Exploited Marine Ecosystems Research Articles

Identifying drivers of change during the recent two decades in the Visayan Sea using a trophic modeling approach

The Visayan Sea is one of the major traditional fishing grounds in the Philippines and is likewise considered as a top contributor to the country’s overall fisheries production. However, fisheries surveys conducted over the past couple of decades have documented changes in the abundance and composition of catches and stocks toward an increasing dominance of invertebrates and low trophic levels fish families. Assessments of the commercially-important pelagic and demersal stocks were used to estimate population parameters that already exceed the sustainable reference limits. These traditional assessments point exclusively to fishing as the likely cause of the observed status and trends, but they fail to incorporate the potential influence of trophic interactions and variable environmental conditions despite a nationally-legislated mandate to apply an ecosystem approach to assessing and managing the country’s fisheries. Thus, an ecosystem model (Ecopath with Ecosim) of the Visayan Sea was constructed to investigate the role and extent of the fishery, trophic interactions, and changing environmental conditions as drivers of stock abundance and ecosystem dynamics. The results suggest that fishing and its corresponding trophic effects are the major drivers of invertebrate and fish biomass and catches in the Visayan Sea over the past two decades, while the environmental trends provide explanations for patterns that cannot be explained by fishing alone. Incorporating sea surface temperature variations and primary productivity anomalies produced the best-fitting models for most of the observed biomass and catch trends. The catches of the small pelagics (i.e., sardines and mackerels) were likewise found to be particularly affected by rainfall, while the biomass and catch of the small demersal fishes also show a sensitivity to chlorophyll-a concentrations. The primary productivity anomalies further showed a significant correlation with the Pacific Decadal Oscillation (PDO), which suggests that bottom-up trophic controls in the system may be affected by long-term regional climatic changes. These findings validate the applicability and necessity of the ecosystem modeling approach in assessing exploited marine ecosystems to complement the analyses from typically single-species population assessments, especially in the face of increasing environmental variability and projected climate change scenarios.

Environmental and anthropogenic driven transitions in the demersal ecosystem of Cantabrian Sea

Abstract In the framework of global human-induced change, marine communities’ often respond to changing conditions abruptly reorganizing into new equilibria. These shifts are difficult to predict and often imply irreversible adjustments due to hysteresis. Unraveling the role of the forces leading regime shifts is a major challenge. We explored the temporal evolution of 63 fish species representing the Cantabrian bentho-demersal community in response to environmental changes and fishing pressure in the period 1983–2018, using survey data. Via multivariate analysis and non-additive modeling of a community index and the system's main stressors, two decadal-scale regimes were revealed, suggesting a non-linear response of the community to its environment. The Integrated Resilience Assessment framework elucidated the response mechanism to the candidate stressors and allowed quantifying resilience dynamics. The decline in fishing pressure in the 1990s was associated with a gradual transition of the system, while further decline during the 2000s eroded the resilience of the system towards changes in its stressors, leading to a discontinuous response expressed as an abrupt, possibly irreversible shift in the 2010s. Given the teleconnected character of marine ecosystems, this regional study endorses the scientific effort for actions facing the dynamic impacts of climate change on exploited marine ecosystems.

Latitude and protection affect decadal trends in reef trophic structure over a continental scale.

