Parasites can have strong effects on invertebrate host behaviour, fecundity and survival in marine ecosystems. However, parasites are often poorly documented and still rarely integrated into marine ecological modelling; comprehensive surveys of infection in marine invertebrates are sporadic at best. For example, rock crabs are an important part of Californian coastal ecosystems, both as regulators of mussel populations and non-native species, and as prey items for predators like sea otters, but their parasite communities and potential effects on crab population dynamics are seldom studied or understood. Here, we present the first report of infection by the trematode Helicometrina nimia in the economically and ecologically important red rock crab (Cancer productus) and Pacific rock crab (Romaleon antennarium). As intermediate hosts, they are a missing link for infection by H. nimia in Californian fish that was unreported until now. Based on these findings, we advocate for further research into parasite diversity and their potential effects on ecologically and commercially important species.

The objective of this paper is to illustrate that economic institutions matter, i.e., that different rules of trade present different incentives for bidding, asking, and trading in new markets, and that these different incentives lead to different price discovery patterns, which yield materially different outcomes. In a laboratory tradable fishing allowance system, when trade takes place through a double auction, which parallels an institution common in extant tradable allowance systems, markets are characterized by high volatility, and equilibrium does not obtain. However, when only leases, and not permanent trades, are permitted in the early periods, volatility is significantly reduced and equilibrium obtains. This dependence of equilibration and outcomes on institutions implies policy-oriented economists must consider institutions in designing new market-based management systems.

Ucides cordatus is a semi-terrestrial crab and key species endemic to mangrove areas of eastern Americas. In North-eastern Brazil this crab holds a major socio-economic function for artisanal fisheries, as in the São Francisco River Estuary (10°30′27″S 36°23′45″W). Nevertheless, decreases in this species’ stock have been reported since 2000, requiring assessments of the crab population for conservation and management purposes. This study aims at assessing the population status and the fishery potential of this species in the mangroves of this estuary and suggests strategies for its fishery and conservation, according to the guidelines of the National Management Plan for U. cordatus Sustainable Use. Six different sites established in 30 km2 of mangroves were sampled, with the density of U. cordatus burrows estimated to evaluate the population structure using the measure of burrow diameters. Results show that the crab mean burrow size was 56.82 (±12.2) mm and that the medium-size crabs (40–70 mm) are the most abundant. The total mean crab density was 1.2 crabs m−2, from which the density of crabs in commercial size (0.85 ± 0.55 crabs m−2) was significantly higher than those in non-commercial size (0.35 ± 0.21 burrow m−2). These mangroves showed a high potential for the crab fishery, with an immediate extractive potential (IEP) of 71.2% and future extractive potential (FEP) of 28.8%. Nevertheless, a lower crab density, probably due to high crab mortality, mangrove deforestation for shrimp farming and high fishery pressure, is a limiting factor for local fishery. We conclude that mangrove areas more appropriate for U. cordatus fishery (extractive areas) show higher mean crab size, IEP and density of commercial crabs, wherein a fixed exploitation rate or/and a fixed escapement rule should be considered. Exclusion areas, intended for the conservation, show lower values of these population parameters and higher FEP, wherein the fishery should be prohibited. These management strategies should also be considered in other Brazilian mangrove areas showing similar crab population structure, thus contributing to the National Management Plan for U. cordatus Sustainable Use.

