Approximately one quarter of the world's tuna catch is taken in the eastern tropical Pacific Ocean (ETP). In that area, the most economically important tuna species, the yellowfin (Thunnus albacares), is often found in association with various species of dolphins. Increasingly since the late 1940s, tuna fishermen have taken advantage of this association and have caught tuna by setting their nets around the highly visible herds of dolphins, which, being mammals, must surface often to breathe. Despite improvements in techniques and in gear that have substantially reduced the number of dolphins killed in the ETP tuna fishery, thousands of dolphins are still killed each year.
When the Congress reauthorized the Marine Mammal Protection Act of 1972 (MMPA) on November 23, 1988, it stipulated several amendments to the act. One of these amendments (Section 110(a)) focused on identifying appropriate research into promising new methods of locating and catching yellowfin tuna without the incidental capture of dolphins. It further directed the Secretary of Commerce to arrange for “an independent review of information pertaining to such potential alternative methods to be conducted by the National Academy of Sciences with individuals having scientific, technical or other expertise that may be relevant to the identification of promising alternative fishing techniques. ” The report from the National Academy of Sciences would then be submitted by the Secretary, together with a proposed plan of research, development, and implementation of alternative fishing techniques, to the Committee on Commerce, Science, and Transpor-
tation of the Senate and the Committee on Merchant Marine and Fisheries of the House of Representatives.
This report, by the National Research Council's Committee on Reducing Porpoise Mortality from Tuna Fishing, provides background information on catching yellowfin tuna and the incidental capture of dolphins in the ETP, recommendations from workshops focusing on improving current fishing techniques, and recommendations for research on alternative techniques.
Catching tuna with purse seines is the most efficient method currently available. There are three major modes of purse-seine fishing. The first is school fishing, in which schools of tuna near the surface are found visually and the purse seine is set around the school. The second, called log fishing, depends on the attractive power of floating objects for tuna. Purse seines are set around natural logs or fish-aggregating devices to catch the fish that are often associated with them. The third method—the main focus of this report—is “dolphin fishing.” Yellowfin tuna and certain species of dolphins are often associated, especially in the ETP. Dolphins are easy to see from a boat because of their frequent surfacing. The purse seine is set around the dolphin herd, and because the tuna are closely associated with them, catching dolphins usually means catching tuna as well. Although a variety of techniques and equipment have been developed to release the dolphins safely, thousands are still killed each year by dolphin fishing.
Although all three methods of purse seining catch tuna, log and school fishing catch mostly small, sexually immature tuna. Dolphin fishing usually catches large fish that are often sexually mature and produces larger average catches than the other methods. Thus, redirecting the fishing away from tuna associated with dolphins would be less efficient and would have a negative effect on the yield of the fishery and perhaps on the conservation of tuna populations. Considering only the point of view of economics and harvesting tuna, large tuna should be sought; fishermen should fish on dolphins and be discouraged from fishing on logs or schools. However, dolphin fishing kills dolphins; to minimize the killing of dolphins, all fishing should be directed away from dolphins. This dichotomy is the basis of the tuna-dolphin problem.
Two operational factors are related to the total number of dolphins killed in purse seining for tuna. The first is the number of times purse seines are set around dolphins, and the second is the number of dolphins killed in each such set. The first factor is affected by market prices, the availability of tuna of different sizes, restrictions such as the policy of some processors not to buy tuna caught on trips that have involved the intentional encirclement or death of dolphins (so-called “dolphin-safe” tuna), and the availability of alternative methods of catching tuna. The second factor depends on conditions such as
the fishermen's motivation, skill, and experience; the condition of the vessel's equipment; weather conditions; and technological developments. Therefore, two general approaches are available to achieve the goal of reducing dolphin mortality—economic and technical—and each approach has several options.
