Working With Fishers:
How the Tuna-Dolphin Problem Was Almost Solved

Martin Hall - Cheif Scientist, Inter-American Tropical Tuna Commission

Seminar Abstract:

    Fishers’ knowledge can be an important tool in mitigating some of the ecological impacts of fisheries. Their knowledge of the ways in which the gear works and of the behavior of target and non-target species are critical elements to reduce bycatches. There is a large accumulation of information on these subjects in the minds of the captains and crews who participate in a fishery. One of the main roles of the scientists involved in solving bycatch problems is to tap this resource, and to separate the insightful observations from the misconceptions and myths that are mixed with them.
    In the eastern Pacific purse-seine fishery, three species of tunas are the target: yellowfin tuna (Thunnus albacares), bigeye tuna (T. obesus), and skipjack tuna (Katsuwonus pelamis). The schools are detected and caught in different ways: they are found associated with groups of dolphins, associated with floating objects, or at the surface, often in association with seabirds. For many years, the main component of the fishery was the capture of large yellowfin tuna in “dolphin sets”. Early in the development of this fishery, many dolphins were killed, and for over a decade the levels of dolphin mortality were high, and probably non-sustainable.
This mortality caused major concerns among managers, environmental groups, and sectors of the industry that saw the public response to the figures, and realized that the issue had to be addressed. In the case of the tuna-dolphin problem in the eastern Pacific, most of the technical and operational solutions came directly from the fishers, or resulted from the interactions between scientists and fishers. Dolphin mortality in the tuna purse-seine fishery results from a combination of factors that include environmental conditions (e.g. currents, visibility), gear and equipment, good judgment by the fishers deciding when to make a set, and skill to perform the maneuvers to release the dolphins.
Scientific studies helped to separate the factors causing or increasing dolphin mortality, but fishers provided the initial clues as to the factors to consider, and most of the suggestions for technical and operational solutions. Seminars for fishing captains became opportunities for the exchange of ideas and experiences among fishers and between them and boat owners, scientists, and managers involved in the problem. The evaluation of the level of skill of the fishers in releasing dolphins also required the development of scientific methods that eliminated confounding effects, after the fishers had identified these as a major source of variation in the results.
    The heterogeneity of the performances led to the proposal to utilize individual vessel limits to reward those better qualified to fish with a reduced impact on the ecosystem. This system promotes “natural selection” of fishers, rewarding those who combined the best knowledge with the motivation to solve the problem.  It provided a significant incentive for the continued acquisition of knowledge that resulted in a dramatic reduction in dolphin mortality of almost 99% between 1986 and 2000.
In recent years, some environmental groups tried to solve the problem by shutting down the fishery on dolphins. This pushed a section of the fleet to concentrate their efforts on the other “dolphin-safe” ways of fishing that have no, or very little, impact on dolphins. Unfortunately, these alternative methods resulted in catches of juvenile individuals of some of the tunas with the consequent reduction in yield of the fishery. This shift also brought to the surface the other ecological impacts of the alternatives. Instead of dolphins, the bycatches were composed of small, immature tunas, sharks, billfishes, mahi-mahi, wahoo, and other species.
    The trade-offs posed a dilemma to all participants, including managers and environmental groups. Would it be ecologically sound to replace a low and controlled dolphin bycatch with a much larger and more diversified bycatch of other species, whose significance couldn’t be assessed? When is total dolphin protection a rational objective for ecosystem management? To the scientists, it presents the challenges of having to provide advice that requires a comparison of “apples and oranges” (i.e. how many sharks and billfishes is a dolphin worth?), and of dealing with perhaps the more fundamental question of bycatch management: is a very highly selective fishery a sustainable way to harvest an ecosystem? 

Speaker Bio:

Martin Hall started his education in Argentina completing his first degree at the University of Buenos Aires and earning his Ph.D. in Fisheries at the University of Washington.  Dr. Hall has served as the Head of the Tuna-Dolphin Program of the Inter-American Tropical Tuna Commission since 1984.  Martin is also an Adjunct Professor at the University of British Columbia and a Member of the Board of Directors of the National Fisheries Conservation Center.  His current research and writing involves global bycatch issues often focusing on the Tuna-Dolphin problem.


HALL, M.A. 1996. On bycatches. Rev. Fish Biol. and Fisheries. Vol. 6:319-352.

HALL, M.A.  1998 . An ecological view of the tuna-dolphin problem. Rev. Fish Biol. and Fisheries.      Vol. 8:1-34.

HALL, M.A. and DONOVAN, G. P . Environmentalists, fishers, cetaceans and fish: is there a         balance and can science help to find it? In Evans, P. and Raga, A, (eds.) “Marine Mammals: Biology and Conservation”  A chapter in a book to be published by Plenum Press in December 2001

HALL, M.A., CAMPA, M. and GOMEZ, M . Solving the tuna-dolphin problem in the eastern Pacific purse-seine fishery. Accepted for publication by the Ocean Yearbook Vol 17.

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