Comparison of auditory evoked potential thresholds in three species of sharks

Abstract

Auditory sensitivity measurements have been published for only 12 of the more than 1,150 extant species of elasmobranchs (sharks, skates, and rays). As a result, there is the need to further understand sound perception in more species from different ecological niches. In this study the auditory evoked potential (AEP) technique was used to compare hearing abilities of the bottom-dwelling New Zealand carpet shark Cephaloscyllium isabellum, and two benthopelagic houndsharks (Triakidae), rig Mustelus lenticulatus, and school shark Galeorhinus galeus. AEPs were measured in response to tone bursts (frequencies: 80, 100, 150, 200, 300, 450, 600, 800, and 1200Hz) from an underwater speaker positioned 55cm in front of the shark in an experimental tank. AEP-detection thresholds were derived visually and statistically, with statistical measures slightly more sensitive (average∼4dB) than visual methodology. Hearing abilities differed between species, mainly with respect to bandwidth rather than sensitivity. Hearing was least developed in the benthic C. isabellum [upper limit: 300Hz, best hearing: 100Hz (82.3+1.5 dB re:1µms-2)]. Hearing was superior in the benthopelagic rig and school sharks [upper limit: 800Hz, best hearing: 100Hz (79.2+1.6 dB re:1µms-2) for G. galeus, and 150Hz (74.8+1.8 dB re:1µms-2) for M. lenticulatus]. The data are consistent with those known for 'hearing non-specialist' teleost fishes that only detect particle motion, not pressure. Further, our results provide evidence that benthopelagic sharks exploit higher frequencies (max.800Hz) than some of the bottom-dwelling sharks (max.300Hz). Further behavioural and morphological studies are needed to identify what ecological factors drive differences in upper frequency limits of hearing in elasmobranchs.