Balanced Harvesting Research Articles

Balanced harvesting of dynamical discrete Ricker & Beverton–Holt system

In this paper, we discuss a dynamic version of the Ricker & Beverton–Holt (R&B–H)model, which states a two populations commercial fishery, where stock-recruitment effects cannot be neglected. We investigate a stable and balanced fish catches strategy that local breeding stocks are preserved abundant and stable. The Ricker & Beverton–Holt model in commercial fishery, based on the Allee effect, is combined by Beverton–Holt Logistic equation and Ricker model, yn+1=azn1+pzne−yn,zn+1=byn1+qyne−zn. where the parameters a,b,p,q, are positive real numbers and the initial values y0,z0 are arbitrary nonnegative real numbers. Using the mean value theorem and Lyapunov functional skills, we obtain the sufficient conditions to guarantee the bounded and persistent solution of the Ricker & Beverton–Holt model, and global asymptotic stability of the equilibrium. Moreover, three numerical examples are given to elaborate on the results.

Fishing for biodiversity by balanced harvesting

AbstractFisheries are damaging and seemingly incompatible with the conservation of marine ecosystems. Yet fish are an important source of food and support the lives of many people in coastal communities. This paper considers an idea that a moderate intensity of fishing, appropriately scaled across species, could help in maintaining biodiversity, rather than reducing it. The scaling comes from an intuition that rates of fishing mortality of species should be kept in line with production rates of the species, a notion known as balanced harvesting. This places species conservation and exploitation on an equal footing in a single equation, showing quantitatively the relative levels of fishing mortality that species of different abundance can support. Using a dynamic model of a marine ecosystem, we give numerical evidence showing for the first time that fishing, if scaled in this way, can protect rarer species, while allowing some exploitation of species with greater production. This works because fishing mortality rates, when scaled by production, are density‐dependent. Such fishing, operating adaptively to follow species' production rates over time, contains a feedback that would help to protect species from overfishing in the presence of uncertainty about how marine ecosystems work.

Review on Ecological Response of Aquatic Plants to Balanced Harvesting

Macrophytes are the main primary producers in lake ecosystems and are the main transmitters of material and energy flows in lake ecosystems, directly influencing the structure and function of lake ecosystems. The balanced harvesting of aquatic plants is a cost-effective scientific management approach to maintain ecosystem health. The article defines “balanced harvesting” as an aquatic plant harvesting technique to optimize the structure of aquatic plant communities, maintain the normal function of the ecosystem material cycle and energy flow, and enhance the stability and resilience of the system. The ecological significance of balanced harvesting in regulating the evaporation coefficient of the subsurface, reducing the accumulation and release of endogenous nutrient loads in lakes, delaying the evolutionary process of marshification, inhibiting biological filling, increasing biodiversity and system stability, and improving the environment of water bodies under the natural laws of adapted aquatic plants is reviewed. The way, time, and method of the balanced harvesting of aquatic plants in Baiyangdian, a grass-type lake in the north, were analyzed in order to provide an important reference for wetland ecological restoration and protection, maintaining the health of the aquatic ecosystem, and making the lake environment sustainable.

Balancing Ecosystems, Harvests, and Seafood Markets

Recognition of competition and predator–prey interactions among species has led some to promote the concept of balanced harvesting, whereby fisheries would remove a proportional, sustainable fraction of all species in the fish community. Practical implementation of such a strategy hinges on understanding the current degree of species selection in fisheries and the factors that drive this selection. This interdisciplinary study measured ecosystem–market symmetry in the New England region by tracking species composition from ecosystem production, to catch, landings, and seafood markets. Strong species selection occurred in the catch and in seafood markets but not by discarding, which suggests that that requiring full retention of all species caught may make a limited contribution to promoting ecosystem–market symmetry. Results from a group of citizen scientists indicate that higher priced species were generally more available in seafood markets and that availability diminished rapidly with distance from shore. We conclude that market‐based selection may be reduced through a combination of locavore consumer education and global marketing strategies.

