Regulating deep sea bottom trawl fisheries

Jon Nevill
5 Nov. 2006

0.Preface

The effects of bottom trawling on the deep sea have been the subject of a variety of scientific papers, especially over the last decade. Some of the most important are listed in the bibliography below. Additionally, a considerable number of reviews, not only of the effects of bottom trawling, but also of options for international regulation of these activities, have appeared since 2001. Amongst the most important of these reviews are: the comprehensive report edited by Thiel & Koslow (2001), Butler et al. (2001), NRC (2002), Roberts (2002), Glover & Smith (2003), FAO (2003), Freiwald et al. (2004), Gianni (2004), Hain & Corcoran (2004), Currie (2004), Morato & Pauly (2004), Rogers (2004a & 2004b), Freiwald & Roberts (2005), Roberts et al. (2005), Gjerde (2006), and Roberts et al. (2006).

Very recently, reviews have been included in documents directed towards the October 2006 meeting of the United Nations General Assembly (UNGA), in particular: Government of Palau (2006), and UN Secretary-General (2006).

The purpose of the present review is to provide a brief summary of key aspects of the current discussion. The intended audience of this paper are marine scientists, conservation biologists, managers and decision-makers, particularly those from Australia, Canada and New Zealand.

1.Abstract:

The deep sea is a major reservoir of the planet’s biodiversity, most of it unknown and unstudied – the “last great frontier on Earth” (Roberts 2005). While much of the abyssal region is sparsely populated, deep sea benthic habitat around features such as seamounts, hydrothermal vents, ridges and trenches is often both rich and abundant. However, these habitats (especially seamounts) are vulnerable, particularly to bottom trawling. Bottom trawls, or demersal trawls which come in contact with the sea floor, effectively destroy complex habitat, built over centuries or millennia by slow-growing invertebrates. Significant damage has already been done which, within the time-scale of a human life, is irreparable – and this damage continues at an increasing rate.

Marine scientists and conservation biologists have been expressing serious concern over the continued use of bottom trawling in the deep sea for more than two decades. During this time new technology has increased the ability of fishers to work the deep sea. Major scientific reports and reviews confirm that, generally speaking, bottom trawling over complex biogenic habitat is biologically unsustainable. Several major international agreements require nations to protect ocean habitats, yet for the most part bottom trawling operations continue under little or no regulation. The United Nations General Assembly commenced an examination of bottom trawl management options in 2002, and is due to reconsider the issue again in October 2006. Under a separate UN process, options for the establishment of high seas protected areas have been under discussion since 1998.

The gravity of the issue requires involvement from the marine science community. Current management arrangements aimed at protecting deep sea biodiversity are not working. New approaches must be devised and implemented without delay. Nations must take action if widespread and effectively irreversible damage over much of the deep ocean is to be prevented. This will not occur without the active involvement of the marine science community.

The United Nations General Assembly will consider new proposals for regulation of these activities at its meeting in October 2006. The Australian Government is currently considering the position it should take at the Assembly. This paper puts the case that Australia should take a strong position (supporting a limited moratorium on high seas bottom trawling) consistent with its internationally acknowledged leadership in the field of marine conservation. Support for the Palau draft resolution is recommended.

2.The importance of deep sea biodiversity:

All life depends (directly or indirectly) on utilising energy either from sunlight or from geochemical sources. The Earth’s surface is characterised by life forms utilising sunlight, and this also applies to the ocean’s shallow layers, which occupy about 70% of the planet’s surface. However only 1% of the energy of sunlight penetrates below 200 m, and only a few specialised plants exist below this level (Roberts et al. 2005). Below 600 m eternal darkness prevails. Here life depends on what falls, or swims, or is swept from the photic zone. Or, where hydrothermal vents or cold seeps exist, on geochemical energy.

For fish and other animals near the surface of the open ocean, life is dangerous. There is nowhere to hide. Most plants and animals here live fast, breed fast and die fast. Many are characterised by rapid growth, rapid propagation strategies and short lives. The largest predators, and some mammalian and reptilian herbivores, provide exceptions to this rule.