The tuna-dolphin problem has several components. First, it is an international problem. Part of the difficulty is due to differing conservation ethics— U.S. laws and policies have the goal of preventing all dolphin mortality from tuna fishing, whereas the laws and policies of other nations are more often directed toward conserving dolphin populations, but not necessarily preventing all mortality. The international scope of the problem was illustrated by a 1991 ruling of a panel of judges that a U.S. embargo imposed in 1990 on Mexican tuna—applied in accordance with the MMPA—violates the provisions of the General Agreement on Tariffs and Trade.
Economic factors also are important. The U.S. tuna fleet in the ETP has become very small, probably because of a variety of economic factors, probably including the recent decision by major canneries to buy only “dolphin-safe” tuna. As a result, regulations on the U.S. fleet and adoption by the U.S. fleet of new gear and techniques might not be effective in further reducing dolphin mortality unless they are supported to some degree by other countries and thus affect the activities of non-U.S. boats as well as U.S. boats. The effects of decisions with respect to buying only certain kinds of tuna will depend on the U.S. share of the market and other factors. Indeed, if the recent rate of its decline continues, the U.S. fleet will soon cease to play a significant role in fishing for dolphin-associated tuna in the ETP.
The committee's analysis made it clear that no methods of catching tuna without killing dolphins—currently available or capable of rapid development —are as efficient as current methods of catching large yellowfin tuna in the ETP. Therefore, although it was not specifically in its charge, the committee focused on modifications of current methods, as well as identifying areas for research that might lead to new methods several years down the road. The committee made no attempt to evaluate the relative costs and benefits of such a research program.
THE CURRENT FISHERY
More than 70 nations participate in the world tuna fishery, but only 10 of those nations account for almost 85% of the catch. In 1989, Japan accounted for about 29% and the United States for 12%. About 36% of the total catch is consumed by Japan and about 31% by the United States. Over the years, the ETP has been one of the most productive tuna fishing areas in the world.
The ETP fishery was formerly dominated by the U.S. fleet. Since 1960, the fleets of nations other than the United States have increased and the U.S. fleet has decreased, especially in recent years. The proportion of the catch taken by
U.S. vessels decreased from 90% in 1960 to 32% in 1988 to 11% in 1991, and that taken by Latin American countries bordering the Pacific Ocean increased from 10% to 47% in 1988 and 57% by the end of 1991.
Until about 1975, the U.S. market consumed about 80% of the catch of surface-caught tuna from the ETP. With the expansion of the non-U.S. fleets during the 1980s, the share of the catch absorbed by the U.S. market declined, falling to 45% in 1987. Most of the difference went to Latin America, Europe, and the Far East.
Of particular interest to the committee is the surface fishery (bait-pole and purse seine) for yellowfin tuna in the ETP. Surface-caught yellowfin and skipjack tuna provide the raw material for the canned light-meat tuna product marketed primarily in the United States, Europe, and the Far East. Over the years, as new fishing areas have become viable, the ETP has contributed a smaller fraction of the world catch of yellowfin and skipjack.
DOLPHIN MORTALITY ASSOCIATED WITH THE TUNA FISHERY
Although no accurate data on dolphin mortality are available for the early years (1950–1972), the increased offshore operation of increasingly sophisticated fishing vessels setting their nets on herds of dolphins clearly led to very high mortality, especially in the ETP. Even though published estimates of dolphin mortality from 1960 to 1972 are based on a small and probably biased data set, and although such estimates have varied among authors and from year to year, it seems likely that more than 100,000 dolphins were killed annually by the U.S. fleet. After 1972, the annual number killed by the U.S. fleet declined to approximately 20,000 in 1979 and an estimated 19,712 in 1988 and 12,643 in 1989. This decline was due to a decrease in the rate at which tuna boats killed dolphins and a decrease in the number of boats in the U.S. fleet. Mortality is much larger among the tuna fleets registered in increasing numbers in other countries. By 1986, only 34 boats of the 103-boat fleet were registered in the United States and subject to National Marine Fisheries Service (NMFS) regulations; by 1991, only 11 U.S. boats fished the ETP. The Inter-American Tropical Tuna Commission (IATTC) estimates that the total kill for 1989 was 97,000–102,000 dolphins, of which the kill of 12,643 attributed to the U.S. fleet was less than 15%. In 1990, total mortality declined to 52,000–56,000 dolphins, of which less than 10% (5,083 dolphins) was attributed to the U.S. fleet. In 1991, average mortality per set has continued to decline and is now close to half of the 1990 values. Fishing effort on dolphins has also declined, and the total mortality for 1991 may be around 25,000 dolphins.
