In addition to the physical impacts of bottom fishing on deep-sea ecosystems, the depletion of deep-sea species is a matter of international concern. Unlike shallow-water, deep-sea species are often slow growing, long lived, 'low productivity' species that are highly vulnerable to depletion.
Most high seas bottom fisheries target low productivity species such as orange roughy in the South Pacific and Indian Oceans, grenadiers in the Northeast Atlantic, redfish in the Northwest Atlantic, and deep-sea sharks (the latter often caught as bycatch in deep-sea fisheries in the Atlantic, Pacific and Indian Oceans and marketed to the cosmetics and dietary supplement industry for their liver or 'squalene' oil). In addition, a large number of species have been recorded in the bycatch of many high seas bottom fisheries, in particular bottom trawl fisheries, the majority of which are likely to be low productivity species. The status of target species and bycatch species in the deep-sea fisheries on the high seas is largely either unknown or, where information is available, considered overexploited or depleted. Regulations are in place in some fisheries in some high seas areas to manage the target catch in deep-sea fisheries. However, few, if any of the fisheries impacting deep-sea stocks or species on the high seas can currently be considered sustainable.
The scientific literature often refers to deep-sea fisheries as 'serial depletion' fisheries and numerous studies or reports confirm the problematic nature of fisheries for deep-sea species. A report published by the Royal Society of Britain in 2009 concluded that deep-sea fisheries in the Northeast Atlantic are depleting populations of deep-sea fish well below the depths at which the fishing takes place. The IUCN Shark Specialist Group classifies the three main species of deep-sea sharks (leafscale gulper shark, Portuguese dogfish, gulper sharks) in the Northeast Atlantic as endangered or critically endangered. In the South Pacific, New Zealand reports a total of 137 species of fish caught in the deep-sea fisheries on the high seas; the status of these species and the impact of the fishing on these species is unknown. At least 50 species have been recorded in deep-sea trawl surveys along the Emperor Seamount chain northwest of Hawaii in the North Pacific, where deep-sea vessels from Japan, Russia and Korea continue to operate on the high seas.
The international Council for the Exploration of the Seas, the scientific advisory body to the European Union and the North-East Atlantic Fisheries Commission, summed up the problem of deep-sea fishing as follows:
At depths between about 400 and 1500m there may be between 40 and 50 demersal species present depending on gear type. Maximum species diversity occurs between 1000-1500m before declining markedly with depth. Deep water species, are typically slow growing, long lived, late maturing and have low fecundity. Fishing has a greater effect on species with such life history trait...making them particularly vulnerable to overexploitation. This applies to both the target and non-target species. A large proportion of deep-water trawl catches (upwards of 50%) can consist of unpalatable species and numerous small species, including juveniles of the target species, which are usually discarded... The survival of these discards is unknown, but believed to be virtually zero due to fragility of these species and the effects of pressure changes during retrieval...Therefore such fisheries tend to deplete the whole fish community biomass." (1)
Not only are deep-sea fisheries for the most part unsustainable, but the economics of deep-sea fisheries are questionable given the low productivity of deep-sea fish stocks. According to a report published in 2009 by the UN FAO, some 285 vessels flagged to 27 countries were estimated to be engaged in high seas bottom fisheries in 2006 (many only fishing part-time on the high seas). Of this number, 80% were flagged to ten counties: Spain, Republic of Korea, New Zealand, Russian Federation, Australia, Japan, France, Portugal, Belize and Estonia. Over one-third were flagged to European Union countries and the EU fleet took half or more of the high seas bottom catch. The majority of the vessels engage in high seas bottom trawling. (2)
The FAO report estimated that the global catch in high seas bottom fisheries in 2006 was approximately 250,000 tonnes, representing 0.3% of the marine catch worldwide. The value of the high seas bottom catch in 2006 was estimated at approximately $450 million US dollars, a small fraction of the overall value of approximately $75 billion dollars of marine catch worldwide. The conclusions of the UN FAO report were similar to the findings of a study on high seas bottom trawl fishing published by IUCN in 2004.
A study released by the Fisheries Centre of the University of British Columbia in 2007 concluded that many deep-sea bottom trawl fisheries on the high seas in recent years would not have been economically viable without state subsidies. And a review of deep-sea fisheries in the Northeast Atlantic by the European Commission in 2007 concluded that many deep-sea fish stocks have such low productivity that â€œsustainable levels of exploitation are probably too low to support an economically viable fishery." (3)
Thus far deep seabed mining activities have been confined to exploratory ventures, which are presumed to have fewer ecosystem impacts than commercial scale mining. However, once exploitation commences as early as 2016, scientists have confirmed that mining activity could cause substantial physical damage to deep-sea ecosystems and is likely to bring large quantities of particle-laden, CO2 and nutrient-rich, cold water to the sea surface. These flows could also potentially be polluted, for example by hydrogen-sulphide, and could create a number of large-scale impacts to alter pelagic and/or benthic ecosystems.
Any mined material that is processed at sea will lead to the deposition of tailings and the remobilization of toxic chemicals, causing damage to ocean life at multiple levels.
Although ongoing exploration is continually advancing our knowledge of the deep ocean, it is also revealing just how much there is still to discover and understand. Huge uncertainties make it very difficult to predict the magnitude of consequences of human activity in the deep ocean. After thirty years of work, researchers continue to find new hydrothermal vent sites in remote locations and new species, adaptations, behaviours and microhabitats. As with bottom trawl fishing, we may well risk losing untold species before we have even discovered them.
(1) From: Report of the Working Group on the Biology and Assessment of Deep-Sea Fisheries Resources (WGDEEP). 3—10 March 2008. Copenhagen, ICES Headquarters. ICES CM 2008/ACOM:14. 531 pp. Pages 70-71.
(2) Bensch, A., Gianni M., Greboval D., Sanders J.S., Hjort A. World Wide Review of Bottom Fisheries in the High Seas. Food and Agriculture Organization of the United Nations. Rome, 2009.
(3) COMMUNICATION FROM THE COMMISSION TO THE COUNCIL AND THE EUROPEAN PARLIAMENT: Review of the management of deep-sea fish stocks. Brussels, 29.1.2007 COM(2007) 30 final