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DOLPHINS AND THE TUNA INDUSTRY 7 Techniques for Reducing Dolphin Mortality The effectiveness of fishing gear is a function of its design and the way it interacts with the animals. Therefore, any successful effort to develop gear that is effective at catching tuna without killing dolphins must involve knowledge of tuna and dolphin behavior as well as good engineering and design. SMALL MODIFICATIONS OF CURRENT METHODS Several small modifications to the current methods of purse seining for tuna have immediate potential for reducing dolphin mortality. Each of these changes could have an incremental effect. The cumulative effect of these and other innovations could significantly reduce the impact of purse seines on dolphins. Medina Double Corkline In spite of dolphins' characteristic trait of jumping well clear of the water, they do not leap over the corkline to freedom. When they make an effort to escape over the corkline, typically during the backdown process, they may push against the corkline, deflect it downward, and swim out. During backdown, the corkline surrounding the backdown channel is tight and resists being submerged. To sink the corkline under this condition, a large number of floats must be submerged. Only at the apex of the backdown channel and only when there is sufficient flow through the channel, does the corkline begin to submerge.
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DOLPHINS AND THE TUNA INDUSTRY FIGURE 7-1 The conventional purse-seine corkline. Drawing by C. Goudey, Massachusetts Institute of Technology, Cambridge. The use of a double corkline has been suggested as a way to ease the dolphins' escape (H. Medina, personal commun., 1990). Unlike a conventional corkline, shown in Figure 7-1 , which runs through the center of each float, the double corkline has each float tied on individually. As seen in Figure 7-2 , this rigging allows each float to move independently, accommodating dolphins' attempts to push their way over the corkline. Rigging a seine in this way seems to present no hardship to the net builder. Hanging the netting to the corkline, in fact, would be much easier and could be done more precisely. The method has the additional advantage of allowing easy replacement of damaged floats. Jet Boat In the present backdown process, use is often made of an inflatable raft with an occupant trying to direct the dolphins toward the end of the backdown channel. In the past, no motorized craft could be used for this task because of FIGURE 7-2 The double corkline. Drawing by C. Goudey, Massachusetts Institute of Technology, Cambridge.
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DOLPHINS AND THE TUNA INDUSTRY the threat posed by the propeller. The introduction of the jet boat as a recreational watercraft now allows an alternative to the unpowered raft in controlling dolphin movements within the backdown channel and aiding in dolphin rescue. A Japanese manufacturer has introduced a fiberglass craft with a 52-horsepower engine that is propelled by a jet pump. This craft is 9 feet long and 5 feet wide, large enough for three occupants, and has a hull that sits low in the water. It can turn within its own length. A demonstration of the craft in San Diego in April 1989, sponsored by the Porpoise Rescue Foundation, indicated that it might be useful both inside and outside the net and before, during, and after backdown as a mobile platform for hand release of captured dolphins. The craft produces noise and bubbles, which may also act as a deterrent to dolphins swimming toward the vessel and swimming away from the release area during backdown. With no exposed propeller, the craft could quickly travel in and out of the net, passing over the corkline without risk to the dolphins of entanglement. Since the demonstration, several vessels of the international fleet have tried the jet craft as a dolphin rescue platform. Early trips revealed mechanical and structural problems with the recreational craft due mainly to the rigorous conditions of commercial purse seining. Two units being tested by the U.S. fleet have undergone some structural and mechanical modifications by both the dealer or manufacturer and by the vessels using them. This has improved reliability but some problems remain. Increasing the crew's familiarity with the craft and storing a suitable inventory of spare parts should yield better reliability. An aluminum version or one patterned after a rigid-hulled inflatable also may increase the utility and durability in this application. A Mexican company is currently developing a jet boat for use in dolphin rescue (M. Hall, personal commun., 1990). In addition, several manufacturers of outboard motors produce propellerless jet models. Current Profiler The Doppler current profiler is a hull-mounted sensor that measures the speed and direction of currents at various depths below the surface. Commercial versions might be useful in providing subsurface current information to vessel operators before setting the seine. One product, designed for commercial fishing, provides subsurface current values at any selected depth (Summers, 1990). Another product, designed for oceanographic applications, provides a profile of the current over a continuous range of depths, plotting the results on a video screen (M. Hall, personal commun., 1990). Such information could be valuable to the captain in determining whether subsurface currents are likely to cause a distorted set with collapses or canopies. If the current is not too strong, a set can be made with much less chance of a malfunction. The presence of a mild subsurface current, if its direction and speed
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DOLPHINS AND THE TUNA INDUSTRY are known ahead of time, does not necessarily spoil a properly oriented set. An excessive subsurface current would indicate the need to move from the area and fish elsewhere. With time, these devices may provide evidence for a correlation between tuna abundance and subsurface currents. Such an understanding could assist in locating tuna not associated with dolphins. Pear-Shaped Snap Rings An innovation that has been adopted by almost half of the U.S. fleet is the pear-shaped snap ring. Introduced primarily as a time-saver and a way to avoid the dangers of a conventional ring stripper, the snap ring helps to reduce the time before backdown begins. Instead of a simple steel ring, the new design is pear-shaped and has a spring-loaded gate portion that can be opened for inserting or removing the purse line. In conventional purse seining, once the rings are up, the rings must be transferred from being supported by the purse line to being supported by the cantilevered ring stripper. With the snap rings, this process is unnecessary and sacking up can