Three species of dolphins are most commonly affected: the spotted dolphin (Stenella attenuata), the spinner dolphin (Stenella longirostris), and the common dolphin (Delphinus delphis). NMFS, which has responsibility for protect-
ing marine mammals under the MMPA, set an annual quota in 1980 of 20,500 dolphins that could be killed by U.S. tuna boats, that quota including subquotas for various species and stocks. Additional regulations apply to fishing techniques.
Improvements in fishing gear and techniques discussed in Chapter 7, the mandatory observer program, and the kill quota were responsible for the dramatic decline in the number of dolphins killed by boats in the U.S. fleet. Currently, only about 0.5% of dolphins encircled by purse seines are injured or killed, and almost all of these are killed in a small number of problem sets. Most sets on dolphins are now zero-kill sets.
Most major modifications of gear and techniques were implemented more than a decade ago. More recent declines in mortality can be traced to improvements in equipment and the performance of the fishermen. Industrial groups have set up national technical advisory offices that, in collaboration with the IATTC, include organizing training courses for vessel captains and crews, inspecting the condition and performance of dolphin-saving gear, and diagnosing individual vessel or skipper problems. The recent declines in mortality, from 130,000 dolphins in 1986 to perhaps 25,000 in 1991, were achieved without any major technological advances or additions to the fishing gear.
Although mortality of dolphins has been drastically reduced, the annual kill is still substantial. In addition to the humanitarian and ecological concern for dolphins, the killing of dolphins is detrimental to fishermen. Dolphins are viewed as a valuable resource to fishermen because they attract and hold large yellowfin tuna near the surface where they can be caught. Thus, reducing dolphin mortality as much as possible is in the interest of the fishermen.
U.S. TUNA AND MARINE MAMMAL POLICY AND ECONOMICS
The U.S. government has been involved in some form of tuna-policy negotiations since the 1940s and in formal regulatory activity concerning tuna fisheries since the 1960s. The relevant laws and activities include the founding of IATTC in 1949 and the Tuna Conventions Act of 1950, the Fishermen's Protective Act (1954), the International Commission on the Conservation of Atlantic Tunas and the Atlantic Tuna Conventions Act (1975), the U.S.-Canada Pacific Albacore Treaty (1982), and the South Pacific Tuna Act (1988). IATTC and the Tuna Conventions Act of 1950 and the Fishery Conservation and Management Act of 1976 have had the greatest impact on the tuna industry.
In addition to the general U.S. tuna-policy framework, the U.S. policies on marine mammal conservation and protection have significantly affected the U.S. high-seas tuna fleet. The most significant of these policies result from the MMPA ( Chapter 2). The act prohibits the taking of any marine mammal. It
(Section 1371) was amended in 1981 to state that “ . . . [the] goal [of zero mortality] shall be satisfied in the case of the incidental taking of marine mammals in the course of purse-seine fishing for yellowfin tuna by a continuation of the application of the best marine mammal safety techniques and equipment that are economically and technologically practicable.”
The tuna fishery is part of a highly capitalized and international food-processing industry. This situation, combined with the migratory nature of tuna, results in complex policy and management conditions that are critical to any effort to preserve and conserve dolphin populations.
