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As the preceding chapters of this section have demonstrated, resource regulation has not been the strong suit of fisheries. Each chapter has identified serious problems of, or challenges to, governance in the world’s fisheries: over-fishing, human-induced ecosystem shifts, threats to livelihoods, pollution, over-dependence on marine sources of fish feed, and quality control. These are well-known problems that have in recent years prompted increasing recognition that fisheries governance has been inadequate to the challenge of maintaining sustainability and livelihoods in maritime areas. While not to excuse governance failures, the preceding chapters have provided a major reason for them: the diversity, complexity, and dynamics of the main segments of the fish chain that we identify militate against the establishment of straightforward, effective governance mechanisms. This task is rendered even more complex when the attempt is made to incorporate all of the segments of the chain into a whole. The intent of this chapter is to reflect on the constitution of the fish chain or, really, the multiple intertwined fish chains that extend from the world’s fisheries, and then to assess the governance challenges specific to governing the interactions within entire fish chains. Both of these tasks have been anticipated in the introductory chapters to this volume and in this section of the book. We begin this chapter with a short reflection on the representation of the chain.

The factors affecting fish yields in lagoons were studied through the stability, species composition and size structure of the yields at high and low fishing intensities, respectively, in Togo and the Ivory Coast. Heavy fishing was followed by the development of a plateau phase resulting from a reorganization of species assemblage. In such a state, exploitation produced only a few dominant species for which average catch lengths were small; which were generally herbivorous and exhibited a continuous reproduction, sometimes a lowering of the age at first sexual maturity, permitting a faster turnover. Even if total catches did not collapse, fish biomass and catch per unit effort decreased when fishing effort increased. One option for management could be to locate the level of fishing effort on the plateau such that fishermen can be at least financially independent and provide sufficient fish for local subsistence.

Resume A new fishing method has been developed during the last twelve years by the tuna baitboats fishing seasonaly (from July to December) in the area of Senegal and Mauritania (West Africa, 12 to 21' N). Three species of tunas, yellowfin, skipjack and bigeye tunas are caught in similar proportions in this fishery. This method has produced a dramatic increase in the baitboat catch per unit of effort (CPUE). The paper describes this new fishing method where the boat is permanently running associated with a very large tuna school, night and day, during several months. A team of two baitboats exploits each school, operating one after the other. The biological and environmental characteristics of this associated-school fishing are analyzed from detailed log book data. The daily positions of each school and the catches by species and sizes are analyzed for each boat and school. The dynamics of the association between the tunas and the baitboat and the dynamics of this exploitation (i.e. input and output of tunas in each school) are discussed in relation to the peculiarities of the local environment (mainly sea surface temperature and bathymetry). The reasons for the increased CPUE in this associated-school fishing are analyzed. Further researches should be conducted in order to better understand how fish behaviour relates to this fishing mode and in order to estimate the potential local yield of the fishery, if increased fishing effort is exerted in the future.

Les pecheries du delta central du Niger font l'objet d'une exploitation intensive depuis de nombreuses annees. L'analyse des debarquements de poisson pendant les deux dernieres decennies laisse apparaitre de fortes fluctuations dans la production qui decroit regulierement de 87 000 t en 1969–70 a 37 000 t en 1984–85. Deux causes peuvent etre evoquees pour expliquer ce phenomene : l'apparition de la secheresse en Afrique et/ou l'augmentation de la pression de peche. Dans le premier cas, les captures annuelles et l'indice d'inondation des plaines, calcules en fonction du cycle hydrologique du delta (de juillet a juin), sont bien correles, ce qui s'explique a posteriori par la composition des captures qui s'effectuent a 69 % sur des poissons de moins de 1 an. Dans le second cas, certains elements suggerent qu'il y a eu une intensification importante de la pression de peche sans que celle-ci puisse etre chiffree. La chute des captures totales ne semble pourtant pas due a une mauvaise exploitation des ressources. Les difficultes ressenties par les pecheurs : reduction des prelevements individuels qui passent de 1 900 kg/an en 1966 a 740 kg/an en 1989, necessite de diversifier les activites en pratiquant l'agriculture ou de migrer vers les lacs de barrage ou a l'etranger, seraient donc dues a des phenomenes naturels (secheresse) ayant entraine par la suite des complications d'ordre sociologique et economique. De fait, la reduction des zones en eau provoque une diminution des sites exploitables et l'emergence de conflits entre villages ou familles pour l'acces a la ressource. Par ailleurs, un certain relâchement du controle des autorites traditionnelles lie a un accroissement demographique important aurait provoque une augmentation du nombre de pecheurs en vingt ans de l'ordre de 20 000 personnes (43 000 en 1966 contre 63 000 en 1989) conduisant a un partage difficile des captures par ailleurs en baisse.

Dans les régions tropicales coralliennes, on a parfois recours au potentiel de production halieutique par unité de surface là où les méthodes classiques d'évaluation s'appliquent difficilement. Dans la région Caraïbe, de nombreuses estimations de production halieutique relative, tant potentielle que réelle, sont disponibles sans qu'il soit possible de les comparer de façon rigoureuse. En Martinique, les pêcheries côtières ont produit en 1987 en moyenne 1.14 t.km-2.an-1 d'espèces démersales, avec des productions par strate comprises entre 0.24 et 8.45 t.km-2.an-1. La production relative moyenne pour les espèces néritiques est de 1.68 t.km-2.an-1. La comparaison des productions relatives observées d'un secteur ou d'une île à l'autre est susceptible de contribuer de façon importante à l'évaluation de l'état d'exploitation des ressources, à condition que les méthodologies d'estimation soient explicitées et qu'une connaissance suffisante de l'effort de pêche et du contexte écologique soit disponible. (Résumé d'auteur)