Habitat Impacts – Otter Trawls

Otter Trawls

2014-05-04 12.37.44Otter trawls are one of the gear types commonly used in both Mississippi state and federal waters. They consist of two doors, the angle of which forces them apart and keeps the net open; a footrope that may be weighted and spans the mouth of the net; and a tickler chain that disturbs the bottom and startles benthic organisms out of the substrate and into the net. Modern trawls have twin trawls off each side of the boat. The extent to which an otter trawl affects the ocean bottom is highly dependent on bottom type. Generally, trawls cause scraping and ploughing, sediment resuspension, physical habitat destruction,  and removal or scattering of non-target benthos (Jones 1992). The trawl doors have the most potential to impact bottom habitat due to their size, weight, and function (Barnette 2001). As trawling occurs,  the doors disturb the upper layer of sediment, causing it to suspend in the water column. The rate of settlement depends on the type of sediment; finer particles such as mud and silt settle much slower than sand. This does have thepotential to affect water turbidity and compress the euphotic zone (North Carolina Division of Marine Fisheries 1999). The footrope does not have a major impact on a flat bottom (ICES 1995), but may cause damage in more complex benthic habitats (Barnette 2001). Trawls have the potential to more severely impact complex bottoms such as coral reefs. However, the use of trawls on coral reefs in the EEZ is prohibited and tickler chains are required to have a weak link (EFH- Amendment 3).


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