Meeresschutzgebiete aus ökologischer Sicht

Die Konzepte für das Fischereimanagement haben in den vergangenen hundert Jahren eine tiefgreifende Wandlung durchgemacht. Sie entwickelten sich in der zweiten Hälfte des vergangenen Jahrhunderts von monospezifischen Ansätzen, in denen einzelne Populationen oder Bestände weitgehend isoliert betrachtet wurden, zum Multispecies-Management, das auch Wechselbeziehungen zwischen genutzten Arten berücksichtigte. Die stark verbesserten Ortungs- und Fangtechniken und die Nutzung noch unterfischter Fanggründe und Bestände hielten die Anlandungen eine Zeitlang auf hohem Niveau. Die rückläufigen Weltfischereierträge in den letzten Dekaden des vergangenen Jahrhunderts, der Kollaps wichtiger Fischereien und die auch von der Fischerei zu verantwortende fortschreitende Degradierung mariner Ökosysteme zeigten jedoch, dass eine nachhaltige Nutzung der fischereilichen Ressourcen bei gleichzeitiger Erhaltung der Ökosysteme mit diesen Konzepten nicht möglich ist. Angesichts dieses Offenbarungseids und unter dem zunehmenden Druck der Naturschützer wurden daher die Konzepte des ökosystemverträglichen Fischereimanagements (EBFM, ecosystem-based fisheries management) und des räumlichen Fischereimanagements (SM, spatial management) entwickelt, bei denen die Prioritäten umgedreht sind: Das Management geht nicht mehr vom Fischereiobjekt, sondern vom Ökosystem aus, das horizontal und vertikal in Zonen unterteilt wird, die zu verschiedenen Zeiten befischt oder unter Schutz gestellt werden können. EBFM zielt darauf ab, gesunde Ökosysteme inklusive der Fischereien zu erhalten, die von diesen Ökosystemen ohne Schädigung getragen werden. Möglicherweise sind diese neuen Konzepte nur wenig realistischer als die Ideen vom langfristigen Dauerertrag oder dem der nachhaltigen Fischerei, die der realen Welt überdimensionierter Fangflotten, unersättlicher Märkte und zahlreicher politischer Fehlentscheidungen nicht standhielten. Die traurige Tatsache ist, dass nicht nur die Fischerei, sondern auch die marinen Ökosysteme sich in einem sehr schlechten Zustand befinden. Um dem abzuhelfen, sind u.a. Schutzgebiete vorgesehen, in denen die Fischerei eingeschränkt oder verboten ist. Zusammen mit anderen Nutzungen wie Offshore-Windparks bedeutet diese neue Raumordnung einen massiven Eingriff in die bisherigen Rechte und Gewohnheiten der Fischer. In dieser Arbeit werden vor dem Hintergrund der Ökosystem-Degradierung einige grundlegende ökologische Zusammenhänge in natürlichen, befischten und geschützten marinen Systemen diskutiert. Dabei stützen wir uns auf empirische und experimentelle Befunde aus Nord- und Ostsee sowie anderen marinen Ökosystemen. Unter dem Strich sollten Schutzgebiete im Rahmen der neuen Managementkonzepte langfristig auch der Fischerei dienen; inwieweit allerdings eine Fischerei unter der künftigen Raumordnung noch sinnvoll ist, steht dahin.

Prey preference of lingcod (Ophiodon elongatus), a top marine predator: implications for ecosystem-based fisheries management

Many highly exploited ecosystems are managed on the basis of single-species demographic information. This management approach can exacerbate tensions among stakeholders with competing interests who in turn rely on data with notoriously high variance. In this case study, an application of diet and dive survey data was used to describe the prey preference of lingcod (Ophiodon elongatus) in a predictive framework on nearshore reefs off Oregon. The lingcod is a large, fast-growing generalist predator of invertebrates and fishes. In response to concerns that lingcod may significantly reduce diminished populations of rockfishes (Sebastes spp.), the diets of 375 lingcod on nearshore reefs along the Oregon Coast were compared with estimates of relative prey availability from dive surveys. In contrast to the transient pelagic fishes that comprised 46% of lingcod diet by number, rockfishes comprised at most 4.7% of prey items. Rockfishes were the most abundant potential prey observed in dive surveys, yet they were the least preferred. Ecosystem-based fisheries management (EBFM) requires information about primary trophic relationships, as well as relative abundance and distribution data for multiple species. This study shows that, at a minimum, predation relative to prey availability must be considered before predator effects can be understood in a management context.

