This study presents a comprehensive and generic framework that provides a typology for the identi... more This study presents a comprehensive and generic framework that provides a typology for the identification and selection of consistently defined ecosystem-based management measures and allows a coherent evaluation of these measures based on their performance to achieve policy objectives. The performance is expressed in terms of their reduction of risk of an adverse impact on the marine ecosystem. This typology consists of two interlinked aspects of a measure, i.e. the "Focus" and the "Type". The "Focus" is determined by the part of the impact chain (Driver-Pressure-State) the measure is supposed to mitigate or counteract. The "Type" represents the physical measure itself in terms of how it affects the impact chain directly; we distinguish Spatio-temporal distribution controls, Input and Output controls, Remediation and Restoration measures. The performance of these measures in terms of their reduction in risk of adverse impacts was assessed based on an explicit consideration of three time horizons: past, present and future. Application of the framework in an integrated management strategy evaluation of a suite of measures, shows that depending on the time horizon, different measures perform best. "Past" points to measures targeting persistent pressures (e.g. marine litter) from past activities. "Present" favours measures targeting a driver (e.g. fisheries) that has a high likelihood of causing adverse impacts. "Future" involves impacts that both have a high likelihood of an adverse impact, as well as a long time to return to pre-impacted condition after the implementation of appropriate management, e.g. those caused by permanent infrastructure or persistent pressures such as marine litter or specific types of pollution.
A risk-assessment identifies the main threats to societal goals. • The effectiveness of EBM was e... more A risk-assessment identifies the main threats to societal goals. • The effectiveness of EBM was evaluated using a risk-based approach. • The exercise suggests improvements to the current knowledge base.
Ecological risk assessment is often applied to guide the decision-making process that underpins e... more Ecological risk assessment is often applied to guide the decision-making process that underpins ecosystem-based management and prioritisation of risk factors for management. Several studies have recently used ecological risk assessment approaches to identify risk factors of greatest concern, but rarely are the underlying methodological decisions discussed in terms of the effect that those decisions have on the outcome of the assessment and ultimately, how that affects prioritisation of risk factors for management. This study therefore evaluates the effect of methodological decisions involving (1) the choice and definition of risk factors, and (2) the calculation of risk scores, providing, where possible, recommendations on what should be the most appropriate methodologies. The definition of risk factors is often determined by the policy context and could result in the comparison of one broadly defined risk meta-factor (e.g. Food Production) with corresponding specific risk factors defined more narrowly (i.e. Oil and Gas production or Offshore Wind). Depending on the method to calculate risk this may result in a systematic bias prioritising any risk meta-factor. For the calculation of individual impact chain risk scores we compared weighted scores with ordinal scores, where the former allows more flexibility to represent the qualitative categories that determine risk and provided results better supported by scientific evidence. A consideration of different risk assessment applications in EBM showed there is no one-size-fits-all solution to this as these methodological decisions need to be considered in concert and the preferred methodology may depend on the context in which the risk assessment is applied. The outcome of the risk assessment should always be accompanied by an explicit consideration of these methodological issues and description of the resulting methodological choices.
Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative ... more Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative impact on benthic fauna. We conducted a large-scale assessment of bottom trawl fishing of benthic fauna in different habitats, using a theoretical, size-based model that included habitat features. Species richness was estimated based on a generalized body mass versus species richness relationship. The model was validated by sampling 33 stations subject to a range of trawling intensities in four shallow, soft sediment areas in the North Sea. Both the model and the field data demonstrated that trawling reduced biomass, production, and species richness. The impacts of trawling were greatest in areas with low levels of natural disturbance, while the impact of trawling was small in areas with high rates of natural disturbance. For the North Sea, the model showed that the bottom trawl fleet reduced benthic biomass and production by 56% and 21%, respectively, compared with an unfished situation. Because of the many simplifications and assumptions required to synthesize these data, additional work is required to refine the model and evaluate applicability in other geographic areas. Our model enables managers to understand the consequences of altering the distribution of fishing activities on benthic production and hence on food web processes. Résumé : Le chalutage de fond cause une perturbation générale des sédiments sur les plates-formes marines et peut avoir un impact négatif sur la faune benthique. Nous avons évalué sur une grande échelle les effets de la pêche au chalut de fond sur la faune benthique dans des habitats différents à l'aide d'un modèle théorique basé sur la taille qui inclut des caractéristiques du milieu. Nous avons estimé la richesse spécifique en nous basant sur une relation entre la masse corporelle généralisée et la richesse spécifique. Le modèle a pu être validé par l'échantillonnage de 33 stations soumises à des intensités diverses de chalutage dans quatre régions à sédiments mous de la mer du Nord. Tant le modèle que les données de terrain montrent que le chalutage réduit la biomasse, la production et la richesse en espèces. L'impact du chalutage est maximal dans les zones à perturbations naturelles peu importantes et faible dans les zones de fortes perturbations naturelles. Dans la mer du Nord, le modèle prédit que la flotte de chalutage de fond réduit la biomasse et la production benthiques respectivement de 56 % et de 21 %, par comparaison aux zones non soumises à la pêche. Puisqu'il a fallu faire de nombreuses simplifications et présuppositions afin de synthétiser ces données, il faudra beaucoup de travail additionnel pour raffiner le modèle et pour vérifier s'il s'applique à d'autres régions géographiques. Notre modèle permet aux gestionnaires de comprendre les conséquences du changement des répartitions des activités de pêche sur la production du benthos et, par conséquent, sur les processus du réseau alimentaire. [Traduit par la Rédaction] Hiddink et al. 736
The impacts of fisheries on ocean resources are no longer considered in isolation but should acco... more The impacts of fisheries on ocean resources are no longer considered in isolation but should account for broader ecosystem effects. However, ongoing ecosystem-wide changes added to the inherent dynamics of marine ecosystems, create challenges for fisheries and fisheries management by affecting our ability to ensure future fishing opportunities and sustainable use of the seas. By reviewing a corpus of fisheries science literature, we contribute to informing managers and policymakers with considerations of the various threats to fisheries and the marine ecosystems that support them. We identify and describe 25 ecosystem challenges and 7 prominent families of management options to address them. We capture the challenges acting within three broad categories: (i) fishing impacts on the marine environments and future fishing opportunities, (ii) effects of environmental conditions on fish and fishing opportunities, and (iii) effects of context in terms of socioeconomics, fisheries manageme...
Ecosystem-Based Management, Ecosystem Services and Aquatic Biodiversity
In this study we present an integrated Ecosystem-Based Management (EBM) approach that attempts to... more In this study we present an integrated Ecosystem-Based Management (EBM) approach that attempts to reconcile several concepts including integrated ecosystem assessment (IEA), marine spatial planning, resilience thinking, and complex adaptive systems. The approach builds on the IEA process but enhances it by explicitly considering the full social-ecological system (SES) and the creation of a generic framework for assessment of ecosystem status and management strategy evaluation.
Fishing has wide-ranging impacts on marine ecosystems. One of the most pervasive signs of intensi... more Fishing has wide-ranging impacts on marine ecosystems. One of the most pervasive signs of intensive fishing is ''fishing down the food web'', with landings increasingly dominated by smaller species from lower trophic levels. Decreases in the trophic level of landings are assumed to reflect those in fish communities, because size-selective mortality causes decreases in the relative abundance of larger species and in mean body size within species. However, existing analyses of fishing impacts on the trophic level of fish communities have focused on the role of changes in species composition rather than size composition. This will provide a biased assessment of the magnitude of fishing impacts, because fishes feed at different trophic levels as they grow. Here, we combine body size versus trophic level relationships for North Sea fishes (trophic level assessed using nitrogen stable-isotope analysis) with species-size-abundance data from two time-series of trawl-survey data (whole North Sea 1982-2000, central and northern North Sea 1925-1996) to predict long-term trends in the trophic structure of the North Sea fish community. Analyses of the 1982-2000 time-series showed that there was a slow but progressive decline in the trophic level of the demersal community, while there was no trend in the trophic level of the combined pelagic and demersal community. Analyses of the longer time-series suggested that there was no trend in the trophic level of the demersal community. We related temporal changes in trophic level to temporal changes in the slopes of normalised biomass size-spectra (which theoretically represent the trophic structure of the community), mean log 2 body mass and mean log 2 maximum body mass. While the size-based metrics of community structure showed long-term trends that were consistent with the effects of increased fishery exploitation, these trends were only correlated with trophic level for the demersal community. Our analysis suggests that the effects of fishing on the trophic structure of fish communities can be much more complex than previously assumed. This is a consequence of sampled communities not reflecting all the pathways of energy transfer in a marine ecosystem and of the absence of historical data on temporal and spatial changes in the trophic level of individuals. For the North Sea fish community, changes in size structure due to the differential effects of fishing on species and populations with different life histories are a stronger and more universal indicator of fishing effects than changes in mean trophic level. 1999; Gislason and Sinclair 2000).
and applied knowledge based on its mission 'To explore the potential of nature to improve the qua... more and applied knowledge based on its mission 'To explore the potential of nature to improve the quality of life'. In this way WUR contributes to solving important questions in the field of healthy food and living environment. Our 5,500 employees and more than 12,000 students are inspired by nature, society and technology, inspiration that has enabled us for more than a century to marvel, to develop knowledge and to apply it worldwide. And we do not do this alone, but as much as possible together with government agencies and public bodies, the business community, non-governmental organisations and other universities and research institutes.
The capacity of ecosystems to supply ecosystem services is decreasing. Sustaining this supply req... more The capacity of ecosystems to supply ecosystem services is decreasing. Sustaining this supply requires an understanding of the links between the impacts of pressures introduced by human activities and how this can lead to changes in the supply of services. Here, we apply a novel approach, assessing 'risk to ecosystem service supply' (RESS), across a range of aquatic ecosystems in seven case studies. We link aggregate impact risk from human activities on ecosystem components, with a relative score of their potential to supply services. The greatest RESS is found where an ecosystem component with a high potential to supply services is subject to high impact risk. In this context, we explore variability in RESS across 99 types of aquatic ecosystem component from 11 realms, ranging from oceanic to wetlands. We explore some causes of variability in the RESS observed, including assessment area, Gross Domestic Product (GDP) and population density. We found that Lakes, Rivers, Inlets and Coastal realms had some of the highest RESS, though this was highly dependent on location. We found a positive j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v relationship between impact risk and service supply potential, indicating the ecosystem components we rely on most for services, are also those most at risk. However, variability in this relationship indicates that protecting the supply of ecosystem services alone will not protect all parts of the ecosystem at high risk. Broad socio-economic factors explained some of the variability found in RESS. For example, RESS was positively associated with GDP and artificial and agricultural land use in most realms, highlighting the need to achieve balance between increasing GDP and sustaining ecosystem health and human wellbeing more broadly. This approach can be used for sustainable management of ecosystem service use, to highlight the ecosystem components most critical to supplying services, and those most at risk.
Global initiatives have been increasingly focusing on mainstreaming the values of biodiversity an... more Global initiatives have been increasingly focusing on mainstreaming the values of biodiversity and ecosystem services into decision-making at all levels. Due to the accelerated rate at which biodiversity is declining and its consequences for the functioning of ecosystems and subsequently, the services they provide, there is need to develop comprehensive assessments of the services and the benefits nature delivers to society. Based on expert evaluation, we identified relevant flow linkages in the supply-side of the socio-ecological system, i.e. from biodiversity to ecosystem services supply for eight case studies across European aquatic ecosystems covering freshwater, transitional, coastal and marine waters realms. Biological mediated services were considered, as well as those reliant on purely physical aspects of the ecosystem, i.e. abiotic outputs, since both have implications for spatial j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v planning, management and decision-making. Due to the multidimensional nature of ecosystems and their biodiversity, our approach used ecosystem components such as habitats and biota as proxies for biodiversity and as the focal point for linkage identification. Statistical analysis revealed the importance of considering mobile biota in the spatial assessment of habitats. Contrary to literature evidences so far, our results showed significantly different and complementary ecosystem services supply patterns across the continuum of aquatic realms. The implemented score of ecosystem services supply has a high potential for integrated aquatic ecosystem service supply assessments in the context of ecosystem-based management.
Aquatic ecosystems are under severe pressure. Human activities introduce an array of pressures th... more Aquatic ecosystems are under severe pressure. Human activities introduce an array of pressures that impact ecosystems and their components. In this study we focus on the aquatic domains of fresh, coastal and marine waters, including rivers, lakes and riparian habitats to transitional, coastal as well as shelf and oceanic habitats. In an environmental risk assessment approach, we identified impact chains that link 45 human activities through 31 pressures to 82 ecosystem components. In this linkage framework N22,000 activity-pressure-ecosystem component interactions were found across seven European case studies. We identified the environmental impact risk posed by each impact chain by first categorically weighting the interactions according to five criteria: spatial extent, dispersal potential, frequency of interaction, persistence of pressure and severity of the interaction, where extent, dispersal, frequency and persistence account for the exposure to risk (spatial and temporal), and the severity accounts for the consequence of the risk. After assigning a numerical score to each risk criterion, we came up with an overall environmental impact risk score for each impact chain. This risk score was analysed in terms of (1) the activities and pressures that introduce the greatest risk to European aquatic domains, and (2) the aquatic ecosystem components and realms that are at greatest risk from human activities. Activities related to energy j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v production were relevant across the aquatic domains. Fishing was highly relevant in marine and environmental engineering in fresh waters. Chemical and physical pressures introduced the greatest risk to the aquatic realms. Ecosystem components that can be seen as ecotones between different ecosystems had high impact risk. We show how this information can be used in informing management on trade-offs in freshwater, coastal and marine resource use and aid decision-making.
The 'Wild Seafood' Provisioning Service (WSPS), on which commercial fisheries rely, is probably o... more The 'Wild Seafood' Provisioning Service (WSPS), on which commercial fisheries rely, is probably one of the best studied marine ecosystem services due to its economic relevance and because extensive information sources exist for assessment purposes. Yet, the indicators often proposed are not suitable to describe the capacity of the ecosystem to deliver the WSPS. Therefore this study proposes surplus production (SP), a well-established concept in fisheries science, as the basis to calculate the capacity of marine ecosystems to provide the WSPS. SP is defined as the difference between stock production (through recruitment and body growth) and losses through natural mortality. This is, therefore, the production of the stock that could be harvested sustainably without decreasing the biomass. To assess the sustainability of the exploitation of the WSPS we also developed an indicator for this based on SP and compared it to existing fisheries management indicators. When both SP-based indicators showed a decreasing trend, contrasting with an increasing trend in the existing fisheries management indicators, the calculation of the SP-based indicators was scrutinized revealing that the weighting of the stocks into an aggregated indicator, strongly determines the indicator values, even up to the point that the trend is reversed. The aggregated indicators based on SP-weighted stocks can be considered complementary to existing fisheries management indicators as the former accurately reflect the capacity of the commercial fish to provide the WSPS and the sustainability of the exploitation of this service. In contrast the existing fisheries management indicators primarily reflect the performance of management towards achieving fisheries-specific policy goals.
... Numerous fry of O. mossambicus were caught with the fine-meshed scoop net in the shallowest pa... more ... Numerous fry of O. mossambicus were caught with the fine-meshed scoop net in the shallowest parts of the littoral zone. The bottom trawl and hoop net yielded fry and juveniles of all otherspecies except Barbus spp. The species composition of gillnet catches (Fig. ...
Ten species of flatfish were studied to see to what extent interspecific competition influences t... more Ten species of flatfish were studied to see to what extent interspecific competition influences their diet or spatial distribution and whether the potential of these flatfish species to avoid interspecific competition through resource partitioning is constrained by specific morphological characteristics. For this, seven morphological characteristics were measured, diet composition was determined from gut content analyses and overlap in distribution was determined from the co-occurrence in trawl hauls. Canonical correspondence analysis revealed the morphological characteristics that were most strongly correlated with the diet composition. Based on these findings the mouth gape was considered to be the most important morphological constraint affecting the choice of food. Two resource dimensions were distinguished along which interspecific competition can act on the flatfish assemblage: the trophic dimension (diet composition) and the spatial dimension (distribution). Resource partitioning was observed along both dimensions separately and, more importantly, the degree of resource partitioning along the two dimensions was negatively correlated. Especially the latter was considered strong circumstantial evidence that interspecific competition is a major factor structuring the flatfish assemblage. Resource partitioning along the two resource dimensions increased with decreasing mouth gape, suggesting that interspecific competition mainly acts on the small-mouthed fish, i.e. juveniles.
