Ecosystem-based Fisheries Management Research Articles

Feeding strategies of the ocean white fish (Caulolatilus princeps) and white spotted sand bass (Paralabrax albomaculatus) inside the Galapagos Marine Reserve

Understanding the diet of two demersal species, the ocean white fish (Caulolatilus princeps) and white spotted sand bass (Paralabrax albomaculatus) provides insights into the trophic strategies they have evolved to co-exist in rocky reefs and soft bottom habitats in the Galapagos Marine Reserve (GMR). We applied two complementary techniques (stomach content and stable isotopes analysis) to determine the trophic habits between species, and categories (sex, life stages and seasons). Sampling was carried out in several sites of fishing importance within the GMR between 2017 and 2018, obtaining 254 stomachs and 58 muscle samples for C. princeps, and 14 stomachs and 34 muscle samples for P. albomaculatus. Trophic spectrum (diet composition), of both predators contained pelagic and benthic prey. The slender anchovy (Anchoa ischana) was the most important prey for C. princeps with no significant differences in the diet between sex, life stages or seasons (p > 0.05); while the most important prey for P. albomaculatus was the threadfin bass (Pronotogrammus multifasciatus). The δ13C and δ15N signatures were significantly different among species (tvalue = 11.81, p < 0.05 and tvalue = 4.67, p <0.05, respectively) suggesting differences in the carbon source (i.e., feeding areas) as well as the preference for different trophic levels (i.e., different prey). Intraspecific analysis in C. princeps showed no differences within sex, life stage and seasons (p > 0.05). Feeding strategies were similar for both predators, with a reduced trophic niche and high variability between preys consumed. This work provides baseline information on two species of ecological and commercial importance within the GMR and highlights the value of trophic studies to generate useful information for an ecosystem-based fisheries management.

Decadal changes in biomass and distribution of key fisheries species on Newfoundland's Grand Banks.

Canadian fisheries management has embraced the precautionary approach and the incorporation of ecosystem information into decision-making processes. Accurate estimation of fish stock biomass is crucial for ensuring sustainable exploitation of marine resources. Spatio-temporal models can provide improved indices of biomass as they capture spatial and temporal correlations in data and can account for environmental factors influencing biomass distributions. In this study, we developed a spatio-temporal generalized additive model (st-GAM) to investigate the relationships between bottom temperature, depth, and the biomass of three key fished species on The Grand Banks: snow crab (Chionoecetes opilio), yellowtail flounder (Limanda ferruginea), and Atlantic cod (Gadus morhua). Our findings revealed changes in the centre of gravity of Atlantic cod that could be related to a northern shift of the species within the Grand Banks or to a faster recovery of the 2J3KL stock. Atlantic cod also displayed hyperaggregation behaviour with the species showing a continuous distribution over the Grand Banks when biomass is high. These findings suggest a joint stock assessment between the 2J3KL and 3NO stocks would be advisable. However, barriers may need to be addressed to achieve collaboration between the two distinct regulatory bodies (i.e., DFO and NAFO) in charge of managing the stocks. Snow crab and yellowtail flounder centres of gravity have remained relatively constant over time. We also estimated novel indices of biomass, informed by environmental factors. Our study represents a step towards ecosystem-based fisheries management for the highly dynamic Grand Banks.

Fluctuations in abundance of the striped venus clam Chamelea gallina in the southern Adriatic Sea (Central Mediterranean Sea): knowledge, gaps and insights for ecosystem-based fishery management