The benefits of implementing no-take Marine Protected Areas (MPAs) for the conservationof highly migratory species are not easy to assess. They depend on several factors, suchas the fish mobility, fisher behaviour and the area covered by the MPA with respect to thedistribution area of the species to protect. In this study, we explore the simultaneouseffects of MPAs and fishing scenarios on skipjack tuna population dynamics, using thespatially-explicit APECOSM-E model. The model represents the size-structured populationdynamics of skipjack tuna in the Indian Ocean and their dependence on climatic variabilityand exploitation by fisheries. Numerical experiments were run from the beginning ofindustrial fisheries in the early 1980s to the year 2030, considering different scenariosfor the future development of fisheries. These scenarios combined different trends infishing effort and technological development, either assuming a continuous increasefollowing historical trends or a stabilization of these factors at present values. Thesimulations were designed to explore the effects of two MPAs of different size andlocation: the recently established Chagos MPA, and a hypothetical MPA covering a largepart of the Western Indian Ocean, where most of the skipjack catches are presently made.We modelled the redistribution of fishing effort around the MPAs assuming that the fishershad partial knowledge of the spatial distribution of the skipjack population. The effectsof the two MPAs on the population dynamics, catch and fishing mortality are shown. Ourresults revealed a very minor effect of the Chagos MPA on the skipjack tuna population,while the Western Indian Ocean MPA had an important impact on the fishing mortality andsucceeded in stabilizing the spawning population. The simulations also showed that theeffect of an MPA depends on the evolution of fisheries and it is therefore important toexplore different fishery scenarios to assess the future benefits of an MPA.

Bycatch in longline fisheries is considered one of the main threats for the conservationof albatrosses and petrels worldwide. However, the relative impact of fisheries on all theaffected populations or species still remains poorly understood. This paper applied aProductivity and Susceptibility Analysis (PSA) and the concept of “Potential BiologicalRemoval Level” (PBR) to assess the relative impact caused by the Uruguayan pelagiclongline fishery on several populations. This two-step approach allowed us to obtain anobjective view of the relative impact of the Uruguayan pelagic longline fleet on most ofthe populations or species of albatrosses and petrels with high association with thisfishery. Of fifteen species considered, fourteen were finally assessed and a ranking ofrisk derived. The concept of PBR was applied to the nine most at-risk species. The impactof fishing on populations could not be straightforwardly inferred from their bycatchrates. Results indicate that large albatrosses (Diomedea spp.) andThalassarche chlororhynchos are more affected than some of the mainspecies caught by the fishery (i.e. Thalassarche melanophrys andProcellaria aequinoctialis). Diomedea exulans fromSouth Georgia is likely to be the population most affected by the Uruguayan fleet. Thiswork should be seen as a case study of the fisheries operating in the southwesternAtlantic. The Uruguayan fleet within its operation area was responsible for only the 4.3%to 12.5% of the total annual effort deployed by the different fleets during 2004–2008. Thecombined impact of these fleets could be sufficiently high to account for many of theobserved declines in the populations of D. exulans, D. dabbenenaand T. chlororhynchos. However, the seabird bycatch numbers formost of the pelagic longline fleets that operate in the southwest Atlantic remain unknown.Applying mitigation measures to reduce the impact of pelagic longline fleets operating inthis region should be considered a high priority.

The Chilean jack mackerel (Trachurus murphyi) is one of the mostimportant exploited fish populations in the world. Its area of distribution covers thesub-tropical waters of the South Pacific Ocean, from South America up to New Zealand andeven Australia. It is subject to high variations in biomass, with annual world catchesvarying from less than 0.5 to almost 5 million tonnes. Management of this species and itsfishery requires a correct understanding of the population structure. Although severalhypotheses have been proposed, suggesting that there are up to four independentpopulations, genetic analysis indicates only a single population in the South PacificOcean. We consider the two most probable structures for this population: a “patchypopulation”, where all the fish belong to a single population that expands and contractsdepending on the biomass; and a metapopulation, where a source population creates severalsubpopulations that can remain independent during prolonged periods, depending on theenvironmental conditions. We studied the conditions for these hypotheses to representreality, especially the demographic structure and existence of different spawning areas.Using knowledge obtained from fisheries and acoustic surveys, we show that if we applytheir definitions strictly, neither of the two hypotheses can be fully rejected.Nevertheless, some particular spatial characteristics observed recently between thePeruvian and Centre-South Chilean parts of the distribution lead us to conclude that themetapopulation definition is likely to better describe the stock. The consequences of eachpopulation structure for fisheries management are listed, showing that the metapopulationhypothesis represents a safer definition for stock assessment. We conclude that T.murphyi can be described as a metapopulation, but also that the definitionsproposed in the literature on metapopulations are not fully adapted to pelagic fishpopulations with a basin-scale distribution range, and suggests specific research thatcould be done in this field.

