that many marine ecosystems are experiencing an accelerating loss of population and biodiversity it is apparent that there is a growing disparity between the available supply of fish and the desire of the growing world population to catch them although studies have begun to question the ecological sustainability of managed fishery systems they often omit the corresponding effects on the economic sustainability of fishery industries this is particularly important in rural coastal areas where the fishing industry is often a dominant employer in this article we analyze the interactions between economic and ecological dynamic systems using a multi agent dynamic model of fishery management multiple agents fishers harvest multiple fish species and adapt the amount and allocation of their effort to their value functions which are given as net profits of the fish harvest sold for a market price this is largely unique in fishery models since many econometric studies view fishers as represented by homogenous average agents we introduce and compare two different decision rules governing the behavior of fishers engaged in a competitive market we demonstrate a situation where both behaviors lead to a decline of all fish stocks as well as profits for most fishers as an alternative we introduce a cooperative approach in which fisheries jointly set sustainable limits for total harvest and effort that are then distributed to the fishers according to distribution rules the simulation reveals that fish stocks and profits can stabilize at significantly higher levels in the cooperative case leading to a continuous accumulation of capital for all fishers this model demonstrates key aspects of overfishing conflicts that can be overcome through planned fishing quotas and cooperative market mechanisms it also demonstrates a novel approach for simulating the dynamic behavior of heterogeneous fishers

buyback subsidies the time consistency problem and the itq alternative this paper deals with the time consistency problem associated with buyback schemes arising from the fact that the schemes may be anticipated by vessel owners after reviewing and elaborating upon the key results of our recently published article on buybacks and limited entry programs we discuss the consequences of combining buybacks with itq schemes or the equivalent instead of limited entry programs we conclude that substituting itq schemes for limited entry programs cannot be relied upon to eliminate fully the time consistency problem we suggest that what may be required is a management program that combines rights based schemes with taxes

bifurcation analysis of zellner s marshallian macroeconomic model the marshallian macroeconomic model in zellner and israilevich 2005 provides a novel way to examine sectoral dynamics through the introduction of a dynamic entry exit equation in addition to the usual demand and supply functions found in models of this class in this paper we examine the possibility of cyclical behavior in the marshallian macroeconomic model and investigate the existence of a hopf bifurcation with respect to the parameter in the entry exit equation

the ivory trade ban is it effective abstract this paper examines the effectiveness of the ivory trade ban when producer and consumer states have different incentives to comply with such a ban the paper distinguishes between two types of producer states those with stable elephant population and those with declining elephant population we compare the independent enforcement level of each of these producer states and a consumer state and show the suboptimality of these levels compared to optimal enforcement level that would result from a cooperative effort the costliness and imperfectness of enforcing constraints on the private taking of elephants creates intergovernmental externalities thus in the absence of binding international law regulation would have to be supplemented with incentives

impact of cultured shrimp industry on wild shrimp fisheries analysis of price determination mechanisms and market dynamics cultured shrimp production has been growing dramatically on the world market over the last 15 years and some of the farm raised species are now considered as price indicators on the main market places one may therefore expect the price of theses cultured shrimp to have an impact on the price formation of other species and especially on wild shrimp with which they compete in this paper the authors address this question in the case of the wild shrimp penaeus subtilis exploited by the french guyana fishery south america and competing on the french market with the cultured thai shrimp back tiger a series of econometric tests issued from the co integration theory is performed between the price series of the two products these tests indicate that the two series are co integrated and that the black tiger market acts as a market leader for the french guyana shrimp product the authors then discuss the reasons of the current predominance of farm raised shrimp on wild caught product and in particular the french guyana shrimp and identify the constraints that the french market demand induces on both producers and importers in the light of this analysis a commercial strategy that would mitigate the impact of the thai shrimp on the french guyana product is suggested

open access harvesting of wildlife the poaching pit and conservation of endangered species abstract we extend the traditional g s model of open access by defining a non concave harvesting function we demonstrate the possible existence of multiple equilibria and perverse comparative statics and show that small changes in the underlying economic parameters may trigger large jumps in species abundance finally we briefly discuss implications for management

