Mixed-fishery or ecosystem conundrum? Multispecies considerations inform thinking on long-term management of North Sea demersal stocks

Mackinson, Steven; Deas, Barrie; Beveridge, Doug BeveridgeD.; Casey, John

doi:10.1139/f09-057

Cited by 77 publications

(41 citation statements)

References 18 publications

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“…but also due to indirect interactions of mixed fisheries (Walters et al, 2005;Mackinson et al, 2009), especially in a fast changing ecosystem such as the Mediterranean. The rapid warming, combined with the expansion of non-indigenous species is definitely changing the suitability of the habitats for traditional commercial species with effects on their resilience to fishing (Libralato et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

Recent Trends and Impacts of Fisheries Exploitation on Mediterranean Stocks and Ecosystems

2017

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This review focuses on the recent data on Mediterranean fishing fleets and landings, results from stock assessments and ecosystem models to provide an overview of the multiple impacts of fishing exploitation in the different Mediterranean geographical sub-areas (GSAs). A fleet of about 73,000 vessels is widespread along the Mediterranean coasts. Artisanal activities are predominant in South Mediterranean and in the eastern basin, while trawling features GSAs in the western basin and the Adriatic Sea. The overall landings of fish, crustaceans and cephalopods, after peaking during mid 90s at about one million tons, declined at about 700,000 tons in 2013. However, while landings are declining in EU countries since the 90s, in non-EU countries a decreasing trend was observed only in the last 5-10 years. The current levels of fishing effort determine a general overexploitation status of commercial stocks with more than 90% of the stock assessed out of safe biological limits. Indicators obtained from available ecosystem models were used to assess the sustainability of the fisheries. They included primary production required to sustain fisheries (PPR), mean trophic level of the catch (mTLc), the loss in secondary production index (L index), and the probability of the ecosystem to be sustainably exploited (p sust ). In areas exploited more sustainably (e.g., Gulf of Gabes, Eastern Ionian, and Aegean Sea) fishing pressure was characterized by either low number of vessels per unit of shelf area or the large prevalence of artisanal/small scale fisheries. Conversely, GSAs in Western Mediterranean and Adriatic showed very low ecosystem sustainability of fisheries that can be easily related with the high fishing pressure and the large proportion of overfished stocks obtained from single species assessments. We showed that the current knowledge on Mediterranean fisheries and ecosystems describes a worrisome picture where the effect of poorly regulated fisheries, in combination with the ongoing climate forcing and the rapid expansion of nonindigenous species, are rapidly changing the structure and functioning of the ecosystem with unpredictable effects on the goods and services provided. Although this would call for urgent conservation actions, the management system implemented in the region appears too slow and probably inadequate to protect biodiversity and secure fisheries resources for the future generations.

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Section: Discussionmentioning

confidence: 99%

Recent Trends and Impacts of Fisheries Exploitation on Mediterranean Stocks and Ecosystems

2017

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“…The MSY target proves specially challenging in mixed Mediterranean fisheries, where more than a hundred commercial species are landed . As each species has specific MSYs, it is extremely difficult to regulate the fishing mortality for each of them independently (Ratz et al, 2007;Mackinson et al, 2009;Guillen et al, 2013), notably when the dynamics of these species may, in turn, be influenced by the environmental (i.e., climate) and fishing impacts (Mueter and Megrey, 2006). Achieving the MSY goal, therefore, is not an easy task because many different contrasting socioeconomic and ecological interests need to be confronted.…”

Section: Introductionmentioning

confidence: 99%

Harvest Strategies for an Ecosystem Approach to Fisheries Management in Western Mediterranean Demersal Fisheries