AbstractAn assessment on the fluctuations in abundance of the striped venus clam (Chamelea gallina) in the southern Adriatic Sea (Central Mediterranean Sea), and the northern Gargano area, has been conducted through both historical information and recent data from monitoring surveys during the period 1997–2019. Production trends, conditions of the commercial stock biomass, and depth distribution pattern of juveniles and commercial sizes were analysed testing temporal differences. Moreover, the exploitation of the clam beds and recruitment events were investigated in 2018–2019. Changes in abundance were analysed using non-parametric tests for both juvenile (length class, LC &lt; 22 mm) and commercial (LC ≥ 22 mm) fractions. Hydrodynamic changes, temperature and salinity variations were explored using a 3D hydrodynamic numerical model (MIKE 3 FM-HD) and statistical analysis, as well as changes in benthic assemblages impacted by hydraulic dredges were investigated through PERMANOVA and other multivariate analysis.The results showed a temporal decline of production and biomass of C. gallina during the 1997–2019 period, and a regression of the depth limit in the clams’ distribution towards shallower waters. A significant reduction in juveniles was observed during 2018–2019 with a very limited recruitment. The fishing exploitation showed high impacts on the commercial stock and benthic assemblages in the summer of 2018. Overall, water currents were predominantly directed offshore in 2018, during the C. gallina spawning period. This could affect the larval dispersal and settlement on unsuitable bottoms. Anomalies in temperature (high peaks in August 2018, &gt; 28 °C) and salinity (low values in spring 2018, &lt; 37 PSU) could have induced stress and mortality events on the entire clam bed in the study area. This first study highlights the need to integrate environmental information in the assessment of commercial stocks of clams in the Adriatic Sea, to better understand climate change effects on the fluctuations and to support effective ecosystem-based fishery management.

Linking climate stressors to ecological processes in ecosystem models, with a case study from the Gulf of Alaska

Abstract As climate stressors are impacting marine ecosystems and fisheries across the world, ecosystem models that incorporate environmental variables are increasingly used to inform ecosystem-based fisheries management. The assumptions around the mechanistic links between climate stressors and the biological processes in these models are important, but the implications for model outcomes of which stressors are captured and how they affect modeled biological processes are seldom explored. Using a whole-ecosystem model (Atlantis) for the Gulf of Alaska, we explore the effects of capturing physical (increased temperature) and biogeochemical (decreased low trophic level productivity) climate stressors, and disentangle the effects of each stressor on the productivity of forage fish, groundfish, and fish-eating seabirds. We then test the effects of alternative model specifications of temperature-driven habitat determination and bioenergetics. Increased temperature resulted in increased weight-at-age and higher natural mortality, while decreased productivity resulted in decreased weight-at-age and higher natural mortality. Model specification of temperature dependence of movement and spawning influenced model outcomes, and decoupling these processes from temperature led to overly optimistic biomass predictions. As the use of ecosystem models to inform fisheries management becomes more operational, we illustrate that the assumptions around the links between climate stressors and ecological processes influence model outcomes.

An updated end-to-end ecosystem model of the Northern California Current reflecting ecosystem changes due to recent marine heatwaves.

The Northern California Current is a highly productive marine upwelling ecosystem that is economically and ecologically important. It is home to both commercially harvested species and those that are federally listed under the U.S. Endangered Species Act. Recently, there has been a global shift from single-species fisheries management to ecosystem-based fisheries management, which acknowledges that more complex dynamics can reverberate through a food web. Here, we have integrated new research into an end-to-end ecosystem model (i.e., physics to fisheries) using data from long-term ocean surveys, phytoplankton satellite imagery paired with a vertically generalized production model, a recently assembled diet database, fishery catch information, species distribution models, and existing literature. This spatially-explicit model includes 90 living and detrital functional groups ranging from phytoplankton, krill, and forage fish to salmon, seabirds, and marine mammals, and nine fisheries that occur off the coast of Washington, Oregon, and Northern California. This model was updated from previous regional models to account for more recent changes in the Northern California Current (e.g., increases in market squid and some gelatinous zooplankton such as pyrosomes and salps), to expand the previous domain to increase the spatial resolution, to include data from previously unincorporated surveys, and to add improved characterization of endangered species, such as Chinook salmon (Oncorhynchus tshawytscha) and southern resident killer whales (Orcinus orca). Our model is mass-balanced, ecologically plausible, without extinctions, and stable over 150-year simulations. Ammonium and nitrate availability, total primary production rates, and model-derived phytoplankton time series are within realistic ranges. As we move towards holistic ecosystem-based fisheries management, we must continue to openly and collaboratively integrate our disparate datasets and collective knowledge to solve the intricate problems we face. As a tool for future research, we provide the data and code to use our ecosystem model.

