Changes to Marine Trophic Networks Caused by Fishing
Andres Felipe Navia López2012, Diversity of Ecosystems
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Abstract
Recent publications that have assessed the relationship between fishing and possible alterations of direct and indirect trophic relationships within impacted ecosystems have detected strong ecological effects, such as trophic cascades and changes in ecosystem control equilibrium, either top-down or bottom-up (Barausse et al.
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The Effects of Fishing on Marine Ecosystems
Advances in Marine Biology, 1998
We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems. Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management.Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities. These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance. The initiation of fishing in an unfished system leads to dramatic changes in fish community structure. As fishing intensity increases the additional effects are more difficult to detect. Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals. However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals. Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time. The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing. Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure. In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure. Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator-prey coupling between invertebrate feeding fishes and sea urchins. Fishing has reduced, and locally extirpated, populations of predatory fishes. These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others. By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds. We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects. We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem.
The trophic-level based model: A theoretical approach of fishing effects on marine ecosystems
Ecological Modelling, 2005
We propose the trophic-level based model as a new approach to analyse the functioning of marine ecosystems in both ecological and fisheries contexts. The model considers a virtual ecosystem where all the animal biomass is distributed along a continuum of trophic level classes. Biomass moves from one class to the upper ones according to predation and ontogenic processes. From a given secondary production occurring at trophic level 2, the ecosystem biomass distribution can therefore be expressed as the result of the biomass flow passing through the ecosystem, from low to upper trophic levels. The model is based on two main equations. One is regarding biomass flow, which decreases according to fishing and natural losses occurring during transfers. The other expresses the speed of the flow per trophic level, assuming that high metabolism rates induce fast transfers at the lower trophic levels. Additionally, various hypotheses of ecosystem functioning are considered, dealing with the extent of top-down controls, the intensity of feedback effects on secondary production through biomass recycling and the occurrence of a biomass inaccessible to fisheries.
The Trophic Spectrum : a tool for assessing the effects of fishing on marine ecosystems at a global scale. ICES CM 2009 / P : 06
1. The EcoTroph model The present study is based on the EcoTroph model (Gascuel 2005, Gascuel et al. 2009), which is proposed as a plug-in module of the Ecopath with Ecosim software (EwE version 6). This model provides a simplified picture of ecosystem functioning; it allows users to represent the distribution of the ecosystem biomass as a function of trophic levels, and to analyse or simulate fishing impact in a very synthetic way. In the EcoTroph approach, the biomass per trophic group and the catch per fishery is represented as a distribution over trophic levels, assuming that the distribution of the biomass (or production or catch) of a trophic group around its mean trophic level follows a lognormal curve. The Biomass (or production or catch) Trophic Spectrum is the curve obtained by summing all biomasses. This representation provides a very synthetic overview of an ecosystem and may help users to think at that scale. Thus, trophic ecosystem functioning can be modelled as a cont...
CONTEXT-DEPENDENT EFFECTS OF FISHING: VARIATION IN TROPHIC CASCADES ACROSS ENVIRONMENTAL GRADIENTS
Ecological Applications, 2008
Marine reserves provide a large-scale experimental framework to investigate the effects of fishing on food web dynamics and how they vary with environmental context. Because marine reserves promote the recovery of previously fished predators, spatial comparisons between reserve and fished sites are often made to infer such effects; however, alternative explanations for differences between reserve and fished sites are seldom tested (e.g., environmental variation among sites). We investigated the context dependency of the predator-urchin-kelp trophic cascade reported in northeastern New Zealand by comparing the abundance of herbivorous sea urchins (Evechinus chloroticus), the extent of urchin barrens habitat, and macroalgal biomass between reserve and fished sites within six locations that span an environmental gradient in wave exposure, sedimentation, and water clarity. At depths where differences in urchin abundance or macroalgal biomass were found between reserve and fished sites we used a model selection approach to identify which variables (fishing or environmental factors) best explained the variation among sites. Differences between reserve and fished sites were not ubiquitous across the locations examined and were highly depth specific. At sheltered locations, urchins were rare and barrens absent at both reserve and fished sites. At moderately exposed coastal locations, actively grazing urchins were most abundant at 4-6 m depth, and significant differences in macroalgal biomass between reserve and fished sites were observed. In contrast, at offshore island locations, urchins extended into deeper water, and differences between reserve and fished sites were found at 4-9 m depth. These differences could only be attributed to trophic cascades associated with protection from fishing in two of the six locations examined. In other cases, variation between reserve and fished sites was equally well explained by differences in sediment or wave exposure among sites. These results suggest that trophic cascades are not ubiquitous to northeastern New Zealand's subtidal reefs and the importance of sea urchins, and indirectly predators, in controlling macroalgal biomass will vary at local and regional scales in relation to abiotic factors. A better mechanistic understanding of how environmental variation affects the strength of species interactions across multiple spatial scales is needed to predict the ecosystem-level effects of fishing.
