Multispecies Fisheries Research Articles

Regional management of multi-species fisheries on the basis of shared stocks and property rights: a Mediterranean case

Fishery management is a complicated task that often results in overfishing, overcapacity, and low profits for the industry. The management of shared fish stocks is particularly problematic, especially if national authorities pursue different objectives. Multi-species fisheries add further complexity to the problem. It is no accident that management tools frequently used in Northern Europe, such as total allowable catches and individual quotas, are not applied in the Mediterranean Sea, where more target species are caught simultaneously. However, the European Commission intends to introduce a market-based driver for a strong, profitable fishing industry by phasing in transferable fishing concessions . This management approach is new for the Mediterranean, and it requires in-depth examination at institutional, legal, and economic levels. In this paper, after a review of the institutional setting, the economic perspective was analyzed by estimating the production function for the Italian small pelagic fishery in the Adriatic Sea. With the addition of Croatia to the European Union, the Adriatic Sea can become a Mediterranean communal exclusive fishing area. The results indicate that output measures such as total allowable catches and individual quotas should not cause serious discarding problems for this multi-species fishery.

Implications of a Discard Ban in Multispecies Quota Fisheries

We present an analysis of quota regulation and discarding in multispecies fisheries, explicitly taking into account the costs of non-compliance with quotas and a possible discard ban, as well as the costs of selective fishing (avoidance effort). We examine the impact of a discard ban on vessels’ profit maximising behaviour, in particular where species quotas are not set in proportion to their availability on the fishing grounds, considering both non-tradeable quotas and ITQs. We show the interdependence between penalty rates for both discards and over-quota landings in determining quota market outcomes. We find that quota prices are sensitive to penalty rates and to the presence of restrictive quotas for “choke” species.

Measuring the social and economic performance of catch share programs: Definition of metrics and application to the U.S. Northeast Region groundfish fishery

In May 2010 the New England Fishery Management Council introduced a catch share, program in the Northeast Multispecies (groundfish) Fishery. Amendment 16 of the Northeast Multispecies Fishery Management Plan allocated quota to 17 self organized groups of permit holders based on their collective catch history. These groups are commonly referred to as Sectors and are similar to harvest cooperatives. Sectors represented a significant shift from previous management approaches reliant on limits to days at sea and other input controls. Given the potential for significant social and economic effects of catch shares and other management programs, social and economic performance measures were developed from 2009 to 2010 by Northeast Fisheries Science Center (NEFSC) social scientists. Previous social and economic monitoring of management outcomes had been ad hoc and provided minimal opportunity for inter-fishery comparison. This paper describes the process of identifying performance measures and associated indicators to serve as the foundation of monitoring social and economic outcomes for all federal fisheries in the U.S. Northeast Region, and for planning NEFSC social and economic research priorities. It then presents how these performance measures were applied to assess the first year of the Amendment 16 Sector program. Challenges and limitations of this process are presented along with a description of efforts underway to broaden the use of these social and economic metrics to other fisheries.

The role of juveniles in structuring demersal assemblages in trawled fishing grounds

The capture of large amounts of small, immature fish of commercial species is a serious problem particularly in multispecies fisheries. Moreover, considerable and increasing interest is being devoted by fishery scientists to identify the distribution and habitat needs of species throughout their life cycle. To elucidate species composition, the abundance of juveniles in the demersal assemblages and the role of different life history (juvenile and adult) stages of target species in structuring demersal communities, two bottom trawl surveys were carried out during the autumn 2003 and 2004. Multivariate analyses were performed on density indices of adults and juveniles life stages of 30 target species and total density indices for the remainder of the catch species. Juveniles represent more than 61% of the total catch in both the years investigated and their abundance and spatial distribution was strictly related to the sea bottom biocoenotic features. Most juveniles were concentrated in the coastal shelf area and in particular in the hauls performed on the Coastal Terrigenous Mud biocoenosis (CTM). The demersal assemblages located in the slope stratum showed, in general, a lower concentration of juvenile specimens; however, some facies of the Bathyal Mud biocoenosis that characterizes the deep layer of our study area showed a very high percentage of juveniles. This information improves our understanding of ecosystem functioning and represents a useful basis for providing advice on the management of multispecies demersal fisheries within an ecosystem approach.

