Globally, spatial distributions of fish stocks are shifting but although the role of climate change in range shifts is increasingly appreciated, little remains known of the likely additional impact ...that high levels of fishing pressure might have on distribution. For North Sea cod, we show for the first time and in great spatial detail how the stock has shifted its distribution over the past 100 years. We digitized extensive historical fisheries data from paper charts in UK government archives and combined these with contemporary data to a time‐series spanning 1913–2012 (excluding both World Wars). New analysis of old data revealed that the current distribution pattern of cod – mostly in the deeper, northern‐ and north‐easternmost parts of the North Sea – is almost opposite to that during most of the Twentieth Century – mainly concentrated in the west, off England and Scotland. Statistical analysis revealed that the deepening, northward shift is likely attributable to warming; however, the eastward shift is best explained by fishing pressure, suggestive of significant depletion of the stock from its previous stronghold, off the coasts of England and Scotland. These spatial patterns were confirmed for the most recent 3½ decades by data from fisheries‐independent surveys, which go back to the 1970s. Our results demonstrate the fundamental importance of both climate change and fishing pressure for our understanding of changing distributions of commercially exploited fish.
Rijnsdorp, A. D., Peck, M. A., Engelhard, G. H., Möllmann, C., and Pinnegar, J. K. 2009. Resolving the effect of climate change on fish populations. – ICES Journal of Marine Science, 66: ...1570–1583.This paper develops a framework for the study of climate on fish populations based on first principles of physiology, ecology, and available observations. Environmental variables and oceanographic features that are relevant to fish and that are likely to be affected by climate change are reviewed. Working hypotheses are derived from the differences in the expected response of different species groups. A review of published data on Northeast Atlantic fish species representing different biogeographic affinities, habitats, and body size lends support to the hypothesis that global warming results in a shift in abundance and distribution (in patterns of occurrence with latitude and depth) of fish species. Pelagic species exhibit clear changes in seasonal migration patterns related to climate-induced changes in zooplankton productivity. Lusitanian species have increased in recent decades (sprat, anchovy, and horse mackerel), especially at the northern limit of their distribution areas, while Boreal species decreased at the southern limit of their distribution range (cod and plaice), but increased at the northern limit (cod). Although the underlying mechanisms remain uncertain, available evidence suggests climate-related changes in recruitment success to be the key process, stemming from either higher production or survival in the pelagic egg or larval stage, or owing to changes in the quality/quantity of nursery habitats.
With the majority of the global human population living in coastal regions, correctly characterizing the climate risk that ocean-dependent communities and businesses are exposed to is key to ...prioritizing the finite resources available to support adaptation. We apply a climate risk analysis across the European fisheries sector to identify the most at-risk fishing fleets and coastal regions and then link the two analyses together. We employ an approach combining biological traits with physiological metrics to differentiate climate hazards between 556 populations of fish and use these to assess the relative climate risk for 380 fishing fleets and 105 coastal regions in Europe. Countries in southeast Europe as well as the United Kingdom have the highest risks to both fishing fleets and coastal regions overall, while in other countries, the risk-profile is greater at either the fleet level or at the regional level. European fisheries face a diversity of challenges posed by climate change; climate adaptation, therefore, needs to be tailored to each country, region, and fleet's specific situation. Our analysis supports this process by highlighting where and what adaptation measures might be needed and informing where policy and business responses could have the greatest impact.
Ecologists and managers need to understand what types of communities emerge with continued human alterations to ecosystems against a background of natural change. Both natural and anthropogenic ...drivers are well known to affect organisms’ distributions; however, it often remains unclear where along a range of environmental and anthropogenic gradients important compositional community changes occur.
We used a big‐data approach, including over 175,000 presence records of benthic genera for the North Sea, to identify environmental (bed shear stress, sediment grain size, temperature) and anthropogenic parameters (trawling effort) driving benthic community composition over a 21‐year period. We applied a Gradient Forest analysis, based on Random Forests, to estimate the locations and importance of thresholds where small cumulative increases in the predictors drive a much greater change in genus composition than would be expected from linear effects.
Shear stress was the most important predictor of benthic community composition. Trawling effort, temperature gradients and sediment grain size were of intermediate importance. This corroborates that current and wave effects (typically associated with seabed substrate types) are primary determinants of benthic communities.
Our results suggest that a genus composition threshold for both infauna and epifaunal benthic communities is crossed when the seafloor is trawled as little as once every 4 years. Higher trawling levels corresponded with gradual compositional change without obvious thresholds, which would be consistent with chronic fishing in the North Sea over the last two centuries having caused persistent, long‐term changes in ecosystem structure and functioning. This was corroborated by the large‐scale spatial patterns of benthic community composition undergoing limited temporal changes during the 21‐year study period.
Synthesis and applications. Although well established in theory, threshold effects are poorly validated in the field. We generated new information on multi‐organism responses to environmental change at the scale of a continental shelf ecosystem and over a multi‐decadal time period. This will help pure and applied scientists better understand the conditions under which community thresholds are crossed and provide environmental managers with empirical evidence that is expected to reduce uncertainty regarding decisions on the protection and sustainable use of the marine environment.
