Fishery Dynamics Research Articles

Influence of migrant Western Regional shark fishers on shark fishing practices along the eastern coastline of Ghana

Sharks have formed an integral part of Ghana’s fisheries for many years, although in many areas outside the Western Region, they are often captured as bycatch. The shark fishery in the Dangme communities along the eastern coastline of Ghana has, however, over the last decade, acquired a commercial character that is believed to have been influenced by migrant fishers from the Western Region. This study thus sought to characterise the influence of the migrant fishers in the development of the thriving shark fishery in Dangme communities. Data collection was through key informant interviews, questionnaire administration to 180 randomly selected native and migrant fishers from the selected communities, and observations of fishing practices. Until the mid-2000 s, only the migrant fishers carried out targeted shark fishing along the Dangme coastline. Presently, however, a significant number of native fishers have redirected their fishing efforts towards shark fishing in the face of dwindling catches from the small pelagic fisheries, which were the primary target of the fisheries. Accounts 75 % of native fishers indicated that the declines in small pelagic fish stocks coupled with the influence of the migrant shark fishers have acted synergistically to influence the shark fisheries dynamics along the Dangme coastline. Despite the average ages of the native and migrant fishers being fairly the same (∼36 years), the migrants possessed a more profound understanding of the marine ecosystem where they operated based on historical antecedents and their longer interactions with the shark fishing zones. Presently, this new fishery, like shark fishing in other shark fishing hotspots in Ghana, is unregulated, but it will be imperative for national fisheries authorities to implement some management measures to reduce fishing pressure on the most vulnerable species.

What are the factors that enable or hinder gender equality? Lessons and experiences on gender dynamics in Mexican small-scale fisheries

In Mexico, women participate along the fisheries value chain, although gender inequality limits their representation and participation in decision-making. This study aims to give account of the evolving participation of women in the different activities of the Mexican fishing sector and to determine how local gender dynamics can enhance or hinder gender equality. We aimed to identify conditions that might limit the participation of women and their access to resources in 22 coastal communities in 5 marine regions of Mexico. We followed a qualitative methodology conducted semi-structured interviews and daily life observations in each coastal community. Results indicate that gender dynamics varied by region, education level, and age group. Access to fisheries and economic resources depends on gender dynamics and resource availability. In communities with more fisheries resources, women participated in more activities related to the fishing sector, whereas women sought out different economic activities in communities with fewer resources. For women, joining the labor market was also highly related to increase household incomes to alleviate poverty. Different power dynamics were evident in four household management models identified in the communities, and in the ways older and newer cooperatives were managed. Power relations and gender dynamics also change the gender division of labor inside and outside of household, male superior power continues to be a predominant social structure. This power is not only conferred between men, but at times also supported by women.

Size-dependent thermal limits in Australian hybrid abalone: implications for productivity shifts with ocean warming

Ocean warming and extreme heatwaves threaten marine species supporting commercial fisheries and aquaculture. Predicting the responses of these industries to chronic and acute warming depends on understanding which life stages are most vulnerable, the potential for stocks to adapt to changing thermal environments, and the availability of thermally adapted genotypes to help enhance stock resilience through strategic interventions. Here, we shed light on some of these knowledge gaps by quantifying the critical thermal maximum (CTmax) of ~ 10–210 g hybrid abalone (Haliotis rubra × H. laevigata) from two farms representing contrasting thermal environments from south-eastern Australia. CTmax was not dependent on body size or provenance (farm) when heating rates were rapid (1 °C per h), but a significant relationship between CTmax and body size was observed when heating rates were slower and more ecologically realistic (1 °C per 12 h). Histological analyses revealed a negative relationship between CTmax and the stage of gonadal development when abalone were exposed to chronic thermal stress conditions. These results suggest that marine heatwaves and ongoing ocean warming might favour smaller, less fecund animals in natural and farm settings. This could potentially impact future harvestable biomass, recruitment and population dynamics in wild-capture fisheries, and production of larger, high-value animals in farm settings. This study adds to a growing body of literature pointing to complex and often negative effects of climate change on commercial fisheries, and the potential need for interventions aimed at bolstering fisheries resilience against the effects of ocean warming.

