Bottom trawling is a diversified fishing method which uses numerous types of gear designs, sizes, rigging and operational methods. Therefore, impact on the bottom habitat will differ among the various bottom trawl fisheries and also to a large extent depend on the bottom conditions in the area fished. During bottom trawling the primary function of the forward parts of the trawl is to maintain bottom contact, provide spread and herd the target species. These parts are the trawl doors, sweeps and bridles, and are essential for proper gear performance and capture efficiency. This document describes the basic principles that can be used to reduce the impact of trawling, some of which are already developed as practical solutions and implemented in commercial fisheries. Overall, however, there are presently few examples of low bottom impact trawl gears in use in commercial fisheries. These basic mitigation measures aim at reducing pressure on the bottom of various trawl components and minimizing the impacted area while trawling.

Modifications to trawl doors that will reduce pressure on the bottom include the use of lighter doors and shortening of the warp-length-to-depth ratio (the extreme result of the latter option is off-bottom trawl doors). The impact by sweeps/bridles can be reduced with the use of discs or bobbins along the cable to raise them off the bottom and by off-bottom rigging of the lower bridle. Pressure of the ground gear can be reduced through the use of lighter gear components and gear components with lifting capabilities.

Reduction of the bottom area that is directly affected by trawl doors can be achieved with the use of high aspect ratio doors and by reducing the shoe angle relative to the towing direction. The affected area by sweeps/bridles can be reduced by shorter bridles, reduced sweep/bridle angle and by discs and bobbins mounted along the length of the wires. Ground gear modifications include reduction of the length of the ground gear and arrangements that reduce the number of contact points between the gear and the bottom.

Implementation of the above options may result in reduced capture efficiency for target species and acceptance of the technology by the fishing industry in their commercial fishing activity might therefore be difficult. Thus, research communities face many challenges to further develop bottom habitat friendly options. Alternatively, to reduce the impact of traditional bottom trawling, a viable option might be to catch some of the targets while they are off-bottom with midwater trawls. This is an option worth considering for fish resources that, as adults, spend part of their life cycles off bottom.

Another alternative for exploiting near bottom organisms is to increase the use of stationary fishing gears which have much less impact on the bottom habitat. For some target species bottom set gillnets and longlines might be both practical and economical viable alternatives to bottom trawling, whereas other species like shrimp and small non-shoaling fish species cannot be captured economically with such gears. For such species, bottom trawling is at present the only viable option.

Finally, a general improvement of the efficiency of bottom trawls can contribute to the reduction of bottom habitat impact, as less effort is needed to catch the allotted quotas. The management regimes in place might, to a large extent, encourage rational exploitation of the resource, such as the individual transferable quotas ITQ management system.