Trophic level-based indicators to track fishing impacts across marine ecosystems
Marine Ecology Progress Series, 2014
Trophic level (TL)-based indicators have been widely used to examine fishing impacts in aquatic ecosystems and the induced biodiversity changes. However, much debate has ensued regarding discrepancies and challenges arising from the use of landings data from commercial fisheries to calculate TL indicators. Subsequent studies have started to examine survey-based and model-based indicators. In this paper, we undertake an extensive evaluation of a variety of TL indicators across 9 well-studied marine ecosystems by making use of model-as well as surveyand catch-based TL indicators. Using detailed regional information and data on fishing history, fishing intensity, and environmental conditions, we evaluate how well TL indicators are capturing fishing effects at the community level of marine ecosystems. Our results highlight that the differences observed between TL indicator values and trends is dependent on the data source and the TL cut-off point used in the calculations and is not attributable to an intrinsic problem with TLbased indicators. All 3 data sources provide useful information about the structural changes in the ecosystem as a result of fishing, but our results indicate that only model-based indicators represent fishing impacts at the whole ecosystem level.
Trophic indicators to measure the impact of fishing on an exploited ecosystem
2011
Trophic indicators to measure the impact of fishing on an exploited ecosystem.-There is currently a global call for more use of an ecosystem approach to fisheries management (EAFM) to provide a holistic view of ecosystem-fisheries interactions. Trophic indicators could therefore be used to support the implementation of an EAFM by providing information on the state of the ecosystem. In this paper we propose a set of indicators such as the marine trophic index (MTI), the fishing in balance (FiB), the cut marine trophic index ( cut MTI) and the pelagic/demersal index (P/D) to assess the dynamics and the trophic changes in the Black Sea large marine ecosytem from 1970 to 2005. Our analysis shows a heavily exploited ecosystem where overfishing and anthropogenic eutrophication are probably responsible. The decline of the MTI, cut MTI and FiB together with the rising trend of the P/D index could be interpreted as a fishing down marine food web process with a strong decrease in abundance of high trophic level species and a considerable increase of low trophic level species.
Impacts of trawling disturbance on the trophic structure of benthic invertebrate communities
Marine Ecology Progress Series, 2001
Bottom trawling causes chronic and widespread disturbance to the seabed in shallow shelf seas and could lead to changes in the trophic structure and function of benthic communities, with important implications for the processing of primary production and the wider functioning of the marine ecosystem. We studied the effects of bottom trawling on the trophic structure of infaunal and epifaunal benthic communities in 2 regions (Silver Pit and Hills) of the central North Sea. Within each region, we quantified long-term (over 5 yr) differences in trawling disturbance at a series of sites (using sightings data from fishery protection flights), and related this to differences in the biomass and trophic structure of the benthic community. There were 27-and 10-fold differences in levels of beam trawl disturbance among the Silver Pit and Hills sites respectively, and we estimated that the frequency with which the entire area of the sites was trawled ranged from 0.2 to 6.5 times yr-1 in the Silver Pit and 0.2 to 2.3 times yr-1 in the Hills. The impacts of fishing were most pronounced in the Silver Pit region, where the range of trawling disturbance was greater. Infaunal and epifaunal biomass decreased significantly with trawling disturbance. Within the infauna, there were highly significant decreases in the biomass of bivalves and spatangoids (burrowing sea-urchins) but no significant change in polychaetes. Relationships between trophic level (estimated using nitrogen stable isotope composition, δ 15 N) and body mass (as log 2 size classes) were rarely significant, implying that the larger individuals in this community did not consistently prey on the smaller ones. For epifauna, the relationships were significant, but the slopes or intercepts of the fitted linear regressions were not significantly related to trawling disturbance. Moreover, mean δ 15 N of the sampled infaunal and epifaunal communities were remarkably consistent across sites and not significantly related to trawling disturbance. Our results suggest that chronic trawling disturbance led to dramatic reductions in the biomass of infauna and epifauna, but these reductions were not reflected in changes to the mean trophic level of the community, or the relationships between the trophic levels of different sizes of epifauna. The trophic structure of intensively trawled benthic invertebrate communities may be a robust feature of this marine ecosystem, thus ensuring the efficient processing of production within those animals that have sufficiently high intrinsic rates of population increase to withstand the levels of mortality imposed by trawling.