Shifts in the pelagic fishery dynamics in response to regional sea warming and fishing in the Northeastern Mediterranean

Shifts in the pelagic fishery dynamics in response to regional sea warming and fishing in the Northeastern Mediterranean

Assessing fish–fishery dynamics from a spatially explicit metapopulation perspective reveals winners and losers in fisheries management

Abstract Sustainable management of living resources must reconcile biodiversity conservation and socioeconomic viability of human activities. In the case of fisheries, sustainable management design is made challenging by the complex spatiotemporal interactions between fish and fisheries. We develop a comprehensive metapopulation framework integrating data on species life‐history traits, connectivity and habitat distribution to identify priority areas for fishing regulation and assess how management impacts are spatially distributed. We trial this approach on European hake fisheries in the north‐western Mediterranean, where we assess area‐based management scenarios in terms of stock status and fishery productivity to prioritize areas for protection. Model simulations show that local fishery closures have the potential to enhance both spawning stock biomass and landings on a regional scale compared to a status quo scenario, but that improving protection is easier than increasing productivity. Moreover, the interaction between metapopulation dynamics and the redistribution of fishing effort following local closures implies that benefits and drawbacks are heterogeneously distributed in space, the former being concentrated in the proximity of the protected site. A network analysis shows that priority areas for protection are those with the highest connectivity (as expressed by network metrics) if the objective is to improve the spawning stock, while no significant relationship emerges between connectivity and potential for increased landings. Synthesis and applications. Our framework provides a tool for (1) assessing area‐based management measures aimed at improving fisheries outcomes in terms of both conservation and socioeconomic viability and (2) describing the spatial distribution of costs and benefits, which can help guide effective management and gain stakeholder support. Adult dispersal remains the main source of uncertainty that needs to be investigated to effectively apply our model to fisheries regulation.

Effects of climate change and variability on large pelagic fish in the Northwest Atlantic Ocean: implications for improving climate resilient management for pelagic longline fisheries

Climate change influences marine environmental conditions and is projected to increase future environmental variability. In the North Atlantic, such changes will affect the behavior and spatiotemporal distributions of large pelagic fish species (i.e., tunas, billfishes, and sharks). Generally, studies on these species have focused on specific climate-induced changes in abiotic factors separately (e.g., water temperature) and on the projection of shifts in species abundance and distribution based on these changes. In this review, we consider the latest research on spatiotemporal effects of climate-induced environmental changes to HMS’ life history, ecology, physiology, distribution, and habitat selection, and describe how the complex interplay between climate-induced changes in biotic and abiotic factors, including fishing, drives changes in species productivity and distribution in the Northwest Atlantic. This information is used to provide a baseline for investigating implications for management of pelagic longline fisheries and to identify knowledge gaps in this region. Warmer, less oxygenated waters may result in higher post-release mortality in bycatch species. Changes in climate variability will likely continue to alter the dynamics of oceanographic processes regulating species behavior and distribution, as well as fishery dynamics, creating challenges for fishery management. Stock assessments need to account for climate-induced changes in species abundance through the integration of species-specific responses to climate variability. Climate-induced changes will likely result in misalignment between current spatial and temporal management measures and the spatiotemporal distribution of these species. Finally, changes in species interactions with fisheries will require focused research to develop best practices for adaptive fisheries management and species recovery.

Scientometric profiling of reservoir fisheries research in India during 1998 – 2019, in comparison to the global scenario

Reservoirs are major inland water resources benefitting society through multiple ecosystem services, including fish production. However, the scope of the reservoirs in India is yet to be explored for its full fisheries potential and the scientific/management personnel are engaged in bridging the yield gap. This paper reviews the research progress made in Indian reservoir fisheries from 1998 to 2019 as a case and compares with global studies using bibliometric indicators extracted from the Web of Science (WoS) database. A total of 7607 papers published globally, mainly by the USA (2662 papers), Brazil (874 papers), and People’s Republic China (678 papers) were considered. India produced 162 publications (2.13% of total papers) during the period mainly authored by research institutes of Indian Council of Agricultural Research (ICAR). The predominant research subjects both globally and in India were ‘Environmental Sciences, Ecology, Marine and Freshwater Biology, and Fisheries’, though the composition varies. The trend in the reservoir research output indicated a shift towards applied research such as spatial planning and cage culture which offers scope for the international scientific fraternity to collaborate with Indian counterparts to solve common researchable issues. Indian authors have collaborated with 29 countries on various researchable issues, and preferred Indian journals for publications. The reservoir research in India is mainly funded by public sources and the extent of work carried out on a particular geographical area depends on the nearness to laboratories and availability of the infrastructure. This study advocates that creation of research network at pan-India level in collaboration with international partners would benefit the reservoir fisheries research in the future. This analysis including the trend and dynamics of Indian reservoir fisheries portrayed as a case study would aid in prioritising research efforts for the development of the sector in India and elsewhere. Keywords: Bibliometric indicators, Collaboration, Reservoir fisheries, Scientometrics, Web of Science