Sustainable Exploitation of Fish Stocks by Long-Term Profit Maximization with Special Regards to Cod in the Baltic Sea

An important aim of fishery management is the conservation and sustainable exploitation of fish stocks whereas maximization of profit is the aim of fishermen. At first view this seems to be contradictory. The main management tools for stock exploitation are fishing effort (summarizing all effort limitations) and the so called technical measures (mesh size). The presented new model, using these control variables, is intended to replace the Gordon Schaefer model and based on the Beverton and Holt yield-per-recruit model. The Beverton and Holt model, however, do not take into account the feedback of stock-size changes on recruitment and therefore also on yield. Overcoming this disadvantage is one finding in this paper. For the computation of optimal exploitation pattern the Shepherd approach for construction of sustainable yield curves was extended by incorporating the control of mesh size along with the current exclusive control of fishing effort. This extension turns all fishing mortality reference points into reference functions of the age at first capture. The sole economic important demersal stock in the western Baltic Sea is the cod stock of that area. This paper describes an equilibrium model for the computation of long-term harvesting strategies for that stock including the control of mesh size into the well-established exploitation models. It was shown that the stock is more reliably protected against collapsing by economic considerations rather than by measures chosen according to the precautionary approach. If the Baltic cod stock is exploited according to the suggested approach with an optimized, much larger mesh size in the steady-state, a larger profit is ensured simultaneously with improved stock conservation. This model can also be applied for the maximization of the overall profit within mixed-species management by overlaying the single-species results. Here, however, it is only possible to find an overall optimum which generally differs from the single species optimum. An economic reasonable limit of exploitation is given by the FMSY-curve – the fishing mortality resulting for a given age at first capture in the maximum yield for this age while the Fpa-curve according to precautionary approach has to be considered as the final line of defense against stock collapse. The precautionary approach only calls for changes in effort limitations or technical measures if a violation of its principles has occurred in a multi-species fishery due to ecological reasons. Apart from stock protection the main objective of this paper is to find at the same time appropriate values for the management control variables defining an equilibrium maximizing the profit (maximum economic yield – MEY) of the fishery.

Measuring fishery profitability: An index number approach

Tracking the financial well-being of vessels that depend on a marine fishery resource is an important function of regulators. This research demonstrates how simple indices can be constructed and utilized to track the economic well-being of vessels operating in the Northeast (USA) Multispecies (Groundfish) Fishery. The indices, which use both public and private data, can separately track trends in inputs, outputs, and prices. For the Northeast Multispecies Fishery, the indices reveal that the economic well-being of the groundfish fleet has improved under catch share management through gains in productivity.

On non-selective harvesting of a multispecies fishery incorporating partial closure for the populations

A prey–predator type fishery model incorporating partial closure for the populations is described in this paper. The proposed model deals with a problem of non-selective harvesting of a prey–predator system in which both the prey and the predator species obey logistic law of growth. The predator dependent Beddington DeAngelis type functional response is taken into consideration. Dynamic behavior of the system is analyzed. Partial closure for the populations is considered as a controlling instrument to regulate the harvesting of the populations. A dynamic framework towards the optimal utilization of the resource is developed using Pontryagin’s maximum principle. The optimal system is numerically solved using an iterative method with Runge–Kutta fourth order scheme. Simulation results show that the optimal control scheme can achieve sustainable ecosystem. Results are analyzed with the help of graphical illustrations.