The U.S. tuna market is 31% of the global tuna market, and an estimated 70% of the U.S. tuna supply is imported in either raw/frozen or canned form. U.S. tuna harvesters and processors have been moving away from the United States, leaving it more dependent on tuna imports. This trend will probably accelerate if any new costs are imposed on U.S. tuna harvesters or processors that are not incurred equally by foreign tuna companies. To the extent that attempts by the United States to reduce dolphin mortality increase costs or reduce productivity for U.S. vessels, these vessels will lose competitive ability in the ETP tuna fishery and are likely to be sold to foreign investors to remain competitive. Whether the U.S. government can (1) prevent the loss of U.S. vessels, (2) require U.S. tuna fishermen to operate at a competitive disadvantage, (3) subsidize fishermen to remain under U.S. jurisdiction, or (4) remove the advantage of foreign vessels by restricting access to the U.S. market remains unclear. Developing engineering-based solutions to the tuna-dolphin problem should be viewed as only the first step in reducing dolphin mortality. Unless the solution is cost-effective, U.S. and foreign tuna harvesters are unlikely to employ new dolphin-saving equipment or procedures or to avoid dolphin-associated fishing altogether.
The process of purse seining any species of fish involves the encircling of the school with a long net to form a circular wall of netting. The net must be deep enough to discourage escape underneath it, and the encircling must be done rapidly enough to prevent escape before the ends are closed. The tuna purse seine, described in detail in Chapter 3, is rectangular, typically much longer than it is deep. A seine is approximately 1 mile long and 600 feet deep.
Once the school is located, a skiff is released from the stern of the vessel, with one end of the net (known as the ortza) attached. The skiff anchors this end of the net while the seiner encircles the targeted school and rejoins the skiff. The ortza is transferred to the vessel and made fast, thus closing the circle. At this point the net forms a vertical cylinder around the school of fish. To allow closure of the bottom of the seine, a series of rings are attached to the leadline through which a purse line is run. During the pursing operation, this
purse line is pulled in from both ends, choking off the bottom of the seine. When the seine is completely pursed and the rings are alongside the vessel, the process of hauling in, or “drying up,” the net can begin.
The remainder of the normal purse-seining operation involves “sacking up” the catch. This consists of reducing the volume of water inside the net until it is possible to bring the catch aboard using a large dip net called a “brailer.” This is done through a process of bringing most of the net aboard, leaving only a small sack of reinforced netting in the water to confine the catch for brailing. Once the fish are removed, the remainder of the seine is brought aboard and made ready for the next set.
BEHAVIOR OF TUNA AND DOLPHINS IN THE ETP
Several species of dolphins are found in association with tuna. The spotted dolphin (Stenella attenuata) is by far the most important from the point of view of its frequency of association with tuna and its use by fishermen for catching tuna. Three stocks of this species are in the ETP. The frequent appearance of spinner dolphins (Stenella longirostris) in sets makes that species significant as well, although in almost all cases it appears in mixed herds with the spotted dolphin. The common dolphin (Delphinus delphis) is another important species, although sets on that species are less frequent than on the other two. A few other species found in association with tuna, but much less frequently, are the striped dolphin (Stenella coeruleoalba), the roughtoothed dolphin (Steno bredanensis), the bottlenose dolphin (Tursiops truncatus), and Fraser's dolphin (Lagenodelphis hosei).
The bond linking tuna and spotted dolphins is remarkably strong. It may persist through much or all of the seining operation. During seining, tuna and dolphins continue to associate so tightly that to catch dolphins also means to catch tuna.
FACTORS AFFECTING DOLPHIN MORTALITY
Many factors other than the total fishing effort on dolphins influence dolphin mortality. Some of the most important are the number of tuna caught, vessel captain, species or stock caught, area, flag of vessel, time of capture (day or night), duration of set, presence or absence of strong currents, occurrence of malfunctions, alignment of fine-mesh panel, and use of dolphin-saving procedures.
Many of these factors are interrelated. For instance, the larger the catch of tuna in a set, the longer the set will last, the larger the number of dolphins that
will be caught, and the more likely it is that the set will finish after dark (dolphin mortality increases markedly after dark) or that a malfunction will occur. Also, different species or stocks of dolphins have different herd sizes and behaviors and inhabit different areas. Some areas and some species or stocks are fished during only part of the year, so spatial, temporal, and species effects cannot be discriminated. This makes it difficult to identify precisely the cause-effect mechanisms that result in the higher or lower mortalities.