Effects of fishing on the structure and functioning of estuarine and nearshore ecosystems
ICES Journal of Marine Science, 2000
Effects of fishing on the structure and functioning of estuarine and nearshore ecosystems. -ICES Journal of Marine Science, 57: 590-602.
The Impacts of Fisheries on Marine Ecosystems and the Transition to Ecosystem-Based Management
Annual Review of Ecology, Evolution, and Systematics, 2008
Fishing remains one of the largest factors modifying marine ecosystems. Because fisheries constitute only one of many anthropogenic effects, management is shifting from single-species approaches toward ecosystem-based management. Interaction webs are a critical nexus to understand linkages, to model ecosystem change, and to apply management directives. Ecosystem-based management requires consideration of both direct and indirect effects of commercial fisheries. But it must also include impacts of bycatch, recreational fisheries, artisanal fisheries, and environmental change that can be large but unanticipated. Synergistic effects of fishing, environmental variation, and climate change increasingly threaten marine ecosystems and complicate management. Here we review the global effects of fisheries and propose an integrated framework for managing biophysical processes and human ecology. To incorporate the multitude of effects, this emerging approach focuses on the dynamics of interact...
Ecological indicators based on trophic spectrum as a tool to assess ecosystems fishing impacts
Ecological Indicators, 2010
Trophic indicators were used to compare two Malian freshwater reservoirs whose main differences are based on their different fishing pressures. Data were collected from a scientific survey of small-scale fishery landings conducted in 2002/2003. The trophic levels of fish species caught by artisanal fisheries are estimated from observations of scientific fishing or from the metabase Fishbase. Important differences exist in the trophic structure of both reservoirs. In Selingue (with high fishing pressure), very few top predators are found in the catches while the low trophic level fishes increase in total catches. In Manantali (with low fishing pressure), the top predators contribute twice as much to catches compared to Selingue. Hence, the mean trophic level of catches in Selingue (2.80) is lower than in Manantali (2.97). When comparing these results with those of study made in 1994/1995, it clearly appears that the effects of the fishing pressure in Selingue are obvious through a decrease of 0.12 in the mean trophic level while in Manantali this mean level has increased by 0.33 due to a recent strategic targeting of top predators. Trophic spectra seem to be relevant tools to characterize exploited fish communities from multi-specific and multi-gear small-scale fisheries catch data.
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Ecological Applications, 2009
Bottom trawling has widespread impacts on benthic communities and habitats. While the direct impacts of trawl disturbances on benthic communities have been extensively studied, the consequences from long-term chronic disturbances are less well understood. The response of benthic macrofauna to chronic otter-trawl disturbance from a Nephrops norvegicus (Norway lobster) fishery was investigated along a gradient of fishing intensity over a muddy fishing ground in the northeastern Irish Sea. Chronic otter trawling had a significant, negative effect on benthic infauna abundance, biomass, and species richness. Benthic epifauna abundance and species richness also showed a significant, negative response, while no such effect was evident for epibenthic biomass. Furthermore, chronic trawl disturbance led to clear changes in community composition of benthic infauna and epifauna. The results presented indicate that otter-trawl impacts are cumulative and can lead to profound changes in benthic communities, which may have far-reaching implications for the integrity of marine food webs. Studies investigating the short-term effects of fishing manipulations previously concluded that otter trawling on muddy substrates had only modest effects on the benthic biota. Hence, the results presented by this study highlight that data from experimental studies can not be readily extrapolated to an ecosystem level and that subtle cumulative effects may only become apparent when fishing disturbances are examined over larger spatial and temporal scales. Furthermore, this study shows that data on chronic effects of bottom trawling on the benthos will be vital in informing the recently advocated move toward an ecosystem approach in fisheries management. As bottom-trawl fisheries are expanding into ever deeper muddy habitats, the results presented here are an important step toward understanding the global ecosystem effects of bottom trawling.