However where complex physical habitat provides safety, such as coastal rocky or coral reefs, more leisurely lifestyles are possible. Lifestyles in the deep ocean are often even slower. Deepwater species (those living below 500 m) often exhibit “K-selected” life-history characteristics markedly different from most shelf species: extreme longevity, late age of maturity, slow growth, and low fecundity (Koslow et al. 2000).

Seamounts are usually the result of volcanic activity, and often occur in clusters or strings. The number of seamounts depends upon definition. The position of about 14,000 seamounts over 1000 m. ‘high’ have been mapped (Kitchingman & Lai 2004), and one estimate puts the count of such seamounts in the Pacific at around 50,000 (Rogers 2004a). However, given a relaxed definition which counts hills smaller than 1000 m. in elevation, a total global count is likely to be considerably higher (perhaps >100,000). Of the 14,000 seamounts mapped by Seamounts Online (by 2004), only 3-4% had been sampled for invertebrates (Stocks 2004).

According to Stocks (2004) discussing surveys over 171 seamounts: “Crustacea is the group that has been recorded from the most seamounts (116). In part, their prevalence may be due to a sampling bias: crab and shrimp are of commercial importance and thus of particular interest in many surveys. Following the Crustacea are Anthozoa (corals and anemones), recorded from 84 seamounts. Also common (recorded on 30-45 seamounts) are gastropods, bivalves, echinoids (sea urchins), ophiuroids (brittle stars), asteroids (sea stars), polychaetes, and hexactinellids (glass and related sponges).”

Koslow et al. (2001) reported surveys of seamounts south of Tasmania: “The fauna was diverse: 262 species of invertebrates and 37 species of fishes were enumerated, compared with 598 species of invertebrates previously reported from seamounts worldwide. On seamounts that peaked at depths <1400 m and that had not been heavily fished, the invertebrate fauna was dense, diverse and dominated by suspension feeders, including a matrix-forming colonial hard coral (Solenosmilia variabilis) and a variety of hard and soft (gorgonian and antipatharian) corals, hydroids, sponges and suspension-feeding ophiuroids and sea stars. Of the invertebrate species, 24 to 43% were new to science, and between 16 and 33% appeared to be restricted to the seamount environment.”

It is not surprising that seamounts provide support for benthic and demersal species; in abyssal environments dominated by deep sediments adjacent to slow moving water, they provide hard substrate in a moving water environment (supplying food and oxygen) to support the development of a huge variety of attached filter feeders. However, due to their size seamounts also create distinctive oceanic environments around and above them. According to Rogers (2004a): “One of the most well-known oceanographic effects of seamounts with potential significance to seamount biology is the formation of eddies of water (so -called Taylor Columns) that are associated with upwellings of nutrient rich waters, leading to increased productivity in waters near the surface.” This effect is thought to partly explain the tendency of pelagic animals to aggregate in the vicinity of seamounts, thus connecting the benthic, demersal and pelagic environments.

Seamounts may play an important role in dispersal, ultimately supporting evolutionary processes in the ocean. According to Rogers (2004a): “Seamounts may also act as refugia for some marine species. Evidence also suggests that seamounts may act as stepping-stones in the transoceanic dispersal of marine species, playing an important role in the evolution of the global marine fauna.” As well, seamounts can act as "islands" in the Darwinian sense, and therefore provide the foundation for the development of new species- some unique to an individual seamount.

In summary, the deep sea contains a wealth of species, habitats and ecosystems with biologies quite different from coastal or pelagic environments. Some of these ecosystems possess exceptional species richness and endemism (Rogers 2004b). While very little of this biota has been subject to scientific investigation, enough is known to underline both its global importance and its vulnerability to disturbance.

3.The impacts of bottom trawl fisheries in the deep sea:

Damage from trawling has been the subject of concern since at least the 14th century (Jones 1992). Bottom trawls (see Figure 2) are large nets which are dragged along the sea floor to harvest benthic and demersal species. Deep sea bottom trawls are larger and stronger than most shallow water trawls, and can operate to around 2 km depth (although most deep sea trawling currently occurs between ~ 500-1500 m). The bottom edge of the trawl carries heavy rollers to keep the trawl base on the floor.

