Fisheries Infosite

Environmental Issue

Bottom trawling - Effects on the seabed habitat

Bottom trawling can damage the marine environment; particularly where trawling occurrs on biogenic and benthic habitats.
Habitats which contain species like deep sea corals are easily damaged by bottom trawls and can take hundreds of years to recover from these effects.
Extent of the issue
Offshore fishing grounds make up around 10 percent of New Zealand's Exclusive Economic Zone. Most of these offshore grounds have been extensively trawled since the 1970s and 80s. Repeated bottom trawling has probably reduced the diversity of life on the seafloor on these fishing grounds and may have reduced the productivity of the marine ecosystems there. Areas outside of these fishing grounds are largely untouched by bottom trawls.  Many species (e,g, rubyfish, hoki, barracouta, mackerels, frostfish and southern blue whiting) are being caught by middle-depth trawls which have less impact on the benthic environment.
The areas fished today have been trawled for the past 10, 20 or 30 years. So it seems likely that the most serious damage to seabed habitats in these places has already occurred.
Current management
Offshore, a range of sensitive deepwater 'seamount' habitats were closed to trawling in 2001. In 2007, further offshore Benthic Protection Areas were closed to bottom trawling and dredging in a collaborative effort between government and industry. Offshore closures now total around 32% of New Zealand's EEZ.
Research is currently underway on effects and recovery of the Chatham Rise seabed from trawling (using analysis of data from a 2007 seafloor survey); there is also research into the 'footprint' of deep sea trawling, relative to diffierent habitat types. All this and other research will help inform further decisions on marine protection in offshore areas.
Future management
Benthic Protection Areas currently protect a range of deep sea areas. So the government is now concentrating on marine protection in inshore waters. As new information around trawling impacts in the deep sea becomes available, the government may review its current suite of protection here. 
Documents / links
Benthic Protection Areas accord, chatham / Challenger project, seamount closure report, reducing bycatch in scampi trawls 2006, modification of marine benthos - Cryer 2002.