Key Features and Context-Dependence of Fishery-Induced Trophic Cascades
Conservation Biology, 2010
Abstract: 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.Resumen: Las cascadas tróficas disparadas por la pesca tienen implicaciones profundas para los ecosistemas marinos y los sistemas socioeconómicos que dependen de ellos. Con el número de casos reportados incrementando rápidamente, han emergido atributos clave y similitudes. Las cascadas tróficas inducidas por pesquerías a menudo presentan tiempos de respuesta diferenciales y trayectorias no lineales entre los niveles tróficos y pueden ser acompañados por cambios en el estado de los ecosistemas. Más aun, su magnitud parece ser dependiente del contexto, variando como una función de la diversidad de especies, la oceanografía regional, la perturbación física local, la complejidad del hábitat y la naturaleza de la pesquería misma. Para conservar y manejar ecosistemas marinos explotados, existe una necesidad imperiosa por mejorar el entendimiento de las condiciones que promueven o inhiben las consecuencias en cascada de la pesca. Más aun, la investigación futura debe examinar la interacción de los efectos tróficos de la pesca con otras perturbaciones humanas, identificar especies estrechamente interactuantes y los atributos del ecosistema que confieren resiliencia a la explotación, determinar los rangos de disminución de depredadores que provoca las cascadas tróficas, identificar antecedentes que indiquen cambios de estado de los ecosistemas y cuantificar la variación en las tasas tróficas en condiciones oceanográficas diferentes. Esta información mejorará los modelos predictivos diseñados para estimar los efectos tróficos de la pesca y permitirá que los manejadores anticipen y eviten las cascadas tróficas inducidas por pesquerías.Resumen: Las cascadas tróficas disparadas por la pesca tienen implicaciones profundas para los ecosistemas marinos y los sistemas socioeconómicos que dependen de ellos. Con el número de casos reportados incrementando rápidamente, han emergido atributos clave y similitudes. Las cascadas tróficas inducidas por pesquerías a menudo presentan tiempos de respuesta diferenciales y trayectorias no lineales entre los niveles tróficos y pueden ser acompañados por cambios en el estado de los ecosistemas. Más aun, su magnitud parece ser dependiente del contexto, variando como una función de la diversidad de especies, la oceanografía regional, la perturbación física local, la complejidad del hábitat y la naturaleza de la pesquería misma. Para conservar y manejar ecosistemas marinos explotados, existe una necesidad imperiosa por mejorar el entendimiento de las condiciones que promueven o inhiben las consecuencias en cascada de la pesca. Más aun, la investigación futura debe examinar la interacción de los efectos tróficos de la pesca con otras perturbaciones humanas, identificar especies estrechamente interactuantes y los atributos del ecosistema que confieren resiliencia a la explotación, determinar los rangos de disminución de depredadores que provoca las cascadas tróficas, identificar antecedentes que indiquen cambios de estado de los ecosistemas y cuantificar la variación en las tasas tróficas en condiciones oceanográficas diferentes. Esta información mejorará los modelos predictivos diseñados para estimar los efectos tróficos de la pesca y permitirá que los manejadores anticipen y eviten las cascadas tróficas inducidas por pesquerías.