Modern trawls are strong enough to destroy anything weak or brittle attached to the sea floor lying in their path – such as coral. On a typical fishing trip in the NE Atlantic, a trawler sweeps ~33 km2 of sea bed. A single trawl can completely destroy a cold-water coral reef which has taken thousands of years to grow (Hain & Corcoran 2004:121). One trawl marketed in 2005 was named “the Canyon Buster” – epitomising the trawl’s effect on the sea floor.

Coral reefs or mounds may be thousands to millions of years old[1]. Deep sea coral structures damaged or destroyed by bottom trawls are often centuries or millennia old (Hall-Spencer et al. 2002[2]). Deep sea sponge communities destroyed by bottom trawls are often decades or centuries old. Bottom trawling over soft sediments disturbs plants and animals years or decades old – with the exception of some of the larger molluscs which can reach ages in excess of 200 years. Ecological recovery times may be an order of magnitude (or more) greater than the typical age of the ecosystem’s living inhabitants. The older and larger deep sea coral reefs which are currently being destroyed are likely to take several thousand years to recover, if recovery is possible[3]. Increasing ocean acidity also presents a long-term threat to such ecosystems.

The effects of bottom trawling on fish populations is exacerbated by the widely used practice of targeting breeding aggregations. Attempts by fishery management agencies to curb this practice are weak or non-existent, in spite of:

  • the FAO Code of Conduct 1995 calls for States to “protect critical… nursery and spawning… habitats” (para. 6.8);
  • the Johannesburg WSSD 2002 calls for States to implement “time / area closures for the protection of nursery grounds and periods…” (Plan of Implementation, para 32c);
  • the Society for the Conservation of Reef Fish Aggregations 2003 calls for “… all fish spawning aggregation sites [should] be conserved” (Statement of Concern 2003); and
  • the World Conservation Congress 2004 urges States to “sustain and protect reef fish and their spawning aggregations…” (Recommendation 3.100).

The most heavily fished deep sea areas have been in the North Atlantic. Catches have been maintained by a ‘mining’ approach – once one area is exhausted, fishing moves to a new location (‘sequential depletion’). Evidence is growing that many, perhaps most, deep sea fisheries cannot be fished sustainably using traditional fishery management approaches (Koslow & Tuck[4] 2001, Morato & Pauly 2004, Bergstad et al. 2005). According to Butler et al. (2003): “… in some cases the biology and ecology of the system may be such that there is no way to fish sustainably”.

The Working Group On The Appraisal Of Regulatory Measures For Deep-Sea Species of the Northeast Atlantic Fisheries Commission (NEAFC), in June 2002 reported that in the Northeast Atlantic: “For the deep-water trawl fisheries the typical development is a rapid increase in catches when a new resource is discovered followed by a decrease reflecting depletion of the resource. The trends in landings and catch per unit effort (CPUE) for most deep-water fisheries currently indicate that fishing pressure is far beyond sustainability” (WGARMDSS 2002). Likewise, a 2002 paper by the European Commission described the orange roughy fisheries in the Northeast Atlantic as being “consistent with a ‘mining’ approach… aggregations are located and then fished out on a sequential basis” (SGFEN 2002).

Scientists involved in assessing the sustainability of deep-sea fisheries in the New Zealand and Australian regions and in the Southwest Indian Ocean have come to similar conclusions. For example, Clark (1999) stated that an analysis of commercial catch and effort data in fisheries for orange roughy on seamounts in New Zealand waters, one of the largest deep-sea bottom trawl fisheries in the southern hemisphere, “show strong declines in catch rates over time, and a pattern of serial depletion of seamount populations, with the fishery moving progressively…to unfished seamounts.”

