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European trawlers are destroying the oceans - старонка 9


Habitat and ecosystem damage

The impact of bottom trawling on ecosystems is believed to be very high. These fishing activities diminish the complexity of benthic communities204. All the components involved in trawling have the capability to affect the seabed205. The net, the chains, the weights and, especially, the doors, can go various centimetres into the seabed (up to 30 cm206) depending on the sediment and the technique used, destroying benthic ecosystems. The width of the scars left behind by trawling can measure between 0.5 and 6 m207. With the introduction of rollers or bobbins on the underside of the net, consisting of large discs in the shape of wheels, trawlers have extended their range of action and impact and are now able to work in rocky areas or reefs, causing their destruction. Despite the scarcity of research on the repercussions of these new devices, some studies have started to show their tremendous impact208, their lesser selectivity209, the serious damage they cause to the substrate and sessile species210 and the damage to the ecosystem and its slow recuperation211.

Deep-sea coral



Deep-sea coral are azooxanthellae polyps that live on sea mounts and mounds of calcium carbonate at depths of more than 200 metres (although in some Norwegian zones they can be found at just 40 metres, and in areas close to the Iberian Peninsula they can reach depths of 3,000 metros) and can form colonies more than 30 km long212. They are distributed throughout European waters from the Arctic to the islands of Madeira and the Canaries, and are even found in the Mediterranean213. Although their biodiversity does not reach the levels of tropical coral reefs, they can be the home to more than 800 species214, including sponges, sea fans, hydroids, anemones, serpulids, barnacles, bivalves, bryozoans, brachiopods, crinoids, tunicates, nemertines, isopods, amphipods, brachyurans, eunicids, cirripeds, cidaroids, gastropods, echinoids, ophiuroids and asteroids215.

These ecosystems are particularly vulnerable as certain species need one year to grow just 5-10 mm, while coral reefs barely manage to grow between 1.3 and 2.5 mm in this time216. Some studies have shown that certain structures can reach 35 metres in height217. This means that a coral reef needs thousands of years to build its structure in the Atlantic and in the event of physical destruction, its recovery will take a very long time indeed.

It has been demonstrated that these reefs are very important for a number of commercial species and are also home to very large concentrations of certain populations of saithe, redfish, ling and tusk (sometimes three times larger than those found in nearby ecosystems)218.

The most common species of coral found on Atlantic reefs is the Lophelia pertusa, normally found alongside other species such as Madrepora oculata, Desmophyllum cristagalli, Enallopsammia rostrata and Solenosmilia variabilis219.

A study carried out to calculate the age of five different coral reefs by means of samples brought up by trawlers off the west of Ireland concluded that some formations of Lophelia Pertusa are 450 years old, while those of Desmophyllum cristagalli reached 4,550 years220. On Sula Ridge (Norway), the age of coral reefs has been calculated at 8,500 years221.

It is known that trawlers are one of the prime causes of the deterioration of these ecosystems in many parts of the world222. Scientists recognise that “generally speaking, wherever trawlers fish on waters above coral reefs there is the risk of causing serious damage”223. Various investigations have corroborated the damage inflicted on coral reefs by these fishing techniques in zones of the Atlantic between 200 and 1,200 metres in depth224. Trawlers are capable of destroying 33 square kilometres of habitat on the continental shelf in just 15 days225. The National Marine Fisheries Service (NMFS) of the United States has estimated that in the case of Alaska a single trawler can drag up 2,200 pounds of deep-sea coral in a single haul226.

In Norwegian waters, trawling has already damaged 30%-50% of coral reefs227. Damage of this magnitude has also been confirmed in other parts of the North Atlantic, such as the Darwin Mounds to the north-east of Scotland, the south of Wyville Thomson Ridge and the Porcupine Seabight in Irish waters.

The coral reefs in Norwegian waters cover a surface area of some 1,500-2,000 square kilometres228: the government has protected three of the most important masses: Sula Ridge, Iverryggen and the recently discovered reef at Røst in the Lofoten Islands. In Swedish waters, two coral reefs in the Kosterfjord also enjoy government protection.

