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In most existing handshake-based collision avoidance (CA) protocols, nodes in the communication range of the transmitter or the receiver are kept silent during an ongoing communication session (CS). In underwater acoustic communication (UWAC), this restriction results in low throughput and long transmission delay. In this paper, we utilize the long propagation delay in the underwater acoustic channel and the (possible) sparsity of the network topology, and formalize conditions for which a node can transmit even when it is located within the communication range of a node participating in a CS. We consider these conditions as design constraints and present a distributed CA handshake-based protocol, which, by jointly applying spatial and time reuse techniques, greatly improves channel utilization. Our simulation results show that our protocol outperforms existing handshake-based protocols in terms of throughput and transmission delay. These gains come at the price of some reduction in fairness in resource allocation.