Daisuke Shiode and Tadashi Tokai
Tokyo University of
Marine Science and Technology
Department of Marine Bioscience
4-5-7 Konan,
Minato, Tokyo, 108-8477 Japan
Abstract
Turtle Excluder Devices (TEDs), to reduce the capture of sea turtles in shrimp trawlers, were first developed in Western Countries from technology existing since the 1960s and designed to make towing more efficient (and hence called “trawling efficiency device”). Since the late 1980s, TEDs became compulsory in the United States (US) and their use spread to other countries following US regulations on shrimp imports that required nations exporting shrimp to the US to introduce TEDs in their shrimp trawlers. This paper reviews experiences in developing and implementing TEDs worldwide, including their main technical and operational features.
INTRODUCTION
In the 1970s, unwanted catch of fish and other species in shrimp trawling were perceived as a problem mainly in the southeastern United States (Seidel, 1975; Watson and McVea, 1977). In the shrimp trawl fisheries operated in the Gulf of Mexico, sea turtles were recognized as bycatch, in addition to jellyfish and fish species (Seidel, 1975). Sea turtles caught in the US shrimp trawl fisheries were the following five species: Kemp’s ridley (Lepidochelys kempii), hawksbill (Eretmochelys imbricata), leatherback (Dermochelys coriacea), green (Chelonia mydas), and loggerhead (Caretta caretta). Time or area closures of fishing operations were first considered to prohibit fishing activities in areas or at times when the probability of interactions with sea turtles was highest. However, since this method caused substantial negative impact on fishermen’s income, further efforts were made in the 1980s to solve the problem through the development of appropriate technology that would reduce bycatch in fishing operations.
Against this background, the US National Marine Fisheries Service (NMFS), in collaboration with others, developed the Turtle Excluder Device (TED) (Seidel and McVea, 1982; Watson, Mitchell and Shah, 1986). In 1983, NMFS started a formal programme urging voluntary introduction of TEDs. However, in spite of this programme, in 1986 the number of shrimp trawlers that had introduced the TED was less than 3 percent of the total (Clark et al., 1991). In 1987 the US Government required, under the Federal Register, fishing vessels of 25 feet length and over to install the TED, while vessels less than 25 feet length were restricted their towing time to only 90 minutes. Such regulations were applied to shrimp trawlers by season or by period, in some fishing grounds all year round, and consequently all the coastal fishing vessels were put under the regulations of either using the TED or limiting towing time to less than 90 minutes (Federal Register, 1987a; 1987b). In 1994 this regulation was applied all year round to shrimp trawl fisheries conducted in all areas, and also to the bottom trawl fishery operated as far north as Cape Charles in the winter season (Federal Register, 1992a, b, c).
The selective fishing gear, designed to separate fish in bottom or shrimp trawls, was developed mainly in the western countries since the 1960s. On the other hand, although the TED was designed to exclude mainly sea turtles, it had been originally developed for making towing effective and hence called “trawling efficiency device”. Actually, NMFS, which first developed the TED, had been originally working on the development of fishing gear designed to efficiently protect juvenile fish. The TED was developed on the hint of Nordmøre grid and is featured as a basic structure consisting of a ridged grid or “separator” with a large mesh net and the escape opening for sea turtles and/or large fishes. Shrimps enter the cod end through the grid and the mesh of the separator, while sea turtles and large fishes are led to the escape opening by being blocked by the separator (Watson, Mitchell and Shah, 1986).
TEDs have a history of various improvements (Clark et al., 1991). Besides the Standard NMFS TED (30-inch opening and 25-inch opening), various types of TEDs with entirely different shapes, sizes, bar intervals and installation angles were developed and used. Examples are the Georgia TED with an elliptical grid, the Cameron TED with a circle entrance, and square-shaped Matagorda (Bay) TED. Both the NMFS type and Cameron type have substantial depth, and for installing them part of the nets has to be cut and separated, while the other two are plain surface type and can be installed directly to the existing nets. The opening was attached to the upper part of the net for the NMFS TED and the Matagorda TED, and to the lower part for the Georgia TED.
