Where is bottom trawling occurring

The capability of the predator to consume large numbers of fish was born, and then kept from extinction by the provision of financial subsidies, at least in some areas, to help allay the enormous costs of operating such large vessels at sea for long periods of time. Of the world's 13 biggest high seas bottom trawling nations, there is only one New Zealand , which does not provide subsidies, suggesting that many deep-sea trawl fisheries would have ended much sooner in the absence of subsidies Sumaila et al.

For many of the target species, recruitment and restoration of populations is a possibility if the level of exploitation is strongly reduced or eliminated, or the exploitation strategy is altered for a number of years, as was the case for Blue ling Large et al. On the other hand, several other species have been fished to very low numbers, often in a decade or two. Patterns of depletion are apparent in the Slender armorhead fishery, where the population was reduced to a fraction of its virgin biomass in 8 years.

Similarly Longfin codling estimated landings were as high as , t in , and 55, t in , and Roundnose grenadier estimated catches were greater than 60, t in but a rapid decline in stocks lead to a moratorium in We show that considerable fish biomass has been removed from the deep-sea, particularly in certain areas and while we do not understand the consequences of that removal yet, it is likely that the deep-sea ecosystem is being changed. For example, many of these fish species, such as the Greenland halibut, are top-predators within their habitats and removing them could cause trophic cascading as previously seen in cod fisheries Frank et al.

Others are mid-level predators and their removal may have more subtle consequences related to the removal of biomass that would otherwise recycle in the benthic ecosystem as these fish grow, reproduce and die. The impact of trawling goes beyond the capture of fish populations since the benthic fauna gets removed from the seabed, thus comprising a large fraction of the bycatch Probert et al.

The routine use of trawls in these fisheries results in considerable environmental modification, loss of habitat structure, and reduction of biodiversity, especially on seamounts Clark et al. In addition, where these fisheries occur along the continental slope, re-suspended sediments can flow down-slope into deeper waters, covering organisms that would otherwise have been out of the way of the trawl Pusceddu et al.

Many of the largest bottom-trawled fisheries, such as Orange roughy and Slender armourhead fisheries occur also on topographic highs, such as seamounts and ridges. Their irregular topography offers a mosaic of habitats while influencing local current velocities and often delivering food particles at a slightly higher rate to fauna.

These habitats are often heavily populated by suspensions feeders, such as habitat forming deep-sea corals and sponges that have been shown to be hundreds of years old, along with a variety of other species Koslow et al.

The deep-sea fish also take advantage of seamounts, where they often aggregate to feed, spawn and live Clark et al.

These aggregations make ideal candidates for deep-sea fisheries, resulting in deep-sea trawl fisheries targeting the summits and occasionally the sides of seamounts at depths shallower than 2, m Clark et al.

All seamounts where bottom trawling occurred and that have been investigated with remotely operated vehicles ROVs or towed cameras show large cleared areas where communities of suspension feeders once lived Koslow et al. Despite knowing that these species live for centuries, we do not know what their rate of reproduction and pattern of recruitment is, so we have no certain way of determining how long it will take for the community to recover. In Europe, these and other NGOs initiated a campaign to ban bottom trawling in deep water, culminating in legislation in The legislation is complex, but essentially bans bottom trawling in waters deeper than m European Parliament and the Council of the European Union, thus providing some protection to both bottom habitat and non-targeted deep-sea fish species.

Within this context, it is worth considering the economic importance of deep-sea fisheries. Much of the reductions in catches reported, especially after , are due to management measures that have been taken to reduce the possibility of species being over-fished.

In some cases, such as with Blue ling, the problem of fishing on spawning aggregations was recognized and protection areas were introduced Large et al. In other cases, landings have been restricted as catch numbers declined e. Sometimes these management measures might have come too late. For most deep-sea fisheries, the lack of biological information combined with assumptions from shallow fisheries prevents them from being suitably regulated from the start.

Combining this, with the much higher catches documented here and hence not officially accounted for, has led to regulations that might not have been strict enough to allow recovery, particularly in mixed-trawl fisheries. For fisheries, such as the Greenland halibut, concerns of depletion led to a reduction of quota which in turn caused high discards from onwards. Some nations have enforced discard bans, but Iceland among others has a record of discarding Beaked redfish, potentially because vessels are not able to acquire quota within the transferable quota system or the fish are undersized.

Finally, there is the problem, of managing trawling in the high seas, that is, in areas of the ocean beyond any national jurisdiction. In an estimated vessels were involved in high seas trawling, with the fisheries often occurring on isolated topographic structures, such as seamounts and ridges Bensch et al. As seamounts have extensive coverage of VME indicator species and are often trawled leading to high degree of environmental damage, Watling and Auster have proposed that seamounts as a whole should be considered as Vulnerable Marine Ecosystems.

This study describes historical patterns in catches of deep-sea trawling fisheries since — by comparing and complementing the FAO landings data with reconstructed unreported landings and discards.

The reconstructed catches also suggest high discarding of Greenland halibut, Beaked redfish, Roundnose grenadier and the grouping Grenadiers nei. The new catch estimates suggest that much more biomass, encompassing both fish and habitat-forming species, has been removed from the deep-sea, altering this ecosystem in ways that have yet to be understood.

LW and CN conceived the study. LV prepared the figures. LV and LW prepared the animation. LV and LW drafted the text and all authors revised and approved the final version of the manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We would like acknowledge our many colleagues who have discussed this topic with us over the years, especially M. Gianni and D.

Curry, and D. Pauly for establishing and maintaining the Sea Around Us. Orlov helped us understand details of the Russian fishery data for the NW Pacific. We would also like to acknowledge M. Clark and T. Morato for their help with the compilation of the deep-sea fish species list. The authors would also like to thank Sarah Popov for producing the cartograms with the Sea Around Us data.

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Koslow, J. Continental slope and deep-sea fisheries: implications for a fragile ecosystem. Seamount benthic macrofauna off southern Tasmania: community structure and impacts of trawling. Lack, M. Large, P. Spatial and temporal distribution of spawning aggregations of blue ling Molva dypterygia west and northwest of the British Isles.

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In this fishing method, large weighted nets are dragged across the ocean floor, clear-cutting a swath of habitat in their wake. Some of these scars will take centuries to heal, if ever. For example, hard corals in Alaska have been dated to be hundreds to thousands of years old, and radio carbon dating on the oldest known deep sea corals indicates they are 4, years in age.

Yet, these pillars of the ecosystem can be destroyed by one swipe of a bottom trawl. A bottom trawl consists of a large tapered net with a wide mouth and a small enclosed end. The mouth of a trawl net has two weighted doors that serve not only to keep the net open, but also to keep the net on the ocean floor.

Norse said. Scientific findings about trawling impacts have led to increasing restrictions on this industrial fishing method. In , the General Fisheries Commission for the Mediterranean banned trawling in the Mediterranean Sea below depths of 1, meters, and the United States closed vast deep-sea areas off Alaska to bottom trawling. There are tens of thousands of trawlers worldwide.

They fish for shrimp and finfishes.