According to the National Research Council of the USA (1990), the incidental capture of sea turtles by industrial shrimp trawl operations in coastal waters is the single human factor that causes the greatest mortality of adult sea turtles in the world. Furthermore, industrial shrimp trawling is extremely inefficient, as only from 8% to 12% of the catch by weight is shrimp. The rest of the catch is referred to as by-catch, most of which is discarded at sea. In fact, shrimp trawling is the fishery that generates the most by-catch and discards in the world.
Fortunately, during the 80s, a technological fix was developed to solve the problem, the Turtle Excluder Device (TED). TEDs are metal grids which basically act as a grading mesh. They are sewn into the body of the trawl net, in front of the collecting bag. The bars of the grid are spaced 4 inches apart, allowing small objects through, such as shrimp, but not sea turtles, which are deflected by the TED downwards, towards a hole through which the turtle escapes. The use of TEDs during shrimp trawl operations reduces sea turtle catch 97%. TEDs also reduce the capture of by-catch from 30% to 70%, without significantly impacting shrimp catch.
Since 1996, the government of the USA imposed an embargo on shrimp imports from nations whose shrimp trawl fisheries interact with sea turtles and do not use TEDs. The government of Costa Rica mandates the use of TEDs to carry out shrimp trawling activities since May 3 of 1996 ((A-JD.I/061-96, La Gaceta #83, 16/5/96).
TEDs in Costa Rica
The Puntarenas Chamber of Fishermen has been collaborating with PRETOMA to carry out research on TED efficiency and evaluate the incidental capture of sea turtles in Costa Rican waters.
Among the most important conclusions:
- The Costa Rican shrimp fleet (45 vessels) captures about 15,000 sea turtles a year, most of which (90%) are olive ridleys (Lepidochelys olivacea) and the rest (10%) are Pacific Greens (Chelonia mydas agassizi). Mortality is approximately 40%, but it is probably higher because recovery and resuscitation techniques are not practiced.
- When targeting pink shrimp (Peneaus brevirostris) at depths ranging from 70 to 100 meters, TEDs work efficiently regarding shrimp retention and sea turtle exclusion.
- When targeting white shrimp (Peneaus occidentalis, P. vannamei) in shallow waters, TEDs tend to get obstructed by the large quantity of logs and organic debri, to such a point that shrimp loss may be as high as 38%. Likewise, captured sea turtles can not escape through the clogged escape hole, and drown.
- Apparently, if the spacing between the grid bars is increased to 8 inches, the loss of shrimp is reduced to 9%, improving the performance of the fishery operation and making the technology more acceptable to the fishermen.
Thanks to the collaboration between these two sectors, Costa Rica developed the Tico TED, a model specifically modified for Costa Rican particular fishing conditions.
Furthermore, we are inviting Sinkey Boone, the Georgia shrimper who invented the TED in 1969, to visit Costa Rica and work with Costa Rican shrimpers for 6 weeks, teaching them techniques and methods to operate TEDs efficiently.