The relative roles of top‐down (consumer‐driven) and bottom‐up (resource‐driven) forcing in exploited marine ecosystems have been much debated. Examples from a variety of marine systems of exploitation‐induced, top‐down trophic forcing have led to a general view that human‐induced predator perturbations can disrupt entire marine food webs, yet other studies that have found no such evidence provide a counterpoint. Though evidence continues to emerge, an unresolved debate exists regarding both the relative roles of top‐down versus bottom‐up forcing and the capacity of human exploitation to instigate top‐down, community‐level effects. Using time‐series data for 104 reef communities spanning tropical to temperate Australia from 1992 to 2013, we aimed to quantify relationships among long‐term trophic group population density trends, latitude, and exploitation status over a continental‐scale biogeographic range. Specifically, we amalgamated two long‐term monitoring databases of marine community dynamics to test for significant positive or negative trends in density of each of three key trophic levels (predators, herbivores, and algae) across the entire time series at each of the 104 locations. We found that trophic control tended toward bottom‐up driven in tropical systems and top‐down driven in temperate systems. Further, alternating long‐term population trends across multiple trophic levels (a method of identifying trophic cascades), presumably due to top‐down trophic forcing, occurred in roughly fifteen percent of locations where the prerequisite significant predator trends occurred. Such alternating trophic trends were significantly more likely to occur at locations with increasing predator densities over time. Within these locations, we found a marked latitudinal gradient in the prevalence of long‐term, alternating trophic group trends, from rare in the tropics (<5% of cases) to relatively common in temperate areas (~45%). Lastly, the strongest trends in predator and algal density occurred in older no‐take marine reserves; however, exploitation status did not affect the likelihood of alternating long‐term trophic group trends occurring. Our data suggest that the type and degree of trophic forcing in this system are likely related to one or more covariates of latitude, and that ecosystem resiliency to top‐down control does not universally vary in this system based on exploitation level.

Primary production and depth drive different trophic structure and functioning of fish assemblages in French marine ecosystems

Investigating the drivers of fish assemblage trophic structure is a critical question, in order to better understand ecosystem functioning, predict the effects of perturbations and implement integrated management of exploited marine ecosystems. Ecosystemic surveys enabled the determination of the trophic structure of the fish assemblages in three French marine ecosystems, namely the Eastern English Channel, the Bay of Biscay and the Gulf of Lions, through the simultaneous collection of qualitative (stable isotopes and energy content) and quantitative (biomass) data. In the Bay of Biscay and in the Gulf of Lions, pelagic primary production supported at least 80% of the fish biomass production, and explained the dominance of pelagic species, but with differences resulting from the different productivity. The lower productivity in the oligotrophic Gulf of Lions led to a lower total biomass, energy density as well as the predominance of zooplankton-feeders. In contrast, fluxes in the Bay of Biscay were sufficient to support a higher biomass of pelagic piscivores, and of species with higher energy content. In the shallow Eastern English Channel, the respective contributions of pelagic and benthic sources were similar. Bentho-demersal species of higher trophic level dominated this assemblage, because of their ability to exploit both pathways. Results of the present study confirmed that fisheries-focused surveys can be used as efficient platforms to address questions about ecosystem functioning. Here, it confirmed the expected differences between ecosystems and the importance of primary production and environment as drivers of fish assemblage structure and functioning. Future studies should nevertheless develop new methods to better assess the paramount role of low trophic level consumers.

Biodiversity-ecosystem functioning relationships in fish communities: biomass is related to evenness and the environment, not to species richness.

The relationship between biodiversity and ecosystem functioning (BEF) is a topic of considerable interest to scientists and managers because a better understanding of its underlying mechanisms may help us mitigate the consequences of biodiversity loss on ecosystems. Our current knowledge of BEF relies heavily on theoretical and experimental studies, typically conducted on a narrow range of spatio-temporal scales, environmental conditions, and trophic levels. Hence, whether a relationship holds in the natural environment is poorly understood, especially in exploited marine ecosystems. Using large-scale observations of marine fish communities, we applied a structural equation modelling framework to investigate the existence and significance of BEF relationships across northwestern European seas. We find that ecosystem functioning, here represented by spatial patterns in total fish biomass, is unrelated to species richness-the most commonly used diversity metric in BEF studies. Instead, community evenness, differences in species composition, and abiotic variables are significant drivers. In particular, we find that high fish biomass is associated with fish assemblages dominated by a few generalist species of a high trophic level, who are able to exploit both the benthic and pelagic energy pathway. Our study provides a better understanding of the mechanisms behind marine ecosystem functioning and allows for the integration of biodiversity into management considerations.