begin immediately after the rings are up. This innovation can save up to 15 minutes, reducing the time that the dolphins are exposed to canopies or net collapse. Small-Mesh Medina Panel It has been suggested that placing extra slack in the large-mesh (4 1/4-inch) netting below the Medina panel would force the small-mesh (1 1/4-inch) netting above to open more during the backdown and make a better backdown. Thus, 10–15% more large-mesh netting would be distributed along the boundary with the small-mesh panel when the net is assembled. Third Fine-Mesh Strip The Porpoise Rescue Foundation is putting a third fine-mesh strip aboard two vessels. Adding this strip below the second fine-mesh strip may help save any dolphins that dive deeply as the backdown is being performed. This strip is made with 2-inch mesh. The 2-inch mesh is being used because it has less drag than finer meshes do while being pulled through the water during backdown. Safety Crook The safety crook is the same aluminum pole that is used in swimming pools to save swimmers in trouble. One end of this pole has a double open-end arc. During the backdown, this safety crook can be used in a speedboat to help guide the dolphins toward the opening that will let them free.
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DOLPHINS AND THE TUNA INDUSTRY MAJOR MODIFICATIONS OF CURRENT METHODS In the previous section, modifications and techniques were discussed that could be incorporated into present purse seines with little cost. In most cases, the potential benefit of the small modifications is the reduction in dolphin mortality during the backdown process. The basic freeing process remains unchanged. This section considers more sweeping changes in gear and methods. Most of the concepts presented have not been tested adequately to assess their impact on dolphin mortality and fishing effectiveness. This section is organized around modifications to reduce two fundamental problems—canopies and roll-ups—and then continues discussion of four classifications of modifications—barriers, species selectivity, backdown-channel changes, and other purse-seine variations—that the committee believes show promise for reducing dolphin mortality. The committee believes that the most promising major alterations in purse-seine gear are the following: Modifications in netting material. Modifications in hang-in ratio. Modifications to the purse cable. Development of lifting surfaces in critical parts of the net. Modifications to Reduce Frequency of Canopies Canopies are billows of netting along the perimeter of the pursed net and backdown channel; they are a common cause of dolphin mortality. These formations are caused by slackness in the upper portions of netting as the corkline is pulled sideways through the water. Causes of canopies can be subsurface currents, improper orientation of the backdown channel with respect to the wind, or improper control of the vessel during backdown. Although these causes cannot always be controlled, modifications to the purse seine that would make it resistant to canopies would be advantageous. Canopies form when the downward pull on the net is overpowered by the drag forces due to water flow through the plane of netting. For most of the setting process, the weight of the rings, purse line, chain bridles, and leadline keeps the netting near the surface essentially vertical. As the net is pursed and the rings become supported by the purse line, only the weight of the netting itself remains to keep it hanging vertically below the corkline. The net configuration changes easily at this stage. Some modifications to the purse seine singly or together would help prevent canopies. The most promising are the following: Netting of reduced hydrodynamic drag. Netting material with increased underwater weight.
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DOLPHINS AND THE TUNA INDUSTRY The following also might help: A wider hang-in ratio (the ratio of the length of the corkline to the length of the webbing attached to it, typically around 80%). Netting twine of less stretch. Netting with additional weight in the form of a false leadline partway down the net. These modifications are most useful when incorporated into the portions of the purse seine that become the backdown channel. Individually or together, these changes could reduce the tendency of the corkline to precede the netting when flow is normal to the netting panel. In general, a low-drag, fast-sinking net is advantageous in purse seining. With the possible exception of the wider hang-in ratio, these modifications should produce a more effective net to capture tuna. At present, nylon netting is used for purse-seine construction because of its low cost, durability, flexibility, and sinking characteristics. Alternative netting materials such as Dacron * (polyester), Kevlar (aramid), and Spectra (ultra high molecular weight polyethylene) may offer advantages, but Kevlar and Spectra are more expensive than nylon. Dacron, in particular, has proved advantageous in other commercial fisheries. Because of its higher density, greater strength, and reduced stretch, its consideration in tuna purse seining may be appropriate. One California netting company has built a purse seine in polyester, which, during use by one vessel, was found to be productive (H. Medina, personal commun., 1990). The company reports a weight advantage, cost advantage, and a sinking rate twice that of a nylon seine of equivalent strength (Kirkland, 1990). The reluctance of seiners to change netting material remains unexplained. Through attrition, the cost of such a change would be small since seine nets have a useful life of only 2–5 years (H. Medina, personal commun., 1990). Modifications to Reduce Frequency of Roll-Ups Roll-ups happen when the lower portion of the seine becomes twisted around the purse cable. Specific data on the frequency of occurrence of roll-ups are not available because roll-ups typically are categorized as a “major malfunction.” In general, sets in which major malfunctions occur have nearly four times the normal rate of dolphin mortality (DeBeer, 1980). In the following discussion of roll-ups, the related event of netting or bridles becoming snagged on the purse cable is also included. Roll-ups typically occur during the setting of the net when the cable is close to the netting. The bad effects of a roll-up begin during the pursing operation when a portion of the cable, entangled with netting, is pulled through the purse rings. The cable invariably becomes jammed and when it comes within reach of the crew, the hauling process must stop while the purse line is cleared. During this delay, net collapse and dolphin entanglement can occur. * Dacron and Kevlar are trademarks of the DuPont Corporation. Spectra is a trademark of Allied Signal, Inc.