Quantifying ecosystem overfishing with a new index of fisheries' impact on marine trophic webs
ICES-CIEM international …, 2005
Disturbance of the Marine Benthic Habitat by Commercial Fishing: Impacts at the Scale of the Fishery
Ecological Applications, 1998
Commercial fishing is one of the most important human impacts on the marine benthic environment. One such impact is through disturbance to benthic habitats as fishing gear (trawls and dredges) are dragged across the seafloor. While the direct effects of such an impact on benthic communities appear obvious, the magnitude of the effects has been very difficult to evaluate. Experimental fishing-disturbance studies have demonstrated changes in small areas; however, the broader scale implications attributing these changes to fishing impacts are based on long-term data and have been considered equivocal. By testing a series of a priori predictions derived from the literature (mainly results of small-scale experiments), we attempted to identify changes in benthic communities at the regional scale that could be attributed to commercial fishing. Samples along a putative gradient of fishing pressure were collected from 18 sites in the Hauraki Gulf, New Zealand. These sites varied in water depth from ϳ17 to 35 m and in sediment characteristics from ϳ1 to 48% mud and from 3 to 8.5 g chlorophyll a/cm 3. Video transects were used for counting large epifauna and grab/suction dredge and core sampling were used for collecting macrofauna. After accounting for the effects of location and sediment characteristics, 15-20% of the variability in the macrofauna community composition sampled in the cores and grab/suction dredge samples was attributed to fishing. With decreasing fishing pressure we observed increases in the density of echinoderms, longlived surface dwellers, total number of species and individuals, and the Shannon-Weiner diversity index. In addition, there were decreases in the density of deposit feeders, small opportunists, and the ratio of small to large individuals of the infaunal heart urchin, Echinocardium australe. The effects of fishing on the larger macrofauna collected from the grab/ suction dredge samples were not as clear. However, changes in the predicted direction in epifaunal density and the total number of individuals were demonstrated. As predicted, decreased fishing pressure significantly increased the density of large epifauna observed in video transects. Our data provide evidence of broad-scale changes in benthic communities that can be directly related to fishing. As these changes were identifiable over broad spatial scales they are likely to have important ramifications for ecosystem management and the development of sustainable fisheries.
Effects of fishing disturbance on benthic communities and secondary production within an intensively fished area
Marine Ecology Progress Series, 2009
Demersal fishing alters seabed habitats and affects the structure and functioning of benthic invertebrate communities. At a critical level of disturbance, such communities may approach an equilibrium disturbed state in which a further increase in disturbance has little additional impact. Such arguments have been used to suggest that an ecosystem approach to fisheries management (EAFM) should protect lightly fished areas and deflect fishing activity into areas that are already intensively fished. In this study, the effects of variation in fishing disturbance on the secondary production, species diversity, abundance, biomass, and community structure of benthic infauna were examined in a region of the German Bight (North Sea) that has been intensively trawled for decades. Variation in fishing disturbance across the study area was determined using automated position registration and vessel monitoring through satellite. Even in such a heavily fished area, linear regression analyses revealed that biomass, species richness, and production decreased significantly with increasing fishing intensity. Although redundancy analyses (RDA) showed that sediment characteristics were influential in determining the structure of the infauna community, partial RDA revealed that fishing continued to have an impact on community structure in terms of biomass. These results suggest that, in implementing an EAFM, managers will need to consider the possibility that, even in areas with high chronic fishing disturbance, further increases in fishing activity may still cause additional damage to benthic invertebrate communities.
When does fishing lead to more fish? Community consequences of bottom trawl fisheries in demersal food webs
Proceedings. Biological sciences / The Royal Society, 2013
Fishing impacts on benthic ecosystems: an introduction to the 2014 ICES symposium special issue
ICES Journal of Marine Science: Journal du Conseil, 2015
Understanding the impacts of fishing on the seabed is a basic requirement for ecosystem-based marine management. It is only recently that we have begun understanding how fisheries-driven perturbations affect ecosystem function, biodiversity, productivity, and resilience. Technical solutions aimed at minimizing seabed impacts are starting to appear, but their efficacy remains to be demonstrated. In 2014, ICES held a symposium on the effects of fishing on benthic fauna, habitat, and ecosystem function, in Tromsø, Norway. The main goals of the symposium were to summarize current understanding of the physical and biological effects of fishing activities on benthic ecosystems, and to review the diversity of technical measures currently available to mitigate these effects. Here, we briefly describe the background to the scientific symposium and highlight the main contributions.