Finally, the skill of the captain has a large effect. Even the best captains occasionally experience a set with high mortality, but in the long run they kill many fewer dolphins than captains of less experience and skill.
ESTIMATES OF DOLPHIN ABUNDANCE
Estimates of dolphin abundance in the ETP have been made by NMFS and IATTC on the basis of observations made from either research vessels or fishing boats. Other methods of estimating abundance, such as mark-recapture experiments, or other sources of data (e.g., sightings from aerial surveys) have proved inadequate for this purpose.
The best available estimate of the average total population of common, spinner, striped, and offshore spotted dolphins in the ETP in 1986 –1990 is slightly over 8,000,000. Estimates of absolute abundance are important for seeing the impact of mortality within a stock due to fishing as a proportion of the total population, not as a number without any frame of reference.
The NMFS and IATTC studies demonstrate that none of the indicators of stock size shows any statistically significant trend in the last 5 years. Before 1982, and especially in the late 1970s, several stocks experienced large declines; however, since 1983 all stocks have been stable, and some appear to be increasing. However, the committee notes that better knowledge of recruitment rates and migration patterns of dolphins and better stock identification of individuals are needed for accurate descriptions of population trends.
TECHNIQUES FOR REDUCING DOLPHIN MORTALITY
After extensive analysis, the committee was unable to identify any currently available alternative to setting nets on dolphins that is as efficient as dolphin seining for catching large yellowfin tuna. The committee also could not identify experimental modifications to gear or techniques of catching dolphin-associated tuna that would reduce dolphin mortality to or near to zero and would be practical in the fishery in the immediate future. Therefore, the committee concentrated on incremental improvements and longer-term research and regulatory options ( Chapter 7).
Several small modifications to the current methods of tuna purse seining
(e.g., the Medina double corkline, jet boats, and the Doppler current profiler) 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 reduce significantly the impact of purse seines on dolphins.
The use of more sweeping changes in purse-seine gear and methods was given major attention by the committee. Modifications to reduce two fundamental problems—canopies and roll-ups—are described in Chapter 7.
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.
Several other concepts explored by the committee also show promise for reducing dolphin mortality. These modifications include inserting barriers between tuna and dolphins, improving the escape of dolphins from the backdown channel, separating the tuna from the dolphins once in the net, releasing dolphins without the backdown procedure, releasing dolphins before backdown, and breaking the tuna-dolphin bond before setting the net.
The committee also explored alternative methods of locating and catching yellowfin tuna when they are not associated with dolphins. These include acoustical methods and fish-aggregating devices.
A variety of techniques are used worldwide to exploit tuna and other midwater schooling fish, but their production rates are much lower than those for the modern purse seiner; therefore, they are not as effective as fishing on dolphins in the ETP for a fishery supplying fish to canneries. Government and industry workshops have explored these alternatives. Methods considered by the committee include live-bait pole-and-line fishing, longlining, midwater trawling, pair trawling, and gillnetting.
Finally, the committee explored regulatory alternatives for reducing dolphin mortality in the ETP purse-seine fishery. The first set of options centers on regulatory alternatives that would further prohibit, directly or indirectly, dolphin mortality. These alternatives include prohibition of dolphin mortality and issuance of dolphin-mortality certificates.
The second set of options centers on alternatives that would create incentives for behavior that reduces dolphin mortality, as opposed to direct or indirect prohibition on dolphin mortality itself. These include incentives for tuna fishing with alternative gear, price incentives for fishing on non-dolphin-associated tuna, and the development of vessel-captain performance standards coordinated with a training and evaluation program.
The committee's recommendations are presented in two parts. The first part treats avenues for developing promising new techniques for reducing dolphin mortality in the existing purse-seine fishery on dolphins. The second part treats research on and development of new methods of harvesting ETP yellowfin not in association with dolphins.