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DOLPHINS AND THE TUNA INDUSTRY The fishing industry has been strongly motivated to reduce the occurrence of roll-ups not only because of dolphin mortality but also because of the effort and danger involved in clearing roll-ups. Industry has eliminated some of the causes, such as reducing the occurrence of broken wire strands through proper maintenance of the purse cable. The use of longer chain bridles has helped to increase the space between the purse cable and the lower edge of the netting. However, these longer chains can themselves cause problems by wrapping around the purse line if they become slack. In 1972, the Southwest Fisheries Center identified an important cause of roll-ups: the rotation of the purse cable during changes in its tension. Experiments with cables that were constructed to be torque balanced were begun aboard commercial tuna seiners. Though notable successes were experienced, cost and difficulty of splicing this unconventional wire rope prevented adoption. In addition, twist induced by the low-helix, three-strand torque-balanced cable passing over the purse block sheaves continued to cause occasional roll-ups. Today, the delays during the hauling process remain an important cause of dolphin drownings. Despite some lingering problems, however, the torque-balanced cable can reduce significantly the frequency of roll-ups. Fortunately, alternatives to conventional wire rope are now available. The successful introduction of Spectra braided line as a replacement for conventional wire rope in a variety of commercial fishing applications suggests its use as a purse cable. It has been reported that the Spectra line can last over 10 times as long as wire rope (Nye, 1990). Because of strength/diameter ratios similar to steel, few changes are needed to accommodate Spectra. Winch drum capacity would remain adequate. In addition to being torque-balanced, none of the problems associated with broken strands would exist, and splicing would be much easier. The use of lead-core synthetic line as a replacement for chain along the lower edge of the seine may also be of value. This material was used by many of the San Diego boats in 1976, just after its introduction by Sampson Ropes (H. Medina, personal commun., 1990; T. Bergen, Sampson Ocean Systems, Inc., personal commun., 1990). Sink rates were adequate but its stiffness caused problems during stacking of the net on deck. The synthetic leadline was abandoned in favor of chain. The stiffness of the leadline during initial use of the product was caused by the type and construction of the lead used in the core. The lead used had to be soft enough for extrusion and was notched to give it flexibility. However, under strain, this lead core would tend to deform, fusing the notches and
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DOLPHINS AND THE TUNA INDUSTRY causing stiffness. Recently, the manufacturer has introduced a harder lead, in cast ingot form, which has excellent flexibility that will not degrade under strain. Benefits that might accrue from the use of this new material would be reduced purse-line jamming, fewer roll-ups, faster sinking rates, and quieter setting while school fishing. Modifications by Insertion of Barriers Between Tuna and Dolphins One of the significant drawbacks among the present methods used to remove dolphins from purse seines is the loss of tuna. Increasing the opportunities for dolphins' escape also increases the risk of losing tuna. Certain techniques that might be appealing because of their possibilities in reducing dolphin mortality are unacceptable commercially. It is well established that tuna are far more likely than dolphins to escape from pursed nets. With this in mind, NMFS's Southwest Fisheries Center experimented with a “backdown zipper” system that would separate the dolphins in the backdown channel from the tuna remaining in the main body of the net. Their approach was to use a line passing under the net partway up the backdown channel. During backdown and when the dolphins were beyond the line, the line would be pulled up, choking off the channel. With the two species separated, efforts to provide escape opportunities for the dolphins could be increased. Unfortunately, the dolphins were not always found on the right side of this zipper line, and the shallow channel would collapse. Experiments were discontinued. It is possible that attempts to learn how to maneuver dolphin herds inside the net would alleviate this problem. The motivation for such gear modification remains sound and deserves continued thought. Opportunities may exist during the set when the two species are spatially separated. At the completion of pursing, dolphins are typically at the end of the net away from the seiner (Norris et al., 1978). During backdown, the dolphins are swept toward the apex of the channel. In both cases, placing a barrier between the species might be feasible. Deploying such a barrier is a challenge, because both species can react adversely to the disturbances caused by such activity. Though still entirely conceptual, the design shown in Figure 7-3, Figure 7-4 through Figure 7-5 can serve as an example of a barrier method. A netting panel of suitable size and shape can be buoyed into place at the proper time. Before deployment, the panel would be secured to the seine netting itself as shown in Figure 7-3. At the appropriate time, a release cord would then allow the panel 's false corkline to pull the barrier to the surface, thereby separating the dolphins in their own netting compartment as shown in Figure 7-4. The main corkline and the netting below it would then be released and the dolphin herd would have an obvious escape route as shown in Figure 7-5. The design and incorporation of this barrier net into the purse seine
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DOLPHINS AND THE TUNA INDUSTRY FIGURE 7-3 A full, deployed purse seine after pursing. The seiner would be to the left. Drawing by C. Goudey, Massachusetts Institute of Technology, Cambridge. without excessively complicating the normal net-handling procedures would require careful thought. The principal advantages of this method are that (1) it could be done early in the set immediately after pursing, and (2) the backdown process would be eliminated. Another approach is placing such a barrier net in the area of the backdown FIGURE 7-4 The barrier net has been released and has buoyed to the surface. Drawing by C. Goudey, Massachusetts Institute of Technology, Cambridge.
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DOLPHINS AND THE TUNA INDUSTRY FIGURE 7-5 The main corkline and net are opened to release the dolphins. Drawing by C. Goudey, Massachusetts Institute of Technology, Cambridge. channel to block the movement of tuna out of the main body of the net. With such a barrier in place, far more obvious escape opportunities could be provided for dolphins without risk of losing tuna. Essential to the success of these methods would be an awareness of the movements of both species in the seine and knowing the right time to activate the raising of the barrier. As discussed in Chapter 5, our knowledge of the tuna-dolphin bond and the movements of both is far from complete. The rational development of such gear modifications awaits the development of a better understanding of species behavior. Species Selectivity The tuna-dolphin problem is a gear-selectivity problem. When netting is involved, the typical approach to such selectivity problems is the use of a specific mesh size that will retain certain fish based on size or herding traits. The situation is simpler when the by-catch species is smaller or is herded less easily than the target species. In such cases, a mesh size is used that retains the desired species while allowing the smaller or more elusive species to escape. The inverse problem—e.g., fish by-catch in a shrimp fishery—can also be solved using mesh size, but less directly. A typical approach is the use of a false net or barrier that deflects the larger or easily herded species away, while the smaller or less easily herded species passes through into the portion of the gear that ultimately retains it. The turtle excluder device is an example of a solution to the inverse problem.
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DOLPHINS AND THE TUNA INDUSTRY Dolphins are far more easily retained in a net than tuna. The problem is therefore inverse: The dolphins must be separated from the tuna using a barrier through which the tuna will want to pass. Once the species are separated, further steps can be taken to release the dolphins, while precautions are taken to prevent tuna from recrossing the barrier. Implementing such a technique in a practical tuna purse-seining operation is far from trivial. Information on tuna-dolphin behavior is inadequate for devising or implementing purse-seine modifications involving mesh selectivity as a means of mitigating the tuna-dolphin problem. More information is needed on the response of each species to various types of barriers. Many attempts to modify gear are based on behavioral differences between tuna and dolphins, as described in Chapter 5 and Chapter 6. One possible approach would be to allow the tuna, which are more active in the net than dolphins, to escape the main body of the net into a secondary enclosure through a passage that discourages their return. The development of such a tuna “check valve” or “diode” has not been attempted, but there are many tools that could be brought to bear. Light, sound, mechanical flaps, or some combination of these could be incorporated into an opening, which would represent an inviting escape opportunity in one direction but prevent passage in the other. Conceptually, a short tunnel with flexible reeds pointed in radially but biased in one direction would function to allow tuna passage only one way. A simple cone of netting as used in a fyke net or fish trap might also work. Determination of the size and clearance requirements of such a device would need some experimentation. Incorporating it into a commercial operation would require some ingenuity. If, on the other hand, a directional light or sound source were discovered that repelled tuna, its placement around a hole in a panel of netting and pointed “downstream” might be an elegant approach. The principal appeal of this concept is that the dolphins would not pass through such an opening, and after the tuna had passed through, the main body of the purse seine could be opened and the dolphins could leave without running the backdown gauntlet. The passage that the tuna would take would lead into a netting chamber that could be hauled aggressively as it would contain no dolphins. This chamber could take the form of a small pursed seine or simply a large sack of netting. Its design would require consideration of the quantities of tuna that would be encountered and their weight. Modifications to Improve Escape of Dolphins from the Backdown Channel The portion of the purse seine that forms the backdown channel is a relatively small part of the overall net; therefore, design modifications may be feasible for the channel that would be impractical for the entire seine. Changes
