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.

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Available from: Michel J Kaiser, Dec 23, 2013
    • "In most discussions and modelling of BH, we tend to think mainly about fish. This thinking may ignore the substantial impact of fishing on the benthos (Hinz et al., 2009), intended or incidental.Garcia et al. (2012)acknowledge that fishing should cover " the widest possible range of species . . . " , and by extension that would include the benthic species, mostly invertebrates, captured by the gear. "
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    ABSTRACT: Balanced harvesting (BH) has been proposed as an alternative to the paradigm of more selective fishing as practiced in most European and North American fisheries management. We examine options for the implementation of BH and evaluate the issues raised in such an implementation. Implementation is considered at the whole ecosystem level, in terms of the patterns of removal for all species, both commercial and bycatch. We suggest that a “laissez-faire” approach analogous to the African lakes where BH was first observed is inappropriate in managed developed world fisheries. We consider two further approaches: focusing on either the species caught or on the sizes of animal alone. We find that aiming to harvest all species with an exploitation rate appropriate to their productivity would require a degree of micro-management that is probably unachievable, with all captured species “choking” the fishery in sequence. The size-based approach works with an exploitation rate appropriate to the productivity at size, with no consideration of the species involved. This might superficially be easier to implement, as management would involve a limited number of size classes only. However, problems may arise due to the likely faster capture of the more easily catchable fish, and also likely targeting of the more valuable species within a size class. We identify a possible third option of “broad brush” métier-based management that may resolve some of these problems. Other issues include the management of protected, endangered, and threatened species (including mammals, reptiles, and birds), the management of already severely depleted stocks, and the capture of benthic invertebrates.
    No preview · Article · Jan 2016 · ICES Journal of Marine Science
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    • "Trawling has been operating on fishing grounds since many years ago, potentially affecting seafloor morphology, sediment characteristics and water turbidity by resuspending sediments (Palanques et al., 2014). Several consequences of bottom trawling have been proposed, such as changes in infaunal benthic communities (Hinz et al., 2009) and epifaunal assemblage structure (Strain et al., 2012), a reduction in the abundance of target and non-target fish by direct removal but also by affecting food availability (Hiddink et al., 2011), and increasing local mortality of hard-bodied and large benthic invertebrates (Kaiser et al., 2006). However, it has been shown that sediment resuspension by trawling would lead to nutrient release and enhance primary production (Jennings et al., 2001), changing benthic communities that may improve feeding conditions (Hiddink et al., 2008), promoting fish growth and increasing fish biomass and fisheries yield (vanDenderen et al., 2013). "
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    ABSTRACT: Trawling is a major concern worldwide and there is considerable debate about its impact on marine ecosystems. The Patagonian Shelf Large Marine Ecosystem (PSLME) is an important fishing area in the Southwest Atlantic where bottom trawling is the dominant fishing method. We investigated the distribution of bottom trawl fishing within this region, defining the areas of highest trawling intensity (hotspots) and evaluating their relationship with marine fronts. We focused on the three main oceanographic fronts, the shelf-break front, the southern Patagonia front and the mid-shelf front. To estimate fishing effort and trawled areas, we used VMS data from 2006 to 2012. Despite being almost a fully trawlable shelf, we found that the spatial distribution of trawling activity is patchy and trawling hotspots were small, comprising annually <5% of the shelf extension or <7% of the total trawlable area. Contrary to what is believed worldwide, our findings suggest that over the PSLME the magnitude of habitat effects as a result of bottom trawling is relatively small. Regarding the three frontal systems studied, only the shelf-break front showed a positive relationship with trawl fishing activity. Although trawling hotspots did not overlap with marine fronts, the shelf-break front receives more trawling effort than expected. We hypothesize that this pattern is due to aggregation of species near or at the front taking advantage of the opportunities provided by this area.
    Full-text · Article · Dec 2015 · Fisheries Oceanography
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    • "Typically, bottom trawling is carried out using heavy ground ropes and chains to drive fish and crustaceans from the seabed into nets (Johnson et al., 2015). Trawling is carried out on many types of grounds, from shallow waters down to the deep continental margins (Puig et al., 2012), by small and large vessels, and for a wide range of target species, including fish and crustaceans (Hinz et al., 2009). These characteristics make bottom trawling one of the preferred methods of industrial fisheries worldwide but, at the same time, one among the human activities at sea most impacting highly vulnerable benthic marine ecosystems (e.g., cold-water corals or coralligenous bottoms; Fowler, 2003; Althaus et al., 2009; Bruckner, 2009; Heifetz et al., 2009; Bongiorni et al., 2010). "
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    ABSTRACT: Bottom trawling represents nowadays one of the most severe anthropogenic disturbances at sea, and determines large impacts on benthic communities and processes. Bottom trawling determines also local sediment resuspension and the effects of the injection of large amounts of surface sediments into the water column have been repeatedly investigated. Few studies have assessed the consequences of sediment resuspension caused by bottom trawling on the quantity, biochemical composition and bioavailability of suspended organic particles and how these eventually rival those exerted by natural storms. To provide insights on this poorly addressed issue, we investigated concentrations and biochemical composition of total and enzymatically digestible pools of particulate organic matter (POM) in the Thermaikos Gulf (Mediterranean Sea) under calm sea conditions, during intensive trawling activities, and after a severe storm. We show here that sediment resuspension caused by trawling can cause large effects on POM quantity, biochemical composition and bioavailability. Both during trawling and after the storm, the relative importance of the carbohydrate pools increased (in the upper water column) and the total lipid concentrations decreased (in the intermediate and bottom layers) when compared to values measured during calm conditions. These results would suggest that bottom trawling could inject in the upper water column POM pools more refractory in nature (e.g., carbohydrates) than those present in calm or after-storm conditions. By contrast, we show also that the bioavailable fraction of biopolymeric C increased significantly during trawling in the upper water column of the shallowest stations and in the bottom water column layer of the deepest ones. These results provide evidence that bottom trawling can influence the overall trophic status of coastal waters, exerting effects similar or stronger than those caused by natural storms, though of variable amplitude depending on the water depth. Since bottom trawling is carried out worldwide and natural storms at sea can be frequent and intense, we claim for the need of assessing new adapting management strategies of bottom trawling in order to mitigate the synergistic impacts of anthropogenic and natural sediment resuspension on coastal biogeochemical cycles.
    Full-text · Article · Nov 2015
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