This study presents a comprehensive and generic framework that provides a typology for the identi... more This study presents a comprehensive and generic framework that provides a typology for the identification and selection of consistently defined ecosystem-based management measures and allows a coherent evaluation of these measures based on their performance to achieve policy objectives. The performance is expressed in terms of their reduction of risk of an adverse impact on the marine ecosystem. This typology consists of two interlinked aspects of a measure, i.e. the "Focus" and the "Type". The "Focus" is determined by the part of the impact chain (Driver-Pressure-State) the measure is supposed to mitigate or counteract. The "Type" represents the physical measure itself in terms of how it affects the impact chain directly; we distinguish Spatio-temporal distribution controls, Input and Output controls, Remediation and Restoration measures. The performance of these measures in terms of their reduction in risk of adverse impacts was assessed based on an explicit consideration of three time horizons: past, present and future. Application of the framework in an integrated management strategy evaluation of a suite of measures, shows that depending on the time horizon, different measures perform best. "Past" points to measures targeting persistent pressures (e.g. marine litter) from past activities. "Present" favours measures targeting a driver (e.g. fisheries) that has a high likelihood of causing adverse impacts. "Future" involves impacts that both have a high likelihood of an adverse impact, as well as a long time to return to pre-impacted condition after the implementation of appropriate management, e.g. those caused by permanent infrastructure or persistent pressures such as marine litter or specific types of pollution.
A risk-assessment identifies the main threats to societal goals. • The effectiveness of EBM was e... more A risk-assessment identifies the main threats to societal goals. • The effectiveness of EBM was evaluated using a risk-based approach. • The exercise suggests improvements to the current knowledge base.
Ecological risk assessment is often applied to guide the decision-making process that underpins e... more Ecological risk assessment is often applied to guide the decision-making process that underpins ecosystem-based management and prioritisation of risk factors for management. Several studies have recently used ecological risk assessment approaches to identify risk factors of greatest concern, but rarely are the underlying methodological decisions discussed in terms of the effect that those decisions have on the outcome of the assessment and ultimately, how that affects prioritisation of risk factors for management. This study therefore evaluates the effect of methodological decisions involving (1) the choice and definition of risk factors, and (2) the calculation of risk scores, providing, where possible, recommendations on what should be the most appropriate methodologies. The definition of risk factors is often determined by the policy context and could result in the comparison of one broadly defined risk meta-factor (e.g. Food Production) with corresponding specific risk factors defined more narrowly (i.e. Oil and Gas production or Offshore Wind). Depending on the method to calculate risk this may result in a systematic bias prioritising any risk meta-factor. For the calculation of individual impact chain risk scores we compared weighted scores with ordinal scores, where the former allows more flexibility to represent the qualitative categories that determine risk and provided results better supported by scientific evidence. A consideration of different risk assessment applications in EBM showed there is no one-size-fits-all solution to this as these methodological decisions need to be considered in concert and the preferred methodology may depend on the context in which the risk assessment is applied. The outcome of the risk assessment should always be accompanied by an explicit consideration of these methodological issues and description of the resulting methodological choices.
Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative ... more Bottom trawling causes widespread disturbance of sediments in shelf seas and can have a negative impact on benthic fauna. We conducted a large-scale assessment of bottom trawl fishing of benthic fauna in different habitats, using a theoretical, size-based model that included habitat features. Species richness was estimated based on a generalized body mass versus species richness relationship. The model was validated by sampling 33 stations subject to a range of trawling intensities in four shallow, soft sediment areas in the North Sea. Both the model and the field data demonstrated that trawling reduced biomass, production, and species richness. The impacts of trawling were greatest in areas with low levels of natural disturbance, while the impact of trawling was small in areas with high rates of natural disturbance. For the North Sea, the model showed that the bottom trawl fleet reduced benthic biomass and production by 56% and 21%, respectively, compared with an unfished situation. Because of the many simplifications and assumptions required to synthesize these data, additional work is required to refine the model and evaluate applicability in other geographic areas. Our model enables managers to understand the consequences of altering the distribution of fishing activities on benthic production and hence on food web processes. Résumé : Le chalutage de fond cause une perturbation générale des sédiments sur les plates-formes marines et peut avoir un impact négatif sur la faune benthique. Nous avons évalué sur une grande échelle les effets de la pêche au chalut de fond sur la faune benthique dans des habitats différents à l'aide d'un modèle théorique basé sur la taille qui inclut des caractéristiques du milieu. Nous avons estimé la richesse spécifique en nous basant sur une relation entre la masse corporelle généralisée et la richesse spécifique. Le modèle a pu être validé par l'échantillonnage de 33 stations soumises à des intensités diverses de chalutage dans quatre régions à sédiments mous de la mer du Nord. Tant le modèle que les données de terrain montrent que le chalutage réduit la biomasse, la production et la richesse en espèces. L'impact du chalutage est maximal dans les zones à perturbations naturelles peu importantes et faible dans les zones de fortes perturbations naturelles. Dans la mer du Nord, le modèle prédit que la flotte de chalutage de fond réduit la biomasse et la production benthiques respectivement de 56 % et de 21 %, par comparaison aux zones non soumises à la pêche. Puisqu'il a fallu faire de nombreuses simplifications et présuppositions afin de synthétiser ces données, il faudra beaucoup de travail additionnel pour raffiner le modèle et pour vérifier s'il s'applique à d'autres régions géographiques. Notre modèle permet aux gestionnaires de comprendre les conséquences du changement des répartitions des activités de pêche sur la production du benthos et, par conséquent, sur les processus du réseau alimentaire. [Traduit par la Rédaction] Hiddink et al. 736
The impacts of fisheries on ocean resources are no longer considered in isolation but should acco... more The impacts of fisheries on ocean resources are no longer considered in isolation but should account for broader ecosystem effects. However, ongoing ecosystem-wide changes added to the inherent dynamics of marine ecosystems, create challenges for fisheries and fisheries management by affecting our ability to ensure future fishing opportunities and sustainable use of the seas. By reviewing a corpus of fisheries science literature, we contribute to informing managers and policymakers with considerations of the various threats to fisheries and the marine ecosystems that support them. We identify and describe 25 ecosystem challenges and 7 prominent families of management options to address them. We capture the challenges acting within three broad categories: (i) fishing impacts on the marine environments and future fishing opportunities, (ii) effects of environmental conditions on fish and fishing opportunities, and (iii) effects of context in terms of socioeconomics, fisheries manageme...
Ecosystem-Based Management, Ecosystem Services and Aquatic Biodiversity
In this study we present an integrated Ecosystem-Based Management (EBM) approach that attempts to... more In this study we present an integrated Ecosystem-Based Management (EBM) approach that attempts to reconcile several concepts including integrated ecosystem assessment (IEA), marine spatial planning, resilience thinking, and complex adaptive systems. The approach builds on the IEA process but enhances it by explicitly considering the full social-ecological system (SES) and the creation of a generic framework for assessment of ecosystem status and management strategy evaluation.
Fishing has wide-ranging impacts on marine ecosystems. One of the most pervasive signs of intensi... more Fishing has wide-ranging impacts on marine ecosystems. One of the most pervasive signs of intensive fishing is ''fishing down the food web'', with landings increasingly dominated by smaller species from lower trophic levels. Decreases in the trophic level of landings are assumed to reflect those in fish communities, because size-selective mortality causes decreases in the relative abundance of larger species and in mean body size within species. However, existing analyses of fishing impacts on the trophic level of fish communities have focused on the role of changes in species composition rather than size composition. This will provide a biased assessment of the magnitude of fishing impacts, because fishes feed at different trophic levels as they grow. Here, we combine body size versus trophic level relationships for North Sea fishes (trophic level assessed using nitrogen stable-isotope analysis) with species-size-abundance data from two time-series of trawl-survey data (whole North Sea 1982-2000, central and northern North Sea 1925-1996) to predict long-term trends in the trophic structure of the North Sea fish community. Analyses of the 1982-2000 time-series showed that there was a slow but progressive decline in the trophic level of the demersal community, while there was no trend in the trophic level of the combined pelagic and demersal community. Analyses of the longer time-series suggested that there was no trend in the trophic level of the demersal community. We related temporal changes in trophic level to temporal changes in the slopes of normalised biomass size-spectra (which theoretically represent the trophic structure of the community), mean log 2 body mass and mean log 2 maximum body mass. While the size-based metrics of community structure showed long-term trends that were consistent with the effects of increased fishery exploitation, these trends were only correlated with trophic level for the demersal community. Our analysis suggests that the effects of fishing on the trophic structure of fish communities can be much more complex than previously assumed. This is a consequence of sampled communities not reflecting all the pathways of energy transfer in a marine ecosystem and of the absence of historical data on temporal and spatial changes in the trophic level of individuals. For the North Sea fish community, changes in size structure due to the differential effects of fishing on species and populations with different life histories are a stronger and more universal indicator of fishing effects than changes in mean trophic level. 1999; Gislason and Sinclair 2000).