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DOLPHINS AND THE TUNA INDUSTRY The details of such an operation would need serious thought including economic assessment and optimization. The advantage is that the catching efficiency of a compact longliner can be combined with the endurance, searching ability, and capacity of the present seiner. Another even more innovative approach incorporates the use of the seiner's helicopter to place a series of longlines in the path of a sighted school of tuna or mixed school of dolphins and tuna. According to the helicopter pilot who devised this technique, the longline could be placed without scattering the school, and the dolphins would not take a hook (K.R. Thomas, Thomas Atmospherics, personal commun., 1990). Because this operation would be directed at specific schools of tuna, catch rates per hook might be extremely high. Conversion costs for such an operation would be low. Experiments are needed to determine whether the tuna will stop to feed if their prime intent is keeping pace with the dolphins and to be sure that the dolphins will not take the bait. The airborne aspects of this technique are the subject of a patent application. According to the inventor, conversion costs for such an operation would be low and negotiations are under way with hook, line, and baiting machine manufacturers with the intent of rapidly commercializing the method. An economic assessment of this technique would also be essential. Midwater Trawls Few alternative methods of fishing offer the productivity rates enjoyed by tuna purse seining in the ETP. A significant exception is trawling and a notable example is the U.S. pollock fishery off Alaska where 100-ton tows are common. Tremendous progress has been made over the last decade in the design of gear for such high-volume trawling. High horsepower vessels, new materials, and the exploitation of the herding characteristics of pollock have allowed the development of midwater trawls in which the area of the mouth of the trawl is measured in acres. The applicability of trawling to tuna fishing in the ETP is unclear. Factors such as the herding characteristics of tuna, the towing speed required, the effect of vessel noise, and the presence of dolphins all prevent the direct extrapolation of most trawling experience. Pair Trawls Several of the committee members believe that pair trawling is not a viable option for catching yellowfin in the ETP, but a few members felt it to be worth considering. A brief description of the French experience is thus provided. In France, midwater trawls have been somewhat successful in capturing albacore in the Bay of Biscay (Prado, 1988). This technique was developed to increase the productivity of small (17–20 meters) longline vessels that normally have low catch rates. Pairs of these vessels were fitted with a midwater trawl normally used for bass. These 400–500 horsepower vessels were able to
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DOLPHINS AND THE TUNA INDUSTRY tow the net at 3.5 to 4.0 knots while achieving a vertical gap of 30–40 meters and a horizontal opening of 60-80 meters. Trawling was done at night on the surface of the water or close to it. The thermocline in this location is 10–15 meters, which is shallow. The sound of the pair trawlers, the tow cables, and the 18-meter meshes in the forepart of the trawl were found to be effective in herding the tuna toward capture. Catch rates of 3–8 metric tons per day have been reported. Catch rates of purse seiners are considerably higher. Incidental Catch of Dolphins in Trawls In evaluating the utility of trawling as a substitute for purse seining, the incidental catch of dolphins in established trawl fisheries is relevant. As discussed earlier, little useful information is available to aid in the design of gear that would select only tuna from a mixed school of tuna and dolphins. Anecdotal reports of bottlenose dolphins being caught in large midwater trawls used along the U.S. east coast exist. Reports compiled by NMFS on marine mammal mortality state a trawl-related incidental catch of 20 and 42 dolphins of all species for years 1987 and 1988, respectively (Waring et al., 1990). Clearly, trawls are not designed to spare dolphins. Specific techniques may be applied, however, to avoid their capture. A Hypothetical Trawling Technique for Tuna in the ETP The committee did not agree on the promise of this option; several members believe that it is not worth pursuing. Perhaps the greatest disadvantage is that if any dolphins were caught in such a net, they would quickly drown and would not be discovered until long afterwards. However, a few members felt that this option might be developed effectively, and therefore it is briefly described. Conventional single-boat midwater trawling probably would not be useful in tuna fishing because of vessel noise and especially because of the high swimming speeds of tuna. By comparison with single-boat trawling, pair trawling offers the following potential advantages: Vessel noise may herd the tuna into the path of the net. Trawl doors are not required. Extreme spreads are possible. The trawl could be larger than a single-boat trawl because twice the horsepower would be available. Pair trawling would not necessarily require purpose-built vessels. Adaptation of purse seiners currently in use in the ETP is feasible. Their seining capabilities may be retained, yielding a combination trawler-seiner. In addition, although present methods of tuna location could be retained, dolphins would not be encircled by a net and their herds would remain intact. The combined horsepower of two 3,800-horsepower seiners would allow