Fishing the line: catch and effort distribution around the seasonal haddock (Melanogrammus aeglefinus) spawning closure on the Scotian Shelf

Permanent and seasonal area closures are a common regulatory strategy in multispecies fisheries; however, few studies have closely examined seasonal closures. We examined the impact of the Browns Bank spawning closure on the spatial distribution of fishing effort and how the fleet utilized a “fishing the line” strategy. Generalized estimating equations were used to examine changes in effort distribution when the closure was and was not in effect. Effort displaced from the bank concentrated primarily within two areas up to 30 km from the closure boundary, one along the east boundary line and one along the west. Trends in catch rate (as value) with distance from the line were further examined using generalized additive models during the closed period, with results differing between regions. In the east, areas of greater catch rate could be identified and typically corresponded to areas of greater effort, while in the west region, no trends in catch rates were often observed, potentially indicating vessel distributions that correspond to the ideal free distribution. Implementation of a seasonal area closure on Browns Bank resulted in concentrations of vessels near the closure boundary, suggestive of a fishing the line strategy, with specific catch rate trends depending on vessel spatial distributions and target species.

Managing interacting species in unassessed fisheries

This paper addresses the management of multispecies fisheries, and suggests the use of restricted fishing policies as an interesting option for unassessed fisheries (as is the case within developing countries). Specifically, we consider a predator–prey system under two potential management policies: an unrestricted regime where agents can compete to harvest from both species, and a second one where they are allowed to harvest only predators. The performance of both policies is compared from an ecological and an economic point of view. For a sufficiently large number of agents (or for strong biological interaction parameters) the assumed restricted fishing policy yields both higher long run stock levels and profits. Thus, this contribution suggests that such a policy, while requiring weaker monitoring/governance than instruments based on outputs (such as quotas or taxes), would meet environmental and economic objectives. Finally, several features of the analysis are discussed, including targeting prey instead of predator and the issue of compliance.

Marine turtle harvest in a mixed small-scale fishery: Evidence for revised management measures

Small-scale fisheries (SSF) account for around half of the world's marine and inland fisheries, but their impact on the marine environment is usually under-estimated owing to difficulties in monitoring and regulation. Successful management of mixed SSF requires holistic approaches that sustainably exploit target species, consider non-target species and maintain fisher livelihoods. For two years, we studied the marine turtle fishery in the Turks and Caicos Islands (TCI) in the Wider Caribbean Region, where the main export fisheries are queen conch (Strombus gigas) and the spiny lobster (Panulirus argus); with fin-fish, green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) taken for domestic consumption. We evaluate the turtle harvest in relation to the other fisheries and recommend legislation and management alternatives. We demonstrate the connectivity between multi-species fisheries and artisanal turtle capture: with increasing lobster catch-per-unit-effort (CPUE), hawksbill catch increased whilst green turtle catch decreased. With increasing conch CPUE, hawksbill catch declined and there was no demonstrable effect on green turtle catch. We estimate 176–324 green and 114–277 hawksbill turtles are harvested annually in TCI: the largest documented legal hawksbill fishery in the western Atlantic. Of particular concern is the capture of adult turtles. Current legislation focuses take on larger individuals that are key to population maintenance. Considering these data we recommend the introduction of maximum size limits for both species and a closed season on hawksbill take during the lobster fishing season. Our results highlight the need to manage turtles as part of a broader approach to SSF management.

Estimation of multi-output production functions in commercial fisheries

Measuring the productivity of vessels in a multi-species fishery can be problematic. Typical regression techniques are not capable of handling multiple outputs while Data Envelopment Analysis (DEA) tends to ignore the stochastic nature of production. Applied economists have devoted considerable time to this problem and have developed several methods of dealing with the issue of multiple output technologies in commercial fisheries. Our paper contributes to this literature by providing another method for estimating production functions of vessels operating in multi-species fisheries. We utilize a two-stage model – with data from the West Coast Limited Entry Groundfish Trawl Fishery – using DEA to aggregate output in the first stage. This aggregate index is then used as the dependent variable in a regression framework, allowing for the estimation of the return to different inputs in fisheries production. This provides information that may be particularly important for fisheries managers.