Research on Multiobjective Optimization Algorithm for Cooperative Harvesting Trajectory Optimization of an Intelligent Multiarm Straw-Rotting Fungus Harvesting Robot

In view of the difficulties of fruit cluster identification, the specific harvesting sequence constraints of aggregated fruits, and the balanced harvesting task assignment for the multiple arms with a series-increasing symmetric shared (SISS) region, this paper proposes a multi-objective optimization algorithm, which combines genetic algorithm (GA) and ant colony optimization (ACO) stepwise, to optimize the multiarm cooperative harvesting trajectory of straw-rotting fungus to effectively improve the harvesting efficiency and the success rate of non-destructive harvesting. In this approach, firstly, the multiarm trajectory optimization problem is abstracted as a multiple travelling salesman problem (MTSP). Secondly, an improved local density clustering algorithm is designed to identify the cluster fruits to prepare data for harvesting aggregated fruits in a specific order later. Thirdly, the MTSP has been decomposed into M independent TSP (traveling salesman problem) problems by using GA, in which a new DNA (deoxyribonucleic acid) assignment rule is designed to resolve the problem of the average distribution of multiarm harvesting tasks with the SISS region. Then, the improved ant colony algorithm, combined with the auction mechanism, is adopted to achieve the shortest trajectory of each arm, which settles the difficulty that the clustered mature fruits should be harvested in a specified order. The experiments show that it can search for a relatively stable optimal solution in a relatively short time. The average harvesting efficiency is up to 1183 pcs/h and the average harvesting success rate is about 97%. Therefore, the proposed algorithm can better plan the harvesting trajectory for multiarm intelligent harvesting, especially for areas with many aggregated fruits.

Balanced harvesting in two predators one prey system

In this research, we discuss balancing two essential ecosystem services, known as resilience and yield, in a harvested two predators one prey system. We study how these two ecosystem services respond to different types of harvesting plans applied to the system. In individual harvesting, we observe that prey harvesting is suitable for generating more yield while either predator harvesting gives more resilience. Several patterns are possible based on the intensity of harvesting efforts applied to prey or the predator in simultaneous harvesting. This study shows that a balanced harvest between prey and predators may give more than the selective harvesting of any species yielding and stabilizing the ecosystem. Even if this fair strategy is not a cooperative situation for both resilience and yield, it may be the most favorable approach to scale those services. Finally, we may state that it would help us correlate the safest position (corresponds to the maximizing resilience yield) and the good views (which corresponds to the maximum sustainable return) to safeguard our ecosystems.

Effects of season and mesh size on the selection of narrow-barred Spanish mackerel, Scomberomorus commerson in the Persian Gulf artisanal gillnet fishery

AbstractIn response to perceived, but unknown variation among the size selection of narrow-barred Spanish mackerel (Scomberomorus commerson) by artisanal gillnetters off Iran, and the need for such data to control exploitation as a precursor to balanced harvesting, the effects of two common mesh sizes (130 and 140 mm stretched mesh opening made from multifilament twine) on catches were investigated over one fishing year (nine months encompassing autumn to spring). Both mesh sizes mostly caught S. commerson at fork lengths (FL) larger than mean sizes at maturity (>67 cm), with the mean size selection incrementally increasing in the 130-mm mesh gillnet from autumn, and especially during spring. The greater selection occurred concurrent with an increasing condition factor (CF) among S. commerson, which typically spawn in late spring/early summer. Conversely, the relative size-selection of the 140-mm mesh gillnet decreased in spring, attributed to increasing CF precluding the capture of larger fish. Such seasonal variation in size selection might be countered by increasing mesh size to ~145 or 150 mm in spring. However, the existing 140-mm mesh might positively affect stock biomass by allowing larger, more fecund fish to avoid capture during spawning. The data support the strong influence of biological and environmental factors on gillnet size selection, which might also extend to other migratory, pelagic species.

Measuring the balance between fisheries catch and fish production

Balanced harvesting has been proposed as a fisheries management strategy to mitigate the impacts of fisheries removal on ecosystem structure. One definition of balanced harvest is that all species should be harvested in proportion to their annual production. However, most marine ecosystems lack comprehensive production estimates necessary to empirically measure the degree of balance. We developed and tested 2 new methods for estimating fish biomass production at the species level with limited data requirements. Application of our techniques to 4 ecological production units in the northwest Atlantic (Mid-Atlantic Bight, Georges Bank, Gulf of Maine, and western Scotian Shelf) from 1991-2013 provided a direct estimate of 1.9 million t yr-1 of total fish production. The degree of balance between catch and production distributions at the species level, assessed using the proportional similarity index, ranged from 0.34 to 0.83 on a scale from near 0 to 1. Increased balance was positively associated with yield in the Gulf of Maine (Spearman’s, p = 0.04). Increased balance was negatively associated with an ecosystem impact indicator in the Gulf of Maine (Spearman’s, p = 0.03) and Mid-Atlantic Bight (Spearman’s, p = 0.02). These case studies provide some evidence of benefit to humans and reduced ecosystem harm from more balanced harvest. More importantly, we provide a unique empirical metric of balanced harvest at the species level, and develop potential indicators and methods for ecosystem-based fisheries management.