Mean Size of the Landed Catch: A Fishery Community Index for Trend Assessment in Exploited Marine Ecosystems

Based on fisheries landings data I propose the size-base index (community level) Mean Size of the Landing Catch (MSL). The MSL index was estimated based on i) high taxonomic resolution data available from auctions (species level), ii) demographic data acquired during auction, namely species landed by “size-box” categories, which is mandatory to be assessed in all EU members state for fisheries quality and statistic proposes. The MSL was calculated from the average inferred size-box categories of a species weighted by their annual catch. The use of MSL allows determining inter-annual changes in the size of the catch when weighted data is available from the fishery. Using the Portuguese fisheries landing data as an example, the MSL revealed that the landing yield of large fish linearly declined over time while the catch of small fishes increased (i.e. survivors to old age was reduced by fishing). The MSL can be easily used to assess trends in marine exploited commercial communities (community rather than population level) and is fully applicable with any species-size data source (e.g. scientific surveys, visual census data). The MSL can also be used as a key indicator within the new ecosystem-based Marine Policy Framework Strategy (ecosystem approach to fisheries), which required the use of size-based indicators for the assessment of fisheries trends in exploited marine communities.

Utilisation de paramètres bioécologiques pour analyser la biodiversité ichtyologique de l’Aire Marine Protégée (AMP) de Joal-Fadiouthau Sénégal et sa périphérie non protégée à la pêche

With global changes, concerns about marine ecosystems and population dynamics are of increasing interest to researchers. As such, knowledge of the specific biodiversity of exploited marine ecosystems is generally considered a key factor in their resilience. This paper is a comparative study that focuses on analyzing the bioecological effects of MPA Joal-Fadiouth on fish populations by comparing the inside vs. outside of the MPA. Data were collected from scientific surveys conducted in cold and hot seasons in 2015. In each survey, 16 stations were sampled; 9 inside the MPA and 7 outside. The MPA is in open Ocean and the analysis of environmental parameters shows that the MPA area is a homogeneous environment. The variability is at the seasonal level. This variability is similar inside and outside the MPA. A total of 67 species in 37 families were found in the reserve, against 41 species in 32 families outside MPA. The biological indicators analysis shows a similar species richness and biomass between the two areas. However, total abundance is higher in the protected area. On the other hand, larger fish are more likely to be outside the protected area. In the MPA, 20 species sampled are in spawning period, but over 80 % of individuals are immature. The Joal-Fadiouth MPA implementation significantly improves the conservation of biodiversity with a dominance of herbivorous species and lower trophic levels. In addition, the reserve is a nursery area for many species (sardines, octopus, and shrimp) and reproduction for some species characteristics of the area, e.g.Hemiramphus brasiliensis and Stephanolepis hispidus.

Integrating spatial indicators in the surveillance of exploited marine ecosystems.

Spatial indicators are used to quantify the state of species and ecosystem status, that is the impacts of climate and anthropogenic changes, as well as to comprehend species ecology. These metrics are thus, determinant to the stakeholder’s decisions on the conservation measures to be implemented. A detailed review of the literature (55 papers) showed that 18 spatial indicators were commonly used in marine ecology. Those indicators were than characterized and studied in detail, based on its application to empirical data (a time series of 35 marine species spatial distributions, sampled either with a random stratified survey or a regular transects surveys). The results suggest that the indicators can be grouped into three classes, that summarize the way the individuals occupy space: occupancy (the area occupied by a species), aggregation (spreading or concentration of species biomass) and quantity dependent (indicators correlated with biomass), whether these are spatially explicit (include the geographic coordinates, e.g. center of gravity) or not. Indicator’s temporal variability was lower than between species variability and no clear effect was observed in relation to sampling design. Species were then classified accordingly to their indicators. One indicator was selected from each of the three categories of indicators, to represent the main axes of species spatial behavior and to interpret them in terms of occupancy-aggregation-quantity relationships. All species considered were then classified according to their relationships among those three axes, into species that under increasing abundancy, primarily increase occupancy or aggregation or both. We suggest to use these relationships along the three-axes as surveillance diagrams to follow the yearly evolution of species distributional patterns in the future.