New SNPs for population genetic analysis reveal possible cryptic speciation of eastern Australian sea mullet (Mugil cephalus)

Sustainable management of sea mullet (Mugil cephalus) fisheries needs to account for recent observations of regional-scale differentiation. Population genetic analysis is sought to assess the situation of this ecologically and economically important fish species in eastern Australian waters. Here, we report (i) new population genetic markers [single nucleotide polymorphisms (SNPs) and potential microsatellites], (ii) first estimates of spatial genetic differentiation and (iii) prospective power tests for designing more comprehensive studies. Six DNA samples from three sampling regions (North Queensland, South Queensland and central New South Wales) on the eastern coast of Australia were used to prepare restriction site associated DNA (RAD) tag libraries from genomic DNA digested with EcoRI and MseI. A pooled sample of regional RAD tag libraries was sequenced using the Roche GS-FLX Titanium platform. A total of 172,837 raw reads (17.4 Mbp) were retrieved, 95,500 of which were used to discover 1267 SNPs and 1417 microsatellites. A subset of 161 SNPs was validated based on 63 additional DNA samples genotyped using the Sequenom MassArray (iPLEX Gold chemistry). Altogether 92 SNPs (57%) were confirmed, with 40% of these marking fixed variants between northern and southern sampling regions. Our preliminary findings indicate a multispecies fishery stock of M. cephalus in eastern Australian waters, but suggest that strong genetic differentiation occurs north of major fishing grounds. Low potential differentiation within major fishing grounds (e.g. FST = 0.0025) can be resolved with a likely power ≥67% by using standard sample sizes of 50 and validated subsets of available markers.

Rights-based management in the Western and Central Pacific Ocean tuna fishery: Economic and environmental change under the Vessel Day Scheme

Defining, strengthening and enforcing rights over fisheries resources is frequently identified as central to overcoming ‘the tragedy of the commons’ and associated environmental and economic challenges in fisheries systems. Though economic theory generally suggests that output control (e.g. quotas) creates the strongest incentives for efficiency and conservation, input controls (e.g. on effort) remain common. This paper explores the rationale for, and implications of, employing a transferable effort scheme in one of the largest and most valuable fisheries. In 2007, eight Pacific Island countries implemented the Vessel Day Scheme with the aims of strengthening their rights over tuna resources and control over economic and environmental trends. Four years since implementation, the scheme has significantly increased economic returns for the island states and generated improvements in data reporting. However, it has not generated a firm limit on fishing effort and its structure has made it difficult to directly target the biological concerns of individual species within the multi-species fishery. In the future, outcomes of the Vessel Day Scheme will continue to be tempered by the structural limitations of effort-based regulatory scheme, market conditions in the sector and the willingness of firms and island states to clarify, abide by and enforce the technical components of the scheme.

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

AbstractWe 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.

An ecosystem modelling framework for incorporating climate regime shifts into fisheries management

Ecosystem-based approaches to fisheries management (EBM) attempt to account for fishing, climate variability and species interactions when formulating fisheries management advice. Ecosystem models that investigate the combined effects of ecological processes are vital to support the implementation of EBM by assessing the effectiveness of management strategies in an ecosystem context. In this study, an individual-based ecosystem model was used to demonstrate how species at different trophic levels and of different life histories responded to climate regimes and how well different single- or various multi-species fisheries at different intensities perform in terms of human benefits (yield) and trade-offs (fishery closures) as well as their impacts on the ecosystem. In addition, other performance indicators were also used to evaluate management strategies. The simulations indicated that under no fishing, each species responded to the regimes differently due to different life history traits and different trophic interactions. Fishing at the level of natural mortality (F=M) produced the highest yields within each fishery, however, an F adjusted for the current productivity conditions (regime) resulted in much fewer fishery closures compared with F=M, indicating the advantage of implementing a policy of a regime-specific F from the stand point of conservation and fishery stability. Furthermore, a regime-specific F strategy generally resulted in higher yield and fewer fishery closures compared with F=0.5M. Other performance indicators also pointed to the advantage of using a regime-specific F strategy in terms of the stability of both ecosystem and fishery production. As a specific example, fishing the predators of Pacific herring under all multi-species fisheries scenarios increased the yield of Pacific herring and reduced the number of herring fishery closures. This supports the conclusion that an exploitation strategy which is balanced across all trophic levels produces better outcomes, as advocated by other researchers.