Model‐based offline reinforcement learning for sustainable fishery management

AbstractFisheries, as indispensable natural resources for human, need to be managed with both short‐term economical benefits and long‐term sustainability in consideration. This has remained a challenge, because the population and catch dynamics of the fisheries are complex and noisy, while the data available is often scarce and only provides partial information on the dynamics. To address these challenges, we formulate the population and catch dynamics as a Partially Observable Markov Decision Process (POMDP), and propose a model‐based offline reinforcement learning approach to learn an optimal management policy. Our approach allows learning fishery management policies from possibly incomplete fishery data generated by a stochastic fishery system. This involves first learning a POMDP fishery model using a novel least squares approach, and then computing the optimal policy for the learned POMDP. The learned fishery dynamics model is useful for explaining the resulting policy's performance. We perform systematic and comprehensive simulation study to quantify the effects of stochasticity in fishery dynamics, proliferation rates, missing values in fishery data, dynamics model misspecification, and variability of effort (e.g., the number of boat days). When the effort is sufficiently variable and the noise is moderate, our method can produce a competitive policy that achieves 85% of the optimal value, even for the hardest case of noisy incomplete data and a misspecified model. Interestingly, the learned policies seem to be robust in the presence of model learning errors. However, non‐identifiability kicks in if there is insufficient variability in the effort level and the fishery system is stochastic. This often results in poor policies, highlighting the need for sufficiently informative data. We also provide a theoretical analysis on model misspecification and discuss the tendency of a Schaefer model to overfit compared with a Beverton–Holt model.

An ecological‐economic fishery model: Maximizing the societal benefit through an integrated approach of fishing and ecotourism

One of the essential tasks of the modern fishery is to integrate fishery‐based tourism with it as a part of sustainable development. Here, we propose and study a two‐species fishery model where the ecological and economic concepts are integrated. The objectives are to demonstrate the effect of fishing tax and tourist entrance fees to stabilize fishery dynamics and maximize revenue generation. For this, we consider a predator–prey fishery model coupled with dynamic harvesting and time‐dependent fish price variation. The prey fish is commercially harvested, and the predatory fish is used for recreation purposes of the visitors with an entry fee. A fishing tax is levied on the fishers to restrict the overfishing of this renewable resource. We provide the local and global stability conditions of different equilibrium points of the system and unveil the broader dynamics through bifurcation analysis. Pontryagin's maximum principle shows the existence of an optimal fishing tax that maximizes overall revenue generation.

Assembling the Right Pieces: Developing an Interdisciplinary Team to Study Disease, Decline, and Recovery of a World‐Class Smallmouth Bass Fishery

Managing and understanding fisheries dynamics are becoming more complex as new and seemingly more complicated environmental factors are identified. Often management requires resources beyond that of any one entity and calls for collaboration among partners with differing priorities and backgrounds to account for the complexity of factors influencing fisheries. We present a collaborative case study from the Susquehanna River basin, Pennsylvania, where Smallmouth Bass Micropterus dolomieu have faced population declines, mortality events, and notable signs of disease in recent years. Collaboration was required to study many facets of the fishery and the environment simultaneously to better understand risk factors and underlying relationships influencing Smallmouth Bass health. The outcomes from this interdisciplinary collaboration allowed for identification of contributing risk factors, led to the development of products and analytical techniques that were mutually beneficial to all partners involved, and provided knowledge that was integrated into fish health and fisheries management.

Bringing in the experts: application of industry knowledge to advance catch rate standardization for northern shortfin squid (Illex illecebrosus)

