Tropical tuna associated with floating objects: a simulation study of the meeting point hypothesis

Among the different assumptions proposed to explain why tropical tuna aggre gate around floating objects ("logs"), one of the most recent is that float ing objects may represent meeting points for tuna. This "meeting point hypo thesis" proposes that tuna can use these floating objects to form larger sc hools after school fission or dispersion. The influence of meeting points o n tuna school sizes is explored through different individual-based models t hat consider a single fusion rule and a variety of fission rules based on e nergetic considerations, the role of school size on school cohesion, predat or at-tacks, and dispersion during the night. Results are first analyzed us ing an averaging approach to study the overall mean school size in habitats having different floating object densities. Second, a dynamic approach is used to compare the temporal dynamics of associated and free-swimming schoo l sizes. The averaging approach indicates that in all the models (except th ose based on energetics), floating objects increase school size, at least u p to a certain object density. The dynamic approach clearly illustrates dif ferent dynamics in the school size of associated, and free-swimming schools . Most of our models show that tuna associated with logs resume schooling i n larger schools after fission events.