Percy Dawson and M.R.Boopendranath
Central Institute of Fisheries Technology, P.O. Matsyapuri, Cochin-682029, India
( Published in Fishing Chimes, Vol.21, No.9 , December 2001 )
Sea turtles are an ancient and widely distributed species whose migratory pattern extends over all the oceans of the world. Due to harvesting of sea turtles and their eggs and their accidental mortality associated with shrimp trawling and other fishing operations, turtles have been threatened with extinction in all parts of the world. Accidental catch of marine turtles are reported to occur particularly along the east coast of India. Marine turtles are endangered species, which are protected under Schedule 1 of the Indian Wildlife Protection Act 1972. They are also protected under the international conventions such as Convention on Migratory Species (CMS) and Convention on International Trade on Endangered Species of Wild Flora and Fauna (CITES), to which India is a signatory. Of the seven species of sea turtles found world wide, five are reported to occur in India. They are Leatherback (Dermochelys coriacea), Green turtle (Chelonia mydas), Hawksbill (Eretmochelys imbricata), Loggerhead (Caretta caretta) and Olive Ridley (Lepidochelys olivacea), of which Olive Ridley is the most common species.
Researchers have developed special equipment known as Turtle Excluder Device (TED) that greatly reduces incidental death of sea turtles in shrimp nets. TEDs were introduced in US shrimp trawling operations in 1980s. A TED is a frame consisting of a grid of bars installed before the cod end of the trawl net at an angle leading upward and downward to an escape slit. Small animals such as shrimp, slip through the bars and are retained in the cod end, while large animals, such as turtles, large fishes and large elasmobranches are stopped by the grid bars and can escape through the opening. Experience has shown that the use of TEDs when combined with other elements of an integrated turtle conservation, can stop the decline in sea turtle population and will, over a period of time, lead to their recovery. Expert Scientific Panel (March, 2000) in their Report Study on the Distribution of Sea Turtles, their Incidental Mortalities in Fishing Nets and Use of Turtle Excluder Device in Fishing Trawlers, submitted to the Ministry of Agriculture, Government of India, has recommended the mandatory use of TEDs by all mechanized trawlers operating in areas where higher incidental mortalities have been recorded, in Indian waters.
Shrimp is the major foreign exchange earner contributing to over 70% of the marine products export earnings. Section 609 of Public Law 101-162 of the US restricts imports of shrimp harvested with fishing equipment such as trawl nets which are not equipped with TEDs that result in incidental mortality of sea turtles. The law ensures that US market demand for imported shrimp does not involve the Endangered Species Act. In October 1996, India, Malaysia, Thailand and Pakistan requested consultation with the United States under WTO dispute settlement procedures regarding US import restrictions, claiming that it is inappropriate for the US to prescribe their national conservation policies. In April 1998, WTO ruled that the trade restrictions were illegal. However, arguments are gaining ground that US laws are covered under exceptions to WTO rules for measures relating to conservation of exhaustible natural resource, but only failed in the way in which the law was administered.
The Code of Conduct for Responsible Fisheries (FAO 1995), which gives guidelines for sustainable development of fisheries, prescribes the need for protecting endangered species like sea turtles. As a signatory, India is duty-bound to conduct research, develop appropriate devices and practices, and implement regulatory measures for the protection of endangered turtles.
Shrimp trawling is currently the most valuable fishing system in India, in terms of the export earnings and domestic supply for fish. Concerns expressed by trawler fishermen over the lessening quantity of shrimp and fish by-catch owing to the installation of TEDs has to be taken into consideration. Standardization of TED for regional bottom trawling operations has to take place before regulations in terms of its mandatory use, can be brought into operation. Trade barriers by the environmentally conscious importing nations of Indian shrimp are still a perceived threat, unless regulatory measures are taken up.
Construction and Installation of CIFT-TED
Construction of the Frame: An oval frame measuring 1000 X 800 mm is constructed of 10 mm diameter stainless steel rod. Five vertical grid bars of 8 mm diameter stainless steel rod are welded to the inside of frame. The spacing between deflector bars is 142 mm and the maximum spacing between the frame and the adjacent deflector bar is 86 mm (Fig.1).