Resumen
Ecologistas y administradores medioambientales necesitan entender el tipo de comunidades que emergen en respuesta a los efectos de las acciones humanas en los ecosistemas, en un contexto de cambio natural. Es bien sabido que tanto los efectos naturales como los antropogénicos impactan las distribuciones de organismos; sin embargo, a menudo no está claro dónde se producen cambios importantes en la composición de las comunidades en un gradiente de variaciones de factores ambientales y antropogénicos.
Realizamos un análisis de ‘big data’, con más de 175,000 registros de presencia de géneros bentónicos en el Mar del Norte, para identificar parámetros naturales (tensión de cizalladura del fondo marino, tamaño de partículas del sedimento, temperatura) y antropogénicos (intensidad de pesca de arrastre) que influencian la composición de la comunidad bentónica en un período de 21 años. Aplicamos un análisis de Gradiente de Bosques Aleatorios (‘Gradient Forests’), una técnica basada en Bosques Aleatorios, para estimar la localización e importancia de los umbrales de transición donde pequeñas variaciones de los predictores provocan cambios mucho mayores en la composición de géneros de las comunidades bentónicas de lo que podía esperarse por efectos lineales.
La tensión de cizalladura es el predictor más importante de la composición de la comunidad bentónica. La intensidad de pesca de arrastre, la temperatura y el tamaño de partículas del sedimento tienen importancia intermedia. Esto corrobora que los efectos de la corriente y las olas (muy relacionados con los tipos de sustrato del fondo marino) son determinantes primarios de las comunidades bentónicas.
Nuestros resultados sugieren que se producen cambios importantes de composición de géneros bentónicos tanto para las comunidades epifaunales como infaunales cuando el fondo marino es sometido a pesca de arrastre tan poco como una vez cada cuatro años. Niveles más altos de pesca de arrastre provocan un cambio gradual de composición sin umbrales obvios, consistente con la hipótesis de que la estructura y funcionamiento de los ecosistemas bentónicos en el Mar del Norte han sufrido cambios persistentes debido a los niveles crónicos de pesca de arrastre que han experimentado durante los dos últimos siglos. Esto es corroborado por las limitadas variaciones en la distribución espacial a gran escala de la composición de comunidades bentónica durante los 21 años del período estudiado.
Síntesis y aplicaciones. Aunque bien establecidos en la teoría, hay pocos datos de campo que validen la existencia de umbrales de transición de ecosistemas. En este trabajo analizamos las respuestas de múltiples organismos al cambio ambiental a la escala de una plataforma continental y durante un período de varias décadas. Nuestros resultados ayudarán a científicos teóricos y aplicados a comprender mejor las condiciones bajo las cuales se cruzan los umbrales de transición de las comunidades bentónicas, y proporcionarán a los administradores ambientales datos empíricos para apoyar decisiones sobre la protección y el uso sostenible del medio marino.
Although well established in theory, threshold effects are poorly validated in the field. We generated new information on multi‐organism responses to environmental change at the scale of a continental shelf ecosystem and over a multi‐decadal time period. This will help pure and applied scientists better understand the conditions under which community thresholds are crossed and provide environmental managers with empirical evidence that is expected to reduce uncertainty regarding decisions on the protection and sustainable use of the marine environment.
The global issues of climate change and marine litter are interlinked and understanding these connections is key to managing their combined risks to marine biodiversity and ultimately society. For ...example, fossil fuel-based plastics cause direct emissions of greenhouse gases and therefore are an important contributing factor to climate change, while other impacts of plastics can manifest as alterations in key species and habitats in coastal and marine environments. Marine litter is acknowledged as a threat multiplier that acts with other stressors such as climate change to cause far greater damage than if they occurred in isolation. On the other hand, while climate change can lead to increased inputs of litter into the marine environment, the presence of marine litter can also undermine the climate resilience of marine ecosystems. There is increasing evidence that that climate change and marine litter are inextricably linked, although these interactions and the resulting effects vary widely across oceanic regions and depend on the particular characteristics of specific marine environments. Ecosystem resilience approaches, that integrate climate change with other local stressors, offer a suitable framework to incorporate the consideration of marine litter where that is deemed to be a risk, and to steer, coordinate and prioritise research and monitoring, as well as management, policy, planning and action to effectively tackle the combined risks and impacts from climate change and marine litter.
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•Climate change influences sources and pathways of global marine litter.•Climate change influences breakdown of marine litter.•Climate change and litter contribute to the spread of non-native species.•Marine litter undermines the climate resilience of marine ecosystems.•Ecosystem resilience approaches can be used to guide research and policy.