consumption and income some simple excercises with panel data this paper reports on the performance of simple versions of the rational expectations permanent income hypothesis of hall 1978 and the error correction approach of davidson et al 1978 in explaining nondurable consumption expenditure from austrian panel data paying particular attention to the characterization of nondurability we examine the parameter restrictions implied by the respective models and then select favoured dynamic consumption income relationship our findings suggest that the models receive limited support only for the narrowest category of nondurables food consumed at home particularly for broader categories the strength of model rejections and the complex dynamic paths observed imply that the models provide an inadequate description of consumption at the micro level

the effects of pricing policies on water conservation and drainage a general model of adoption of input conserving technologies by competitive firms is introduced using drip irrigation as an example an environmental regulation such as a drainage effluent charge is shown to influence adoption early adopters are likely to be producers with less efficient fixed assets land of low quality or antiquated capital higher input costs higher water prices or greater depth to groundwater and in more environmentally sensitive regions simulations show that drainage regulations can be expected to play a major role in adoption of more efficient irrigation technologies in california thus conservation may be a key to solving resource scarcity problems and reducing external environmental costs

optimal harvesting of stochastic spatial resources abstract we characterize the optimal harvest of a renewable resource in a generalized stochastic spatially explicit model despite the complexity of the model we are able to obtain sharp analytical results we find that the optimal harvest rule in general depends upon dispersal patterns of the resource across space and only in special circumstances do we find a modified golden rule of growth that is independent of dispersal patterns we also find that the optimal harvest rule may include closure of some areas to harvest either on a temporary or permanent basis biological reserves reserves alone cannot correct open access but may under sufficient spatial heterogeneity and connectivity increase profits if appropriate harvest controls are in place outside of reserves

on the existence of nonoptimal equilibria in dynamic stochastic economies abstract the question of the existence of the stationary equilibrium for distorted versions of the standard neo classical growth model is addressed in this paper the conditions presented guaranteeing the existence of nontrivial equilibrium for the class of economies under study are simple and intuitively appealing while the existence proof developed is elementary examples are given illustrating that economies with distortional taxation endogenous growth with externalities and monopolistic competition can all fit into the framework provided journal of economic literature classification numbers c62 e30 e60

common pool equities an arbitrage based non cooperative solution to the common pool resource problem abstract it is proposed that a new type of property right termed a common pool equity can solve the common pool resource problem this equity may be presented to any firm that extracts from the resource for a share in profits it is shown that a profit arbitrage condition ensures that the market and socially efficient solutions correspond whenever market power is absent the cost externalities are fully internalized

technology and the future bioeconomy new discoveries in life sciences and the challenge of climate change are leading to the emergence of the bioeconomy where basic methods of advanced biology are applied to produce a wide array of products while also improving environmental quality the emergence of the bioeconomy is a continuing evolutionary process of transition from systems of mining nonrenewable resources to farming renewable ones this transition benefits from the modern tools of molecular biology that have expanded the human capacity to breed new organisms and utilize them to increase productivity in agriculture and fisheries as well as produce a wide array of products that were extracted in the past this transition is leading to the integration of the agricultural sector with the energy and mineral sectors the introduction of biotechnology has already improved the productivity of medicine as well as agriculture but in the case of agriculture has encountered resistance and regulatory constraints the evolution of the bioeconomy requires continuous public investment in research and innovation as well as the establishment of a regulatory framework and financial incentives and institutions that would lead to continuous private sector investment in the development and commercialization of new products one of the biggest challenges is the development of a regulatory framework that would control possible human and environmental externalities from new biotechnology products and at the same time not stifle innovation jel classifications q1 q2 q3 q4 q5

an assessment of alternative methods of estimating the effect of the ivory trade ban on poaching effort the ban on international trade in ivory introduced by the international community in 1989 was intended to protect the declining stock of african elephant loxodonta africana by providing a barrier between the range state and the principal consuming nations if there is a residual trade then the efficiency of the ban is determined by the decline in the price paid to poachers and the responsiveness of poaching effort to changing prices this paper concentrates on the latter issue and provides a review of a number of alternative approaches to modelling poaching effort with extensions it is found that even low residual prices would induce a level of effort that would significantly depress elephant numbers

fisheries management under cyclical population dynamics cycles in environmental conditions e g sea surface temperature directly impact fish growth this paper extends the classical gordon schaefer fishery model by replacing the constant growth rate with a cyclical growth rate the optimal harvest rate is shown to fluctuate but the cycle of the harvest rate lags the cycle of the biological growth function with the highest harvest rate occurring after biological conditions start to decline simulations contrast various fishing policies and illustrate the proclivity to crash a fishery if it is wrongfully managed as if there is a constant growth rate with i i d environmental shocks finally we show that small cyclical fluctuations in one species can result in large fluctuations in the optimal harvest rate of another species if the fish species are interlinked through predator prey relationships

inefficiency of credible strategies in oligopolistic resource markets with uncertainty abstract the implications of different information patterns for firms in oligopolistic resource markets are considered the traditional open loop nash equilibrium with static information sets is one of many possible nash equilibria and is not suitable for stochastic environments when shocks to resource growth are serially uncorrelated there are no gains from conditioning the harvest on past stock levels and the feedback or credible nash equilibrium is the appropriate nash equilibrium concept this credible equilibrium assumes that firms have knowledge of current stocks of reserves which typically leads to more rapid extraction of the resource and possibly extinction since the open loop nash equilibrium is efficient when demand is iso elastic and extraction costs are zero it is clear that an increase in information can be detrimental to firms in the industry

fisheries management with stock growth uncertainty and costly capital adjustment we develop a dynamic model of a fishery which simultaneously incorporates random stock growth and costly capital adjustment numerical techniques are used to solve for the resource rent maximizing harvest and capital investment policies capital rigidities bring diminishing marginal returns to the current period harvest and introduce an incentive to smooth the catch over time with density dependent stock growth however catch smoothing increases stock variability resulting in reduced average yields the optimal management policy balances the catch smoothing benefits against yield loss we calibrate the model to the alaskan pacific halibut fishery to demonstrate the main insights

an open access fishery with rational expectations explain the evolution of the fish stock and the boat fleet as well as determine their equilibrium levels 2 while the changes in the fish stock are described by a biological rule entry and exit from the fishing industry are determined by how expectations are formed we examine a general model in which entry and exit are proportional to the present value of expected profits and compare two special cases of adaptive myopic expectations and rational expectations although both expectations mechanisms lead to the same equilibrium values they lead to different adjustment paths where expectations solely depend on current values myopic expectations it is well known that boats enter the fishery only when the fish stock is greater than its steady state stock 3 with rational expectations however boats may enter when the fish stock is much lower than its steady state value provided the boat fleet is sufficiently small this difference in adjustment is observable and in principle leads to an obvious test on how agents form expectations section 2 develops a general dynamic model for studying fisheries in section 3 we show that the model standardly used in the literature is equivalent to a myopic adaptive expectations model a rational expectations model is analyzed in section 4 the standard and rational expectations models are compared in section 5 section 6 illustrates this comparison using a simulation based on a schaefer model of the pacific halibut fishery section 7 presents the conclusions

the complex interactions of markets for endangered species products economic models of trade in endangered species products often do not incorporate four focal arguments in the policy debate over trade bans 1 law abiding consumers may operate in another market separate from illegal consumers that trade would bring online 2 legal trade reduces stigma which affects demand of law abiding consumers 3 laundering may bring illegal goods to legal markets when trade is allowed 4 legal sales may affect illegal supply costs this paper analyzes systematically which aspects of these complicated markets separately or in combination are important for determining whether limited legalized trade in otherwise illegal goods can be helpful for achieving policy goals like reducing poaching

efficiency inducing tax for a common property oligopoly the author characterizes the markov perfect tax that induces a common property oligopoly to extract efficiently a nonrenewable resource for linear and isoelastic demand he provides closed form expressions of the unique specific tax industry profits may be higher or lower in the oligopoly with the tax relative to the competitive equilibrium with property rights for linear or isoelastic demand there exists no feasible open loop tax that induces efficient extraction in this case the policymaker gains no advantage from being able to make binding commitments copyright 1992 by royal economic society

