Observed changes in the species composition of tuna schools in the Gulf of Guinea between 1981 and 1999, in relation with the Fish Aggregating Device fishery
IRD, Dep. HEA, BP 5045, 34090 Montpellier, France
2 Instituto Español de Oceanografía, Apartado de Correos 1373, 38080 Santa Cruz de Tenerife, Islas Canarias, Spain
3 Instituto Español de Oceanografía, Maria de Molina 8, 28002 Madrid, Spain
Accepted: 13 June 2000
This paper compares the species composition of free swimming schools and schools associated with fish aggregating devices (or FADs) observed by scientists in the eastern equatorial Atlantic during the early eighties and late nineties. This comparison shows that in free swimming schools, big changes in the species composition have occurred. The main change is a rarefaction of mixed species free schools (skipjack and small yellowfin or bigeye). This change is probably a real biological one, and possibly a consequence of the large numbers of FADs seeded in the area since 1990. Nowadays, most small tuna living in the equatorial area appear to be concentrated under these drifting FADs instead of in free schools. Further study is recommended in order to evaluate the validity and interpretation of this result and to examine its implications.
Key words: tuna / fish aggregating device / FAD / species assemblage / behavior / schools / purse seine fishery / Eastern Central Atlantic
© Elsevier, Inra, Ifremer, Cemagref, Ird, Cnrs, 2000