Bottom trawls destroy coral structures within their sweep[5]. Anderson & Clark reported one of the few observer studies of coral bycatch from a virgin seamount site – the South Tasman Rise. In the first year of the study trawls averaged in excess of 10 tonne of coral per tow[6] (more than twice the weight of orange roughy caught per tow), with the seasons operations harvesting around 12,000 tonnes of coral (extrapolated from the measured 1762 t.). The actual tonnage destroyed would be far higher, as a large proportion of delicate coral falls through the trawl mesh. Close to 100% coral cover was reported on unfished seamounts compared with only 2-3% cover on heavily fished seamounts. Not unexpectedly, coral bycatch at the site dropped dramatically over the three years of the observer study (Anderson & Clark 2003).

These estimates of coral destruction align with Koslow et al. (2001): “Trawl operations effectively removed the reef aggregate from the most heavily fished [southern Tasmanian] seamounts.” In an earlier study of 14 seamounts in this area, Koslow & Gowlett-Holmes (1998) reported sampling benthic biomass on both heavily fished and unfished or lightly-fished seamounts. Benthic biomass on the heavily fished seamounts was 83% below levels on the remaining seamounts. These results indicate that bottom trawling causes extensive damage to vulnerable benthic ecosystems. In some cases this damage extends to effective annihilation of local ecosystems.

Once a commercial trawl ground is located, the area is likely to be trawled repeatedly, while the surrounding areas are also likely to be targeted. Given the ability of bottom trawls to almost completely remove benthic habitat, the sharp declines in catch commonly observed in deep sea trawl operations are not unexpected.

Endemism in some groups of seamounts appear to be high (from the limited data currently available). Estimates of such endemicity have varied from 9% to 35% at different locations (Gianni 2004:7). According to Koslow et al. (2000): “[Seamount] fauna… is typically restricted to the seamount environment and is characterised by high levels of endemism, which suggests limited reproductive dispersal”.

Roberts concluded, in relation to seamount fisheries, “Many species, it seems, have extremely limited geographical distributions and are restricted to closely spaced ranges of underwater peaks. The potential for trawl damage to cause extinctions is high” (Roberts 2002). Rogers (2004a) shares this view: “the limited range of many seamount species means that the extinction of endemic seamount animals [as a result of bottom trawling activities] is also likely”. According to Edgar et al. (2005): “Population declines of marine species approaching extinction will generally go unnoticed because of the hidden nature of their environment and lack of quantitative data”. Morato et al. (2006) express the same concern: “… species extinctions may follow if fishing on seamounts is not reduced.”

What proportion of the world’s seamounts have been damaged by trawling, and what proportion have been badly damaged? What proportion are inaccessible to trawling operations, and where are these areas located? Information is not available to answer these questions. However, there is no doubt that a great deal of damage has already been done.

Clark & O’Driscoll (2003) reported that about 80% of known seamounts (of the appropriate depth range) in the New Zealand EEZ had been fished by 2000, and a similar figure may well be accurate in the Australian EEZ. Unfished seamounts, if they exist, should be protected as a matter of urgency. As an interim measure, bottom trawling below 400 m. should be immediately banned in Australian waters pending a scientific investigation of the extent and degree of damage, as well as identification of location and quality of remaining cold-water coral habitats.

Surveys of the Norwegian EEZ in 1997-98 indicated that between 30% to 50% of deep water coral areas had been destroyed as a result of bottom trawling (Fossa et al. 2002), and remaining coral areas were granted partial protection by Norwegian law (see below). Similar surveys have not yet been undertaken in Australia. Limited surveys of Tasmania’s seamounts by the CSIRO found substantial trawl damage; however no information is available on damage in a national context. Some, but not all Tasmanian seamounts have been protected by the recently declared Huon Marine Protected Area, which extended the Tasmanian Seamounts Reserve declared in 1999.

Damage to deep sea habitat caused by bottom trawling is equivalent to damage caused to shallow coral by blast fishing – a practice now outlawed by all effected nations. Deep sea trawling is analogous to clearfelling a forest to capture a flock of birds. Moreover, instances of deliberate destruction of coral prior to trawling have been reported (Fossa et al. 2002) – a practice which may be widespread.

According to Rogers (2004b): “There is no other human activity [compared to deep-sea bottom trawling] related to the gathering of biological or mineral resources for which impacts on the environment are so poorly understood or managed.”