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DOLPHINS AND THE TUNA INDUSTRY the use of a net with approximately 266,000 pounds of drag. Though the drag would vary considerably with speed, 7,600 horsepower would be sufficient to pull a very large net. Depending on the extent to which large mesh or ropes could be used, vertical openings of 550 feet and horizontal openings of 3,000 feet might be possible. Based on the French experience, the towing speed does not have to equal or surpass the swimming speed of tuna, at least not at night. If the passage to the cod end of the net is viewed by the tuna as a possible escape route, high towing speeds may not be required. The same speedboats that are used in purse seining may be useful in tuna midwater trawling. Several of the small craft could be used to direct a school of dolphins into the gap between two approaching pair trawlers. Eventually, optimal values of pair-trawl speed and vessel separation would be determined. Data on the vertical separation of tuna and dolphins during normal swimming and during a chase would be essential to allow the selective catch of tuna; indeed, if tuna and dolphins are not adequately separated, this technique might kill more dolphins than purse seining does. The depth of the headrope could be set either by varying the speed or the length of tow cable (typical of most midwater trawling) or by the use of surface buoys on pendants of specific length. The intention would be to place the headrope of the trawl between the two species or slightly deeper. Experimentation would be required to learn the best depth for minimizing tuna loss without risk of capturing dolphins. Such a pair-trawling operation can be undertaken only if the vertical separation of the two species is predictable or if they do not associate at night. Certainly the depth of the headrope should be well below the deepest dolphin, even though the upper portions of the tuna school may be lost. In addition to the risk of killing dolphins, a disadvantage of this method is the requirement of two seiners for one fishing operation. This problem is lessened, however, because most of the trip time is spent searching, and two vessels would offer increased search coverage. Gillnets Gillnets can be a selective method of capture in some fisheries. In other fisheries, or when used irresponsibly, they can be indiscriminate in their catch. Productivity with gillnets is similar to longline rates and falls far short of purse-seine rates. Marine mammals often are entangled in gillnets, and it is extremely doubtful that a pure catch of tuna could be pulled from an aggregation of mixed species. A dolphin mortality of three animals per net has been observed in the Japanese driftnet fishery for albacore (Anon., 1990). The committee recommends against the use of gillnets as an alternative to purse seining in the ETP.
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DOLPHINS AND THE TUNA INDUSTRY REGULATORY ALTERNATIVES The behavior of the tuna fishermen can be changed voluntarily or through regulation. The tuna fishermen themselves have instituted or suggested changes in their tuna-seining processes over the past two decades. Some of these changes have been voluntary, and some have been stimulated by laws and regulations. Unless additional voluntary change is anticipated, further development of law and policy must be considered if behavior is to change and if dolphin mortality is to be reduced. Any of the changes referred to in the above sections on alternative fishing methods, if not voluntarily adopted, would have to be the subject of regulatory action. Education and training, discussed in the next section, may stimulate voluntary changes in methods of tuna seining. The purpose of this section is to enumerate the major alternatives for regulatory action, the assumption being that voluntary action may not be sufficient to accomplish various public-policy goals with respect to the tuna-dolphin issue. The following discussion of the alternatives should not imply that any particular alternative should or should not be implemented. It is intended simply to show the range of possible public-policy options. The success of such options would depend on the degree to which they were implemented by all nations with boats fishing for tuna in association with dolphins. The first set of options centers on regulatory alternatives that would further prohibit, directly or indirectly, dolphin mortality. Immediate Prohibition of All Dolphin Mortality from Fishing This alternative would consist of an immediate prohibition of purse seining on tuna associated with dolphins. The IATTC staff (J. Joseph, personal commun., 1990) is quite confident that a prohibition of dolphin fishing in the ETP would result in a substantial reduction in the overall production of yellowfin. In addition, if some of the fishing capacity were redirected toward smaller yellowfin, the overall biomass of yellowfin might be significantly reduced as well. Some of this loss would be made up by increased catches of skipjack, but the level of that catch cannot be predicted, because the availability of skipjack in the ETP varies greatly from year to year. The IATTC staff is not able to make accurate predictions of the long-term effects of catching only small fish on the spawning biomass and subsequent recruitment of yellowfin because no apparent relationship has been observed between spawning biomass, as currently estimated (see Figure 7-10), and recruitment. This may be due to the lack of a relationship over the range of observed stock sizes or due to deficiencies in the data. IATTC is continuing to work on this problem. The lowest spawning biomass was estimated at about 90,700 metric tons (Figure 7-10). Females do not reach sexual maturity, on the
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DOLPHINS AND THE TUNA INDUSTRY FIGURE 7-10 Estimates (in short tons) of the biomass of large yellowfin (upper panel) and of all yellowfin (lower panel) in the eastern Pacific. (1 short ton = 0.907 metric ton.) Source: Adapted from IATTC, 1990a. average, until they exceed 40 pounds, which is about the average size of the yellowfin taken in the fishery for fish associated with dolphins ( Figure 7–11). The most recent IATTC estimate (IATTC, 1991b) of the long-term effect of a prohibition of dolphin fishing in the ETP is that it would result in a