Sources of fisheries information outside of fishery-independent surveys (e.g. fishery-dependent data) are especially valuable for species that support productive fisheries and lack reliable biological information, such as the northern shortfin squid (Illex illecebrosus). Fishery-dependent data streams are available for most species, however collaboration with industry members is critical to ensure that these fishery-dependent data are collected, applied, and interpreted correctly. Despite the need for collaboration and the frequency that fishery data are used in scientific research, there is limited literature on the structure of interactions and knowledge sharing that inform the analysis and application of fishery data. Between 2019 and 2022, a group of researchers collaborated with members of the northern shortfin squid fishing industry to bring together research data sets and knowledge from harvesters and processors to better describe the fishery dynamics, distribution, life history, and oceanographic drivers of the species. The collaboration focused on developing custom standardized fishery catch per unit effort (CPUE) indices to provide indicators of population trends that accounted for the impacts of technical and economic aspects of harvesting, processing and marketing on fishing effort, selectivity and landings of northern shortfin squid. We describe the methods used to inform and interpret the CPUE analyses, focusing on novel structure of interactions we had with industry members, and suggest best practices for integrating industry knowledge into CPUE standardization. The information shared and research products produced through this science-industry research collaboration advanced understanding of northern shortfin squid population and fishery dynamics, and contributed directly to the 2022 stock assessment and management process. Given the complex and stochastic nature of the northern shortfin squid population and fishery, we found it critical to maintain open communication and trust with processors and harvesters, who have unique insight into the factors that may be driving changes in catch, landings, and productivity of the valuable resource species.

Using fishers’ local ecological knowledge for management of small-scale fisheries in data-poor regions: Comparing seasonal interview and field observation records in East Africa

Fishers, scientists and policy makers need to describe, understand and “agree on” variations in fish catches caused by exploitation and climate change for effective fisheries management. To achieve this, relevant data with sufficient spatiotemporal resolution is a necessity. In regions of the Global South, such as the Western Indian Ocean (WIO), fish catch data useful for management is scarce or non-existing. Still, the potential of local ecological knowledge to provide such information has not been fully utilised in these regions. In this study, we evaluated fishers’ local ecological knowledge (based on interviews) against detailed seasonal fish catch variability data based on catch per unit effort (CPUE) records. Because of the importance of the monsoon seasons for marine resource variability, differences in fish catches during the northeast (NE) and southeast (SE) monsoon seasons were investigated. Fishers’ perceptions generally agreed with catch data records, both showing that the NE monsoon season generally provides higher catch rates than the SE monsoon season. The fishers’ perceptions at two of the landing sites (Nyamisati and Shangani) contradict the recorded observations by showing highest fish catches during the SE monsoon season. It was clear, however, that fishers’ perceptions in these two sites focused on the most valuable target species (prawn and tuna in Nyamisati and Shangani, respectively) rather than total catches. In this particular case, fishers’ perceptions facilitated the significance of taking target species into consideration. The findings of this study highlight the importance of integrating local ecological knowledge into scientific research to help understand the complex dynamics of coastal fisheries and improve the management of data-poor fisheries.

Population dynamics and yield estimation of Common Carp (Cyprinus carpio, Linnaeus, 1758) in Ayalew reservoir, Gamo Zone, Southern Ethiopia

Common carp (Cyprinus carpio) is an introduced fish species in Ayalew reservoir. This study provides the first results on fishery dynamics of the species in the reservoir. The study was aimed at estimating important population dynamics parameters and production potential. Total length (TL) and total weight (TW) data were collected from a total of 276 fish samples (141 females and 135 males). The obtained data were analyzed using FiSAT II software. Jones length-based cohort analysis model and length-based Thompson and Bell yield prediction models were employed to estimate the population and production potential. The mean total length was 26 cm and the dominant length groups ranged from 17 to 33 cm were 87%. The length-weight relationship parameters were (TW = 0.0565TL2.53, R2 = 0.95) and the condition factor K = 1.29. The parameters of von Vertalanffy growth curve were L∞ = 41 cm, k = 0.52, to = -2.29, θ = 2.9 and A0.95 = 5.5 years. The estimated values of the total, natural and fishing mortalities were Z = 1.23, M = 0.55 and F = 0.68, respectively. The current exploitation rate was 0.55 which indicates slightly overexploitation. The estimated fish population and the annual fish yield were 59,304 and 1.5 tons, respectively. However, investigation on reproductive biology, limnolocal aspects and stock enhancements should be required for the sustainability of these resources.

Bio-economic indicators of fisheries: impact of variations in landings and fish size on market prices in Istanbul Fish Market.

Fisheries are of immense importance to Mediterranean countries, for protein, employment and livelihoods. Studies addressing the factors affecting fish price dynamics are of interest to examine their drivers as prices often dictate target fisheries. This study investigates fish market prices in relation to landings and fish sizes from Türkiye's largest fish market in Istanbul as the study site. A total of 39 wild marine taxa were examined for their landed catch (kg) and average prices (per unit/TRY) from 2006 to 2019. We found fish prices increased from small pelagic to medium pelagic to demersal fish. GAM model results for inter-species tests showed a strong positive effect of local maximum length (p<0.01) and a weaker positive effect of trophic level and vulnerability (p<0.1) on fish market price, but that landings amounts have no significant effect as a single predictor. Monthly price variations of bluefish and bonito were completely different than other species dynamics, as the last substantial commercial medium pelagic fish species left; highest monthly prices were related to the highest monthly landings for bonito and for the non-closure period for bluefish. Market prices as economic indicators for fisheries may have the potential to reveal ecosystem variations as well as socioeconomic drivers. Databases including extensive data for key fish sales centers can be used to help understand fishery dynamics from an ecosystem perspective, especially for data-poor regions like Türkiye.