Simulation of fisheries systems is a widely used approach that integrates monitoring and assessment tools. We applied the ALADYM (age-length based dynamic model) simulation model to three different studies aimed at investigating correlations between pressure and population metrics, exploring the viability of different mortality levels in long-term scenarios and predicting the effects of combined management measures. Uncertainty was incorporated into the simulations following the Monte Carlo paradigm. Three stocks were used for these exercises: red mullet in the central-southern Tyrrhenian Sea and European hake in both the Bay of Biscay and the Aegean Sea. The analysis of the relationships between total mortality and indicators highlighted significant pairwise negative correlations for red mullet. These signals of decline were supported by the spawning potential ratio indicator (mean exploited to mean unexploited spawning-stock biomass ESSB/USSB), which was low compared to target levels. It only remained within safe bounds (>0.2; probability: 0.90–0.95) at total mortality levels lower than 1.6. The simulation results for European hake in the Bay of Biscay showed that a sustainable exploitation rate might range from 0.87 to 1.04. The benefits of combined management measures were demonstrated for European hake in the Aegean Sea, and with a further dataset on the Eastern cod stock in the Baltic Sea.

Many factors influence the dynamics of fisheries and feedback mechanisms amongst these factors are poorly understood. The ecological systems are too large and complex to conduct controlled experiments and economic adjustments to changes in fish populations defy traditional equilibrium analysis. New modelling approaches are required to identify the driving forces behind the dynamics of exploited fish populations, assess likely consequences of alternative management measures, and achieve consensus among stakeholders.

We present an interdisciplinary modelling approach that can be used easily to assess dynamic consequences of alternative assumptions for certain key biological and economic parameters, and incorporates the input of various stakeholder groups in the fishery. Contributions of scientists, economists and managers to the model can be augmented with contributions from the fisherfolk.

Our approach is illustrated by a dynamic computer model capturing the interactions of three demersal fish species on Georges Bank, namely Atlantic Cod (Gadus morhua), Haddock (Melanogramus aeglefimts) and Pollack (Pollachius virens), population sizes of which are assumed to be density-dependent for the purposes of the model and are significantly affected by management decisions. The model addresses how management measures for one species influence the population dynamics of other commercially exploited species. Various scenarios are run to explore the implications of viable management strategies under alternative assumptions on the driving forces behind complex ecological-economic processes. The analyses indicate that neither small reductions in effort nor mesh size increases are likely to prevent the further demise of the Georges Bank ground fisheries, and, in fact, stocks of the three targeted species may decline. Alternative management measures seem to be necessary to prevent collapse, and might include various strategies, such as effort controls and mesh size reductions, in conjunction with a dramatic change in fishing technology. The assessment and viability of alternative management measures in turn require that consensus is generated among stakeholders about data and models.

Consideration of control rules as part of fisheries management plans is becoming a common practice. Control rules may be simple or complex and utilise model- or observation-based indicators of the status of the stock to control exploitation through limitation of effort or catches. Rules that control harvest (HCR) often utilize commercial fishery data in the calculation of future catches. However, commercial fishery data may be inaccurate and that can compromise the effectiveness of the HCR in maintaining the stock for secure future harvesting. The idea of fishery-independent HCR has arisen because of these problems. Indicators of the status of a stock are derived from standardised fish surveys, commonly trawl surveys repeated annually. A management strategy that relies on such information also requires adoption of appropriate and effective control rules that utilise such information. Here, we draw attention to diverse HCR, including fishery-dependent examples that have been considered, tested or already adopted for fisheries management. Our intention is to stimulate ideas for HCR that are usable with, or adaptable to fishery-independent indicators.