Signatures of the collapse and incipient recovery of an overexploited marine ecosystem.

The Northwest Atlantic cod stocks collapsed in the early 1990s and have yet to recover, despite the subsequent establishment of a continuing fishing moratorium. Efforts to understand the collapse and lack of recovery have so far focused mainly on the dynamics of commercially harvested species. Here, we use data from a 33-year scientific trawl survey to determine to which degree the signatures of the collapse and recovery of the cod are apparent in the spatial and temporal dynamics of the broader groundfish community. Over this 33-year period, the groundfish community experienced four phases of change: (i) a period of rapid, synchronous biomass collapse in most species, (ii) followed by a regime shift in community composition with a concomitant loss of functional diversity, (iii) followed in turn by periods of slow compositional recovery, and (iv) slow biomass growth. Our results demonstrate how a community-wide perspective can reveal new aspects of the dynamics of collapse and recovery unavailable from the analysis of individual species or a combination of a small number of species. Overall, we found evidence that such community-level signals should be useful for designing more effective management strategies to ensure the persistence of exploited marine ecosystems.

Dynamic Complexity in Exploited Marine Ecosystems

Abstract Marine ecosystems are increasingly recognized as exhibiting the principal hallmarks of complex systems, including the possibility of sudden shifts in state among alternative basins of attraction and both periodic and aperiodic dynamical behavior. Over the last several decades a well-defined theory of complexity has emerged integrating earlier (and inter-related) concepts based on catastrophe, bifurcation, and chaos theory. In this review, we trace aspects of the historical development of these ideas and their application to marine systems. The manifestations of nonlinear dynamics in marine ecosystems include regime shifts; mirage correlations in which causally-connected system components can appear to be in-phase, asynchronous, or anti-correlated over different stanzas of time; and related state-dependent behavior in which the response of a focal variable to a driver differs depending on the present state of the system. We describe the analytical underpinnings of each of these dynamical behaviors. Although nonlinear dynamical systems are often portrayed in a deterministic setting, we emphasize the phenomenon of stochastic resonance in which an underlying nonlinear system acts as a noise amplifier in the presence of random perturbations. We next review the tools available for analyzing nonlinear dynamical systems based on the concept of state-space reconstruction and the application of techniques in nonlinear time series analysis. Finally, we address the management implications of nonlinear dynamics in exploited marine species and argue that considerations of predictability and forecast skill can serve as effective criteria for model selection and inference.

Ecological indicators to capture the effects of fishing on biodiversity and conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in 2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data availability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii) mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species, and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our understanding of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses, and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems.

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Comparative analyses of the dynamics of exploited marine ecosystems have led to differing hypotheses regarding the primary causes of observed regime shifts, while many ecosystems have apparently not undergone regime shifts. These varied responses may be partly explained by the decade-old recognition that within-system spatial heterogeneity in key climate and anthropogenic drivers may be important, as recent theoretical examinations have concluded that spatial heterogeneity in environmental characteristics may diminish the tendency for regime shifts. Here, we synthesize recent, empirical within-system spatio-temporal analyses of some temperate and subarctic large marine ecosystems in which regime shifts have (and have not) occurred. Examples from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and Eastern Scotian Shelf reveal the largely neglected importance of considering spatial variability in key biotic and abiotic influences and species movements in the context of evaluating and predicting regime shifts. We highlight both the importance of understanding the scale-dependent spatial dynamics of climate influences and key predator–prey interactions to unravel the dynamics of regime shifts, and the utility of spatial downscaling of proposed mechanisms (as evident in the North Sea and Barents Sea) as a means of evaluating hypotheses originally derived from among-system comparisons.

