The development of MAC protocols for UWSNs is a challenging task due to energy limitations, long propagation delays and low data rates. In fact, acoustic communication suffers from latencies five orders of magnitude larger than radio communication. Therefore, a naive carrier-sensemultiple-access (CSMA) MAC protocol would require a very long listen time resulting in low throughput and poor energy efficiency. Efforts have been made to define MAC protocols based on contention-free and contention-based techniques. The JANUS protocol defines a MAC protocol that has been proven to be effective in multiple conditions but few studies have investigated its energy efficiency with respect to other underwater MAC protocols. To this end, the aim of this research is to provide an experimental comparative study of several types of MAC protocols, including the one defined in the JANUS standard, in terms of energy efficiency, fairness, and throughput.