ALADYM (age-length based dynamic model) is an age-length based simulation model designed to predict the consequences of management scenarios on a single population, in terms of different metrics and indicators. Removals are simulated as total mortality modulated using a selectivity pattern and a fishing activity coefficient. ALADYM uses the classical equations of population dynamics to create a tool that uses fishery-independent information (e.g. from trawl surveys) as the primary source. The formulation of population dynamics at a small time scale (month) allows to model the effects of harvest controls that evolve through the year, which is particularly useful for fast growing species. The possibility of specifying a vector of natural mortality by age/length makes the model more suitable for situations where stocks are exploited at an early life stage, as in many Mediterranean fisheries, while introducing variations along the time of the harvesting pattern accounts for non-equilibrium situations. Stochastic effects can be added to some key life-history traits to incorporate uncertainty in input parameters and in their relationships. ALADYM can be used for a range of applications such as comparing management strategies, evaluating indicator changes or searching for reference points.

We present a simulation bioeconomic model based on an age-structured population biological sub-model and an economic sub-model with vessel-specific dynamics, applied to two red shrimp (Aristeus antennatus) stocks in the NW Mediterranean. The model is dynamic, the economic sub-model is disaggregated at the level of vessel and the two sub-models are linked by means of a fishing mortality vector. We analyzed the projection of selected indicators (catches, overall profits, fishing mortality and spawning stock biomass) for the target species of the deep-water trawl fishery in the NW Mediterranean, red shrimp. We built three alternative management scenarios based on input control and we examined the performance of these management strategies against the current management policies. The three alternative management strategies were: i) increase the cost of effort by eliminating the fuel tax exemption currently in place, ii) limit the nominal effort level (days at sea) to current levels, in order to offset the increasing trend observed in the last decade, and iii) change the selectivity patterns of the trawl by increasing mesh size. Our results show that for the two stocks analyzed, any of the three management measures (input controls) would be beneficial both to the stock and the fleets (over the medium and long terms) when compared with the projections over time of the statusquo. Improving the selectivity of the fishing gear is more beneficial than limiting nominal effort or increasing the cost of effort. Comparing the performance of the management strategies on two stocks, one heavily fished and the other moderately so, we show that none of these management measures is able to substantially redress the situation of a heavily fished stock, implying that for the full recovery of heavily fished red shrimp stocks, we need to contemplate even stricter measures of management.

Understanding the incentives influencing the attitudes and behaviour of resource users is a crucial input to the design of institutions for resource management. Typically fishers have been expected to exploit resources in an independent profit-maximizing manner, which is in line with common property theory, although these expectations are not always met because fishers' behaviours and attitudes are generally more heterogeneous than previously considered. Attitudinal differences between participants in the inshore commercial fishery of Wales, UK, were investigated. Semi-structured face-to-face interviews were conducted with 161 fishers from the five main sectors, namely mobile gear fishers, crustacean potters, whelk potters, line/net fishers and transient fishers. Unprompted expressions of attitudes and responses to open-ended questions underwent thematic-coding and were analysed with fishers' responses to structured questions. Investigation into whether the incentive to participate in resource stewardship varied between sectors as predicted by common property theory found attitudinal similarities across the sectors, but also certain important differences. Results suggested an attitudinal continuum, with mobile gear fishers and crustacean potters at the two extremes, and intermediate positions occupied by transient fishers, whelk potters and line/net fishers. Mobile gear fishers believed most strongly that their fishery was controlled too tightly and was impacted by other fishers and other anthropogenic influences. Crustacean potters believed most strongly that conservation of stocks was necessary and that minimum landing sizes were not overcautious. The attitudes that characterized each sector were related to the characteristics of the sector and its resource base, and generally concurred with theoretical predictions. In particular, target species' mobility and past sector experiences predicted the inclination of fishers in each sector towards resource stewardship. The observed attitudinal differences implied varying personal discount rates that may affect how respondents respond to and comply with management tools. Furthermore, attitudinal differences among sectors mean that an effective management tool in one sector may be inappropriate or counterproductive in another.

