JACINTO, RD*; NAGLE, L; PATEK, SN; SUMMERS, AP; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Berkeley; Univ. of California, Irvine: Keeping an open mind: investigating poacher skeletal morphology

Poachers (Agonidae) are an obscure family of fish nested within the sculpins. They are benthic fish typically found in the sub-arctic waters of the Northern Pacific. Poachers are an intriguing family in that they possess a wide range of body forms (44 species in 22 genus) characterized by bony dermal plates that cover their bodies. Some members possess well-defined post-cranial pits that are developed to varying degrees. Agonids make several low-pitched humming sounds, but the method of sound production has not been determined. Our project focuses on the unusual anatomy of the post-cranial pit and its possible applications, specifically in bioacoustics. A high-resolution CT scan of Bothragonus swani (Rockhead Poacher) was used for anatomical study. Using a 3-D imaging program we observed the depth and diameter of the cranial cavity and the distinct skeletal morphology of the anterior half of B. swani. The anterior-most ribs have been modified to closely follow the contours of the calcified pit and may be the source of the humming sounds via stridulation. Bones in very close proximity to the calcified pit are also present and appear to be closely associated with a series of skull bones that lead to projections that cradle the animal’s ear bones, the otoliths, potentially serving as a specialization for hearing. We also identified and described several different sound types from Agonopsis vulsa (Northern Spearnose Poacher). Recordings were taken at different times of the day and in different situations (single fish and grouped with others). Perhaps the most interesting sounds recorded were those below the threshold of human hearing (sub 20Hz) called infrasound.