Use a midwater/semi-pelagic trawl instead of bottom/demersal trawl
Overall effectiveness category Likely to be beneficial
Number of studies: 1
Background information and definitions
Trawling is a method of fishing that involves pulling a fishing net (trawl) through the water behind one or more vessels. Semi-pelagic trawls (also referred to as midwater trawls) are types of trawls where the nets are towed through the water above the seabed, whereas demersal trawls (also referred to as bottom trawls) tow their nets along, or close to, the seabed. Semi-pelagic trawl gear does not come into contact with the seabed, resulting in less damage to the seabed. Using a semi-pelagic trawl instead of a demersal trawl may potentially reduce the impact on the seabed and disturbances or damages to subtidal benthic invertebrates (Moran & Stephenson 2000).
Moran M.J. & Stephenson P.C. (2000) Effects of otter trawling on macrobenthos and management of demersal scalefish fisheries on the continental shelf of north-western Australia. ICES Journal of Marine Science, 57, 510–516.
Supporting evidence from individual studies
A replicated, controlled study (date of study unspecified) in six seabed plots in the Indian Ocean, north-western Australia (Moran & Stephersn 2000) found that fishing with a semi-pelagic trawl did not reduce invertebrate abundance to the extent that fishing with a standard demersal trawl did. Following fishing with a semi-pelagic trawl, abundance of large sessile invertebrates (>20 cm) did not change and was similar to non-trawled plots, whereas following each fishing event with a demersal trawl their abundance was reduced by approximately 16% (data presented on a logarithm scale). The semi-pelagic trawl caught fewer commercially targeted fish than the demersal trawl. Two types of otter trawls were tested; a semi-pelagic trawl, deployed approximately 15 cm above the seabed (no contact), and a standard demersal trawl towed along the seabed (in contact). An area of seabed at 50–55 m depth that had never been trawled was divided into six 360 x 925 m plots: two plots/gear type and two non-trawled plots. Each trawled plot was trawled four times. Invertebrates attached to the seabed (>20 cm, reported as being mostly sponges, soft corals, and gorgonians) were counted from video camera recordings before and after each fishing event in trawled and non-trawled plots.Study and other actions tested