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DOLPHINS AND THE TUNA INDUSTRY FIGURE 7-11 Percent maturity of female yellowfin tuna as a function of average weight and age. Data from IATTC, 1990b. 30–60% reduction in ETP yellowfin catch, as well as a significant reduction in yellowfin stocks, if no alternative method were developed to capture large yellowfin. Dolphin Mortality Certificates Under this alternative, certificates would be issued to the captain of each vessel in the tuna fleet for a certain share of the total allowable dolphin mortality. The certificates would be broken down into units of, say, 1–10 dolphins each. The permitted level of dolphin mortality for each captain would be equal to his number of certificates. These certificates could be nontransferable, in which case a captain would be limited to the mortality on his original certificates, or transferable among captains, perhaps on a market basis, in which case a captain could buy certificates from other captains. In either case, when a captain reached the mortality totaling the number of certificates he possessed, he would have to stop fishing on dolphin-associated tuna. This alternative would make sense only if the total dolphin mortality would be reduced steadily over time. To achieve reduction in total mortality, each captain would have to surrender a percentage of his certificates each year. Under a transferable system, a captain could purchase more certificates from another captain. The price of a certificate could be determined by the market
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DOLPHINS AND THE TUNA INDUSTRY for the certificates among the captains, not by the government. Under this plan, the government would simply record certificate transfers and monitor compliance. Under a nontransferable system, all captains would reduce their dolphin mortality by an equal percentage each year. The second set of options discussed below centers on alternatives that would create incentives for behavior that reduces dolphin mortality, as opposed to direct or indirect prohibition on dolphin mortality itself. Incentives for Tuna Fishing with Alternative Gear Under this alternative, positive incentives for switching to alternative fishing gears would be created, probably in the form of subsidies for purchasing or constructing vessels or gear designed for fishing methods other than purse seining. Price Incentives for Fishing on Non-Dolphin-Associated Tuna The argument has been made that one of the factors associated with dolphin mortality is the premium price paid for larger yellowfin tuna, which are more likely to associate with dolphins. This alternative would involve altering the price structure for tuna to eliminate the perceived or real advantages of purchasing larger yellowfin. This change would probably have to be made through the mechanism of a tax or tariff on yellowfin over a certain size or through a price incentive for other species such as skipjack. The major canning firms in the U.S. market recently (1990) created such a disincentive by announcing that they would no longer purchase tuna taken in association with dolphins in the ETP. Although the mechanisms of this proposal are unclear, this move would appear to place a significant constraint on fisheries involving dolphin mortality, at least those delivering tuna to canneries owned by these firms. The important questions concerning this proposal from the point of view of this committee are the following: How will the proposed program be monitored? The initial understanding is that the existing U.S. and international observer programs will be continued, although they would have to be expanded considerably to serve a certification function for all countries and vessels involved in dolphin-related tuna fisheries. Will the monitoring and enforcement of this program be done through government programs, such as the NMFS observer program, through international or regional programs involving such organizations as IATTC, or through the mechanisms described in the Dolphin Protection Consumer Act of 1990 (P.L. 101 –267, Title IX)? How will any potential embargoes on tuna products coming into the United States under the 1988 amendments to the Marine Mammal Protection
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DOLPHINS AND THE TUNA INDUSTRY Act of 1972 (MMPA) affect international or foreign nation observer programs? What, in turn, will be the effect of changes in foreign-nation observer programs on the ability of canning companies or the U.S. government to monitor catches of tuna associated with dolphin mortality? What will be the effect of the canning-company decisions on the U.S. high-seas fleet operating in the ETP? Five general alternatives present themselves: Fishing on school fish not associated with dolphins outside the 200-mile Exclusive Economic Zones of the Resource Adjacent Nations in the ETP. Making arrangements with Resource Adjacent Nations to fish on school and log fish within their Exclusive Economic Zones. Moving from the ETP to other fishing areas and fishing on school and log fish. (This option does not consider the fate of coastal canneries left behind.) Selling dolphin-associated tuna through other outlets. Perhaps sale of U.S. vessels to nations willing to continue dolphin fishing in the ETP. The recent decline in the number of U.S. vessels that fish on dolphins in the ETP might be an early indication of the economic consequences of the canneries' decision. Captain Performance Standards The 1988 amendments to the MMPA mandate that the Secretary of Commerce develop and implement “a system of performance standards to maintain the diligence and proficiency of certificate holders” among the U.S. captains, the implication being that a similar system of performance standards would be expected of foreign fleets as well. The implementation of such an international system is now being developed through IATTC. NMFS also is developing a system whereby captains in the U.S. fleet would be penalized when their performance was below a given standard. Training and Evaluation of Fishing Captains Initial Training Most captains of tuna vessels learn their craft from another captain aboard a boat and serve as navigators for several years before being put in charge of a vessel. If they serve under a captain with a record of low dolphin mortality, they are likely to be well trained and motivated in this regard, although the degree of motivation also tends to depend on the individual. In addition, some governments require that captains undergo more formal