Cascading effects of over-fishing marine systems
Trends in ecology & evolution, 2005
Profound indirect ecosystem effects of over-fishing have been shown for coastal systems such as coral reefs and kelp forests. A new study from the ecosystem off the Canadian east coast now reveals that the elimination of large predatory fish can also cause marked cascading effects on the pelagic food web. Overall, the view emerges that, in a range of marine ecosystems, the effects of fisheries extend well beyond the collapse of fish exploited stocks.
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Scientific Reports, 2017
While the direct physical impact on seabed biota is well understood, no studies have defined thresholds to inform an ecosystem-based approach to managing fishing impacts. We addressed this knowledge gap using a large-scale experiment that created a controlled gradient of fishing intensity and assessed the immediate impacts and short-term recovery. We observed a mosaic of taxon-specific responses at various thresholds. The lowest threshold of significant lasting impact occurred between 1 and 3 times fished and elicited a decrease in abundance of 39 to 70% for some sessile epifaunal organisms (cnidarians, bryozoans). This contrasted with significant increases in abundance and/or biomass of scavenging species (epifaunal echinoderms, infaunal crustaceans) by two to four-fold in areas fished twice and more. In spite of these significant specific responses, the benthic community structure, biomass and abundance at the population level appeared resilient to fishing. Overall, natural temporal variation in community metrics exceeded the effects of fishing in this highly dynamic study site, suggesting that an acute level of disturbance (fished over six times) would match the level of natural variation. We discuss the implications of our findings for natural resources management with respect to context-specific human disturbance and provide guidance for best fishing practices. An Ecosystem-Based Approach to Fisheries (EAF) 1 takes account of the interaction between exploited species and their ecosystems. EAF is embodied in legislation such as the U.S. Magnuson-Stevens Fisheries Conservation and Management Act in relation to the effects of fishing on Essential Fish Habitat and in Europe through the Marine Strategy Framework Directive (MSFD) 2 , which seeks to define targets for 'Good Environmental Status' (GES) 3 . Fishing impacts on seabed ecosystems can be reduced by spatial and temporal closures 4 . However, such approaches often do not account for displacement effects and can potentially lead to worse outcomes if fishing is displaced to areas where the ecosystem components are more sensitive to disturbance 5 . The quantification of fishing intensity thresholds for ecosystem components other than the target species (below which the maintenance or recovery of ecosystems is not impeded by fishing activity) would offer the possibility of a more sophisticated management. The latter approach could be implemented with real-time incentives such as habitat quotas that promote fishing behaviours that minimise their associated impacts 6 . Studies that have quantified the impact of fishing on benthic communities have used small-scale "Before-After Control-Impact" (BACI) experiments 7 or have been large-scale long term studies of chronic fishing activities by commercial vessels. In general, smaller-scale studies give relatively short recovery times while larger-scale studies estimate recovery times from <3 years 8, 9 to 5-10 years . The spatial scale of disturbance and proximity of potential recruits appear to be important factors that explain the mechanism of recovery 12 . Recovery rate is habitat-and fishing gear-dependent 13 . Recovery times following scallop dredging on sand and gravel are longer than for beam trawling or otter trawling 13 , with scallop dredging having the greatest negative impact across all habitat types 11 . Typically, fishing is likely to have a prolonged negative effect on communities and habitats in areas that experience low natural disturbance but reduced effects in more dynamic habitats . Some habitats are highly sensitive to fishing disturbance with a very limited capacity for recovery, e.g. biogenic habitats such as maerl beds, and reef-forming biota such as bivalves, sponges and corals . In contrast, areas subjected to high natural disturbance, such as shallow wave-swept areas, are characterized by communities adapted to these more disturbed conditions and tend to be species-poor and dominated by small short-lived species, and are therefore
Global analysis of response and recovery of benthic biota to fishing
2006
Abstract: Towed bottom-fishing gears are thought to constitute one of the largest global anthropogenic sources of disturbance to the seabed and its biota. The current drive towards an ecosystem approach in fisheries management requires a consideration of the implications of habitat deterioration and an understanding of the potential for restoration. We undertook a meta-analysis of 101 different fishing impact manipulations. The direct effects of different types of fishing gear were strongly habitat-specific.
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