Comparative biology of tropical Lethrinus species (Lethrinidae): challenges for multi‐species management

Life-history characteristics of six tropical Lethrinus species sampled from the Great Barrier Reef World Heritage Area were compared. Two species groups were identified based on fork length (LF ): large species with maximum LF > 640 mm (longface emperor Lethrinus olivaceus, yellowlip emperor Lethrinus xanthochilus and spangled emperor Lethrinus nebulosus) and small species with maximum LF < 480 mm (Pacific yellowtail emperor Lethrinus atkinsoni, pink ear emperor Lethrinus lentjan and ornate emperor Lethrinus ornatus). Lifespan was not correlated with LF . Early growth for all species was rapid and similar during the first few years of life, but coefficients of the von Bertalanffy growth function varied considerably among species. Growth also differed between sexes for L. atkinsoni. Reproductive characteristics varied among species, with peak periods of spawning occurring in November to December for L. atkinsoni, July to August for L. nebulous, September to October for L. olivaceus and a protracted season for L. lentjan, although fewer samples were available for the last two species. Sex-specific LF and age distributions and gonad histology of L. lentjan were suggestive of a functional protogynous reproductive pattern, as observed in other lethrinids. Gonad histology indicated non-functional protogynous hermaphroditism for L. atkinsoni and L. nebulosus. The diversity of life histories among these closely related species emphasizes the difficulty in devising single management strategies appropriate for multi-species fisheries and illustrates the importance of understanding species-specific life histories to infer responses to exploitation.

An analysis of fishing gear competition. Catalan fisheries as case studies

An asymmetric index was developed to measure the competition relationships among fishing fleets (or gears or metiers ) in a multispecies fishery. This index can be used to measure the degree of dominance of each fleet and its level of independence from competition. To illustrate the concepts, the index is applied to two case studies using two datasets, both from Catalonia, NW Mediterranean. The results show that in both case studies the dominance of bottom trawl over most other gears (especially small-scale ones) is evidenced and quantitatively measured. Bottom trawl is also highly independent of the others. Purse seine appears to be quite independent, but not dominant over the other gears. A practical use of these asymmetric indices is to assist fisheries managers in the decision-making process to optimize the allocation of fishing effort, including energy efficiency, and to reduce environmental impact.

Impacts of Drought, Flow Regime, and Fishing on the Fish Assemblage in Southern Australia’s Largest Temperate Estuary

We analysed a 25-year time series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses that under conditions of reduced freshwater inflows and high fishing pressure: (1) the structure of fish assemblages in the lower Murray River system have changed, (2) species diversity of fishes has declined and (3) population age structures of large-bodied, late-maturing, native fish (Macquaria ambigua, Argyrosomus japonicus, Rhombosolea tapirina and Acanthopagrus butcheri) have been reduced. Annual catches and effort in the lower Murray River system were stable for 25 years, but proportional contribution to the total catch from each of freshwater, estuarine and adjacent marine habitats, and the species within them varied. Fish assemblages generally differed between subsequent 5-year periods, with the exception of 1989–1993 when floods occurred in 4 out of 5 years, and the following 5-year period (1994–1998). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H 2) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches, whilst species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species: golden perch (M. ambigua), black bream (A. butcheri), mulloway (A. japonicus) and a fourth species with an intermediate strategy, greenback flounder (R. tapirina). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand or recover from deteriorated environmental conditions associated with a historically extreme drought in the lower Murray River system. Management of these species should seek to preserve the remnant population age structures and then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries in changeable environments, such as occur in estuaries and other end-river environments, requires a suite of indicators that address changes in fish assemblages and populations.