and applied knowledge based on its mission 'To explore the potential of nature to improve the qua... more and applied knowledge based on its mission 'To explore the potential of nature to improve the quality of life'. In this way WUR contributes to solving important questions in the field of healthy food and living environment. Our 5,500 employees and more than 12,000 students are inspired by nature, society and technology, inspiration that has enabled us for more than a century to marvel, to develop knowledge and to apply it worldwide. And we do not do this alone, but as much as possible together with government agencies and public bodies, the business community, non-governmental organisations and other universities and research institutes.
The capacity of ecosystems to supply ecosystem services is decreasing. Sustaining this supply req... more The capacity of ecosystems to supply ecosystem services is decreasing. Sustaining this supply requires an understanding of the links between the impacts of pressures introduced by human activities and how this can lead to changes in the supply of services. Here, we apply a novel approach, assessing 'risk to ecosystem service supply' (RESS), across a range of aquatic ecosystems in seven case studies. We link aggregate impact risk from human activities on ecosystem components, with a relative score of their potential to supply services. The greatest RESS is found where an ecosystem component with a high potential to supply services is subject to high impact risk. In this context, we explore variability in RESS across 99 types of aquatic ecosystem component from 11 realms, ranging from oceanic to wetlands. We explore some causes of variability in the RESS observed, including assessment area, Gross Domestic Product (GDP) and population density. We found that Lakes, Rivers, Inlets and Coastal realms had some of the highest RESS, though this was highly dependent on location. We found a positive j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v relationship between impact risk and service supply potential, indicating the ecosystem components we rely on most for services, are also those most at risk. However, variability in this relationship indicates that protecting the supply of ecosystem services alone will not protect all parts of the ecosystem at high risk. Broad socio-economic factors explained some of the variability found in RESS. For example, RESS was positively associated with GDP and artificial and agricultural land use in most realms, highlighting the need to achieve balance between increasing GDP and sustaining ecosystem health and human wellbeing more broadly. This approach can be used for sustainable management of ecosystem service use, to highlight the ecosystem components most critical to supplying services, and those most at risk.
Global initiatives have been increasingly focusing on mainstreaming the values of biodiversity an... more Global initiatives have been increasingly focusing on mainstreaming the values of biodiversity and ecosystem services into decision-making at all levels. Due to the accelerated rate at which biodiversity is declining and its consequences for the functioning of ecosystems and subsequently, the services they provide, there is need to develop comprehensive assessments of the services and the benefits nature delivers to society. Based on expert evaluation, we identified relevant flow linkages in the supply-side of the socio-ecological system, i.e. from biodiversity to ecosystem services supply for eight case studies across European aquatic ecosystems covering freshwater, transitional, coastal and marine waters realms. Biological mediated services were considered, as well as those reliant on purely physical aspects of the ecosystem, i.e. abiotic outputs, since both have implications for spatial j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v planning, management and decision-making. Due to the multidimensional nature of ecosystems and their biodiversity, our approach used ecosystem components such as habitats and biota as proxies for biodiversity and as the focal point for linkage identification. Statistical analysis revealed the importance of considering mobile biota in the spatial assessment of habitats. Contrary to literature evidences so far, our results showed significantly different and complementary ecosystem services supply patterns across the continuum of aquatic realms. The implemented score of ecosystem services supply has a high potential for integrated aquatic ecosystem service supply assessments in the context of ecosystem-based management.
Aquatic ecosystems are under severe pressure. Human activities introduce an array of pressures th... more Aquatic ecosystems are under severe pressure. Human activities introduce an array of pressures that impact ecosystems and their components. In this study we focus on the aquatic domains of fresh, coastal and marine waters, including rivers, lakes and riparian habitats to transitional, coastal as well as shelf and oceanic habitats. In an environmental risk assessment approach, we identified impact chains that link 45 human activities through 31 pressures to 82 ecosystem components. In this linkage framework N22,000 activity-pressure-ecosystem component interactions were found across seven European case studies. We identified the environmental impact risk posed by each impact chain by first categorically weighting the interactions according to five criteria: spatial extent, dispersal potential, frequency of interaction, persistence of pressure and severity of the interaction, where extent, dispersal, frequency and persistence account for the exposure to risk (spatial and temporal), and the severity accounts for the consequence of the risk. After assigning a numerical score to each risk criterion, we came up with an overall environmental impact risk score for each impact chain. This risk score was analysed in terms of (1) the activities and pressures that introduce the greatest risk to European aquatic domains, and (2) the aquatic ecosystem components and realms that are at greatest risk from human activities. Activities related to energy j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s c i t o t e n v production were relevant across the aquatic domains. Fishing was highly relevant in marine and environmental engineering in fresh waters. Chemical and physical pressures introduced the greatest risk to the aquatic realms. Ecosystem components that can be seen as ecotones between different ecosystems had high impact risk. We show how this information can be used in informing management on trade-offs in freshwater, coastal and marine resource use and aid decision-making.
The 'Wild Seafood' Provisioning Service (WSPS), on which commercial fisheries rely, is probably o... more The 'Wild Seafood' Provisioning Service (WSPS), on which commercial fisheries rely, is probably one of the best studied marine ecosystem services due to its economic relevance and because extensive information sources exist for assessment purposes. Yet, the indicators often proposed are not suitable to describe the capacity of the ecosystem to deliver the WSPS. Therefore this study proposes surplus production (SP), a well-established concept in fisheries science, as the basis to calculate the capacity of marine ecosystems to provide the WSPS. SP is defined as the difference between stock production (through recruitment and body growth) and losses through natural mortality. This is, therefore, the production of the stock that could be harvested sustainably without decreasing the biomass. To assess the sustainability of the exploitation of the WSPS we also developed an indicator for this based on SP and compared it to existing fisheries management indicators. When both SP-based indicators showed a decreasing trend, contrasting with an increasing trend in the existing fisheries management indicators, the calculation of the SP-based indicators was scrutinized revealing that the weighting of the stocks into an aggregated indicator, strongly determines the indicator values, even up to the point that the trend is reversed. The aggregated indicators based on SP-weighted stocks can be considered complementary to existing fisheries management indicators as the former accurately reflect the capacity of the commercial fish to provide the WSPS and the sustainability of the exploitation of this service. In contrast the existing fisheries management indicators primarily reflect the performance of management towards achieving fisheries-specific policy goals.
... Numerous fry of O. mossambicus were caught with the fine-meshed scoop net in the shallowest pa... more ... Numerous fry of O. mossambicus were caught with the fine-meshed scoop net in the shallowest parts of the littoral zone. The bottom trawl and hoop net yielded fry and juveniles of all otherspecies except Barbus spp. The species composition of gillnet catches (Fig. ...
Ten species of flatfish were studied to see to what extent interspecific competition influences t... more Ten species of flatfish were studied to see to what extent interspecific competition influences their diet or spatial distribution and whether the potential of these flatfish species to avoid interspecific competition through resource partitioning is constrained by specific morphological characteristics. For this, seven morphological characteristics were measured, diet composition was determined from gut content analyses and overlap in distribution was determined from the co-occurrence in trawl hauls. Canonical correspondence analysis revealed the morphological characteristics that were most strongly correlated with the diet composition. Based on these findings the mouth gape was considered to be the most important morphological constraint affecting the choice of food. Two resource dimensions were distinguished along which interspecific competition can act on the flatfish assemblage: the trophic dimension (diet composition) and the spatial dimension (distribution). Resource partitioning was observed along both dimensions separately and, more importantly, the degree of resource partitioning along the two dimensions was negatively correlated. Especially the latter was considered strong circumstantial evidence that interspecific competition is a major factor structuring the flatfish assemblage. Resource partitioning along the two resource dimensions increased with decreasing mouth gape, suggesting that interspecific competition mainly acts on the small-mouthed fish, i.e. juveniles.
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Papers by Gerjan Piet