Trawl disturbance on benthic communities: Chronic effects and experimental predictions

School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey LL59 5AB, United Kingdom.
Ecological Applications (Impact Factor: 4.09). 05/2009; 19(3):761-73. DOI: 10.1890/08-0351.1
Source: PubMed


Bottom trawling has widespread impacts on benthic communities and habitats. While the direct impacts of trawl disturbances on benthic communities have been extensively studied, the consequences from long-term chronic disturbances are less well understood. The response of benthic macrofauna to chronic otter-trawl disturbance from a Nephrops norvegicus (Norway lobster) fishery was investigated along a gradient of fishing intensity over a muddy fishing ground in the northeastern Irish Sea. Chronic otter trawling had a significant, negative effect on benthic infauna abundance, biomass, and species richness. Benthic epifauna abundance and species richness also showed a significant, negative response, while no such effect was evident for epibenthic biomass. Furthermore, chronic trawl disturbance led to clear changes in community composition of benthic infauna and epifauna. The results presented indicate that otter-trawl impacts are cumulative and can lead to profound changes in benthic communities, which may have far-reaching implications for the integrity of marine food webs. Studies investigating the short-term effects of fishing manipulations previously concluded that otter trawling on muddy substrates had only modest effects on the benthic biota. Hence, the results presented by this study highlight that data from experimental studies can not be readily extrapolated to an ecosystem level and that subtle cumulative effects may only become apparent when fishing disturbances are examined over larger spatial and temporal scales. Furthermore, this study shows that data on chronic effects of bottom trawling on the benthos will be vital in informing the recently advocated move toward an ecosystem approach in fisheries management. As bottom-trawl fisheries are expanding into ever deeper muddy habitats, the results presented here are an important step toward understanding the global ecosystem effects of bottom trawling.


Available from: Michel J Kaiser, Dec 23, 2013
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    • "Jennings et al., 2001), reduced biodiversity and habitat homogenization (e.g. Dayton et al., 1995), and changes in community composition (Hinz et al., 2009). Large vulnerable species (e.g. "
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    ABSTRACT: Bottom-trawl fisheries are expanding into deeper habitats and higher latitudes, but our understanding of their effects in these areas is limited. The ecological importance of habitat-forming megabenthos and their vulnerability to trawling is acknowledged, but studies on effects are few. Our objective was to investigate chronic effects of otter trawl fishery on substratum and megabenthos on the shelf (50– 400 m) and slope (400– 2000 m) in the southern Barents Sea. The study area represents a wide range in the history of fishing intensity (FI). Physical impact of trawling, density of trawl marks (TMs), was quantified on 250 video transects from shelf and slope, and megabenthos (.2 cm) composition was studied on 149 video transects from the shelf. The number of satellite-recorded vessels within grid cells 5 × 5 km was used as a proxy for FI in the TM analysis and for the megabenthos records within a 2-km radius around the transects. The effects of using different search area sizes were tested. Patterns in the density of TMs and megabenthos composition were compared with FI using linear regression and correspondence analysis. Occurrence of TMs was not directly related to FI but to bottom type, whereas megabenthos density and diversity showed a negative relation. For 79 of the 97 most common taxa, density was negatively correlated with FI. The sponges Craniella zetlandica and Phakellia/Axinella were particularly vulnerable, but also Flabellum macandrewi (Scleractinia), Ditrupa arietina (Polychaeta), Funiculina quadrangularis (Pennatulacea), and Spatangus purpureus (Echinoidea) were negatively correlated with FI, whereas asteroids, lamp shells, and small sponges showed a positive trend. Our results are an important step towards the understanding of chronic effects of bottom trawling and are discussed in relation to the descriptors " Biological diversity " and " Seafloor integrity " in the EU Marine strategic framework directive.
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    • "The direct impacts on fauna through dislodgement or damage of individuals are the most obvious effects caused by fishing gear, but the range of biological changes extends well beyond these physical impacts and can significantly alter the community composition and foodweb architecture in the ecosystems subjected to fishing disturbance . On the shelf high levels of trawling results in changes to overall community composition through substantial habitat alterations, removal of non-target species, and through attraction of scavengers and predators to trawled areas (Tillin et al., 2006; Hinz et al., 2009). "
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    • "It is well known that impacts of chronic trawl disturbance are cumulative and can cause significant decrease in biomass of epifaunal species such as sponges, corals, or echinoderms (Collie et al., 1997; Wassenberg et al., 2002; Burridge et al., 2003) and lead to profound changes in benthic assemblage composition (Kaiser et al., 2002; Hinz et al., 2009; Atkinson et al., 2011), although sometimes it is not possible to separate the effect of fishing from other environmental variables (Queirós et al., 2006; Atkinson et al., 2011). In the heavily fished North Sea, which has also been subjected to fishing activity for many centuries, benthic communities showed decreases in abundance of bivalves (Frid and Clark, 2000) and benthic diversity (Kaiser and Spencer, 1996; Jennings and Reynolds, 2000) over a 60-year period. "
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