Deep-water longline fishing has reduced impact on Vulnerable Marine Ecosystems

29 April 2014

Source:Scientific Reports

Authors: Christopher K. Pham, Hugo Diogo, Gui Menezes, Filipe Porteiro, Andreia Braga-Henriques, Frederic Vandeperre & Telmo Morato

The expansion of fishing activities into deeper waters1 is unquestionably one of the principal threats to the world's ocean health2. Most deep-sea fisheries are unsustainable not only for target species but also for non-target fauna and their habitats3. Unless some radical changes in governance and management are being made4, damages to deep-sea ecosystems will soon be irreversible. The United Nations have recognized this issue and has urged governments and Regional Fishery Management Organizations to assess the impact of deep-sea fisheries on Vulnerable Marine Ecosystems (VMEs), particularly on cold-water coral ecosystems5. To reach this goal, impact assessments of different types of deep-sea fishing gear and of specific fishery are urgently needed6.

Cold-water corals are of significant ecological7 and economical value8, providing habitat for a wide variety of organisms9, 10, many that are of commercial interest9, 11. They are found in all oceans, in a wide variety of settings including continental shelves, fjords, canyons, seamounts, mounds or island slopes12 and are considered as biodiversity hotspots, comparable to the diversity found in tropical coral reefs13. In contrast to tropical reefs, the cold temperatures and inconstant food supply in the deep-sea implies that most of cold-water corals have high longevity and reduced growth rates14, 15, 16, long reproductive cycles and low rates of recruitment17. Such life history characteristics imply that cold-water ecosystems have a reduced capacity to recover from disturbance events, such as deep-sea bottom fishing18.

Deep-sea bottom trawling is the most destructive form of deep-sea fishing19 and an issue of global concern (Fig. 1), since it removes most of these habitat-building organisms from the sea floor20. Furthermore, trawling modifies the seafloor morphology and its physical properties21, with dramatic consequences on benthic communities20, 22. Not surprisingly, increasing pressure is being made to ban the use of deep-sea bottom trawls in European waters19. Therefore, alternative fishing techniques that maintain the health of deep-sea ecosystems and tolerate appropriated human uses of the marine environment for the benefit of current and future generations are required.

Bottom longline is a passive fishing gear considered to have low impact on the benthic environment23 but quantitative information is still scarce. Although bycatch of cold-water corals and sponges have been reported for some bottom longline fisheries24, 25, 26, 27, 28 no studies have effectively assessed the overall level of impact of bottom longline and compared to that of other gear types. Such comparison would help determine the future of deep-water fisheries and contribute to their sustainability. Here, we assessed the impact of deep-sea longline on benthic communities, using data collected aboard commercial fishing vessels, experimental fishing surveys and underwater footage, and compared with the known impact of bottom trawling.

For more, go to: www.nature.com/srep/2014/140429/srep04837/full/srep04837.html