Bridging the gap in fishing effort mapping: a spatially-explicit fisheries dataset for Campanian MPAs, Italy

Recent technological advancements have facilitated the extensive collection of movement data from large-scale fishing vessels, yet a significant data gap remains for small-scale fisheries. This gap hinders the development of consistent exploitation patterns and meeting the information needs for marine spatial planning in fisheries management. This challenge is specifically addressed in the Campania region of Italy, where several Marine Protected Areas support biodiversity conservation and fisheries management. The authors have created a spatially-explicit dataset that encompasses both large-scale (vessels exceeding 12 meters in length) and small-scale (below 12 meters) fishing efforts. This dataset (available at https://doi.org/10.6084/m9.figshare.23592006) is derived from vessel tracking data and participatory mapping. It offers insights into potential conflicts between different fishing segments and their interactions with priority species and habitats. The data can assist researchers and coastal management stakeholders in formulating policies that reduce resource competition and promote ecosystem-based fisheries management. Furthermore, the provided mapping approach is adaptable for other regions and decision-making frameworks, as we are committed to sharing the tools and techniques we employed.

Biomass and sustainable yields of Eurasian perch (Perca fluviatilis) in small boreal lakes with respect to lake properties and water quality

Understanding of factors that explain variation in potential fisheries yields is essential for the ecosystem-based management of lake fisheries. We used mark-recapture and Nordic survey net sampling to obtain estimates of Eurasian perch (Perca fluviatilis) abundance in 28 small (13.3 ha ± 11.4 ha, mean ± S.D.) boreal lakes. A size-structured population model was calibrated for each lake using further individual data to derive estimates of potential yields. Principal component scores formed from physical and chemical environmental parameters and a simple score reflecting the relative photic area of the lakes were then used to explain variation in theoretical yields to identify potential environmental proxies for fisheries management purposes. The estimated mean biomass of perch in the study lakes was 52.4 ± 51.2 kg ha−1, and the maximum sustainable yield, obtained with environment-dependent recruitment size was estimated to be 9.4 ± 12.1 kg ha−1 yr−1. The estimated yields were highest in shallow lakes with good oxygen saturation and with high percentage of euphotic bottom while excess nutrients decreased yields and alkalinity was marginally predictive for catch of large individuals. Our study provides quantitative estimates of potential yields of varyingly sized perch and helps to develop environmentally informed management for small lakes of which some are surprisingly productive.

Modeling the spatiotemporal patterns and drivers of Dungeness crab fishing effort to inform whale entanglement risk mitigation on the U.S. West Coast

Understanding and characterizing the spatiotemporal dynamics of fishing fleets is crucial for ecosystem-based fisheries management (EBFM). EBFM must not only account for the sustainability of target species catches, but also for the collateral impacts of fishing operations on habitats and non-target species. Increased rates of large whale entanglements in commercial Dungeness crab fishing gear have made reducing whale-fishery interactions a current and pressing challenge on the U.S. West Coast. While several habitat models exist for different large whale species along the West Coast, less is known about the crab fishery and the degree to which different factors influence the intensity and distribution of aggregate fishing effort. Here, we modeled the spatiotemporal patterns of Dungeness crab fishing effort in Oregon and Washington as a function of environmental, economic, temporal, social, and management related predictor variables using generalized linear mixed effects models. We then assessed the predictive performance of such models and discussed their usefulness in informing fishery management. Our models revealed low between-year variability and consistent spatial and temporal patterns in commercial Dungeness crab fishing effort. However, fishing effort was also responsive to multiple environmental, economic and management cues, which influenced the baseline effort distribution pattern. The best predictive model, chosen through out-of-sample cross-validation, showed moderate predictive performance and relied upon environmental, economic, and social covariates. Our results help fill the current knowledge gap around Dungeness crab fleet dynamics, and support growing calls to integrate fisheries behavioral data into fisheries management and marine spatial planning.

The challenges of modelling and assessing fisheries resources

Abstract Many years after the publication of Beverton and Holt’s on the Dynamics of Exploited Fish Populations in 1957, many of the problems that they highlighted remain unsolved. For example, accurately estimating critical biological and fishing processes such as growth, natural mortality, recruitment, and selectivity continues to be challenging. Despite the lack of progress in some areas, there have been advances in our understanding of other areas of fisheries modelling and analysis, including the development of integrative studies of marine resources for the application of an ecosystem-based fisheries management. In this context, ICES Journal of Marine Science solicited contributions to the themed article set (TS) “Advances and challenges in the modelling and assessment of fishery resources”. Here, we summarize the contributions included in this TS that provide examples of emerging tools that are able to account for different issues of a stocks’ assessments and integrated analyses.