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DOLPHINS AND THE TUNA INDUSTRY and specialized instruction on fishing laws and regulations, as well as in the use of fishing gear and techniques required for fishing for tuna in association with dolphins. Unless they comply with this requirement, captains are not issued the license that permits them to fish on dolphins. NMFS conducts such workshops for captains of U.S. vessels, with the following agenda: Introduction. Training requirements. Responsibilities of the Tuna-Dolphin Management Branch. The MMPA. Certificates of inclusion. International aspects of the tuna-dolphin problem. The observer program. Reporting requirements. Mortality reduction technology. Suggestions from the participants for improving dolphin safety. Marine mammal identification and geographical distribution. Quotas. Dolphin safety gear requirements. General procedural requirements. Dolphin safety and release procedures. Observers. IATTC organizes workshops and seminars for captains, crews, and managers of tuna vessels in the international fleet. These workshops typically include: Activities of IATTC's international tuna-dolphin program. Historical review of the purse-seine fishery in the ETP. Fleet sampling and mortality estimation. Historical review of incidental dolphin mortality. International controversy over the tuna-dolphin program. Factors affecting dolphin mortality; responsibilities of captains and companies. Laws and regulations. Comparison of mortality rates, such as those between captains and between fleets. IATTC gear program and services; recent gear innovations. Review of dolphin safety gear. Meetings with individual captains to discuss their performances. Measuring the Captains' Performance Some of the factors affecting dolphin mortality, such as gear malfunctions or subsurface currents, are beyond the control of captain and crew. However, the crew's skill and motivation play a major role in determining a vessel's dolphin mortality
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DOLPHINS AND THE TUNA INDUSTRY record. The best captains train their crews in the procedures for reducing dolphin mortality and instill in them the desire to do their best in every set to avoid killing dolphins. Even the best captains occasionally experience a set with high mortality, but in the long run their records show the difference (see Figure 6-3). From the point of view of management, captains who are responsible for the most mortality must be identified and measures must be taken, which may range from requiring additional training to revoking their fishing licenses. To assess a captain's performance fairly, the effects of biases arising from fishing in different areas or on different stocks should be removed. This approach is used by IATTC. Alternatively, a simpler measure of performance may be used with the assumption that the effects of these factors will even themselves out over a long period of time for all captains. In 1989, NMFS proposed a system of the latter type, in which the average mortality per set from one trip would be compared with the average value for all captains. If the figure for a trip exceeded the average by 50% or more, certain actions would be taken. This system is being revised; new guidelines were not available for this report. Remedial Actions Procedures have been developed for dealing with captains with records of high dolphin mortality. When such a captain has been identified, an expert-captain panel is convened. A group of experienced captains from a national fleet, both active and retired and with low dolphin mortality records, meets with the captain in question, reviews data from his trips, and discusses problems and solutions. This approach has proved to be effective, but it has some drawbacks. Small fleets may not have enough captains in port at any one time to convene such a panel, and new fleets may not have enough captains, active or retired, with sufficient experience to form an effective panel. The rapid expansion of foreign fleets in the 1980s created a need for vessel captains, and many were promoted from the ranks or brought in from fisheries in the Atlantic and Indian oceans. This development resulted in a large number of relatively inexperienced captains who were unfamiliar with fishing on dolphins and who are now in various stages of learning. Because of these problems, IATTC is providing the technical expertise for the assessment and correction of captain performance for the international fleet. In the United States, the Porpoise Rescue Foundation tracks the performance of all U.S. fleet captains and intervenes when necessary. Other countries have their own national programs, usually coordinated through industry associations or specialized organizations, which monitor the performance of the captains of the national fleet. The procedures vary for dealing with captains with records of high dolphin mortality. The captain 's record and the magnitude of the problems experienced are considered before action is
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DOLPHINS AND THE TUNA INDUSTRY taken. IATTC cooperates with all these national initiatives and provides data and technical support for their interpretation. Both NMFS and IATTC offer services to the fleets for testing dolphin safety gear. These services involve a trial set to evaluate the condition and operation of the net and the other gear. The procedure is especially recommended when a captain is experiencing chronic problems that may be due to gear that is in poor condition or is used incorrectly. IATTC also offers set-by-set analyses of observed trips, detailing the use of dolphin safety equipment.
Representative terms from entire chapter: