Species diversity, fishing induced change in carrying capacity and sustainable fisheries management

It is well established in the fisheries management literature that marine ecosystems are complex and marine species depend on one another. As a result, it is important to account for species diversity to ensure sustainable management. In addition, recent research published in the marine sciences literature has provided unequivocal evidence that fishing activities destroy habitats and inhibit production of planktons. This paper illustrates that if a conventional bioeconomic model is employed, an optimum effort policy as opposed to quota appears to result in sustainable management even if fishing impacts carrying capacity. However, the so-called optimum effort may collapse the stock if species diversity is not accounted for. Conversely, if species diversity and the impact of fishing on carrying capacity are considered, neither the equilibrium quota nor effort may guarantee sustainable yield.     

Fishing in a Shallow Lake: Exploring a Classic Fishery Model in a Habitat with Shallow Lake Dynamics

Renewable resources such as fish exist within habitats. Harvesting activities may directly impact the habitat, beyond the influence caused by changing the balance between species. When harvesting activities impact stock size and habitat health in different ways, both states must be explicitly considered. A classic fisheries model is embedded in a habitat that exhibits shallow lake dynamics, where carrying capacity depends on habitat health and fishing effort damages the habitat. Hysteresis in the habitat dynamics can manifest itself as multiple steady states for both the dynamic and open access solutions. Numerical explorations of the model suggest that a new fishery in such a setting should often be managed to protect the health of the habitat, while it may not be optimal to restore a fishery in an already degraded habitat. Conventional policy tools applied in their classic form are unlikely to be effective.     

Biological “hot spots” and their effect on optimal bioeconomic marine reserve formation

Biological “hot spots” are regions within a fishery that possess a larger growth potential than the surrounding areas. This paper analyzes how these biological hot spots influence the optimal bioeconomic marine reserve formation within a fishery. The presence of biological hot spots within a fishery creates an environment within which it is optimal to establish a marine reserve that increases the productivity and therefore the value of the fishery. This result is analyzed using heterogeneity in the intrinsic growth rates and carrying capacities within a fishery. Simulation results illustrate that the optimal reserve size in the presence of biological hot spots depends not only on the productive capacity of the reserve and the surrounding fishing grounds, but also on the degree of heterogeneity between the two regions.     

A Reconsideration of the Bioeconomics of Marine Sanctuaries: Commentary on Jon Conrad's Paper

Conrad (1999) examined the bioeconomics of marine sanctuaries and found: (1) a sanctuary that takes up a large share of the potential grounds can make fishing uneconomic, (2) a sanctuary of roughly the same size as the grounds can significantly reduce the standard deviation of the stock on the grounds when both stocks are growing randomly. It is argued that when one divides a fishery into grounds and a sanctuary the firm cost parameter should be adjusted in value as well as the capacity parameters. With this modification one finds that fishing grounds of smaller sizes are more profitable relative to their size than larger grounds and that the reduction in variability of stocks on the fishing ground is relatively smaller. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Sushi or Fish Fingers? Seafood Diversity,Collapsing Fish Stocks,and Multispecies Fishery Management*

We present a model of a multispecies fishery, and we show the following. (i) Consumer preferences for seafood diversity can trigger a sequential collapse of fish stocks under open‐access fishery. (ii) The stronger the preferences are for diversity, the higher is the need for coordinated multispecies regulation. (iii) Second‐best optimal management of only one (or a few) species is less strict than socially optimal management of the same species. (iv) Myopic regulation of one species, ignoring spillovers to other species, can cause depletion of other stocks that would not be depleted under open access.     

Evaluating the effects of area closure for recreational fishing in a coral reef ecosystem: The benefits of an integrated economic and biophysical modeling

This paper presents an integrated agent-based model of recreational fishing behavior within a reef ecosystem as a platform for the evaluation of recreational fishing management strategies. Angler behavior is described using econometrically estimated site choice models, with site choice among anglers driven by site attributes and angler characteristics. The biophysical model represents the marine reef environment as a system with different trophic levels identifying algal and coral growth as well as two types of fish (piscivores and herbivores). Ecosystem dynamics are driven by interactions within the trophic levels and interaction between fish populations and fishing activities.The model is used to simulate recreational fishing activities and their interactions with the environment. Recreational fishing sites from the Ningaloo Marine Park, an iconic coral reef system in Western Australia, are used as a case study. A set of management strategies, including “business-as-usual” and different site closure durations, are assessed for two different levels of fishing pressures. The results show that not only the effectiveness but also the distribution of management impacts across space and over time can be very different from what one would expect without the benefit of integrated modeling.     

Fishing Revenue, Productivity and Product Choice in the Alaskan Pollock Fishery

A key element in evaluating fishery management strategies is examining their effects on the economic performance of fishery participants, yet nearly all empirical studies of fisheries focus exclusively on the amount of fish harvested. The economic benefits derived from fish stocks involve the amount of revenue generated from fish processing, which is linked to both the way fish are harvested and the products produced from the fish. In this study we econometrically estimate a flexible revenue function for catcher-processor vessels operating in the Alaskan pollock fishery, recognizing potential endogeneity and a variety of fishing inputs and conditions. We find significant own-price supply responses and product substitutability, and enhanced revenues from increased fishing days and tow duration after a regulatory change introduced property rights through a new fishing cooperative. We also find significant growth in economic productivity, or higher revenues over time after controlling for observed productive factors and price changes, which exceeds that attributable to increased harvest. These patterns suggest that the move to rights-based management has contributed significantly to economic performance in the pollock fishery.     