Abstract
Until the late 19th century, extensive beds of flat oyster Ostrea edulis populated the Central North Sea, which have vanished after intensive fisheries. At present, various initiatives are ...being carried out to investigate the potential to restore this former key species in the area. This historical ecological study contributes by delineating the former oyster bed area and through an assessment of its limits against known gradients in the North Sea. Extensive data from historical maps, texts, and ship-based surveys were used to synthesize our knowledge on the former beds. It was revealed that the area with oyster beds covered ∼6.2% of the total North Sea bottom, with a delineation that could partly be explained by hydrodynamic and temperature gradients. The position and extent of the area are notably different from the area that is used in recent feasibility studies on the restoration of North Sea oyster beds. The offshore oysters lived on muddy sand in relatively cold conditions, and there are several indications that their reproductive rate was low. The apparent disappearance of cold water adapted flat oysters will challenge restoration projects. This study provides indispensable information for the future restoration of flat oyster beds in the North Sea.
Phytoplankton primary production is at the base of the marine food web; changes in primary production have direct or indirect effects on higher trophic levels, from zooplankton organisms to marine ...mammals and seabirds. Here, we present a new time‐series on gross primary production in the North Sea, from 1988 to 2013, estimated using in situ measurements of chlorophyll and underwater light. This shows that recent decades have seen a significant decline in primary production in the North Sea. Moreover, primary production differs in magnitude between six hydrodynamic regions within the North Sea. Sea surface warming and reduced riverine nutrient inputs are found to be likely contributors to the declining levels of primary production. In turn, significant correlations are found between observed changes in primary production and the dynamics of higher trophic levels including (small) copepods and a standardized index of fish recruitment, averaged over seven stocks of high commercial significance in the North Sea. Given positive (bottom‐up) associations between primary production, zooplankton abundance and fish stock recruitment, this study provides strong evidence that if the decline in primary production continues, knock‐on effects upon the productivity of fisheries are to be expected unless these fisheries are managed effectively and cautiously.
Phytoplankton primary production (PP) is at the base of the marine food web. Here, we show that there has been a significant decline in PP in the North Sea, from 1988 to 2013. Sea surface warming and reduced riverine nutrient inputs likely contributed to the declining levels of PP. In turn, changes in PP were positively associated with changes in zooplankton abundance and fish recruitment. This study provides strong evidence that if the decline in PP continues, knock‐on effects upon fisheries productivity are to be expected unless these fisheries are managed effectively.
1. Well-designed marine protected area (MPA) networks can deliver a range of ecological, economic and social benefits, and so a great deal of research has focused on developing spatial conservation ...prioritization tools to help identify important areas. 2. However, whilst these software tools are designed to identify MPA networks that both represent biodiversity and minimize impacts on stakeholders, they do not consider complex ecological processes. Thus, it is difficult to determine the impacts that proposed MPAs could have on marine ecosystem health, fisheries and fisheries sustainability. 3. Using the eastern English Channel as a case study, this paper explores an approach to address these issues by identifying a series of MPA networks using the Marxan and Marxan with Zones conservation planning software and linking them with a spatially explicit ecosystem model developed in Ecopath with Ecosim. We then use these to investigate potential trade-offs associated with adopting different MPA management strategies. 4. Limited-take MPAs, which restrict the use of some fishing gears, could have positive benefits for conservation and fisheries in the eastern English Channel, even though they generally receive far less attention in research on MPA network design. 5. Our findings, however, also clearly indicate that no-take MPAs should form an integral component of proposed MPA networks in the eastern English Channel, as they not only result in substantial increases in ecosystem biomass, fisheries catches and the biomass of commercially valuable target species, but are fundamental to maintaining the sustainability of the fisheries. 6. Synthesis and applications. Using the existing software tools Marxan with Zones and Ecopath with Ecosim in combination provides a powerful policy-screening approach. This could help inform marine spatial planning by identifying potential conflicts and by designing new regulations that better balance conservation objectives and stakeholder interests. In addition, it highlights that appropriate combinations of no-take and limited-take marine protected areas might be the most effective when making trade-offs between long-term ecological benefits and short-term political acceptability.
In this paper we demonstrate that low level 'artisanal' fishing can dramatically affect populations of slow-growing, late-maturing animals and that even on remote oceanic islands, stocks have been ...depleted and ecosystems degraded for millennia. Industrialised fisheries have developed during different decades in different regions of the world, and this has almost always been followed by a period of massive stock decline. However, ecosystems were not pristine before the onset of industrial fishing and it is difficult to assess the 'virgin' state of a population given that it may have been subject to moderate or even high levels of fishing mortality for many centuries. A wide range of information is available to help define or deduce historic marine population status. These include 'traditional' written sources but also less conventional sources such as archaeological remains, genetic analyses or simple anecdotal evidence. Detailed information, collected specifically for the purpose of determining fish stock biomass tends to exist only for recent decades, and most fishery assessments around the world (and thus time-series of biomass estimates), are less than 30 years long. Here we advocate using a wider range of multidisciplinary data sources, although we also recognise that it can be difficult to separate natural variability associated with changing climatic conditions from human-induced changes through fishing. We consider whether or not recovery of degraded ecosystems is ever possible and discuss a series of one-way ratchet like processes that can make it extremely difficult to return to a former ecosystem state.
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