Observed changes in the species composition of tuna schools in the Gulf ofGuinea between 1981 and 1999, in relation with the Fish Aggregrating Device fishery

This paper compares the species composition of free swimming schools and sc hools associated with fish aggregating devices (or FADs) observed by scient ists 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). Thi s change is probably a real biological one, and possibly a consequence of t he large numbers of FADs seeded in the area since 1990. Nowadays, most smal l tuna living in the equatorial area appear to be concentrated under these drifting FADs instead of in free schools. Further study is recommended in o rder to evaluate the validity and interpretation of this result and to exam ine its implications. (C) 2000 Ifremor/CNRS/INRA/IRD/Cemagref/Editions scie ntifiques et medicales Elsevier SAS.