Spawning aggregation dynamics of brown-marbled grouper and camouflage grouper at a remote Indian Ocean atoll

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 22:145-157 (2013) - DOI: https://doi.org/10.3354/esr00534 Spawning aggregation dynamics of brown-marbled grouper and camouflage grouper at a remote Indian Ocean atoll Jude Bijoux1,7,8,*, Laurent Dagorn1, Paul D. Cowley2, Monique Simier3, Pierre-André Adam4, Jan Robinson5,6 1Institut de Recherche pour Développement (IRD), UMR 212 - EME (Exploited Marine Ecosystems), PO Box 570, Victoria, Mahé, Seychelles 2South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa 3Institut de Recherche pour le Développement (IRD), UMR 212 - EME (Exploited Marine Ecosystems), Centre de Recherche Halieutique Méditerranéenne et Tropicale, Avenue J. Monnet, BP 171, 34203 Sète Cedex, France 4Island Conservation Society, Pointe Larue, Mahé, Seychelles 5Seychelles Fishing Authority, PO Box 449, Victoria, Mahé, Seychelles 6ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia 7Present address: Seychelles Fishing Authority, PO Box 449, Victoria, Mahé, Seychelles 8Present address: South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa *Email: judebijoux@gmail.com ABSTRACT: The protection of grouper spawning aggregations is a global conservation issue: populations of many grouper species are threatened with collapse due to exploitation of this critical life history behaviour by fisheries. Effective protection of spawning aggregations requires information on spawning site fidelity, residence time and timing of arrivals at, and departures from, the site. To estimate these parameters at a spawning aggregation site at Farquhar Atoll, southern Seychelles, 12 brown-marbled groupers Epinephelus fuscoguttatus and 20 camouflage groupers E. polyphekadion were tagged with acoustic transmitters, and their presence and absence was monitored by an array of acoustic receivers positioned at the site over 2 spawning seasons (2010/2011 and 2011/2012). Spawning aggregations formed during 3 consecutive spawning months each season and overlapped spatially and temporally in the 2 species. Intra- and inter-season site fidelity was high, with 91.7% of tagged E. fuscoguttatus and 89.5% of tagged E. polyphekadion detected at the site 1 yr after tagging. The majority (2010/2011: 82.4%, 2011/2012: 80.0%) of fish detected in a spawning season visited the site during at least 2 spawning months. Residence time at the fish spawning aggregation site was influenced by sex (E. fuscoguttatus only) and spawning month (both species). Distinct periodicity in lunar timing of arrivals and departures was observed in both species. This study highlights the spatio-temporal scales involved during spawning aggregations of 2 long-lived, slow-growing coral reef fishes, which need to be considered for their effective management. KEY WORDS: Spawning aggregation dynamics · Lunar and diel periodicity · Residence time · Site fidelity · Groupers · Epinephelus · Seychelles Full text in pdf format PreviousNextCite this article as: Bijoux J, Dagorn L, Cowley PD, Simier M, Adam PA, Robinson J (2013) Spawning aggregation dynamics of brown-marbled grouper and camouflage grouper at a remote Indian Ocean atoll. Endang Species Res 22:145-157. https://doi.org/10.3354/esr00534 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 22, No. 2. Online publication date: December 02, 2013 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2013 Inter-Research.

Taylor's law and body size in exploited marine ecosystems

Taylor's law (TL), which states that variance in population density is related to mean density via a power law, and density-mass allometry, which states that mean density is related to body mass via a power law, are two of the most widely observed patterns in ecology. Combining these two laws predicts that the variance in density is related to body mass via a power law (variance-mass allometry). Marine size spectra are known to exhibit density-mass allometry, but variance-mass allometry has not been investigated. We show that variance and body mass in unexploited size spectrum models are related by a power law, and that this leads to TL with an exponent slightly <2. These simulated relationships are disrupted less by balanced harvesting, in which fishing effort is spread across a wide range of body sizes, than by size-at-entry fishing, in which only fish above a certain size may legally be caught.