In order to effectively encourage the use of TEDs, there is a need to show that TEDs can provide benefits also to the fishermen themselves by decreasing losses of shrimp catches and alleviating their work in sorting out shrimp, in addition to excluding sea turtles. For this reason, in the early 1990s experiments to assess the combined use of TEDs and other bycatch reduction devices (BRDs) were actively conducted (Watson et al., 1993). Christian et al. (1993) summarized the results of the approaches to the issue of fish bycatch in shrimp trawling and emphasized the effectiveness of the “fish-eye” (opening part attached to the net for escape of fish) and the importance of the installing angles of TEDs. Rogers et al. (1997) tested the combined use of TEDs and the fish-eye devised by fishermen and used for half a century in Louisiana to avoid fish bycatch. They pointed out that vibration of TEDs was related to losses in shrimp catch. Watson et al. (1993) carried out diving observations and experiments to examine the proportion of bycatch reduction to shrimp harvesting with the use of a pilot BRD, and 30 different combinations were tested in real fishing grounds. The most efficient among those combinations (achieving 50 percent reduction in bycatch of fish while harvesting 90 percent or more of shrimps) were those with a large mesh funnel net, extended funnel net and fish-eye type. Those with extended funnel net, large mesh funnel net and of HSB type showed the best proportion of shrimp harvest, while those attached with fish-eye proved most effective in reducing bycatch of fish.
Furthermore, during two shrimp fishing seasons (spring and autumn) in 1993, trawling experiments aimed at assessing BRD were carried out in three areas along the coast of Louisiana. As a result of using two devices designed by contracted agents (Authement-Ledet 2 and CJ Kiffe) and two NMFS-type designs (Extend Funnel, Skirted Extended Funnel), those using extended funnel nets, with some modifications, showed the best combination of reducing fish bycatch and shrimp loss (Mitchell et al., 1995). Results of these experiments and research have been collated as a guide to more appropriate use of TEDs (Mitchell et al., 1995). Subsequently, improvement and assessment experiments of TEDs were continued, and Rogers et al. (1997) tested two BRDs, one with a fish-eye in the back of the TED (upper part of cod end, bottom of extension, and side of the extension) and the other with an extended funnel. The former was easier to be attached but showed 3-7 percent losses of shrimps, while the latter with an extended funnel had a rather complex structure but showed no losses of shrimp catches. The Andrews 5-inch TED showed an effect of reducing bycatch of juvenile red snappers by over 70 percent while limiting the losses of shrimp catches.
In this way, the technological improvement of TEDs advanced as they were introduced to other countries in the world. However, it has recently been noted that the size of the opening of TEDs is too small for loggerhead turtles and green turtles to escape (both species are granted special protection) and thus enlargement of the opening has been proposed (Epperly and Teas, 2002). As a result, the US Government changed the size of the openings provided for offshore areas to 71 x 26 inches from 35 x 12 inches in the Atlantic and 32 x 10 inches in the Gulf of Mexico.
Soft-type TEDs
Soft-type TEDs consist of nets of different size, without metal frames and are used mainly for exclusion of jellyfish. One of the soft-type TEDs is the Morison Soft TED, which consists of exclusion nets with 203 mm mesh size attached inside the shrimp trawling net and an escape opening for large living species like sea turtles. In this device, jellyball jellyfish (Stomolophus melagris) and horseshoe crabs (Limulus polyphemus), as well as large living species like rays, sharks and sea turtles were excluded from the nets while, shrimps enter into cod end, passing through the net mesh (Kendall, 1990).
Development and improvement of SOFT-TED in Australia
The type of TEDs developed in the United States could not be directly introduced to the Australian shrimp fisheries. This was due to the fact that the size of NMFS-TED was too large for Australian trawl fishing gears and the fishing methods different (in the United States only the end tip of the net, including cod end, is retrieved on deck, while in Australia the entire net is retrieved onboard). In Australia, special consideration was given to the safety of the crew and to losses of shrimp catch. Consequently, with the aim of spreading soft-type TEDs, diverse experiments were carried out in Australia to verify the efficiency of soft-TEDs in reducing losses of shrimp harvest and reducing fish bycatch (Kendall, 1990; Kennelly et al., 1992; Andrew, Kennelly and Broadhurst, 1993; Robins-Troeger, 1994). Furthermore, a composite TED (AusTED) was developed with the aim of securing safety in fishing operations and improving bycatch exclusion functions (Mounsey, Baulch and Buckworth, 1995; Robins-Troeger, Buckworth and Dredge, 1995). AusTED consists of (i) flexible grid; (ii) net opening hoops; (iii) large mesh panels; (iv) escape gap cover; (v) accelerator funnel; (vi) grid support floats, and (vii) escape gap.
Flexible and soft grids were introduced to the AusTED, while retaining the characteristics of the conventional TED. Aus-TED was tested at the following five sites: shallow, estuarine, mud-bottom sites to deep-water, oceanic, and sand-bottom sites. No significant difference was observed in the shrimp catch rate between the control net and the nets equipped with AusTED, while sea turtles and short-tail stingray were excluded from the nets equipped with AusTED.