Exploring fishing impacts on the structure and functioning of the Yellow Sea ecosystem using an individual-based modeling approach

The Yellow Sea is a marginal sea in the Northwestern Pacific where the fishery resources have been overfished and the community structure has greatly changed over the past six decades. Ecosystem modeling approaches are valuable tools to uncover potential mechanisms behind the ecosystem changes. Here, we developed ‘OSMOSE-YS’, an individual-based multi-species OSMOSE model that includes important commercial pelagic and demersal fish and invertebrates in the Yellow Sea. Simulations were carried out under three fishing scenarios to investigate how different levels of fishing pressure may have impacted the Yellow Sea ecosystem. Results indicate that the biomass of demersal fish continued to decline during 1970–2014, while the biomass of pelagic fish and invertebrates fluctuated periodically. Long-term fishing pressure has led to the reduction of total biomass, body sizes, and longevity of the modelled species. Under low-fishing condition, the ecosystem biomass is restored and the proportion of elder and larger individuals increases. On the contrary, high-fishing condition further decreases the proportion of high-trophic-level species. OSMOSE-YS serves as a baseline model to investigate ecosystem responses to different fishing strategies, in support of ecosystem-based fisheries management in the Yellow Sea.

Spatiotemporal fishing effort simulations and restriction scenarios in Thermaikos Gulf, Greece (northeastern Mediterranean Sea)

Spatiotemporal simulation modeling is used in the context of ecosystem-based fisheries management to investigate different management options, including the size and allocation of marine protected and fisheries restricted areas. Here, we used ecospace to assess the effectiveness of existing and potential future spatiotemporal fishing restrictions in the heavily exploited Thermaikos Gulf, Greece for the years 2000–2025 (calibration period 2000–2016; projection period 2017–2025). ecospace combines temporal biomass and commercial catch data with spatial habitat and other environmental data, as well as species ecological preferences, feeding, and dispersal rates to depict changes in trophic interactions, biomasses, and commercial catches in time and space. ecospace simulations supported the empirical data demonstrating that fisheries restricted areas are effective tools for rebuilding the biomass of exploited stocks, with their size and location playing a significant role in the way that different organisms respond to protection. Nevertheless, our results suggested that in order to achieve the highest benefits of protection, fisheries restricted areas would need to be accompanied by a parallel reduction in total fishing effort, rather than a redistribution of fishing activities. Such redistribution would just move the pressure on the boundaries of protected areas, causing a local increase of commercial catches owing to the beneficial spillover effects of protection. One of the tested spatiotemporal restriction scenarios (MPA 5) suggests certain additional management measures on top of the existing restrictions for all four fishing fleets operating in the area. This scenario predicted a considerable increase in the biomass of key commercial and vulnerable species groups, including hake, flatfishes, anglerfish, sharks, and rays and skates, by the end of the simulation period in 2025.

Tracing growth patterns in cod (Gadus morhua L.) using bioenergetic modelling.

Understanding individual growth in commercially exploited fish populations is key to successful stock assessment and informed ecosystem-based fisheries management. Traditionally, growth rates in marine fish are estimated using otolith age-readings in combination with age-length relationships from field samples, or tag-recapture field experiments. However, for some species, otolith-based approaches have been proven unreliable and tag-recapture experiments suffer from high working effort and costs as well as low recapture rates. An important alternative approach for estimating fish growth is represented by bioenergetic modelling which in addition to pure growth estimation can provide valuable insights into the processes leading to temporal growth changes resulting from environmental and related behavioural changes. We here developed an individual-based bioenergetic model for Western Baltic cod (Gadus morhua), traditionally a commercially important fish species that however collapsed recently and likely suffers from climate change effects. Western Baltic cod is an ideal case study for bioenergetic modelling because of recently gained in-situ process knowledge on spatial distribution and feeding behaviour based on highly resolved data on stomachs and fish distribution. Additionally, physiological processes such as gastric evacuation, consumption, net-conversion efficiency and metabolic rates have been well studied for cod in laboratory experiments. Our model reliably reproduced seasonal growth patterns observed in the field. Importantly, our bioenergetic modelling approach implementing depth-use patterns and food intake allowed us to explain the potentially detrimental effect summer heat periods have on the growth of Western Baltic cod that likely will increasingly occur in the future. Hence, our model simulations highlighted a potential mechanism on how warming due to climate change affects the growth of a key species that may apply for similar environments elsewhere.