Standardizing fishery-dependent catch-rate information across gears and data collection programs for Alaska sablefish (Anoplopoma fimbria)

Abstract Indices of abundance used to inform stock assessment models are commonly derived from fishery-dependent data sources. However, fishery catch-per-unit-effort (CPUE) are often confounded by a myriad of factors for which corrections must be made using model-based standardization methods. The Alaska sablefish (Anoplopoma fimbria) fishery provides a fitting case study of such issues, wherein a regulatory change in 2017 disrupted historic fishery dynamics, promoting a rapid transition in use of pot gear over demersal hook-and-line gear in the Gulf of Alaska. To address this, we combined across both observer and logbook programs (data sources) and gear types to develop an intercalibrated abundance index. We first regressed observer records against vessel logbooks to understand potential biases that may arise from combining data sources during the CPUE standardization process. Here, we found that both data sources exhibited strong agreement in reported CPUEs when compared on a set-by-set basis. Therefore, we intercalibrated both CPUE data sources and developed an index of abundance that incorporated catch records from both demersal hook-and-line and pot gear fisheries for sablefish in Alaska, to account for the recent rapid change in gear use. This standardized index of abundance compared favourably with an index generated from a fishery-independent hook-and-line survey currently used in management, suggesting it is representative of sablefish population trends. Our findings not only represent a valuable contribution to the management of sablefish in Alaska, but also provide a widely applicable framework for standardizing fishery-dependent CPUE data to support the management of multi-gear fisheries.

Socio-ecological drivers of demersal fishing activity in the North Sea: The case of three German fleets

Worldwide, fisheries face the consequences of climate change and compete with expanding human activities at sea, which may trigger unforeseen reactions of fishers. Hence, knowledge on drivers of fishing behavior is crucial for management and needs to be integrated in resource management policies. In this study, we identify factors influencing fishing activity of North Sea demersal fleets. First, we explore drivers of the North Sea demersal fisheries in scientific literature. Subsequently, we study the effects of identified drivers on the spatio-temporal dynamics of German demersal fisheries using boosted regression trees (BRT), a supervised machine learning technique. An exploratory literature review revealed a lack of studies incorporating biophysical, economic and socio-cultural fishing drivers in a single quantitative analysis. Our BRT analysis contributed to filling this research gap and highlighted the importance of biophysical drivers such as temperature, salinity, and bathymetry for fishing behavior. Contrary to findings of previous studies, our empirical analysis identified quotas and market prices to be irrelevant, except for low brown shrimp prices, which counter-intuitively increased fishing effort. Moreover, economic and socio-cultural variables influencing brown shrimp fishing effort differed from the other fleets, especially determined by increased effort on workdays and reduced effort when fuel prices were high. Our findings provide key information for marine spatial planning and supports the integration of fishing fleet behavior into policies.

Improving sustainable practices in tuna purse seine fish aggregating device (FAD) fisheries worldwide through continued collaboration with fishers

More than a decade of bottom-up collaborative workshops and research with fishers from the principal tropical tuna purse seine fleets to reduce ecological impacts associated with the use of fish aggregating devices (FADs) has yielded novel improved sustainable fishing practices in all oceans. This integrative effort is founded on participatory knowledge-exchange workshops organized by the International Seafood Sustainability Foundation (ISSF), referred to as “ISSF Skippers Workshops”, where scientists, fishers, and key stakeholders examine and develop together ways and tools to minimize fishery impacts. Workshops organized since 2010 have reached fleet members in 23 countries across Asia, Africa, the Americas, Europe, and Oceania, with over 4,000 attendances, mostly skippers and crew, operating in the Indian, Atlantic, and Pacific oceans. Structured and continued open transparent discussions on ocean-specific options to minimize FAD associated bycatch, ghost fishing and marine pollution have produced an array of novel co-constructed solutions and a better understanding of ecosystem and fishery dynamics. Dedicated at sea research cruises in commercial purse seiners have enabled testing some of the ideas proposed in workshops. Results obtained were then communicated back to fishers for a double loop learning system resulting in solution refinement and/or adoption. Furthermore, fishers’ increased trust and stewardship have stimulated unprecedented large-scale science-industry research projects across oceans, such as multi-fleet biodegradable FAD trials, the adoption and widespread use of non-entangling FADs, and the development and adoption of best practices for the safe handling and release of vulnerable bycatch. This model of collaborative research is broadly applicable to other natural resource conservation fields. Support for long-term inclusive programs enabling harvesters to proactively collaborate in impact mitigation research contributes to improved scientific advice, voluntary compliance, and adaptive management for lasting sustainability trajectories.