Empirical move‐on rules to inform fishing strategies: aNewEngland case study

AbstractIncreasingly, fisheries are being managed under catch quotas that are often further allocated to specific permit holders or sectors. At the same time, serious consideration is being given to the effects of discards on the health of target and non‐target species. Some quota systems have incorporated discard reduction as an objective by counting discards (including unmarketable fish) against the overall quota. The potential effect of the introduction of a quota system that includes accountability for discards on the fishing strategies employed by fishermen is enormous. This is particularly true for multispecies fisheries where healthy and depleted stocks co‐exist; resulting in a trip's catch being applied to very large and very small stock quotas simultaneously. Under such a scenario, fishermen have a strong incentive to minimize (i) catch of low‐quota or ‘choke’ stocks, (ii) regulatory discards due to minimum size limits and (iii) catch partially consumed by predators. ‘Move‐on’ rules (i.e. event‐triggered, targeted, temporary closure of part of a fishery when a catch or bycatch threshold is reached) have been employed in a variety of fisheries. However, their efficacy has been limited by a lack of empirical analyses underpinning the rules. Here, we examine the utility of spatiotemporal autocorrelation analyses to inform ‘move‐on’ rules to assist a sector of theNewEnglandMultispeciesFishery to reduce discards and maximize profits. We find the use of empirical move‐on rules could reduce catch of juvenile and choke stocks between 27 and 33%, and depredation events between 41 and 54%.

Fish Assemblages in the Degraded Mangrove Ecosystems of the Coastal Zone, Benin, West Africa: Implications for Ecosystem Restoration and Resources Conservation

Mangrove forests are unique habitats in their function as potential food source and nurseries, and support an important fisheries resource. In the Benin coastal zone, the mangrove fishes have been surveyed to investigate fish species diversity, community structures and ecosystem degradation impacts in order to protect and to improve the mangrove fish resources. Results from wet, high-water and dry season samplings revealed that the two dominant mangrove species, Rizophora racemosa and Avicennia africana, are being intensively degraded for domestic use such as firewood and house building. Fifty one (51) fish species belonging to 25 families were recorded with Eleotridae (7 species), Cichlidae (5 species), and Mugilidae (5 species), the most speciose families. Dominant trophic guilds were detritivores (54.57%) and planktinovores/microcarnivores (30.41%). Six (6) species, Sarotherodon melanotheron, Dormitator lebretonis, Gerres melanopterus, Hemichromis fasciatus, Ethmalosa fimbriata, and Aplocheilichthys spilauchen, dominated the samples and accounted for about 80.27%. Sarotherodon melanotheron constituted the major dominant species and accounted numerically for about 29% of the total catches and 46.7% of the total biomass. The Margalef index of species richness ranged between 2.42 and 4.43, the Shannon-Weaver index of species diversity between 1.39 and 2.27, and the evenness between 0.50 and 0.62. Lower indices were observed for the highly degraded and the moderately degraded sites whereas higher indices were recorded for the less degraded and the restored sites. Species richness, species diversity and dominant species abundance were positively correlated with depth and transparency and negatively correlated with temperature. Multi-species fisheries dominate the coastal zone with Sarotherodon melanotheron, Dormitator lebretonis, Gerres melanopterus, Ethmalosa fimbriata, Liza falcipinus, Mugil sp. and Chrysichthys nigrodigitatus, the major species in the commercial catches. In addition to the mangrove destruction, the hydro electrical dam have greatly modified the Mono River flooding regime, water quality and the fish composition of the Benin coastal lagoon system. An integrated approach of the mangrove resource management/conservation, including intensive mangrove restoration, management of key fish species, freshwater prawns (Macrobrachiun sp.), peneids shrimps, mangrove oysters (Crassostrea sp.), and crabs (Callinectes sp., Cardiosoma sp.), and habitat protection is required for ecosystem recovery and sustainable exploitation.