This research will investigate sound source localization by fishes to ascertain how fish integrate the various sound cues available to them to behave appropriately in complex acoustic environments. Evidence suggests that the capacity for sound source localization is common to mammals, amphibians, birds and reptiles, but surprisingly it is not known whether fishes locate sound sources in the same manner. Therefore, sound source localization by fishes remains an important topic in biology and in the hearing sciences. This study will test the major assumptions of several related theories, including the leading theory of sound source localization by fishes. The plainfin midshipman fish (Porichthys notatus), in which females locate males by sounds that the males produce, will be used as a general model to investigate how fishes localize underwater sound sources. Two hypotheses will be tested: 1) fish orient to the direction of acoustic particle motion to localize sound sources (a major assumption of several, related theories including the leading theory of sound source localization), and 2) both particle motion and sound pressure detection (via the swimbladder) are necessary for sound source localization, but neither alone is sufficient. As an integral part of this research program, both graduate and undergraduate students will receive training and mentoring. In addition, annual public lectures regarding this research will be presented at the University of California Bodega Marine Laboratory.
Our proposed research investigated sound source localization by fishes. Evidence suggests that the capacity for sound source localization is common to mammals, amphibians, birds and reptiles, but surprisingly it is not known whether fishes locate sound sources in the same manner. In fact, sound source localization by fishes remains an important topic in biology and in the hearing sciences since the leading theory in this field is rather complex and most fish species lack the cues that are theoretically necessary to perform such a task. Currently, the nature of sound source localization by fishes remains a profound mystery. Based on the results of this study, we have published three peer-reviewed papers, one book chapter and are currently working on one last empirical data paper to be submitted to a peer-reviewed journal within the next six months. Our first paper titled: "Sound source localization by the plainfin midshipman fish, Porichthys notatus." was published in the Journal of the Acoustical Society of America (2011) vol. 127: 3101-3113. The aim of this study was to use plainfin midshipman fish (Porichthys notatus) as a general model to explore how fishes localize an underwater sound source in the relatively simple geometry of a monopole sound field. The robust phonotaxic responses displayed by gravid females toward a monopole sound projector (J9) broadcasting a low-frequency (90 Hz) tone similar to the fundamental frequency of the male’s advertisement call were examined. The projector’s sound field was mapped at 5 cm resolution azimuth using an 8-hydrophone array. Acoustic pressure was measured with the array and acoustic particle motion was calculated from pressure gradients between hydrophones. The response pathways of the fish were analyzed from video recordings and compared to the sound field. Gravid females at initial release were directed toward the sound source and the majority (73%) swam to the playback projector with straight to slightly curved tracks in the direction of the source and in line with local particle motion vectors. In contrast, the initial direction of the control (sound off) group did not differ from random. This report is the first to compare fish localization behavior with directional cues available in the form of local particle motion vectors. We also published last year a paper on the use of different antibiotics to chemical ablate the fish lateral line titled: 'Reevaluating the use of aminoglycoside antibiotics in behavioral studies of the lateral line' in Hearing Research (2011) vol 272:1-4. We also published a book chapter titled "Sound Source Localization and Directional Hearing in Fishes" based on some of our work in the Encyclopedia of Fish Physiology: From Genome to Environment, volume 1, pp. 298-303. The book chapter summarizes what is currently known about sound source localization and directional hearing in fishes. More recently we published the results of our sound playback experiments of fish to a dipole sound source in a paper titled: "Local acoustic particle motion guides sound source localization behavior in the plainfin midshipman fish, Porichthys notatus" in the Journal of Experimental Biology (2012) vol 215: pages152-160. Here, sound source localization behavior was studied in the plainfin midshipman fish (Porichthys notatus) by making use of the naturally occurring phonotaxis response of gravid females to playback of the male’s advertisement call ("hum"). The observations took place in an outdoor, 4 m diameter, circular, concrete tank. A dipole sound projector was placed at the center of the tank and an 80-90 Hz tone (the approximate fundamental frequency to the male’s advertisement call) was broadcast to gravid females that were released from alternative sites about 100 cm from the source. The phonotaxic responses of females to the source were recorded, analyzed and compared to the sound field. One release site was approximately along the vibratory axis of the dipole source, and the other was approximately orthogonal to the vibratory axis. The sound field in the tank was fully characterized through measurements of the sound pressure field using hydrophones and acoustic particle motion using an accelerometer. These measurements confirmed that the sound field was a nearly-ideal dipole. When released along the dipole vibratory axis, the responding female fish took, essentially, straight paths to the source. However, when released approximately 90o to the source’s vibratory axis, the responding females took highly-curved paths to the source that were approximately in line with the local particle motion axes. These results indicate that the acoustic cues used by fish during sound source localization include the axes of particle motion of the local sound field.