Trends in abundance indices derived from commercial fisheries for priority marine stocks in the Azores.

Large-scale assessments of fish and shellfish populations may be valuable for identifying the impacts of fishing pressure on stocks, but they are rarely possible due to a lack of long-term datasets. In this study, a two-part mixed-effect model for lognormal data was used to obtain historical abundance indices for 16 priority fish and shellfish stocks in the Azores region derived from catch per unit effort (kg per day at sea per vessel) and landing per unit effort (kg per landing per vessel). This data was obtained over the past 30 years under the EC Data Collection Framework and, in addition to information on effort and catch, included details about the fishing operation such as quarter, vessel length and fishing gear. This information was analysed to investigate how abundance indices changed over the years, verify if trends from different data sources were different and, if possible, relate these results to the population and fishery dynamics. The abundance indices derived from both datasets were generally in agreement with each other. Declining trends have been observed for some commercially important species, such as forkbeard Phycis phycis, European conger Conger conger, parrotfish Sparisoma cretense, red scorpionfish Scorpaena scrofa, offshore rockfish Pontinus kuhlii, common spiny lobster Palinurus elephas, splendid alfonsino Beryx splendens and alfonsino B. decadactylus, which is concerning because they are particularly slow-growing, long-lived and have low natural mortality, making them susceptible to overfishing. The results of this study are very important and should help future stock assessment and management initiatives.

Limited conservation efficacy of large-scale marine protected areas for Pacific skipjack and bigeye tunas

Large-scale, no-take marine protected areas (MPAs) have been established in several locations in the Pacific and expansion of such areas to reach 30% of the ocean area is actively promoted in some quarters. Justification for the establishment of large oceanic MPAs often includes the conservation benefits that they would bring for tuna stocks, which are the subject of important commercial fisheries in the Pacific. The aim of this paper was to evaluate the conservation efficacy of an existing MPA, the Phoenix Islands Protected Area (PIPA) and a series of large hypothetical MPAs each constituting approximately 33% of the western and central Pacific Ocean, for two important and contrasting tuna species, skipjack and bigeye tuna. The evaluation was conducted by comparing control and counterfactual simulations in which the estimated population and fishery dynamics of the species were modelled using a high-resolution modelling framework known as SEAPODYM (Spatial Ecosystem And Population DYnamics Model). We found that stock-wide conservation benefits of the PIPA for these species, assuming that total fishing effort is maintained, to be weak to non-existent, and only modest increases in spawning biomass of both species occur within and in the near vicinity of the PIPA itself. For the larger 33% hypothetical MPAs, changes in stock-wide spawning biomass were estimated to be -0.1% to +5.8% for skipjack tuna and +4.8% to +12.0% for bigeye tuna. Conservation efficacy of MPAs for species such as tropical tunas is limited by their wide larval dispersal and high mobility of later life stages, which spatially dissipate the protective effects of MPAs. Also, the displacement of fishing effort from MPAs to areas remaining open can have negative consequences for stocks and fisheries performance in those areas. We conclude that large oceanic MPAs are not likely to be effective frontline management tools for tropical tunas and other species having similar life history characteristics.

Periodic solution of a bioeconomic fishery model by coincidence degree theory

In this article we use coincidence degree theory to study the existence of a positive periodic solutions to the following bioeconomic model in fishery dynamics { d n d t = n ( r ( t ) ( 1 − n K ) − q ( t ) E n + D ) , d E d t = E ( A ( t ) q ( t ) α ( t ) n n + D − q 2 ( t ) α ( t ) n 2 E ( n + D ) 2 − c ( t ) ) , where the functions r , q , A , c and α are continuous positive T-periodic functions. This is the model of a coastal fishery represented as a single site with $n(t)$ is the fish stock biomass, and n(t) is the fishing effort. Examples are given to strengthen our results.