This paper proposes a multichannel MAC protocol in underwater acoustic sensor networks for transmitting monitoring data. Since the transmission speed of acoustic wave is much slower than terrestrial, the propagation delay in the water is much more also. Moreover, due to the long propagation delay, the hidden terminal problems are more severe. For solving the long propagation delay and hidden terminal problems, the bandwidth utilization of exist mechanisms is much less. To increase the bandwidth utilization, multichannel concept is proposed but suffers from the rendezvous and complicated hidden terminal problems. In this paper, a receiver oriented multichannel protocol is proposed. In this protocol, the negotiations and communications are based on the channels and the time of receivers. By reducing the number of communication times, the waiting time of the network is reduced and the bandwidth utilization is improved. Performance study reveals that the proposed protocol outperforms existing work in terms of bandwidth utilization, collision problem as well as network throughput.