Construction of TED extension: The TED extension is constructed of single piece of polyethylene netting of 40 mm stretched mesh size and 1.5 mm diameter twine of size 150 X 60 meshes. The 60 mesh sides of the netting piece are sewn together to construct a cylinder (Fig.2).
Construction of hoop: A single hoop having a diameter of 900 mm is constructed of 8 mm stainless rod, for attachment to the leading edge of the TED extension (Fig.3).
Fixing the grid at the correct angle: The hoop may be laced to the TED extension leaving 5 meshes from the leading edge. For ease of installation, another hoop could be attached to the other end of the extension. The TED frame may be slid into the extension. Using the hoops, the extension tube may be stretched so that it is taut. The TED extension may be so positioned that the extension seam is at the bottom. Starting from the rear edge of the extension, 36 meshes forward from the rear edge of extension along the seam may be counted followed by counting of 75 meshes perpendicular to the seam to arrive at the top center attachment point. Later the TED frame may be attached to the extension netting. The sides of the secured TED frame may then be sewn to the extension netting (Fig.3 & 4). Grid angle should be between 40 to 55 degree from the horizontal for proper operation.
Cutting the exit hole: The mesh cut may be begun in front of the top center of the TED frame and continued to cut along the frame maintaining mesh distance from the frame, to either side until 1st and 5th grid bars are reached. The distance between 1st and 5th grid bars is 620 mm. 19 meshes may be turned and cut forward on either side. They may be turned again and cut to obtain a rectangular opening of 40X19 meshes in the extension.
Construction and attachment of exit hole cover (flap): The exit hole cover is made of a single piece of depth stretched and heat set polyethylene netting of 90 X 50 meshes, with 25 mm stretched mesh size and 1.0 mm diameter twine size.
The center mesh of 96 mesh edge of the flap may be attached to the center mesh of forward edge of the exit hole opening and this may be continued to 45 meshes of the flap to 20 meshes of the opening on either side of the attachment point. Remaining meshes of the flap may be sewn to the extension meshes to provide strength and shape to the flap. Along the sides may be attached 30 meshes of the flap to 19 meshes of the extension ahead of the TED frame. Six meshes of the extension ahead of the TED frame. The remaining 14 meshes of the flap are to be left unattached.
Construction and installation of accelerator funnel: Two trapezoidal pieces of depth stretched and heat set polyethylene netting (25 mm stretched mesh size and 1.0 mm diameter twine size) with 75 meshes each in the leading edge may be cut; 30 and 42 meshes each in depth with a cutting rate of 1NIB resulting in 55 and 47 meshes, respectively, in the rear edge (Fig.5). The two pieces are sewn together along the tapered edges, beginning from the leading edges, to form the funnel. The funnel may be installed inside the extension, forward of TED frame with the longer half of the funnel positioned opposite to the exit hole. The funnel is sewn to the TED extension, immediately after the hoop, which is attached to the leading edge. Attach 150 meshes of the funnel may be attached, mesh to mesh to the 150 meshes of the extension. The longer half of the funnel, may be secured at appropriate intervals, to the grid bars, a few centimeters from the bottom.
Attachment of floats: Two 150 mm hard plastic floats are to be attached to the outside of TED on the upper side, to the frame at the junction of outer grid bars, and another float is to be attached to the top of the hoop as shown in Fig.4, for weight compensation and stability, during operation.
Installation of TED in trawl: The complete TED is installed between cod end and hind belly extension of the trawl, with the exit hole facing upwards, by joining the edge meshes.
Operation and Maintenance
Before shooting the gear, the net should be inspected to ensure that the netting ahead of the TED is not twisted. The speed of vessel should be increased before deploying the otter boards, so that the TED extension will ride high in water and twists, if any, could be easily detected. If twists are present, they should be removed before deployment of the gear.
While hauling the gear, it is better to keep the vessel against the current or maintain a low speed, in order to prevent the catch from being washed forward, to the exit hole. Once the otter boards are hauled up, the vessel should maintain speed and direction for a few minutes so that all catches are washed past the TED, into the cod end. After each haul, the accumulated trash and debris that may clog the grid may be removed. Also, any gilled fish in the netting around the TED may be removed in order to permit good filtration.
It is important to check the grid angle on a regular basis, and make sure that it is between 40 to 55 degree, from the horizontal. This can be done as follows: