Hearing in New Zealand reef fishes: Effects of ontogeny, swim bladders and aquaculture noise on hearing thresholds

Abstract

The majority of reef fishes have a biphasic life cycle, including a pelagic dispersal phase. Despite the growing body of evidence suggesting marine larvae are actively swimming towards appropriate settlement habitats, using acoustic cues, relatively little is known about their hearing ability. Using auditory evoked potentials, hearing was examined for; the ontogenetic development of two fish species, snapper (Pagrus auratus) and hapuka (Polyprion oxygeneios); the effects of the absence of a swim bladder; and the effects of aquaculture noise. Juvenile snapper demonstrated mid to poor hearing ability, with no clear trend in their hearing thresholds over their first year. Hapuka had poor hearing around the late-stage larval period, however, their hearing ability dramatically improved throughout their first year. This data suggests that the ontogenetic development of hearing is species specific, and could be a result of species‟ life history strategies. There is evidence that fish without swim bladders are able to orient to ambient underwater sound, but very little is known about their hearing ability. Therefore, hearing thresholds were measured in three temperate blennioid fishes lacking swim bladders. Hearing in these species was comparable to other fish species that possess swim bladders, indicating that perhaps it is the presence of a specialisation that is important for enhanced hearing ability. There is some evidence of reduced hearing in fishes when exposed to anthropogenic noise. Given that a number of studies on fish hearing have been carried out on aquacultured fish, thresholds used to calculate the distance at which fish larvae can detect reefs could be underestimated. The effects of low-intensity noise exposure on juvenile snapper was tested in the current study, demonstrating significant negative effects on their hearing ability. An extended reef based model was used with data from the current study, and the calculated distances support the theory that pre-settlement fish are detecting and actively orienting to reef noises from a significnat [i.e. significant] distance offshore. In conclusion, the results from the present study have improved our general understanding of hearing in temperate marine fishes, and in the role of underwater sound in the orientation of larval fish towards reefs.