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Turtle excluder device
A turtle excluder device (TED) is a specialized device that allows a captured sea turtle to escape when caught in a fisherman's net.
In particular, sea turtles can be caught when bottom trawling is used by the commercial shrimp fishing industry. In order to catch shrimp, a fine meshed trawl net is needed. This results in large amounts of other marine organisms being also caught as bycatch. When a turtle gets caught or entangled in a trawl net, it becomes trapped and is unable to return to the surface. Since sea turtles are air-breathing animals with lungs, they cannot survive long underwater without surfacing and will eventually drown.
The first TED was based on a device called the jellyball shooter, which is used to prevent fouling by cannonball jellyfish (Stomolophus meleagris) in shrimp trawls. TEDs were later developed in the 1970s by Wil Seidel, who worked for NOAA. Some resistance to the use of TEDs has arisen from the belief that the use of the devices actually causes fishermen to lose shrimp and other targeted species.
In 1987, the United States required all shrimp trawlers to equip their nets with turtle excluder devices. Two years later the shrimp-turtle law was implemented. This required all countries that export shrimp to the US to certify that the shrimp they shipped were harvested by boats equipped with TEDs. Countries that cannot guarantee the use of the escape devices were banned from exporting shrimp to the US.
In 1996, the government of India proposed legislation for the requirement of modified "indigenous" TEDs, which they called TSDs (turtle saving devices), to be used by local fishermen. This was a response to the declining olive ridley population that were nesting in beaches such as in Odisha. The modified TSDs were similar to standard TEDs except for having fewer bars. This resulted in the increase of the distance between each pair of bars to ensure that bigger specimens of shrimp and fish were able to pass through the TSD and into the net.
The use of the devices ideally allow all bycatch larger than ten centimeters (10 cm) to escape the nets unharmed. This selectivity is achieved by metal grids integrated into the trawl net structure. The grids act as a barrier for keeping large creatures such as turtles from passing through the bars into the back of the net.
A small opening in the net is then available either above or below the grid so that the creatures that are stopped by the TEDs are allowed to escape the net, relatively unharmed. Targeted species such as shrimp however, are pushed to the back of the net. The target design effectiveness of TEDs is 97%, but the field effectiveness is often far lower. Seagrasses and other debris reduce fishing effectiveness of TEDs and in some situations may block sea turtles from exiting the net. In addition, it is easy to tamper with TEDs so as to increase the fishing efficiency of the net, while eliminating the turtle-excluding properties of the TED.
While turtle excluder devices have been somewhat successful in lessening sea turtle casualties as by-catch, they still have a few failings and drawbacks.
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Turtle excluder device
A turtle excluder device (TED) is a specialized device that allows a captured sea turtle to escape when caught in a fisherman's net.
In particular, sea turtles can be caught when bottom trawling is used by the commercial shrimp fishing industry. In order to catch shrimp, a fine meshed trawl net is needed. This results in large amounts of other marine organisms being also caught as bycatch. When a turtle gets caught or entangled in a trawl net, it becomes trapped and is unable to return to the surface. Since sea turtles are air-breathing animals with lungs, they cannot survive long underwater without surfacing and will eventually drown.
The first TED was based on a device called the jellyball shooter, which is used to prevent fouling by cannonball jellyfish (Stomolophus meleagris) in shrimp trawls. TEDs were later developed in the 1970s by Wil Seidel, who worked for NOAA. Some resistance to the use of TEDs has arisen from the belief that the use of the devices actually causes fishermen to lose shrimp and other targeted species.
In 1987, the United States required all shrimp trawlers to equip their nets with turtle excluder devices. Two years later the shrimp-turtle law was implemented. This required all countries that export shrimp to the US to certify that the shrimp they shipped were harvested by boats equipped with TEDs. Countries that cannot guarantee the use of the escape devices were banned from exporting shrimp to the US.
In 1996, the government of India proposed legislation for the requirement of modified "indigenous" TEDs, which they called TSDs (turtle saving devices), to be used by local fishermen. This was a response to the declining olive ridley population that were nesting in beaches such as in Odisha. The modified TSDs were similar to standard TEDs except for having fewer bars. This resulted in the increase of the distance between each pair of bars to ensure that bigger specimens of shrimp and fish were able to pass through the TSD and into the net.
The use of the devices ideally allow all bycatch larger than ten centimeters (10 cm) to escape the nets unharmed. This selectivity is achieved by metal grids integrated into the trawl net structure. The grids act as a barrier for keeping large creatures such as turtles from passing through the bars into the back of the net.
A small opening in the net is then available either above or below the grid so that the creatures that are stopped by the TEDs are allowed to escape the net, relatively unharmed. Targeted species such as shrimp however, are pushed to the back of the net. The target design effectiveness of TEDs is 97%, but the field effectiveness is often far lower. Seagrasses and other debris reduce fishing effectiveness of TEDs and in some situations may block sea turtles from exiting the net. In addition, it is easy to tamper with TEDs so as to increase the fishing efficiency of the net, while eliminating the turtle-excluding properties of the TED.
While turtle excluder devices have been somewhat successful in lessening sea turtle casualties as by-catch, they still have a few failings and drawbacks.