Individual Rationality and the “Zonal Attachment” Principle: Three Stock Migration Models

Shared fish stocks migrate across borders between different countries’ exclusive economic zones. This paper discusses the individual rationality of fish-sharing agreements based on the zonal attachment of such stocks. Three types of migrations are considered: (i) a common stock that grows and reproduces and is then distributed in given proportions between two countries’ zones at the beginning of each fishing season; (ii) sub-stocks that breed and grow independently in their separate zones but spill over between zones according to relative abundance; (iii) a stock that grows and breeds in one country’s zone but migrates into the zone of another if it exceeds a certain size. It is shown that in all these cases the minor partner in a fish-sharing agreement may not have an incentive to cooperate unless he gets a larger share of the cooperative profits than that corresponds to his share of the stock. This is particularly likely to happen when the unit cost of fish does not depend on the stock. An exception could occur if stock migration depends on the stock level; the major partner could then keep the entire stock by fishing it down to a critical level.     

Assessing the ecological and economic benefits of a no-take marine reserve

The management of marine resources is often impeded by a lack of models to integrate ecological and economic information on exploited populations. We used available biological and economic data for an overexploited population of the leopard grouper (Mycteroperca rosacea) to study if closing parts of the population to fishing would allow sustainable use and maximum economic benefits. Our results suggest that fishing should be closed in all spawning areas and in at least 50% of the adjacent areas. High non-consumptive benefits would be achieved with large closures because the abundance of the leopard groupers, which is an important attribute for SCUBA divers, would increase. In a no-take reserve, the welfare gains of divers seemingly could compensate for losses incurred by fishers if parts of their fishing grounds are closed. An adaptive management scheme could provide a way to incorporate newly available information into management decisions for the no-take reserve.     

A model for estimating fish population and optimal fishing effort in lakes and rivers

We developed a model for estimating the fish population for various species in lakes and rivers. Our estimation focuses, in its first step, on fish species that breed outside the lake. Using the annual outside supply of fingerlings, natural survival rate and reported amounts of fish caught, we estimated fish stock. Given the estimated stock for fish bred outside the lake, we can evaluate the catch rate. Assuming equal catch rates for other species, and given the amount caught for each species, we are able to evaluate each species stock. Using the proposed technique, we evaluated various species stocks in the Sea of Galilee (Lake Kinneret) in Israel. Using our suggested technique for evaluating fish stock, we calculated the optimal effort of fishing needed for maximizing steady state profit of the fishers.     

Boundary conditions for the sustainable use of major fish stocks in the Baltic Sea

The history of the management of Baltic fishery resources suggests that both biological and non-biological factors influence management decisions and that both types of information are essential for management which promotes sustainability. There is a direct link between the exploitation level and the risks for fishing as an economic activity due to fluctuations in the resource. This paper analyses the sustainability of the present catch levels of major Baltic fish stocks. By examining the rate of fishing mortality and recruitment variability, the possibility of sustaining present catch levels can be investigated. Current catch levels of Baltic cod and some salmon stocks are not sustainable whereas sprat and herring catches are. High rates of fishing mortality of cod and salmon may endanger stocks if a drop in the recruitment causes an increase of the fishing mortality rates in order to sustain short-term catches. By analysing the trade off between exploitation level and risk of stock decline, managers can obtain a basis for quota negotiations.     

海洋资源环境承载力评价研究进展

我国海洋经济的高速增长导致近岸海洋资源趋紧、海洋环境污染加剧,引起了社会各界对海洋资源环境过载问题的高度关注。近年来,海洋资源环境承载力评价研究取得了诸多进展,体现在:(1)对海洋资源环境承载力的概念及内涵有了更加深刻的理解;(2)推动了海洋资源环境单要素承载力和综合承载力评价方法研究;(3)海洋资源环境承载力评价研究的综合应用。通过总结发现,当前海洋资源环境承载力评价对象比较局限,反映承载体与承载对象之间动态关系的评价方法还较为薄弱。因此,在陆海统筹目标下的资源环境承载力综合集成评价需求下,海洋分类评价研究的当务之急是建立基于多要素的海洋资源环境承载力评价技术框架。     

Spatial distribution of species populations,relative economic values,and the optimal size and number of reserves

We examine the tradeoff between the number and average size of nature reserves. When the costs of enforcing reserve boundaries are negligible, we find analytically that the relative price of biodiversity has a positive impact on the optimal total reserved area but an ambiguous impact on the optimal number of reserves. Simulation modeling of floral diversity in a tropical timber concession reveals that the resolution of this ambiguity depends on spatial distributions of the populations of tree species: whether or not they are spatially aggregated (clumped). The impact of biodiversity price on optimal reserve number remains analytically ambiguous when enforcement costs are not negligible. Multiple reserves being economically superior to a single reserve now requires, in addition to aggregation, a biodiversity price that is sufficiently high to offset the effects of enforcement costs. Most of our simulation scenarios generate threshold biodiversity prices that do not exceed a leading estimate of the marginal value of a higher plant species in the bioprospecting literature. Several smaller reserves evidently can be economically superior to a single larger one even in the presence of enforcement costs.      