Brewer et al. (1998) assessed 16 types of BRDs developed for use in the northern Australian Shrimp Fisheries (NPF), in three experimental cruises in the Gulf of Carpentaria. All four types with declination-type grids (Super Shooter, Nordmore grid, AusTED and NAFTED) proved very effective in excluding large sharks and rays as well as sea turtles. These were also effective in excluding some catch of unwanted small fish, when used in combination with other BRDs, especially with fish-eye and square-mesh windows. The rate of such fish exclusion was 0-39 percent. On the other hand, the escape rate of fish with the super shooter was only 2-12 percent in the scientific survey using research vessels and about only 4 percent in experimental operations using fishing vessels, respectively.
With the aim of further improving the bycatch-reduction features of the AusTED and of diffusing it among fishermen in Australia, AusTED II was developed through experiments and research by the Australian Fisheries Research and Development Corporation (FRDC Project 2000/170) and the Queensland Department of Primary Industries (McGilvray, Mounsey and MacCartie, 1999; Robins and McGilvray, 1999). The structure of the original AusTED was simplified (reducing the number of components), and the cover of the opening, the large mesh panel and net opening hoops were removed. Furthermore, square windows were installed at the back (front) of the grid. The accelerator funnel was changed into a guiding flap equipped with chains around it.
Diffusion of TEDs to other countries
A workshop was held in Mexico in 1986 that resulted in promoting the spread of TEDs to other countries. In Indonesia, more than 1 000 TEDs were employed in the fishing operations conducted by joint ventures with Japan in the western area, and fishing gear specialists were sent to NMFS for training (Watson, Mitchell and Shah, 1986).
In order to cope with the US regulation on shrimp imports, TEDs were also introduced to Southeast Asian countries including Thailand, Malaysia, and the Philippines, mainly by the initiatives of the Southeast Asian Fisheries Development Center (SEAFDEC). Bundit et al. (1997) tested two types of TEDs (Thai-Ku and Thai Turtle Free Device, TTFD) that had been jointly developed by Thailand and SEAFDEC, in addition to three types of US-developed TEDs (Anthony Weedless, super shooter, and Bent pipe) and two types of Mexican-developed TEDs (Georgia Jumper, Mexican). It resulted that TTFD was the best in terms of both sea turtle exclusion rate and positive effects on shrimp harvest. Similar experiments and training programmes aimed at promoting diffusion of TEDs among fishermen were carried out in Malaysia, the Philippines, Indonesia, and Brunei, and the effectiveness of TTFD was widely recognized. However, fishermen did not venture to use TEDs because: (i) little or no bycatch of sea turtles occur in ordinary shrimp trawling operations in the region; (ii) there is a danger in handling fishing gear due to the additional heavy-weight device, and (iii) large quantities of marine debris entering into the net block the grid mesh and thus lower the shrimp catch rate. Actually, no sea turtles entered into the nets during the experiments. For this reason, along with the efforts to diffuse TEDs, those countries are now carrying out, jointly with the Kyoto University of Japan (SEASTAR 2000 project), follow-up studies on sea turtle behaviour in order to study the differences between distribution/migration areas of sea turtles and shrimp trawling grounds in the region. Matsuoka and Kan (1991) carried out a series of experiments near Yule Island in Papua New Guinea, using experimental shrimp trawling nets attached with a TED designed to have a passive function, using an inner funnel for harvesting only shrimp and excluding finfish as well as side windows to exclude finfish bycatch. They reported that, with the attachment of this type of TED, 75.8 percent of javalinfish was excluded with no reduction of shrimp catches.
In the early 1980s, India conducted experiments for assessing the effectiveness of TEDs at Orissa beach (Silas, Rajagopalan and Bastian Fernando, 1983; Silas et al., 1983). In the mid-1990s activities were expanded to include development and diffusion of TEDs, which lead to the development of the CIFT-TED by the Central Institute of Fisheries Technology (CIFT) (Dawson and Boopendranath, 2003). About 500 sets of CIFT-TED were distributed for free to fishermen in the surrounding areas (Sankar and Raju, 2003).
In addition, activities to encourage the use of TEDs have been promoted in Mexico, Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica and Panama in Latin America, as well as Kenya, Nigeria and other countries in Africa. However, sufficient and detailed data and information are not available as yet on the actual use, diffusion and types of TEDs.
Meanwhile, for further improvement and refinement of TEDs, the survival of sea turtles that escape should be examined and clarified. Although some indirect estimates are available based on stranded turtles during the shrimp trawling season (Crowder et al., 1994; Caillouet et al., 1996), more detailed studies are necessary as basis for future improvements.
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