PENINGAKATAN KAPASITAS NELAYAN DALAM MENDUKUNG PENANGKAPAN IKAN BERKELANJUTAN DI PAAP TELUK KOLONO PROVINSI SULAWESI TENGGARA

The management of fisheries access areas is one form of ecosystem-based fisheries management, which integrates marine protected area activities with controlled fishing activities carried out by local fishermen. The objective of sustainable fishing activities in the Kolono Bay Fisheries Access Area is to enhance the capacities of both the local fishermen and the PAAP management. This initiative involves the participation of 15 managing fishermen from five villages: All located in the Kolono Bay area. The project commences with the formation of groups, followed by discussion forums group, guided by a facilitator from RARE Indonesia Sultra. The DFG sessions were held twice, each with distinct themes: (1) issues and challenges encountered by fishermen during fishing activities in Kolono Bay, and (2) concerns related to climate change. Participants exhibited great enthusiasm throughout the engagement, as evidenced by the active sharing of the challenges they have faced concerning their fishing activities in Teluk Kolono during the FGD sessions. The outreach material was presented in simple language to ensure participants' comprehension. In general, it can be concluded that the information provided during this engagement has the potential to enhance the capacities of fishermen engaged in PAAP management in Teluk Kolono to support sustainable fishing.

Ecosystem-based fishery management that accounts for trade-offs between fishing and enhancement stocking: A case study of Juehua Island in the Bohai Sea

The implementation of marine ecosystem management requires modeling that accounts for the trade-off between exploitation in fisheries and protection activities (e.g., enhancement and release, artificial reefs). Researchers are increasingly interested in the trends of fishery resources under these joint driving forces due to the negative impacts of resource exploitation and the positive impacts of marine protection. Using the sea around Juehua Island in China’s Bohai Sea as a case study, we developed a marine ecosystem model based on the Ecopath with Ecosim software to analyze the trends in fishery resources driven both by fishing and stock enhancement. When the fishing effort exceeded 42 % of the 2019 value, the biomass of top predator Platycephalus indicus decreased by 50 %, indicating a regime shift. When the fishing effort increased to 340 % of the 2019 level, the ecosystem shifts to an alternative stable state occurs, indicating destabilization of the marine ecosystem. The impact of fishing effort on the marine ecosystem was not well compensated by release of a single target species. We also designed an orthogonal experiment with three factors (the key species Fenneropenaeus chinensis, Paralichthys olivaceus, and Charybdis japonica) and four restocking release levels to determine both the optimal release rate for each species individually and the optimal combination of different species. If the 2019 fishing effort is maintained, the release of 125 × 106 juvenile F. chinensis, 400 × 103 juvenile P. olivaceus, and 15 × 106 juvenile C. japonica would be an optimal solution to improve the marine biomass, trophic level, and biodiversity. Our results provide insights into ecosystem-based management strategies for implementing a policy to limit fishing in the study area and for scientifically determining the restocking release rates.

Assessing the Ecological Conversion Efficiency of Chub Mackerel, Somber japonicus, in Wild Conditions Based on an In Situ Enriched Simulation Method.

Understanding the ecological conversion efficiency of a fish species can be used to estimate the potential impact of the marine food web and accordingly provides scientific advice to ecosystem-based fishery management. However, only laboratory experiments may limit the accuracy of determining this index. In this study, food ingestion and ecological conversion efficiency of wild chub mackerel (Somber japonicus), a typical marine pelagic fish, were determined with gastric evacuation method in laboratory and in situ enriched simulation conditions. Additionally, the effect of temperature and body weight on ecological conversion efficiency was further estimated based on the 2D interpolation method. The results showed that, at 25.1 °C, the ecological conversion efficiency determined in-lab (35.31%) was significantly higher than in situ (23.85%). Moreover, the interpolation model estimated that with an increase in temperature (10-27 °C), the ecological conversion efficiency initially decreased, followed by an increase when the temperature reached 18 °C, but the ecological conversion efficiency generally decreased against the body weight at each temperature. The findings of this study enhanced the understanding of the energy budget of chub mackerel and also provided an efficient method for the determination of wild fishes that are difficult to sample in situ and domesticate in the laboratory.

Explicitly incorporating ecosystem-based fisheries management into management strategy evaluation, with a focus on small pelagics

The need to transition from traditional single-species fisheries management approaches towards ecosystem-based fisheries management (EBFM), or an ecosystem approach to fisheries, is widely recognised. EBFM is particularly important when considering management actions for economically valuable fisheries for small pelagic forage fish, given their key ecological role. Management strategy evaluation (MSE) is an effective approach to advance the quantitative implementation of EBFM by enabling stakeholders to explore trade-offs among competing ecosystem-related objectives. This paper puts forward six different approaches to advance EBFM with MSE explicity, by taking advantage of data and research already available and by guiding future research. These approaches can be grouped into those which (i) involve the operating model and/or link directly to the operating model while potentially providing additional performance metrics to evaluate ecosystem objectives, (ii) can be incorporated into the performance metrics, and (iii) involve the harvest control rule of the management procedure. This review demonstrates that immediate steps can be taken to implement EBFM targeted at quantitative tactical management, even without a complex, data-rich ecosystem operating model.

Using ecosystem models to inform ecosystem-based fisheries management in Europe: a review of the policy landscape and related stakeholder needs

The need to implement an ecosystem-based fisheries management (EBFM) is enshrined in numerous regulations and strategies, at both global and European level. In practice, it is challenging to implement EBFM because it requires a complex evaluation of interlinked management effects and environmental and climate forcing on multi-species interactions, habitat status and human activities. Ecosystem models are one of the most critical research tools to inform EBFM, because they can integrate a wide variety of data, examine multiple and complex ecosystem interactions, and can make forecasts based on specific management scenarios. However, despite clear progress in marine ecosystem modelling, many models do not address policy goals and targets, which hinders uptake in policy. In this paper, we review the global and European policies and implementing bodies which directly or indirectly have a repercussion on the implementation of EBFM. Moreover, we highlight specific stakeholder needs related to the implementation of EBFM in European waters, which ecosystem models could help address. We review the policy commitments that drive these needs and the concerns raised by stakeholders during a survey and dedicated workshop. Key topics of concern were effects of climate change; bycatch; protected areas/fisheries restricted areas; and reducing the impacts of trawling. Stakeholders also provided specific questions related to these topics which ecosystem models could help address. Scenario and data results visualizations, as well as specific barriers in using the results of ecosystem models for decision-making are also discussed. A close involvement of stakeholders in scenario development and in designing graphical outputs is important, and can help overcome some of the main barriers that can hinder uptake of models and scenarios, including a lack of understanding of the benefits and limits of ecosystem models; insufficient involvement and interaction with stakeholders; and inadequate characterization of uncertainties.

Evaluating the efficacy of fisheries management strategies in China for achieving multiple objectives under climate change

It is increasingly recognized that effective fisheries management needs to take into account not only the target species, but also the broader scope of biological, environmental, socio-economic and institutional factors pertaining to human utilization of fishery resources. This recognition has stimulated a global call for the Ecosystem-Based Fisheries Management (EBFM), with an increasing appreciation of its merits in the face of climate change. In this study, we applied the concept of EBFM to China's fisheries and tested the performance of various fisheries management strategies, including status quo management and alternative strategies with different objective priorities, under contrasting climate warming scenarios. We used the Ecopath with Ecosim (EwE) as an operating model, with an explicit consideration of trophic interactions, and specifically quantified the trade-offs across multiple metrics (i.e., sustainable fishery production, economic profitability, seafood security, and ecosystem health). No single strategy was superior across all the four dimensions. Importantly, the existing approach to fisheries management underperformed in most metrics, with the current fishing intensity exceeding the level that would maximize multispecies yields (fMSY) and total profits (fMEY). In contrast, an alternative harvest control rule (HCR) strategy, designed to respond to variations in biomass, provided inherent resilience of the ecosystem under climate warming, resulting in increased commercial fish biomass, improved profit and seafood supply, as well as enhanced ecosystem structure and function across various time-climate scenarios. From a tactic perspective, the multiple species management strategies of “fMSY” and “fMEY” can be better suited for the highly mixed fishery context in China. These alternatives also consistently demonstrated superior performance compared to the existing fisheries management strategy. Our work reveals potential trade-offs among diverse ecosystem services and provides a framework using EwE model for quantifying possible performance of management strategies under climate change, leading to more informed and transparent decision-making.

Trophic interactions and the diet composition of sympatric finfish predators in the tropical demersal ecosystem in the Bay of Bengal.

The dietary composition, foraging strategies, and interspecific trophic interactions were identified for four major demersal carnivorous finfishes, namely, croaker Otolithes ruber, hairtail Trichiurus lepturus, threadfin bream Nemipterus japonicus, and lizardfish Saurida undosquamis, along the north-western part of Bay of Bengal from 2014 to 2016. Two species, Trichiurus lepturus and Saurida undosquamis, were identified as finfish feeders due to the high number of teleost (clupeids and engraulids) prey. One species, Nemipterus japonicus, had a significantly different diet of metapenaeids and charybdids, and was identified as a shellfish feeder. The final species, Otolithes ruber, preyed equally on crustaceans and teleosts, and was identified as a shellfish-finfish feeder. The feeding activity of all four species was lower during peak spawning periods and tended to increase with maturity. Feeding preferences varied with seasons. The trophic level ranged from 3.49 to 4.01, classifying the four species as medium-carnivores or meso-predators. Niche breadth ranged from 0.170 to 0.421, with seasonal and ontogenetic variations. Individual or subgroup specialization was observed on dominant prey, but intraspecific diet variations indicated all four species to be opportunistic predators. There was substantial prey overlap for Saurida undosquamis with Otolithes ruber and Trichiurus lepturus, which increased ontogenetically and coincided with their peak spawning. Sharing of abundant prey resources together with temporal and ontogenetic resource partitioning at intra- and interspecific levels possibly lowered dietary competition, thereby facilitating the coexistence of these demersal predators. This study provides new information on feeding interactions from a tropical demersal ecosystem that can be applied for the ecosystem-based management of trawl fisheries.

Trophic guilds of marine predators in the California Current Large Marine Ecosystem

Quantifying trophic relationships of marine species is fundamental to the construction and performance of ecosystem models, development of effective ecosystem-based fisheries management strategies, and support of trait-based approaches to ecological risk assessment. Accounting for food web dynamics in taxonomically diverse ecosystems, such as the California Current Large Marine Ecosystem (CCLME), is especially challenging because of the sheer number of trophic linkages and their inherent variability. Consequently, analyses that can inform the most appropriate means of aggregating species or other taxonomic groups into assemblages or guilds are critical to reducing system complexity for modeling and management, particularly when data are limited. To provide a methodological approach that is globally applicable in such cases, we define trophic guilds within biogeographic regions of the CCLME, compare results among these regions, and discuss ecological and management implications. Within each biogeographic region, predator guilds were clearly demarcated by foraging habitat (benthic, nearshore pelagic, offshore pelagic), scale of foraging movements, and trophic position. Furthermore, trophic guilds were distinctive for each region, with species composition and the noted ecological characteristics largely driving guild structure. Predator species that are reliant on continental slope and offshore foraging habitat, such as adult Pacific Hake, have diets that are representative of these areas and are similar throughout the CCLME. Generally, larger, more mobile predators that typically feed in deeper offshore waters, including swordfish, sea lions, and sharks clustered together in multiple bioregions along the coast; all reliant primarily on fishes and squids. Throughout bioregions, groundfishes preyed on benthic invertebrates (e.g., decapods, amphipods, polychaetes), while shelf-oriented pelagic predators, including smaller salmon, preyed on pelagic invertebrates (e.g., euphausiids, copepods, gelatinous zooplankton). A large number of forage taxa that are well represented in this study have dynamics largely dependent on oceanographic conditions at a regional scale (e.g., decapods), basin scale (e.g., copepods), or a combination of both (e.g., euphausiids, Northern Anchovy). Such distinctions indicate that spatial and temporal scales of coherence of predators and prey also must be considered in development of ecosystem models and evaluation of management strategies. Our study quantifies the spatial coherence of predator guilds integrated over decades within and across bioregions of the CCLME, providing an improved understanding of regional ecosystem functioning. The analytical approach we developed may be easily extended to address similar ecological and ecosystem based fisheries management priorities in other marine regions.