et al. 2017

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The serious overfishing of most Mediterranean stocks demands urgent reforms of the management measures aiming to guarantee the sustainability of resources, notably when compared with the improvement observed in other European areas. The new EU Common Fisheries Policy (CFP) constitutes an excellent opportunity to introduce the changes needed for such a reform. According to this CFP, all European fish stocks should be brought to a state where they can produce at MSY by 2020 at the latest. The CFP also establishes that the objective of sustainable exploitation should be achieved through multiannual plans (MAPs) adopted in consultation with relevant stakeholders having fisheries management interests such as fishermen, non-governmental organizations, and policy makers. Together with the MSY and MAP approaches, the new CFP contains several other measures, directed to guarantee the ecological and socio-economic sustainability of fisheries by means of the implementation of the ecosystem approach to fisheries management (EAFM). With this new perspective, the CFP wants to avoid past failures of fisheries management based on monospecific approaches. This study is a first step toward the application of the EAFM in the Balearic Islands by means of the development of a harvest strategy with defined objectives, targets, limits, and clear management control rules aimed at optimizing socioeconomic and ecological objectives in the framework of the new CFP. Different management scenarios designed to achieve that goal were modeled for the main demersal commercial fisheries from the study area, the bottom trawl, and small-scale fisheries. The work begins with a general description of those fisheries, their main fishing grounds, and assessments of the exploitation status of the main target stocks in order to establish the current situation. Secondly, alternative management scenarios to maximize catch and profits while considering societal objectives were evaluated by means of bio-economic models. Thirdly, management measures were provided based on the previous modeling and discussions with stakeholders. Finally, a monitoring scheme was outlined to assess the progresses of the proposed management actions. This work is intended to be a working example of co-management (fishers, policy-makers, and scientists) in the Mediterranean in the framework of the new EU CFP.

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“…Some studies, however, have suggested that top-down effects, such as predation by sprat on zooplankton, are equally important in what is termed a "wasp-waist" system (14). For demersal piscivorous fish species like cod and whiting, the importance of fishing activity and predator-prey interactions has also been clearly demonstrated (15). Seabirds are also important predators and they are considered sensitive to change in the abundance of planktivorous fish, particularly sandeel and juvenile clupeids, i.e., sprat (14,16,17).…”

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Interaction between top-down and bottom-up control in marine food webs

Lynam

Llope

Möllmann

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

240

169

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Climate change and resource exploitation have been shown to modify the importance of bottom-up and top-down forces in ecosystems. However, the resulting pattern of trophic control in complex food webs is an emergent property of the system and thus unintuitive. We develop a statistical nondeterministic model, capable of modeling complex patterns of trophic control for the heavily impacted North Sea ecosystem. The model is driven solely by fishing mortality and climatic variables and based on timeseries data covering >40 y for six plankton and eight fish groups along with one bird group (>20 y). Simulations show the outstanding importance of top-down exploitation pressure for the dynamics of fish populations. Whereas fishing effects on predators indirectly altered plankton abundance, bottom-up climatic processes dominate plankton dynamics. Importantly, we show planktivorous fish to have a central role in the North Sea food web initiating complex cascading effects across and between trophic levels. Our linked model integrates bottom-up and top-down effects and is able to simulate complex long-term changes in ecosystem components under a combination of stressor scenarios. Our results suggest that in marine ecosystems, pathways for bottomup and top-down forces are not necessarily mutually exclusive and together can lead to the emergence of complex patterns of control.trophic control | ecosystem modeling | marine food web functioning | wasp-waist | regime shifts T he question of whether food webs are resource-(bottom-up) or predation-(top-down) controlled is one of the most fundamental research questions in ecology (1-3). Marine ecosystems, originally thought to be mainly steered by bottom-up control, have recently been shown to exhibit periods of top-down control due to the extraction of large predators through fishing (4-7) or climate oscillations (8). Furthermore, experimental evidence shows climate warming may exert a host of indirect effects on aquatic food webs mediated through shifts in the magnitudes of top-down and bottom-up forcing (9, 10). However, for large marine ecosystems that are not amenable to experimentation studies, investigations of how interactions in their complex food webs mediate the influence of both top-down (e.g., fishing) and bottom-up (e.g., climate change) control are lacking or are based on aggregated species complexes. We model an extensive historical dataset for the North Sea (over 45 y) at the lowest possible resolution (often species) to determine key interactions between species and estimate their responses to pressures. The model reveals both simple (direct) and complex (indirect) pathways linking plankton to seabirds and can highlight the wider effects of climate change and potential actions by fishery managers.The North Sea is one of the most anthropogenically impacted marine ecosystem and is thought to be fundamentally driven from the bottom-up through climatic (temperature-related) influences on plankton, planktivorous fish, and the pelagic stages of demersal fish (11-13). Som...

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Mixed-fishery or ecosystem conundrum? Multispecies considerations inform thinking on long-term management of North Sea demersal stocks

Cited by 77 publications

References 18 publications

Recent Trends and Impacts of Fisheries Exploitation on Mediterranean Stocks and Ecosystems

Recent Trends and Impacts of Fisheries Exploitation on Mediterranean Stocks and Ecosystems

Harvest Strategies for an Ecosystem Approach to Fisheries Management in Western Mediterranean Demersal Fisheries

Interaction between top-down and bottom-up control in marine food webs

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