The management of fisheries in European Union (EU) waters has generally been regulated through government institutions and agreed quota allocations. This top-down management approach may have contributed to the continued decline of targeted fish stocks by forcing fishers to compete for limited resources without engendering a sense of resource stewardship. In attempting to reverse this decline, scientists and managers should examine management systems that do not solely depend on top-down approaches, and the Inshore Potting Agreement (IPA) is an example. The IPA is a voluntary fishery management system designed and operated by inshore fishers of south Devon, England. The IPA was conceived to reduce conflict between static-gear (pot and net) and towed-gear (trawl and dredge) fishers, and is regarded as a successful fisheries management regime by fishers and managers because it has effectively allowed fishers from both sectors to operate profitably on traditional fishing grounds. Another study determined that the IPA has incidentally protected benthic habitat complexity. Fishers from the static-gear and towed-gear sectors were interviewed to determine the evolution and function of the IPA, and to establish the factors that ensure the high level of regulatory compliance amongst fishers from both sectors. Towed-gear fishers gave significantly different responses to the same questions asked of static-gear fishers, and were generally less satisfied with the existence of the IPA. Multivariate analyses of the interview data suggested that fishers who thought the IPA was a good system also thought the system provided pot protection, but had experienced inter-sector conflict. Fishers who thought the IPA provided no personal benefit also thought that static-gear fishers should be more restricted, and that towed-gear corridors or more seasonal-use areas should be established within the existing IPA area. However, fishers from both sectors agreed that the IPA has maintained traditional practices of the local fishing industry, and that the system has conserved target finfish and scallop species. A number of factors were identified as critical to the success of the IPA. These included the voluntary nature of the agreement, the limited number of organizations representing fishers and very high level of membership of those organizations, and the simplicity of the system. Regulatory compliance is enhanced through the ability of fishers' organizations to respond rapidly to inter-sector conflict issues.

An advection diffusion reaction model was used to estimate movement and tag attrition parameters from skipjack tuna tagging data off the Maldives. Two sets of data were available from the experiments carried out during two distinct periods: 1990–1991 and 1993–1995. The results of the analysis were compared with the previous analyses and discussed in relation to management of skipjack fisheries in the Maldives and in the Indian Ocean. The movements were found to be highly variable in space and time, and few consistent patterns were observed between the two data sets. Similarly, significantly different estimates of fishing and natural mortality rates were observed from the two data sets. These differences were found, in part, to be due to the uneven distribution of tag releases in both space and time. Estimates of movement and attrition rates show that emigration from the Maldivian fishery to the rest of the Indian Ocean’s was small. The exploitation rate was found to be substantial, contributing about 30-40% of the total attrition in the fishery area. Such levels of localized exploitation may be maintained by steady immigration from outside of the Maldives, but more extensive tagging is required to be certain. The impact of tuna fisheries elsewhere in the Indian Ocean on the domestic Maldivian fishery cannot be determined until a comprehensive large-scale tagging program, including all the fisheries in the Indian Ocean, is completed.

The present paper suggests a method for estimating the fishing power of vessels and for analysing fleet dynamics. The approach is based on quantification of stocks catchability (q), derived from fishing mortality coefficients (F) as calculated by virtual population analysis. Catchabilities for each harvested stock are thus estimated relatively to the fishing effort (fn) of each vessel, according to the equation: q = (F/fn). A linear model is then fitted to these catchabilities. The model allows the identification and quantification of trends in average mortality rates per fishing hour for each stock. Under some assumptions, trends are interpreted as variations in the overall fishing power of each fleet. The approach is applied to three industrial and semi-industrial fleets of Brittany (Lorient, Concarneau and Douarnenez) and to the main gadoid stocks they exploit off the west coast of Scotland (ICES area VIa), and in the Celtic Sea (ICES area VIIf,g,h) for Concarneau. Results show large variations in fishing power. Particularly, a marked increase trend in the fishing power exerted on saithe (Pollachius virens) is highlighted for the three fleets, over the period 1983-1989. These variations can be explained by the redirection of fishing strategies, which may occur on a large scale. Thus, we show how the collapse of saithe stock at first led the three fleets to intensify the harvesting of saithe, and from 1989 on, to adopt different strategies. The possible causes of the observed dynamics are discussed, as well as their consequences for fisheries management. In particular, the relevance of direct control of fishing effort as a regulatory tool is questioned.