Resource Characteristics, Extraction Costs, and Optimal Exploitation of Mineral Resources

This paper modifies the traditional theories ofnon-renewable resource exploitation where reserve sizeis assumed to be the major determinant of extractioncosts. In a competitive model of resourceexploitation, characteristics of aggregate reservesare considered as a determinant of extraction cost. Then dynamic solutions for the price and exploratoryefforts are developed. Various price paths arefeasible under different assumptions with regard tothe changes in the reserve characteristics over time. Past empirical research shows that there is noconsistent price path for all materials. In fact, itis the quality of newly discovered reserves as well astheir size that has affected material prices. Todemonstrate the complexity of a firm's decision torecover mineral from new deposits, potentials forsubstantial high quality marine mineral resources areevaluated as a substitute for land-based resources.However, several factors including the decreasingtrend in marine mining R & D expenditures and thepotential impact of large-scale marine mining on priceof minerals indicate that mining of mostnon-hydrocarbon marine minerals will not take place inthe near future.     

情感信任情景下创业网络结构特征对吸收能力的影响

创业网络构建与开发是克服创业企业新生性成长劣势和获得各种资源的有效途径。基于社会网络理论和吸收能力理论，结合中国关系社会的现实情境，构建创业网络结构、情感信任与吸收能力关系的理论模型。研究发现，网络规模、网络强度和网络多样性对吸收能力均具有显著正向影响；情感信任对吸收能力具有显著正向影响；情感信任正向调节网络强度、网络多样性与吸收能力的关系。结果可为创业者从网络结构和关系信任方面调整创业活动以提高企业吸收能力提供启示。     

Aquaculture,capture fisheries,and wild fish stocks

This paper employs a general equilibrium model to examine how the rise of aquaculture and changes in wild fish stocks are related for herbivorous fish species. Two influences, human population growth and technological improvement in aquaculture, are studied. Both of these factors raise aquaculture production, but human population growth reduces wild fish stocks, while technological progress in aquaculture raises wild stocks.     

Intertemporal choice of marine ecosystem exploitation

Exploitation of the marine ecosystem brings with it an intertemporal choice: there is a choice of catching the fish today, or restrain from fishing with the option of an increase in the benefit from future harvest. In a marine ecosystem under common pool management regime the contribution margin from catching the fish belongs to the fisher, while the benefit from the investment of leaving the fish in the sea will be shared in the common pool. The intertemporal choice therefore creates a driver for short sighted use of the ecosystem. The intertemporal balance of the exploitation is analyzed by applying capital theory to a size-based ecosystem model. The model reveals a need for intertemporal balance with respect to both fish size and harvest volume. The management therefore is, at an ecosystem level, to set target and regulate not only harvest volume but also size.     

Nature Reserves as a Bioeconomic Management Tool: A Simplified Modelling Approach

This paper demonstrates analytically how a nature reserve may protect the total population, realize maximum sustainable yield (MSY) and economic yield (EY) and how this depends on biological growth, migration, reserve size and economic parameters. The pre-reserve population is assumed to follow the logistic growth law and two post-reserve growth models are discussed to explore the importance of model assumptions for assessment of reserves. The post-reserve growth has either a common carrying capacity as in the pre-reserve case, or each sub-population has its own carrying capacity proportionate to its distribution area. A combined model, as a continuum of the two models, is also formulated and briefly discussed. Population protection against extinction is assured against low cost harvesting, including zero cost, when relative reserve size is greater than relative migration. Reserve size may be tuned to realize MSY in one model, but not in the other. Economic yield is generally greater in the former, but maximum EY cannot be realized in any one.     

Costs and Benefits of Bycatch Reduction Devices in European Brown Shrimp Trawl Fisheries

Discarding of juvenile fish is a wellrecognised problem in shrimp fisheries. In manycases, these fish are commercial species that,if not caught, could increase the productivityof other fisheries. In January 2003, Europeanlegislation was implemented by Member Statesrequiring all vessels fishing for brown shrimpto use selective trawls in order to minimisethe bycatch of other commercial species. Incomplying with the regulations, however, thecatch rate of the target species (the shrimp)is likely to be reduced. In this paper, we usea bioeconomic model to assess the impact ofbycatch reduction devices on fishing effort,catch and profitability in the European Crangon fisheries. The potential benefits (interms of higher future yields and consequentlyhigher profits) to the white-fish fisheries arealso estimated. From the model results, theregulation is expected to result in a netreduction in the profitability of the shrimpfishers. However, the benefits to thewhite-fish fishers is expected to more thanoffset this cost, resulting in an overall netbenefit.