Global in scope and regionally rich: an IndiSeas workshop helps shape the future of marine ecosystem indicators

This report summarizes the outcomes of an IndiSeas workshop aimed at using ecosystem indicators to evaluate the status of the world’s exploited marine ecosystems in support of an ecosystem approach to fisheries, and global policy drivers such as the 2020 targets of the Convention on Biological Diversity. Key issues covered relate to the selection and integration of multi-disciplinary indicators, including climate, biodiversity and human dimension indicators, and to the development of data- and model-based methods to test the performance of ecosystem indicators in providing support for fisheries management. To enhance the robustness of our cross-system comparison, unprecedented effort was put in gathering regional experts from developed and developing countries, working together on multi-institutional survey datasets, and using the most up-to-date ecosystem models.

Safeguarding, Integrating and Disseminating Knowledge on Exploited Marine Ecosystems: the Ecoscope

no abstract

Lessons in modelling and management of marine ecosystems: the Atlantis experience

AbstractModels are key tools for integrating a wide range of system information in a common framework. Attempts to model exploited marine ecosystems can increase understanding of system dynamics; identify major processes, drivers and responses; highlight major gaps in knowledge; and provide a mechanism to ‘road test’ management strategies before implementing them in reality. The Atlantis modelling framework has been used in these roles for a decade and is regularly being modified and applied to new questions (e.g. it is being coupled to climate, biophysical and economic models to help consider climate change impacts, monitoring schemes and multiple use management). This study describes some common lessons learned from its implementation, particularly in regard to when these tools are most effective and the likely form of best practices for ecosystem‐based management (EBM). Most importantly, it highlighted that no single management lever is sufficient to address the many trade‐offs associated with EBM and that the mix of measures needed to successfully implement EBM will differ between systems and will change through time. Although it is doubtful that any single management action will be based solely on Atlantis, this modelling approach continues to provide important insights for managers when making natural resource management decisions.

Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 420:241-252 (2010) - DOI: https://doi.org/10.3354/meps08847 Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery K. Laneri1,7,*,**, M. Louzao1,2,8,*,**, A. Martínez-Abraín1, J. M. Arcos3, E. J. Belda4, J. Guallart5, A. Sánchez3, M. Giménez 3, R. Maestre3,6, D. Oro1 1IMEDEA (CSIC-UIB), Miquel Marquès 21, 07190 Esporles, Mallorca, Spain 2Departamento de Biología de Organismos y Sistemas, Universidad de Oviedo, Catedrático Rodrigo Uría s/n, 33071 Oviedo, Spain 3SEO/BirdLife, C/Múrcia 2-8, local 13, 08026 Barcelona, Spain 4Instituto de Investigación para la Gestión Integrada de Zonas Costeras, Universidad Politécnica de Valencia, Ctra. Nazaret-Oliva s/n, 46730 Gandia, València, Spain 5Laboratorio de Biología Marina, Departamento de Zoología, Universitat de València, 46100 Burjassot, València, Spain 6Institut d’Ecologia Litoral, Jacinto Benavente 21, 03560 El Campello, Alicante, Spain 7Present address: Fundació Institut Català de Ciències del Clima (IC3), Doctor Trueta 203, 08005 Barcelona, Catalonia, Spain 8Present address: Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, 04318 Leipzig, Germany *‑Corresponding authors. Email: karinalaneri@gmail.com, maite.louzao@ufz.de**These authors contributed equally to this work ABSTRACT: Unintended mortality in longlines emerged in the early 1990s as one of the most important threats for pelagic seabirds worldwide. Most of the studies were focused on highly developed industrial fisheries, overlooking bycatch in small-scale artisanal fisheries. However, bycatch in small-scale fisheries might have negative effects similar to those of industrial fisheries when they overlap with hotspot areas of top predators. Moreover, different types of fishing gear coexist in the same oceanographic area, particularly in highly exploited marine ecosystems such as the western Mediterranean. We quantify for the first time the influence of trawling regime on Cory’s shearwater Calonectris diomedea bycatch in the western Mediterranean longline artisanal fishery. The availability of trawling discards has substantial influence on the foraging and breeding ecology of many seabirds, and trawling inactivity may drive shearwaters to seek alternative food resources, such as baits used in longline fishing. Based on our previous knowledge of the system, we also tested other variables affecting bycatch over 8 yr (1998 to 2005). Within this 2-fishery framework, we found that trawling regime, longline fishing time and breeding stage were key factors explaining shearwater attendance to longline vessels, but mainly trawling regime and fishing time increased the incidental capture of Cory’s shearwaters. More specifically, during the pre-breeding and chick-rearing periods, bycatch dramatically increased during sunrise sets in the absence of trawling activity. Importantly, this study indicates the need for an integrated multi-fisheries management approach for the conservation of seabirds and highlights the necessity of banning longline fishing during periods of trawling inactivity. KEY WORDS: Small-scale fishery · Interactions between fisheries · Multi-fisheries management · Trawling inactivity · Cory’s shearwater · Mitigation measures · Western Mediterranean Full text in pdf format Supplementary material PreviousNextCite this article as: Laneri K, Louzao M, Martínez-Abraín A, Arcos JM and others (2010) Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery. Mar Ecol Prog Ser 420:241-252. https://doi.org/10.3354/meps08847Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 420. Online publication date: December 16, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Environmental mediation of Atlantic cod on fish community composition: an application of multivariate regression tree analysis to exploited marine ecosystems