Recommendations Concerning the ETP Tuna-Dolphin Fishery
The committee judges that improvement in captain performance is the single most important step that can be taken to reduce dolphin mortality in the ETP purse-seine fishery. Therefore, the committee recommends that an international meeting be convened of representatives of government and industry from all countries engaged in the ETP purse-seine fishery. The purposes of this meeting would be the following:
Develop an educational certification and monitoring protocol for all captains in the international fleet.
Initiate research on the development of incentives to improve captain performance.
The committee recommends that two approaches, short term and long term, be undertaken in gear and methods research and development. These approaches are the following:
A number of small modifications of current methods could be built and tested immediately on commercial fishing trips. The most promising modifications are the current profiler, jet boat, double corkline, pear-shaped snap rings, and polyester net. The committee emphasizes that it is of paramount importance that an international program be developed to systematically deploy, test, and evaluate these modifications of current methods.
A number of major modifications of current methods need to be researched and developed on a long-term basis. These modifications include inflatable sections or partitions in the net, lifting surfaces, modified purse cable, new netting materials, and modified net designs. The committee recommends a long-term engineering approach toward eliminating major causes of dolphin mortality in the purse-seine process—canopies, roll-ups, and collapses in the backdown channel.
Research is needed for a better understanding of the behavior of both dolphins and tuna and the bond between them. Details, costs, and potential benefits of many of the concepts delineated above cannot be judged at present.
Fishermen need both incentives and options to make further progress in
reducing dolphin mortality. The individual fisherman alone cannot be expected to develop the options that offer significant improvements if they represent major changes to the present gear because fishermen who adopt gear that is likely to reduce dolphin mortality might incur economic losses. The committee recommends that a program of research be established to develop options and to demonstrate them to the industry. Such a program should include two facets:
An experimental research program of innovative gear to investigate performance and techniques. This program would have access to a modern commercial purse seiner as a dedicated vessel that would not be constrained by the normal pressures of tuna productivity. Because the capture of animals by fishing gear involves interactions between the animals and the gear, the research must include a program of behavioral studies focused on the reactions of both tuna and dolphins to fishing gear and other stimuli. Techniques would include underwater video observation by remote-operated vehicle and acoustic sensing and tracking. Most of the effort would be at sea with deployed gear.
The information gained from the research above would then be used to develop rational purse-seine modifications and alternative harvesting methods based on the engineering requirements of the fishery. This focus would use analysis and modeling to develop, refine, and evaluate each concept to ensure a reasonable chance of success before it was attempted as a commercial prototype. After the analysis and modeling, promising prototypes would be field-tested.
The committee recommends that a program of research on the behavior of tuna and dolphins be established and that it have the following components:
Simultaneous tracking of dolphins and associated yellowfin.
Tracking flotsam-associated yellowfin.
Studies using fish-aggregating devices (FADs).
Satellite monitoring of radio-tagged dolphins.
Recommendations for Research on Harvesting Tuna Not in Association with Dolphins
Even if harvest of yellowfin tuna in association with dolphins continues, the committee recommends that major research be undertaken to explore new methods of harvesting yellowfin not in association with dolphins in the ETP. The promising avenues of research identified by the committee are as follows:
Research into the night behavior of tuna and dolphins. If large yellowfin
do not associate with dolphins at night, purse seining or trawling could be done at night, which would reduce dolphin mortality significantly.
Research into new methods of purse seining.
Research on existing FADs and new technologies such as submerged FADs, which may have a greater potential than surface FADs for attracting and holding commercially harvestable schools of large yellowfin tuna.
The use of satellite oceanographic techniques to locate aggregations of tuna not associated with dolphins in the ETP.
The use of alternative techniques of locating tuna that do not depend on the sighting of dolphins.
Assessment of the impact on tuna populations if purse seining for tuna in association with dolphins is discontinued.