poverty trap and global indeterminacy in a growth model with open access natural resources abstract in this paper we use global analysis techniques to analyze an economic growth model with environmental negative externalities giving rise to a three dimensional dynamic system the framework is the one introduced by wirl 1997 53 the dynamics of our model admits a locally attracting stationary state p 1 which is in fact a poverty trap coexisting with another stationary state p 2 possessing saddle point stability global dynamical analysis shows that under some conditions on the parameters if the initial values of the state variables are close enough to the coordinates of p 1 then there exists a continuum of equilibrium trajectories approaching p 1 and one trajectory approaching p 2 therefore our model exhibits global indeterminacy since either p 1 or p 2 can be selected according to agent expectations moreover we prove that conditions guaranteeing the attractivity of p 1 also imply the saddle point stability of p 2 however when p 1 is not attractive numerical simulations show the possible existence of one or two limit cycles an attractive one surrounding p 1 and one endowed with a two dimensional stable manifold surrounding p 2

does the public sector obey the rational expectations permanent income hypothesis a multi country study of the time series properties of government expenditures 1989 does the public sector obey the rational expectations permanent income hypothesis a multi country study of the time series properties of government expenditures applied economics vol 21 no 9 pp 1257 1266

an analysis of the world s environment and population dynamics with varying carrying capacity concerns and skepticism abstract because of the open access nature of the environment we consider an ad hoc adjustment of people s environmental footprint to the quality of the environment the adjustment is motivated by environmental concern but hindered by skepticism about announced changes in the state of the environment changes in the quality of the environment affect earth s carrying capacity by expanding the lotka volterra predator prey model to include these features we show that despite skepticism the environment does not deteriorate to a state in which humans cannot exist we also show that in the ideal case of no skepticism the interplay between the non optimally changing environmental concerns and carrying capacity leads the world s environment and human population to a unique interior steady state along an oscillating course these results require no further technological social or international progress

competitive versus efficient extraction of a common property resource the groundwater case abstract in this paper socially optimal and private extraction of a common property aquifer are compared open loop equilibrium and feedback equilibrium in linear strategies have been computed to characterize private extraction the use of these two equilibrium concepts allows us to distinguish between cost and strategic externalities as long as the open loop solution captures only the cost externality and the feedback solution captures both the results show that strategic behaviour increases the overexploitation of the aquifer compared to the open loop solution however if the groundwater storage capacity is large the difference between the socially optimal and private extraction the latter characterized by a feedback equilibrium is negligible

equilibrium in a production economy with an income tax this paper develops a method to study an infinite horizon production economy distorted by a state dependent income tax this setting permits taxes to depend on the capital stock an endogenous state variable and thus captures situations where the evolution for capital and taxes is jointly determined to solve this model the consumption function is represented as a fixed point of a nonlinear monotone operator that is defined such that its nth iteration computes the consumption function n steps away from the horizon for a corresponding finite horizon economy the oparator s monotonicity is exploited in proving the existence of and constructing an equilibrium copyright 1991 by the econometric society

bioeconomics of spatial exploitation in a patchy environment abstract this paper presents a model of renewable resource exploitation that incorporates both intertemporal dynamics and spatial movement the model combines the h s gordon vernon smith hypothesis of a rent dissipation process with ricardian notions that resources are exploited across space in a pattern dependent upon relative profitabilities the population structure is characterized in a manner consistent with modern biological ideas that stress patchiness heterogeneity and interconnections among and between patches generally we find the equilibrium patterns of biomass and effort across the system to be dependent upon bioeconomic conditions within each patch and the nature of the biological dispersal mechanism between patches we use simple examples to illustrate how the distribution of effort throughout the system reflects the heterogeneity and the spatial biological linkages

surprises in the consumption function the life cycle hypothesis has been the dominant theoretical basis for empirical work on the aggregate consumption function for about a quarter of a century under it real consumption is proportional to real life cycle wealth where the factor of proportionality depends on real interest rate expectations and the demographic structure of the population life cycle wealth is the sum of financial and human wealth however because the latter is the present real value of the stream of labour and transfer income expected over the life cycle it is not directly observable this fact has led to a great variety of proxying devices in empirical applications and in consequence much looseness in the interpretation of very different models as being all consistent with life cycle theory indeed one can argue that this has protected the hypothesis from being seriously tested and perhaps rejected an insight associated with friedman 1957 is that the view taken by consumers of life cycle income does not alter by much from period to period since there is greater persistence in life cycle income than in current income this also explains the greater persistence of consumption than of current income intuitively this would suggest that lagged consumption being related to last period s perception of life cycle income which in turn is not much different from this period s perception should have a major role in predicting current consumption this intuition was formalised by hall 1978 using ideas familiar from the study of stock market prices and the term structure of interest rates hall showed that if the real rate of interest is constant and given a number of other assumptions including no transitory element in consumption then the life cycle hypothesis implies that

subsidies buybacks and sustainable fisheries abstract most fisheries subsidies which on a worldwide scale are immense are probably detrimental to resource conservation however payments used to buy out excess fishing capacity are often represented as useful subsidies on the grounds that overcapacity encourages overfishing and causes economic waste some commentators on the other hand assert that most buyback subsidies are ineffective because additional capacity tends to seep back into the fishery over time in this paper we take the latter argument further and demonstrate that buyback subsidies if they come to be anticipated by fishermen will generally have a negative effect on economic performance and resource conservation consequently buyback subsidies are perhaps over rated as a management tool

issues and concerns in developing regulated markets for endangered species products the case of rhinoceros horns a proposal for addressing rhinoceros poaching is to legalise the trade in rhino horn and adopt a regulated market approach rma overturning the current trade ban this orthodox economic prescription aims to reduce incentives to poach endangered wildlife by driving down the market price of their products via auctioned stockpile releases biologists are clear however that securing a stockpile for some species needs biological success in captive breeding programmes cbps which varies markedly across species and habitats rhinoceros herds in a cbp would need spatially extensive terrain and costly permanent security measures and this only appears feasible for the less aggressive white rhino we argue that market price would actually need to be sustained at a high level to cover protection costs over the longer reproduction cycles in cbps and that without extensive monitoring and the correct institutional structures being in place legalising trade may encourage rather than prevent poaching supplementary policy measures that differentiate among consumer groups would also likely prove necessary

contribution of fisheries and aquaculture to food security and poverty reduction assessing the current evidence following a precise evaluation protocol that was applied to a pool of 202 articles published between 2003 and 2014 this paper evaluates the existing evidence of how and to what extent capture fisheries and aquaculture contribute to improving nutrition food security and economic growth in developing and emergent countries in doing so we evaluate the quality and scientific rigor of that evidence identify the key conclusions that emerge from the literature and assess whether these conclusions are consistent across the sources the results of the assessment show that while some specific topics are consistently and rigorously documented thus substantiating some of the claims found in the literature other areas of research still lack the level of disaggregated data or an appropriate methodology to reach consistency and robust conclusions more specifically the analysis reveals that while fish contributes undeniably to nutrition and food security the links between fisheries aquaculture and poverty alleviation are complex and still unclear in particular national and household level studies on fisheries contributions to poverty alleviation lack good conceptual models and produce inconsistent results for aquaculture national and household studies tend to focus on export value chains and use diverse approaches they suggest some degree of poverty alleviation and possibly other positive outcomes for adopters but these outcomes also depend on the small scale farming contexts and on whether adoption was emergent or due to development assistance interventions impacts of fish trade on food security and poverty alleviation are ambiguous and confounded by a focus on international trade and a lack of consistent methods the influences of major drivers decentralization climate change demographic transition are still insufficiently documented and therefore poorly understood finally the evaluation reveals that evidence based research and policy narratives are often disconnected with some of the strongest and long lasting policy narratives lacking any strong and rigorous evidence based validation building on these different results this paper identifies six key gaps facing policy makers development practitioners and researchers

stationary markov equilibria in an olg model with correlated production shocks in this paper the author examines the existence of stationary equilibria in an overlapping generations model where production shocks are correlated over time in general the system is complicated by dynamic indeterminacy and possibility of sunspot equilibria however there exists a time homogeneous markov process of the state variable that represents a nonsunspot dynamic equilibrium the long run analysis establishes a sufficient condition for the existence of a nontrivial stationary equilibrium moreover it is shown that the conventional restrictions on the production function are not sufficient to prevent the economy from converging to zero production and consumption copyright 1994 by economics department of the university of pennsylvania and the osaka university institute of social and economic research association

optimal institutional arrangements for transboundary pollutants in a second best world evidence from a differential game with asymmetric players abstract this paper uses a dynamic model with asymmetric players to explore the question in a second best world should environmental regulations for transboundary pollutants be carried out locally or centrally we find that combined payoffs are larger with decentralized control if payoffs are sufficiently heterogeneous and initial pollution stocks are sufficiently small this result is obtained because the central authority applies one shadow price to pollution i e it uses uniform standards whereas local authorities use different shadow prices and therefore different standards

the dynamic efficiency costs of common pool resource exploitation we conduct the first empirical investigation of common pool resource users dynamic and strategic behavior at the micro level using real world data fishermen s strategies in a fully dynamic game account for latent resource dynamics and other players actions revealing the profit structure of the fishery we compare the fishermen s actual and socially optimal exploitation paths under a time specific vessel allocation policy and find a sizable dynamic externality individual fishermen respond to other users by exerting effort above the optimal level early in the season congestion is costly instantaneously but is beneficial in the long run because it partially offsets dynamic inefficiencies jel d24 q21 q22

uniqueness of markov equilibrium in stochastic olg models with nonclassical production a large class of stochastic olg economies with nonclassical production is shown to possess a unique markov equilibrium me which is also the unique sequential equilibrium additional properties such as monotonicity continuity and smoothness of the me are also discussed

banking on extinction endangered species and speculation many wildlife commodities such as tiger bones bear bladders ivory and rhino horn have been stockpiled in large quantities by speculators who expect that future price increases justify forgoing the interest income associated with current sales when supply from private stores competes with supply from wild populations in nature and when speculators are able to collude it may be optimal to coordinate on an extinction strategy we analyse the behaviour of a speculator who has access to a large initial store and finds that it is optimal to deter poachers entry either by depressing prices carefully timing own supply or by depressing wild stocks which strategy maximizes profits critically depends on the initial wildlife stock and initial speculative stores we apply the model to the case of black rhino conservation and conclude it is likely that banking on extinction is profitable if current speculators are able to collude contrary to conventional wisdom we also find that extinction is favoured by such factors as low discount rates or high growth rates

the optimal number of firms in the commons a dynamic approach we consider a common property resource sold in imperfectly competitive markets there is a dynamic externality current harvests lower future stocks raising future harvest costs and a static crowding externality increasing industry size raises costs but lowers prices thus it has ambiguous welfare effects the optimal industry size typically changes over time so that a first best outcome cannot be obtained with a fixed number of firms single firm exploitation is optimal only under special circumstances the socially optimal open loop steady state industry size corresponds to the static optimum both generally differ from the closed loop steady state optimum

decentralized regulation of a common property renewable resource industry with irreversible investment abstract the effectiveness of output controls for rationalizing a common property renewable resource has been called into question by the theoretical work of j r gould economica nov 383 402 1972 a proper examination of this question requires an intertemporal analysis one that takes into account that asymmetries between persistent factors of production immaleable capital and factors that are instantaneously consumed labor or ldharvest effort we present here a nonlinear intertemporal model of a renewable resource industry under conditions of irreversible capital investment and undertake to analyze its dynamics both at open access and under centralized optimal management we then examine the theoretical possibility of decentralized regulation by pigouvian taxes and reconsider the proposition of gould

surprises in the consumption function incomplete current inflation and moving average errors a note in an important paper hall i978 demonstrated that the joint assumptions of the life cycle hypothesis rational expectations and the constancy of the real rate of interest give rise to the startling implication that the flow of real consumption should only be related to its value in the previous period and a random error this error reflects new information which accrues between the previous and current period formally

entry and price dynamics in a perfect foresight model abstract this paper studies firms entry and price dynamics in a model that combines the assumptions of free entry and perfect foresight with the hypothesis of consumer s loyalty postulated by phelps and winter the analysis of the transition to long run equilibrium reveals that in such a model the entry of firms is related to the difference between current prices and costs in relation to the growth of the firms output it is shown that the model is consistent with gibrat s law finally it is shown that the size distribution of firms approaches asymptotically a pareto distribution

stationary equilibria in an overlapping generations economy with stochastic production abstract this paper generalizes the analyses of the existence uniqueness and stability of a non trivial steady state equilibrium in galor and ryder j econ theory49 1989 360 375 to an overlapping generations economy with stochastic production the study establishes sufficient conditions for the existence of a non trivial stationary equilibrium as well as for the existence of a globally unique and stable non trivial stationary equilibrium it is shown that the existence of a non trivial stationary equilibrium is not assured by conventional regularity conditions on the production function and preferences furthermore multiplicity and indeterminacy of long run equilibria appear to be commonplace journal of economic literature classification numbers c62 e13 o41