Use of passive acoustics for assessing behavioral interactions in individual toadfish

Most passive acoustics studies focus on daily and seasonal timing and location of choruses of calling fish, particularly sciaenids. Because male toadfish Opsanus spp. are stationary for extended periods, it is possible to extract detailed information about their calls and interactions, making them a powerful model for passive acoustics studies on commercially important species. Toadfishes of both sexes produce a short, pulsatile agonistic grunt, and mates produce a boatwhistle advertisement call for male-male competition and to attract females. We identify unseen vocal individuals (oyster toadfish O. tau and Gulf toadfish O. beta) near a stationary hydrophone and describe call variability and changes over short- and long-term periods, source levels, call propagation, and directionality. Calls exhibit a directional pattern related to the heart-shaped swim bladder morphology, generating a maximal level behind the fish; grunt frequency spectra allow differentiation of individual callers over multiweek periods. Boatwhistle parameters of oyster toadfish calls change geographically, seasonally, and with temperature, and males call day and night. The Gulf toadfish call rate increases during twilight, when individuals produce shorter and simpler calls. Finally, nearby calling males compete acoustically by increasing their calling rates or producing a grunt (an acoustic tag) during another male's boatwhistle. Toadfishes have been successful models for addressing numerous questions in unseen fish by means of passive acoustics.