An adaptation of the von Bertalanffy growth model is formulated to describe the phenotypic plasticity of fish somatic growth in relation to trophic conditions. The model is developed for the North sea Downs herring (Clupea harengus). It suggests that annual growth variability during 1974-1990 was mainly due to the combined effects of herring abundance and wind-induced turbulence (coincident with the spring stratification of the water column). Springtime turbulences cause reduced and delayed planktonic blooms preceding the annual foraging period of Downs herring. The negative relation observed between herring abundance and growth is hypothesized to be due to intra-specific competition for trophic resources. Incorporated into the calculation of yield per recruit, the established growth model provides slightly more optimistic diagnoses while dropping the classic assumption of constant weight at age.

Yield-per-recruit models are often used to provide management guidance for the efficient use of a fish cohort and to estimate the biological reference points, such as F0.1 or FMAX. Although model parameters are usually age-specific, these parameters are thought to be more likely related to length than age. In this study, age- and length-structured models are compared in calculating yield per recruit, F0.1, and FMAX at which the yield per recruit is maximized. Using a Monte Carlo simulation approach, I also compare differences in effects of uncertainties of the model parameters on yield-per-recruit analysis and estimation of F0.1, and FMAX using age- and length-structured models. This study shows that differences are small in estimating yield per recruit, F0.1, and FMAX using two types of models when there are no error variances in the model parameters. However, such differences increase with the uncertainties of the model parameters. The yield-per recruit, F0.1, and FMAX estimated using the age-structured model tend to have smaller values and variations compared with those estimated using the length-structured model. This study indicates that although the length-structured model can better incorporate the information observed from fisheries, age-structured yield-per-recruit model can provide estimates of yield per recruit, F0.1, and FMAX, more precisely and more conservatively, and thus is preferred from the conservation viewpoint in fisheries management.

In 1983, the European Community (EC) agreed on a system for the conservation and management offishery resources which is based largely on the use of annual total allowable catch (TAC). Nevertheless, the state of many European stocks of demersal species has worsened since 1983. A review of TAC enforcement shows that landings have exceeded TACs to a limited extent for these resources. The contrary is observed for the stocks of pelagic species of which the state has improved although landings have frequently been larger than TACs. This double paradox generates a feeling of limited impact of the TAC system implemented by the EC. To investigate the reasons, the closeness between agreed TACs and scientific recommendations has been examined. The results show that the TAC decision process gives some preference to stability but attention is paid to the scientific recommendations. Finally, the lack of accuracy of predicted changes of fishing mortality in catch forecasts is found to have played a critical part in the failure of TACs to avoid the deteriorations of resources observed in EC waters. It leads to the conclusion that evaluation of risks in the TAC decision process and participation of actors of the fishing sector in risk management are important matters that cannot be avoided if one wants to improve the legitimacy of fisheries management and therefore its efficiency.

Management techniques in two sea scallop Placopecten magellanicus fisheries in Nova Scotia are compared and contrasted. In one, traditional management methods are used to protect the stock from overexploitation. In the other fishery, enterprise allocations in the form of quota shares are used to mimic property rights. Over the past decade, the fleets' reactions to stock conditions have been dramatically different. It is argued that the evidence supports a quasi-property management regime, though other factors are at play as well.