Nor should we forget the temporary trawling prohibitions established by the EU in the sea mounts of the Darwin Mounds (close to the Hebrides off Scotland)229, in the Porcupine Seabight (to the west of Ireland)230, and the proposal to establish a similar zone inside the 100 mile limit around the archipelagos of the Azores, Madeira and the Canaries231.

The inadequacies of European legislation and the reticence of fisheries’ administrations mean that other zones of enormous ecological value are not being protected, despite “reefs” are included in Annex I of the EU Habitats Directive 92/43/EEC (but there are not any specific mention about deep-sea corals), due to the fact that they fall outside the 12 mile limit of jurisdictional waters. These include the Rockall Bank, between Scotland and the Faeroes; Wyville Thomson Ridge, also off Scotland; Chapelle Bank in the Bay of Biscay; the Galician Bank to the north-west of Spain; Gorridge Bank to the south of Portugal; etc.




Different trawling methods all have an effect on the seabed232. While beam trawlers are designed to trawl over the surface of the seabed with raised weights and at great speed, the scars they leave behind are less than those made by stern trawlers.

Some studies have proved that the reduction in invertebrates (echinoderms, polychaetes and molluscs) in trawled zones reach figures up to 65% when compared with areas where this kind of fishing has not taken place233. However, there is very little information available on the true impact of trawling on the seabed as there are hardly any virgin areas that have not been affected by the repercussions of this fishing technique to serve as a point of reference. Furthermore, part of the information compiled comes from indirect sources (not from field samples), such as the comparison between the number and volume of accidental catches caught in the nets234.

Research in various zones has confirmed that discards can give rise to episodes of anoxia on the seabed235, increase the mortality of target species236 and cause changes in the structure and composition of species237, while at the same time attracting the presence of scavengers and altering the benthic structure238. Even discarding parts of these species—something that frequently happens in the Norway lobster fisheries of the North Atlantic, where just the tail is kept and the head is thrown overboard— can inhibit the movements of certain benthic species239. The estimate240 of discards reaching the seabed in the southern sector of the North Sea is 0.6-0.4 g/m2.

The concentrations of biomass in a particular area due to discards have resulted in changes in the behaviour of certain species241, such as the seabirds and marine mammals that follow fishing boats as an easy source of food. There is no consensus as to whether the discards are positive or negative for seabirds. While on occasions they can represent an advantage by increasing available food during the breeding season242, they can also generate a demographic explosion of the most opportunistic species to the detriment of other, more vulnerable, ones243. An increase in the availability of discards can also provoke more aggressive behaviour in certain species and greater kleptoparasitism244. In any event, the reproductive success of all species depends on the availability of food, and thus the real problem is not the reduction in the number of discards, but overfishing.

Seagrass meadows (phanerogams)



There are various species of marine seagrass growing in the shallow waters of Europe on top of sandy seabeds in depths ranging from the surface to 40-50 metres. They are widely distributed from the Mediterranean to the Arctic245. In the North Atlantic, the most common species are Zostera marina, Zostera nolti (and Z. angustifolia, which is sometimes regarded as a variety of Z. marina)246, while the Cymodocea nodosa is more common in southern European waters (and Halophila decipiens also extends to the Canary Islands). In the Mediterranean, in addition to Cymodocea and Zostera, the endemic species is Posidonia oceanica.

Other European seagrasses include Ruppia maritima and R. cirrhosa, which do not form large marine meadows but tend to be found alongside Zostera communities247.

One of the most important phanerogams is Posidonia oceanica, due to the size of the areas it covers, the high level of biodiversity it gives home to and its extremely important role in the ecosystem. Unfortunately, it is also one of the most threatened communities. Up to 1,400 different species248 can be found in these meadows, and at the same time they can generate between 4 and 20 litres of oxygen per square metre each day and 38 tonnes of biomass per hectare per year249. These are important reproductive and spawning grounds for commercially valuable species which constitute the most important ichthyologic community in the infra-coastal Mediterranean environment250. The meadows of Zostera and Cymodocea are also highly important for anatids and marine reptiles, as well as hundreds of other organisms251.

Some of these communities can be extremely long-lived. While their clones can reach thousands of years of age, the structures they form, together with some coral reefs, have been dated at millions of years old252.

Despite the fact that Posidonia is protected by various laws (such as the EU Habitats Directive which includes it in Annex 1 as a priority habitat; or EC Regulation 1626/94 of the European Commission for the Conservation of Fisheries Resources of the Mediterranean), illegal trawling is decimating its populations and is regarded as one of the main causes of the deterioration of Mediterranean benthos253; between 40% and 50% of the meadows of Posidonia have been damaged by trawling254.

Estimates of the impact of trawling on these meadows calculate that a trawler can drag up between 100,000 and 363,000 leaves of Posidonia per hour, depending on the time of year and the density of the meadow, seriously damaging the rhizome system255. Ten trawler hauls over one of these meadows are enough to cause the loss of 10% of its coverage256.

The destruction of the meadows of Posidonia by trawlers affects the groupings and communities of many species of fish and invertebrates as well as epiphyte plants257. Amphipods seem to be a good indicator for confirming damage on these marine phanerogams258.

European Union laws regard the meadows of Posidonia as a priority habitat, but they do not include other seagrasses such as Zostera spp. or Cymodocea Nodosa, of incalculable ecological value.

Coralligenous beds



This biotope is characterised by the predominance of animal species with a calcareous structure such as sea fans, corals and false corals, as well as encrusting bryozoans and arborescent sponges. They live on hard substrates such as rocky seabeds and underwater caves, canyons or cliffs. Coralligenous beds can be found in shallow waters and up to depths of more than 100 metres259.

There are very few studies on the impact of fishing on coralligenous beds in Europe. In other areas, such as Australia and Alaska, it has been confirmed that many of them are long-lived species that are very vulnerable to disturbances and have serious difficulties in recuperating260. Trawling over these ecosystems can reduce biomass, which can be up to 106% higher than the biomass in zones where trawling is a regular occurrence, and are home to a number of species 46% higher261.

The sea fans and soft corals are particularly vulnerable to physical destruction. Depending on the damage inflicted and the species affected, the recovery of these ecosystems can take between 10 and 125 years262.

In the Mediterranean, the main components of coralligenous beds are sea fans (Paramuricea clavata, Eunicella verrucosa, E. filiformis, Elisella paraplexauroides and Lophogorgia ceratophyta), large bryozoans and false corals (Pentapora fascialis, Myriapora truncate and Sertella beaniana), arborescent and other sponges (Axinella damicornis, Axinella cannabina, Axinella polypoides, Haliclona mediterranea, Verongia aerophoba, Spirastrella cunctatri and Petrosia ficiformis), polychaetes (Salmacina dysteri and Serpula vermicularis), ascids (Polyclinidae spp., Didemnidae spp. and Halocynthia papillosa), cnidarians such as red coral (Corallium rubrum) and other corals (Alcyonum acaule, A. Palmatum, Parazoanthus axinellae, Leptosammia pruvoti) and some red seaweeds (Neogoniolithon mamillosum, Mesophyllum lichenoides, Peyssonnelia squamaria, Pseudolithophyllum expansum). This ecosystem is home to considerable biodiversity which includes echinoderms (Sphaerechinus granularis, Centrostephanus longispinus, Marthasterias glacialis, Antedon mediterranea and Hacelia attenuata), molluscs, crustaceans (Stenopus spinosus, Palinurus elephas) etc., and different species of fish, such as moray eels (Muraena helena), congers (Conger conger), grouper (Epinephelus marginatus), salemas (Salpa salpa), seabream (Oblada melanura, Diplodus annularis and Diplodus vulgaris), numerous chromis (Chromis chromis) and swallow-tailed seaperch (Anthias anthias).

These communities are regarded as particularly vulnerable and sensitive to large-scale damage263. European Union legislation only makes note of red coral in Annex V of the Habitats Directive.

It is calculated that in certain zones, 57% of discards are consumed by seabirds, 3% by animals in the water column and 49% by scavengers on the seabed264 (crabs, starfish, ophiuroids, etc.). Other estimates bring seabird consumption down to 20% or 25%265. It would appear that fish hardly get any benefit from discards apart from a few species (such as capelin) and then only occasionally266.
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