Spatial changes in the sensitivity of Atlantic cod to climate-driven effects in the plankton

Recent strategies to sustain fish stocks have suggested a move towards an ecosystem based fisheries management (EBFM) approach. While EBFM considers the effect of fishing at the ecosystem level, it generally struggles with climate-driven environmental variability. In this study we show that the position of a fish stock within its distributional range or thermal niche (we use Icelandic and North Sea cod as examples of stocks at the centre and edge of their niche, respectively) will influence the relative importance of fishing and climate on abundance. At the warmer edge of the thermal niche of cod in the North Sea, we show a prominent influence of climate on the cod stock that is mediated through temperature effects on the plankton. In contrast, the influence of climate through its effects on plankton appears much less important at the present centre of the niche around Iceland. Recognising the potentially strong effect of climate on fish stocks, at a time of rapid global climate change, is probably an important prerequisite towards the synthesis of a cod management strategy.

Climate, plankton and cod

While a few North Atlantic cod stocks are stable, none have increased and many have declined in recent years. Although overfishing is the main cause of most observed declines, this study shows that in some regions, climate by its influence on plankton may exert a strong control on cod stocks, complicating the management of this species that often assumes a constant carrying capacity. First, we investigate the likely drivers of changes in the cod stock in the North Sea by evaluating the potential relationships between climate, plankton and cod. We do this by deriving a Plankton Index that reflects the quality and quantity of plankton food available for larval cod. We show that this Plankton Index explains 46.24% of the total variance in cod recruitment and 68.89% of the variance in total cod biomass. Because the effects of climate act predominantly through plankton during the larval stage of cod development, our results indicate a pronounced sensitivity of cod stocks to climate at the warmer, southern edge of their distribution, for example in the North Sea. Our analyses also reveal for the first time, that at a large basin scale, the abundance of Calanus finmarchicus is associated with a high probability of cod occurrence, whereas the genus Pseudocalanus appears less important. Ecosystem-based fisheries management (EBFM) generally considers the effect of fishing on the ecosystem and not the effect of climate-induced changes in the ecosystem state for the living resources. These results suggest that EBFM must consider the position of a stock within its ecological niche, the direct effects of climate and the influence of climate on the trophodynamics of the ecosystem.

Trophic amplification of climate warming

Ecosystems can alternate suddenly between contrasting persistent states due to internal processes or external drivers. It is important to understand the mechanisms by which these shifts occur, especially in exploited ecosystems. There have been several abrupt marine ecosystem shifts attributed either to fishing, recent climate change or a combination of these two drivers. We show that temperature has been an important driver of the trophodynamics of the North Sea, a heavily fished marine ecosystem, for nearly 50 years and that a recent pronounced change in temperature established a new ecosystem dynamic regime through a series of internal mechanisms. Using an end-to-end ecosystem approach that included primary producers, primary, secondary and tertiary consumers, and detritivores, we found that temperature modified the relationships among species through nonlinearities in the ecosystem involving ecological thresholds and trophic amplifications. Trophic amplification provides an alternative mechanism to positive feedback to drive an ecosystem towards a new dynamic regime, which in this case favours jellyfish in the plankton and decapods and detritivores in the benthos. Although overfishing is often held responsible for marine ecosystem degeneration, temperature can clearly bring about similar effects. Our results are relevant to ecosystem-based fisheries management (EBFM), seen as the way forward to manage exploited marine ecosystems.

How Have Institutional Barriers Impacted Implementation of Ecosystem Based Fishery Management in the US

Thesis (Master's)--University of Washington, 2016-08