Changes in species abundances caused by climatic variability have long been linked to alterations in community composition, species interactions and maintenance of biodiversity in marine ecosystems. Here we use multivariate regression tree (MRT) analyses to quantify how changes in species abundances and environmental variability contributed to observed patterns of community composition in the Gulf of St. Lawrence during 2 contrasting periods (the cooler and less saline period 1991 to 1995 and the warmer and more saline period 1997 to 2003). Broad-scale patterns of commu- nity composition in both periods were consistently explained by the depth and salinity of the benthic environment, but biological factors differed. In the cold period, the previous year's catches of snow crab Chionoecetes opilio and northern shrimp (mainly Pandalus borealis) were most important, while in the warm period the previous year's catch of Atlantic cod Gadus morhua dominated. MRT models further identified spatially discrete areas where communities are characterized by relatively high abundances of these species. These results indicate that environmental variability leads to dynamic and spatially explicit responses not only of single species, but of marine communities. Applications of ecosystem management in the face of climate change must take this into account.

Key Features and Context‐Dependence of Fishery‐Induced Trophic Cascades

Trophic cascades triggered by fishing have profound implications for marine ecosystems and the socioeconomic systems that depend on them. With the number of reported cases quickly growing, key features and commonalities have emerged. Fishery-induced trophic cascades often display differential response times and nonlinear trajectories among trophic levels and can be accompanied by shifts in alternative states. Furthermore, their magnitude appears to be context dependent, varying as a function of species diversity, regional oceanography, local physical disturbance, habitat complexity, and the nature of the fishery itself. To conserve and manage exploited marine ecosystems, there is a pressing need for an improved understanding of the conditions that promote or inhibit the cascading consequences of fishing. Future research should investigate how the trophic effects of fishing interact with other human disturbances, identify strongly interacting species and ecosystem features that confer resilience to exploitation, determine ranges of predator depletion that elicit trophic cascades, pinpoint antecedents that signal ecosystem state shifts, and quantify variation in trophic rates across oceanographic conditions. This information will advance predictive models designed to forecast the trophic effects of fishing and will allow managers to better anticipate and avoid fishery-induced trophic cascades.