RETRACTED ARTICLE: Soft computing approach based energy and correlation aware cooperative data collection for wireless sensor network

Energy plays the predominant constraint in wireless sensor network (WSN) hence, an energy and correlation aware cooperative data collection (ECCDC) method of soft computing approach has been discussed in this work. This work is an attempt to maximize the life span of the network by identifying and rectifying the major energy exploiting activities of WSN and it also defines a hierarchical network structure with balanced clusters and energy harvesting sensor nodes. These sensor nodes select the Cluster Heads (CHs) among themselves using a low overhead passive clustering approach. The cluster balancing has been performed by acknowledging only the most deserved sensor nodes as their members. The members co-operatively collect the data from the region of interest. During every time slot, the cluster members are chosen for reporting, based on the mutual correlation, link quality of the member with the CH and the residual energy of the member nodes. The fraction of data collected at the CH is then sent through the optimized inter-cluster paths to the sink, wherein the received data are used for estimation, based on the node’s position and correlation pattern. This proposed system of optimize method reduces the energy consumed, due to the transmission of redundant data and the data loss by preferring optimized data paths.

Impacts of predator–prey interaction on managing maximum sustainable yield and resilience

This paper gives a broad outline of some comparative analysis of two ecological services, namely, yield and resilience of a generalist predator–prey system. Although either prey or predator species can be harvested at maximum sustainable yield (MSY) level, yet there is a trade-off between yield and resilience. When both the species are harvested simultaneously, MSY increase by changing catchabilities always increases the system resilience both in prey- and predator-oriented fishery. In particular, a prey-oriented fishery with low prey catchability gives more yield and resilience but in case of predator-oriented fishery with high predator catchability, gives more of these ecological services. Thus to get both the optimum yield and resilience, a balanced harvesting approach is needed between the prey and predator trophic levels. Throughout the analysis, we use both the analytical as well as numerical techniques.

Exploring Balanced Harvesting by Using an Atlantis Ecosystem Model for the Nordic and Barents Seas

“Balanced Harvesting” (BH) has been suggested as a possible strategy to meet the objectives of the Ecosystem Approach to Fisheries, ensuring a high sustainable yield while maintaining ecosystem structure and function. BH proposes a moderate fishing mortality in proportion to productivity spread across the widest possible range of species, stocks, and sizes in an ecosystem producing a sustainable and overall non-selective harvest. The Norwegian and Barents Seas have been subjected to moderate fishing pressure on commercial species, and elements of an ecosystem-based approach to management for many years, but not the fishing pattern proposed by BH. By using an Atlantis ecosystem model of the Nordic and Barents Seas, we investigated the effects of applying a BH regime to a region with existing successful fisheries management. This was done by running simulations with combinations of historic fishing pressure and fishing mortality rates proportional to 25% of the productivity of most species and sizes. The simulations were then compared to a control run where the historical fisheries were applied. The model results showed that implementing a BH regime in the Norwegian and Barents Seas would only produce marginal increases in total yields of currently commercially exploited stocks, likely because the Norwegian fisheries are already mostly well managed. However, expanding the fishery to include species that are not commercially exploited today did produce higher yields, especially on lower trophic levels. This study represents the first attempted examination of implementing BH based on productivity using an Atlantis ecosystem model, as well as the first investigation of BH in the Norwegian and Barents Seas. We use this model as a case study to identify the gains that species-based BH can be expected to give over well-implemented traditional fisheries management rather than simply comparing to an over-exploited system.

What unmanaged fishing patterns reveal about optimal management: applied to the balanced harvesting debate

Abstract Balanced harvesting (BH)—the idea of harvesting all species and sizes in proportion to their production rate—has been a topic of recent debate. Developed world fisheries tend to fish more selectively, concentrating on certain species and sizes preferred in the market. However, fishing patterns in some developing countries, with a range of different fishing gears and more generalist markets, more closely resemble BH. The BH debate therefore hinges on whether selective fisheries should become more balanced, whether unselective fisheries should do the opposite, both, or neither. In this study, we use simple and general analytical theory to describe the ideal free distribution that should emerge in unmanaged fisheries, and we show that this ideal free distribution should approximately produce BH only when prices, catchabilities, and fishing costs are similar across species and sizes. We then derive general properties of yield and profit maxima subject to conservation constraints. We find that BH is unlikely to be optimal in any fishery but may be closer to optimal in fisheries in which it emerges without management. Thus, BH may be more useful as a heuristic for understanding differences between fisheries in locally appropriate management than as an exact management strategy.

Emergence of balanced harvesting in an agent-based model of an open-access small-scale fishery

Fisheries management strategies in which large fish are selectively targeted and younger, smaller fish are protected can lead to disruption of stocks, truncation of the population size spectrum, and impaired recruitment. Balanced harvesting is an alternative approach, which distributes fishing mortality across a wide range of species and sizes in proportion to their natural productivity. Here, we investigate outcomes from an agent-based model of fishing, coupled with an ecological model for the dynamics of a single fish species in a small-scale fishery. In the model, individual fishing agents make decisions about whether to enter or exit the fishery, and what size fish to target, based on economic calculations about short-term profitability of alternative actions. Fishing mortality, aggregated across agents, affects the biomass and size structure of the stock, which in turn affects individual agents’ yields, creating a feedback loop. We show that the autonomous fishing agents self-organise to produce a Nash equilibrium, in which yields are equalised across agents. The aggregate fishing mortality that emerges in this equilibrium state is closely aligned with the distribution of productivity across body size. We conclude that balanced harvesting is an emergent outcome of the model. This occurs despite the absence of any externally imposed regulations on total fishing effort, catch or target sizes. However, controls on overall harvesting pressure are required to avoid overfishing.

Managing yield and resilience in a harvested tri-trophic food chain model

In this article, we compare the two ecological services known as yield and resilience, for a tri-trophic food chain model consisting of a prey, an intermediate predator and a top predator. For this comparison process, we use both analytical and numerical techniques. It is shown that a variety of patterns are possible based on the intensity of efforts distributed among different trophic levels. Thus we may suggest that fishing down the food chain, as suggested by Pauly et al. (1998) is not bound to happen. Our analysis also shows that balancing the harvest between prey, intermediate predator and top predator could give more yield and stabilizing the ecosystem, than the selective harvesting of any one species. This balanced harvesting may not be a win–win situation for yield and resilience, but it could be a most favourable strategy to balance them. This research would help to correlate resilience with yield and determines the desirable selection of two policies, resilience maximizing yield or maximum sustainable yield to safeguard ecological communities.

Balanced harvesting could reduce fisheries‐induced evolution

AbstractCurrent fisheries management pays little attention to fisheries‐induced evolution. Methods of exploitation that have benefits in the short term while ameliorating selection in the longer term would therefore be advantageous. Balanced harvesting is a potential candidate. This tries to bring fishing more in line with natural production, and some short‐term benefits for conservation of aquatic ecosystems and for biomass yield have already been documented. It is also predicted to be relatively benign as a selective force on fish stocks, because it keeps the overall distribution of mortality relatively close to natural mortality. We test this prediction, coupling an ecological model of marine, size‐spectrum dynamics to an adaptive dynamics model of life history evolution. The evolutionary variable is the reproductive schedule, set by the maximum body mass and the mass at maturation. The prediction is supported by our numerical analysis: Directional selection under balanced harvesting is approximately an order of magnitude weaker than in a standard fishery in which fish experience a fixed rate of fishing mortality after recruitment. The benefit of balanced harvesting follows from relatively little fishing on large fish, due to the low somatic production rates the big fish have. These results therefore support the general argument for protecting big, old fish, both for ecological and for evolutionary reasons. Slot fisheries that protect large fish share some qualitative features with balanced harvesting and show similar evolutionary benefits.

How should fishing mortality be distributed under balanced harvesting?

Zhou and Smith (2017) investigate different multi-species harvesting scenarios using a simple Holling-Tanner model. Among these scenarios are two methods for implementing balanced harvesting, where fishing is distributed across trophic levels in accordance with their productivity. This note examines the effects of a different quantitative implementation of balanced harvesting, where the fishing mortality rate is proportional to the total production rate of each trophic level. The results show that setting fishing mortality rate to be proportional to total production rate, rather than to productivity per unit biomass, better preserves trophic structure and provides a crucial safeguard for rare and threatened ecological groups. This is a key ingredient of balanced harvesting if it is to meet its objective of preserving biodiversity.

