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

Among the different assumptions proposed to explain why tropical tuna aggregate around floating objects ("logs"), one of the most recent is that floating objects may represent meeting points for tuna. This "meeting point hypothesis" proposes that tuna can use these floating objects to form larger schools after school fission or dispersion. The influence of meeting points on tuna school sizes is explored through different individual-based models that consider a single fusion rule and a variety of fission rules based on energetic considerations, the role of school size on school cohesion, predator at-tacks, and dispersion during the night. Results are first analyzed using 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 school sizes. The averaging approach indicates that in all the models (except those based on energetics), floating objects increase school size, at least up to a certain object density. The dynamic approach clearly illustrates different dynamics in the school size of associated, and free-swimming schools. Most of our models show that tuna associated with logs resume schooling in larger schools after fission events.