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Assessing cumulative impacts on seabed ecosystems

29.11.2010
Příroda
Assessing cumulative impacts on seabed ecosystems


Understanding the impacts of human activities on marine ecosystems is important to ensure their sustainability. New research has indicated that seafloor ecosystems are less likely to recover from fishing if they are in rocky or reef habitats and if dredging and bottom trawling equipment is used for shellfish and various fish species. When fishing is combined with the extraction of aggregate for mineral resources, the impacts are even more damaging.

The aim of the EU Marine Strategy Framework1 is to achieve good environmental status for all marine waters by 2020. To do this Member States are developing marine strategies to serve as action plans for applying an ecosystem-based approach to the management of human activities. Recently the European Commission has adopted a decision outlining the criteria necessary to achieve good environmental status for Europe's seas2.

Understanding the impact of human activities is crucial to developing such strategies, however, there are gaps in our knowledge, particularly concerning the interaction of different human activities. The study considered two major pressures that particularly affect the seabed ecosystem: trawling for fish and removing aggregate for mineral sources. It analysed vessel monitoring system (VMS) data for vessels using sea bottom fishing gear in the UK's seas for 2006 and 2007.

Approximately half of the UK seabed was affected by seafloor fishing in both years. The majority of fishing took place in sand habitats. The intensity of fishing, i.e. how many times an area was fished in a year, varied considerably between habitats and was the lowest in sand and the highest in mud.

The recovery time of habitats was influenced by the type of fishing gear and the habitat. In general, recovery periods were longest in hard habitats consisting of reefs and rocks and shortest in soft habitats. For example, when using trawling equipment, some research has indicated that mud habitats can recover in days, whereas it can take several years for hard habitats to recover. On the other hand, all habitats require years to recover from fishing that uses, for instance, shellfish-dredging techniques (when sediment becomes severely disturbed).

The study indicated that shellfish-dredging in sand and gravel and trawling in muddy sand and reef habitats all occurred too frequently for the habitats to recover in 19 per cent of the UK's seabeds. This information on the sensitivity of different habitats to different fishing methods could prove useful in marine management and developing marine strategies.

The study also investigated the possible cumulative impact of fishing and aggregate extraction from seabeds. It indicated that aggregate extraction had a greater impact than fishing for all types of habitat, regardless of the fishing gear used. When the impacts of fishing and aggregate extraction were combined, the estimated recovery from extraction was responsible for 68 to 100 per cent of the recovery time.
Future research could investigate how different impacts interact in more detail and consider different types of impacts, such as oil and gas extraction, renewable energy structures, dumping pipelines and cables.

Source: Foden, J., Rogers, S.I. & Jones, A.P. (2010) Recovery of UK seabed habitats from benthic fishing and aggregate extraction - towards a cumulative impact assessment. Marine Ecology Press Series. 411:259-270.

Contact: jo.m.foden@uea.ac.uk
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