Habitat Impacts – Otter Trawls – TX Shrimp

Otter Trawls

2014-05-04 12.37.44Otter and beam trawls are the most common gear used in both Texas state and federal waters (Texas Trawl Gear Characterization). Barnette (2001) compiled a review of habitat impacts of gear types commonly used in the Southeastern United States, including the Gulf of Mexico, as there is concern over what affect trawls have on the ocean floor and essential fish habitat (EFH). Beam trawls are similar in construction to otter trawls, but contain a metal frame that spreads the mouth of the net. The gear is not designed to contact the substrate (Texas Trawl Gear Characterization). The effect beam trawls have on the ocean floor is similar to that of otter trawls, so they are not discussed separately here (ICES 1973; Barnette 2001).

Otter trawls are one of the gear types commonly used in both Texas 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 the potential 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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