Trawling

A large percentage of the fish captured in global and Canadian fisheries is caught using a bottom trawl or dragger. Bottom trawling involves pulling a large net along the ocean floor. Any type of fishing gear that contacts the seafloor has the potential to disrupt habitat; however, bottom trawling has been acknowledged to be the most destructive form of fishing commercially practised.

A growing body of scientific literature articulates the ecological damage associated with bottom trawling. There is scientific agreement that bottom trawling is the most damaging gear type to benthic (bottom-dwelling) populations, communities, and habitats. Bottom trawling not only impacts the seafloor but also changes the ambient water quality due to the disturbance of nutrients and sediment settled on the seafloor. The benthic food web is altered through the landings of targeted species, discarding of unwanted species, mortality and injury of species escaping trawl nets, and alteration of the relative abundance of various species groups (community structure). The severity and longevity of trawling impacts depends on factors such as depth, substrate, fishing intensity (i.e., the frequency of trawling), natural disturbance regime, and the life histories of the species being impacted. In areas of high natural disturbance, such as sandy bottoms with heavy tidal and wave forces, bottom trawling may be an acceptable method to capture fish.

^{Image credit: Joe Shoulak (www.joeshoulak.com).}

There are currently few restrictions on where, when, and how often a bottom trawl can be deployed in Canadian waters.

As of fall 2007, the Canadian government is consulting with the Canadian public on its policy to address habitat impacts from fishing gears. The David Suzuki Foundation believes that the policy as currently written does not measure up to international best practice and is narrow in scope.

To help inform the policy debate, the David Suzuki Foundation recently released a report entitled Dragging Our Assets: Toward an ecosystem approach to bottom trawling in Canada that outlines a broader vision for managing the ecological impacts from bottom trawling.

The David Suzuki Foundation recommends the following:

- An immediate prohibition on the expansion of bottom trawling into frontier areas consistent with interim measures found in the UN Sustainable Fisheries Resolution.

- A significant reduction in the use of bottom trawls in deepwater habitats.

- An interim moratorium on bottom trawling in Oxygen Minimum Zones until sufficient scientific research into chemical and biological process in these habitats has been undertaken.

- An immediate prohibition of the use of bottom trawls in “sensitive areas” (i.e., corals and sponges) consistent with the UN Sustainable Fisheries Resolution.

- Zoning and restricting of bottom-trawl gears to areas of highest catch.

- Zoning and restricting of bottom-trawl gears to areas of high natural disturbance.

- Implementation of a system of no-trawl zones for all habitat types similar to that found in New Zealand, where all types of benthic habitats will receive some level of protection from fishing-gear impacts.

- Preferential allocation of resource access to gear types that significantly reduce and limit the potential impact on benthic habitats.

^{Sponges, corals, and Greenland halibut captured in 2006 by bottom trawling in a “frontier area” in Canada’s North Atlantic waters. Photo credit: DFO.}

International Concerns

Of immediate international concern is the practice of deep-sea bottom trawling on the high seas. The deep-sea trawl fishery is relatively new and has emerged as a result of technological advances (GPS and imaging, for example). Nets can now be dropped into areas where substrate conditions, or uncertainty of those conditions, used to bring too high a risk of net damage. Areas of the ocean that were once safe from direct physical impacts from bottom trawling are now exposed to new, destructive threats. Species living in deep-sea habitats have several unique characteristics: they tend to be long-lived, slow-moving, slow to mature and reproduce, and unaccustomed to disturbance. Trawling over their habitat causes immense damage to both the habitat and the species assemblages.

Management of the oceans on the high seas is carried out through the United Nations but is ultimately the responsibility of member states. In December 2006, the United Nations passed the Sustainable Fisheries Resolution. The Resolution calls for Regional Fisheries Management Organizations to immediately (before December 2008) manage bottom trawling on the high seas to ensure that it does not occur on habitats where there may be significant adverse impacts. More information on the campaign to control high-seas bottom trawling can be found at www.savethehighseas.org/.