Overfishing As a Legitimate Management Goal

The efficiency of the production chain of aquaculture plants is influenced among others by the fish efficiency – the mass surplus per assimilated food. A new indicator – the stock efficiency as a function of fishing mortality and mesh size – was introduced for wild fish stocks, which describes more or less the same context. The stock efficiency provides a measure of how much yield per assimilated food quantity can be harvested. Over-utilization leaves food resources unutilized. Under-utilization causes a larger stock size and consequently a lack of food for the remaining fish. The fish cannot feed at the maximum consumption rate because the ecosystem is not able to produce enough food. This is compensated by lower growth rates or by cannibalism. In the case of starving fish, we know from aquaculture that the fish efficiency and thus the productivity of the aquaculture plant decreases. Similar results are obtained for wild fish stocks. Fishing with small meshes and high fishing mortalities results in a high stock efficiency, and therefore, in larger catches per assimilated food quantity. Fisheries targeting predator and prey fish at the same time take place in many marine ecosystems. The interdependencies between predator and prey fish were analyzed based on a theoretical example. It was quantitatively shown that the achievement of high total yields is only possible if the predator-fish stock is overexploited. In this case, it is possible to fish the part of the prey stock, which has been used before exclusively as a feed for the predator fish stock. It is clear that recruitment must be closely watched when applying such an exploitation pattern. Fishing with small meshes and high fishing mortalities were successfully used for a long time within the so-called balanced harvesting approach. It is known that much larger total yields can be expected when employing balanced harvesting compared to yields actually obtained by single stock optimization.

Balanced harvesting is the bioeconomic equilibrium of a size-structured Beverton-Holt model

Balanced harvesting (BH) was introduced as an alternative strategy to size-at-entry fishing with the aim of maintaining ecosystem structure and functioning. BH has been criticized on a number of grounds, including that it would require an infeasible level of micromanagement and enforcement. Recent results from a size-spectrum model show that the distribution of fishing mortality across body sizes that emerges from the behaviour of a large number of fishing agents corresponds to BH in a single species. Size-spectrum models differ from classical size-structured models used in fisheries as they are based on a bookkeeping of biomass transfer from prey to predator rather than a von Bertalanffy growth model. Here we investigate a classical Beverton-Holt model coupled with the Gordon-Schaefer harvesting model extended to allow for differential fishing pressure at different body sizes. This models an open-access fishery in which individual fishing agents act to maximize their own economic return. We show that the equilibrium of the harvesting model produces an aggregate fishing mortality that is closely matched to the production at different body sizes, in other words BH of a single species. These results have significant implications because they show that the robustness of BH does not depend on arguments about the relative production levels of small versus large fish.

Balanced harvesting can emerge from fishing decisions by individual fishers in a small‐scale fishery

AbstractCatching fish in proportion to their productivity, termed balanced harvesting, has been suggested as a basis for the ecosystem approach to fishing. Balanced harvesting has been criticized as uneconomical and unachievable because of the level of micromanagement it would require. Here, we investigate the consequences of allowing a fixed number of fishers in a small‐scale fishery to choose what size fish to attempt to catch. We examine this from a game‐theoretic perspective and test our predictions using an agent‐based model for fishers’ decisions coupled with a size‐spectrum model for the dynamics of a single fish species. We show that small‐scale gillnet fishers, operating without size‐based regulations, would end up catching small and large fish in proportion to their productivity, in other words balanced harvesting. This is significant because it shows that, far from being unachievable, balanced harvesting can emerge without external intervention under some circumstances. Controls are needed to prevent overfishing, but minimum size regulations alone are not sufficient to achieve this, and actually reduce the sustainable yield by confining fishing to a relatively unproductive part of the size‐spectrum. Our findings are particularly relevant for small‐scale fisheries in areas where there is poverty and malnutrition because here provision of biomass for food is more important than the market value of the catch.

Balanced harvesting: The institutional incompatibilities

Balanced harvesting is the name of a newly proposed approach to fishing which promises the extraction of high and sustainable fisheries yields while maintaining the structure of the ecosystem from which those yields could be obtained. This is to be achieved through exposing all components of ecosystems (from zooplankton to top predators, including seals, sea birds and marine mammals) to a fishing mortality proportional to their size-specific productivity. This study briefly analyses the incompatibility between balanced harvesting (and its implications) and the stated missions of two major organizations, FAO (which stresses the need of selective fishing in its Code of Conduct for Sustainable Fisheries) and IUCN (which maintains the Red List of Threatened Species), but which have issued reports or organized conferences promoting balanced harvesting. The study also demonstrates the incompatibility of balanced harvesting with the recently reformed Common Fisheries Policy of the European Union. While balanced harvesting appears partly compatible with declared fisheries policies of a few countries, e.g. with regard to whaling, sealing, and indiscriminate biomass fishing, it is not only incompatible with the basic tenets of fisheries science, but also with the vision, gradually emerging globally, that marine organisms such as marine mammals, sea turtles, sea-birds and other fauna have an intrinsic value and right to life that should not be undermined by more of the indiscriminate fishing which currently shapes much of our interactions with the oceans.