The Influence of Noise on Fish

Over the last few years an increasing amount of man-made noise from shipping, power plants etc. has been added to the natural sound levels. This underwater noise pollution has various effects on the behaviour, physiology, communication and most likely the fitness of aquatic animals. While there is growing knowledge that anthropogenic noise has negative effects on the life of aquatic mammals, in particular of whales, much less is known about fishes. A few data show that noise can affect hearing or even damage inner ear sensory cells, but almost nothing is known on the influence on acoustic communication and whether intense noise can elicit stress in fishes. Three series of experiments are planned to answer these questions. The first step involves investigating to what degree the auditory sensitivities of hearing specialists, which possess morphological structures to enhance hearing, and hearing non-specialists are impaired during the presentation of noise. The hearing sensitivity will be measured over the whole frequency range of fishes during exposure to white noise (equal energy at each frequency) or to noise recorded in the field underwater. The Auditory Brainstem Response (ABR) recording technique will be utilized in order to measure the auditory sensitivity in fishes. The ABR method is a non-invasive electrophysiological recording of neural acitivity elicited by acoustical stimuli. This method was successfully established at the Bioacoustics Research Lab at the Institute of Zoology in the course of the preceding project. The influence on acoustic communication will be investigated by measuring the response of the auditory brainstem during the playback of conspecific sounds under various noise conditions after adapting the ABR technique. The noise-induced stress response will be measuring via the levels of stress hormones, especially of cortisol, in the fish holding water. This will be done in cooperation with Dr. Rui Oliveira from the Instituto Superior de Psicologia Aplicada in Lisbon, Portugal, who developed a technique for measuring steroids in water. For comparative purposes, mostly sound-producing hearing specialists such as catfishes, cyprinids and labyrinth fishes, along with non-specialists such as sunfishes and cichlids will be chosen for this study. This will be the first comprehensive investigation showing the influence of noise on hearing, communication and stress. Together with life history data it will help to clarify the immediate effects and dangers of (man-made) noise on fishes.

The main topic of the project was to clarify to which extent noise impairs hearing in fishes and stresses animals. In order to answer these questions we developed and utilized non-invasive techniques (non invasive recording of auditory evoked potentials, AEPs, and non invasive determination of hormones). Long-term exposure to high noise levels resulted in temporary hearing loss in fishes and decreased their ability to resolve temporal patterns of sounds (Wysocki and Ladich 2005a). Furthermore it could be shown, that in the presence of noise the hearing sensitivity decreased due to masking phenomena (Wysocki and Ladich 2005b). The influence of ship was investigated in two studies. In 2003 organizers of the first powerboat race at an Austrian lake asked us to measure underwater noise. This was required by local district authorities of Upper Austria due to concerns of fishermen on Lake Traunsee. Data showed that sensitive fish species are able to detect noise up to a distance of 300 m (Amoser et al. 2004). Ship noise could be a potential stressor for native freshwater fish species. Ship noise recorded near Vienna and played back in the laboratory resulted in an increase of the stress hormone cortisol in the aquarium water (Wysocki at al, submitted). Measurements of man-made noise were followed by those of natural ambient noise levels in a large number of freshwaters in Austria to figure out if fishes are adapted to high or low noise levels in their habitats. A large number of freshwater fish species possess excellent hearing sensitivities due to accessory hearing structures similar to the middle ear ossicles in mammals. Experimental removal of these Weberian ossicles resulted decrease in auditory sensitivity up to 32 dB (Ladich and Wysocki 2003). A long time cooperation with A.H. Bass from the Cornell University, Ithaca, NY, was continued to study neuronal control of sound production in fishes. In contrast to other fish species described so far neurons controlling sound production in piranhas were located in the spinal cord and not the hindbrain (Ladich and Bass 2005). Data gained in the course of this project were included in four book chapters on hearing, sound production and the evolution of hearing in fishes (e.g. Ladich and Popper 2004).