The world catch of tuna reached 3.1 million tonnes in 1984, of which 2 millions tonnes were composed of the so-called major tunas and marlins and the reset was composed of several species of small tuna and frigate mackerel. The catch in the Atlantic and Mediterranean, 532,000 tonnes in 1985, represented approximately 16% of this total.
In the Atlantic, the most important commercial species are yellowfin (Thunnus albacares), big-eye (T. obesus), skipjack (Katsuwonus pelamis), albacore (T. alalunga) and bluefin (T. thynnus); these five species totaled 444,000 tonnes in 1985 and the first three, exclusively tropical, represented approximately 80% of this total, that is 70% the eastern tropical Atlantic catch.
The annual catch of yellowfin, skipjack and bigeye taken off the west coast of Africa is close to 250,000 tonnes. These species are exploited only in a very small proportion, around 15 to 25%, by coastal countries. However, since the establishment of the 200 mile Exclusive Economic Zones (EEZ), numerous countries of the region are aware of the resources they possess, and logically desire to create and develop their tuna fishing activities for the more oceanic major species as well as for the generally more coastal small tuna and frigate mackerel.
In order to assure a rational exploitation of this resource, a specialized commission, the International Commission for the Conservation of Atlantic Tuna (ICCAT), was created 20 years ago at the initiative of the FAO. This international commission that brought together 22 member countries, is entitled, on the basis of results of scientific investigations, to make recommendations with a view to maintain populations of tuna and related species at a level permitting harvest at a maximum sustainable yield.
The publications of ICCAT are very numerous and varied, and are available to anyone interested. However they very rarely contain thematic or regional syntheses and form a voluminous collection which is very complex for non-specialists to comprehend.
In order to make the pertinent information on this important regional resource easily accessible, the Committee for the Eastern Central Atlantic Fisheries (CECAF) has initiated this synthetic study at the request of its member states.
The area of the study corresponds to the area of distribution of the eastern Atlantic tropical tuna and extends from Mauritania (25°N) to Angola (20°S). The limit at 30° W, historically accepted for Atlantic tuna, has been retained as the western limit. The sub-sector to the south of 5° S and to the west of 5°W has been eliminated from the study zone as the tuna captured in this sector seem to be associated with stocks of South American affinities. The study zone is therefore comparable to the CECAF zone, but is however noticeably different (figure 1.1).
After a brief review of the systematics of the principal species of tuna and marlin caught in the tropical eastern Atlantic (chapter 2) and of the characteristics of the climatic and oceanographic environment (chapter 3), a detailed description of fisheries of the region and the history of their development is presented (chapter 4). An examination of the migration and biology of the principal species (chapter 6) precedes a chapter treating the relations between tuna and the environment (chapter 7). Next is a description of population dynamics methods that have been utilized in the tropical Atlantic to evaluate the abundance of stocks and to estimate the changes in the level of exploitation as a function of the development of the fisheries (chapter 8).
Figrue 1.1 Study Area