Commercial fishing: the wider ecological impacts

Transcription

1 THE BRITISH ECOLOGICAL SOCIETY Ecological Issues Series Commercial fishing: the wider ecological impacts Edited by: Geoff Moore & Simon Jennings Written by: John Croxall - BAS, Cambridge Bob Furness - University of GIagow Phil Hammond - SMRU, University ofstandrews Simon Jennings - CEFAS, Lowestof) and the University OfEastAnglia Mike Kaiser - University of Waks Bangor Enrique Macpherson - C W, Bhnes, Spain Geoff Moore - UMBS Millport Stuart Rogers - CEFAS, Lowestof) Ecological Society

2 'l'hr Rrirish Ecological Sociery and published for them by lllaclcwcll Science Ltd. Prinred 2nd bound in Grear Britain by (:ambridgr Universiry I'resa

3 FISHERIES IMPACTS Contents Key Points Commercial fishing: the wider ecological impacts 1.1 Introduction... 1 Fishing gears and their operation Pelagic drifting gears 2.1 Gear selectivity Bottom set gears Pelagic mobile gears Bottom mobile gears SCUBA diving, explosives, poisons Effects of litter from fishing gear 3.1 Ghost fishing Ingestion offragments offishinggear by marine mammals, turtles and seabirds Vulnerability of different marine habitats 4.1 Mud Gravel and mixed grounds Maerl Sea mounts Relative vun Effects on non-target organisms Sea birds Sea mammals Sea turtles Sea snakes Benthic scavengers

4 6 Community and ecosystem responses 6.1 Community diversity Habitat structure Benthopelagic coupling Species interactions Assessing fisheries effects Conservation aspects and the way f omd 7.1 Marine reserves Practical conservation measures Further reading Glossary Acronyms Addresses of contributors iv

5 KEY POINTS Fishing provides food, income ($US80 billion per year) and employment for 200 million people. However, fishing does have environmental costs which threaten marine ecosystems and the sustainability of the fished resource. 6 The greatest impacts of fishing tend to occur when an unfished environment is first exploited. The relative impacts of fishing depend on the balance between fishing and natural disturbance. 6 Fishing gears are designed to maximize yields of target species while minimizing the costs of capture. These gears have direct and indirect effects on the marine environment, resulting in by-catches of unwanted species and damage to marine habitats. Sand and gravel seabeds in shallow water are relatively resilient to the effects of towed gears, such as trawl nets, because they are adapted to natural disturbance. Habitats most at risk are coral reefs, maerl beds and seagrass meadows. Recovery may take many years, especially in the deep sea. 6 Species most at risk from the direct and indirect effects of fishing are characterized by late maturity, large body size and low potential rates of poputation increase. Species least at risk have high population recovery rates and morphologies that can withstand contact with fishing gears. 6 The populations most at risk from pelagic gears are those of some seabirds (especially albatrosses), turtles, sharks and marine mammals. By-catches of birds or marine mammals are high in some long-line, gill or seine net fisheries but mitigation measures can reduce by-catches without reducing catches of target species. b Lost nets and traps may continue to catch fish. Such 'ghost fishing' will continue until the gears are broken up or overgrown with fouling organisms. 6 Fishery discards provide important food material for surface-feeding seabirds, whose populations will inevitably suffer if discarding practices are reduced. Discards that sink provide food for benthic scavengers. Fishing can have indirect effects on the structure of marine communities and ecosystems. Some coral reefs have shifted from coral- to -algal-dominated phases following fishing. In many other ecosystems, however, fishing does not have clear effects on interactions and changes are largely due to the loss of vulnerable species. 6 Fishing as with other human activity that provides food, income and employment, has some undesirable impacts on the environment. Managers have to balance the costs of these impacts against the benefits derived from the food, income and employment that fishing provides and against the costs of producing protein in other ways. 0 Effective fisheries conservation will maximize the long-term yields of protein and income from fisheries while minimizing environmental impacts. Marine reserves (no-take zones) can help protect vulnerable habitats and species of conservation concern. V