In underwater sensor networks (UWSNs), one of the main concerns is to reduce the energy consumption in order to maximize the lifetime. This work focuses on multiple sensor networks governed by different authorities. If the authorities are willing to cooperate by forwarding each others' packets, the global lifetime could be increased. However, a selfish authority could exploit the others' collaborative behaviors. To investigate this cooperation, we apply concepts such as evolutionary game theory. A first analysis of a simple model determines that cooperation underwater can emerge without incentives. Then, we explore with an extended model what influences cooperation and in which way. Finally, we demonstrate how a new authority can fine tune its strategy when deploying its UWSN.