Possible universality in the size distribution of fish schools

Motivated by the finding that there seems to be some universality in the size distributions of tropical tuna fish schools over several years and in various conditions, we conjecture that a simple model, inspired by a physical model of particle aggregation [H. Takayasu, Phys. Rev. Lett. 63, 2563 (1989)], can be applicable to many instances of schooling in fish, or even of animal grouping in general. This model, which makes no assumption about the specific details of how fish aggregate to form a school but rather assumes that they are able to do so, predicts not only the power-law behavior observed in nature, but also its particular exponent as well as deviations from pure power-law towards exponential decay.