Bottom (inshore) trawling - Effects on sea bed habitats
Issue
Bottom (inshore) trawling can damage the marine environment; particularly where trawling occurrs on biogenic habitats like bryozoans, mussels and sponges.
Risk
These are important nursery areas for some commercial species. Marine life and productivity of commercial fisheries can also be significantly affected by sediment plumes created by bottom trawling through muds and silts.
Extent of the issue
Most inshore fishing grounds around New Zealand have been extensively trawled (and in some places dredged) since the 1960s and 70s. In these places, repeated bottom trawling has probably reduced the diversity of life on the seafloor and the productivity of marine ecosystems.
Trends
The areas fished today have been heavily trawled for the past 10, 20, 30 or 40 years. So it seems likely that the most serious damage to seabed habitats in these places has already occurred. Over the past 20 years, increasing numbers of inshore areas have been closed to bottom trawling and dredging. More of these closures are likely, as part of the government's Marine Protected Areas programme.
Current management
Some sensitive inshore habitats were recognised as important fish nurseries and closed to commercial trawling and dredging in the 1980s; some voluntary commercial closures also exist. A range of trawl restrictions exist in many other parts of New Zealand, including Cable Protection Zones, Marine Reserves and a number of Mataitai Reserves created during the 1980s, 90s and 2000s.
Future management
Managing the effects of bottom trawling on the seabed will be considered as part of future management in inshore trawl fisheries.
Documents / links
Marine Protected Areas Policy and Implementation Plan, Simon Thrush 1998, Jake Rice, global analysis - Kaiser 2006
