Imagine yourself standing under a train trestle, and a train passes overhead. You feel the vibrations in your feet as it approaches, reaching out with your arm you grab the support to assure your footing. Your eardrums ring with the screeching sound of metal scraping metal, the clang of each car passing jars your body. Finally, it passes but there is a lag in your senses, an echo of the train, as your body starts to recover. Now imagine living under that trestle. Would you be able to hear noises that could alert you to danger? Could you have successful communication with another person without confusion? Would you just “get used to it,” as if the trains didn’t exist? Are you able to move away from the tracks, and how far away from the tracks do you have to be for the trains to no longer have an effect or be a distraction? Now replace the tracks with the surface of a body of water, the train with a boat motor, and you with a fish.
Hearing is very important to the survival and fitness of most fishes. It plays an important role in the detection, reaction, and evasion of predators. Hearing is also important to most fish in the role of prey detection and capture. In some species, the sense of hearing is used to detect receptive spawning partners. So, the question of can fish hear in a noisy environment, is an important one. By analyzing the processes in which fish hear, defining what noise is to a fish, and comparing relative data involving the effects of noise on fish in a lab environment, we can develop a better understanding of how noise could be affecting fish in their natural environment.
Hearing is the faculty of perceiving sound. The perception of sound to a fish occurs by the stimulation of sensory hair cells. Fish have sensory hair cells located in the inner ear and their lateral line pores. The sensory hair cells detect the oscillation of pressure through water. These sensory cells are part of the acoustico-lateralis system. When oscillation occurs, it stimulates the sensory hair cell sending a neural transmission to the brain to be processed. The detection of oscillation, stimulation of the sensory hair cells, and processing of the neural transmission in the brain is hearing for a fish (University of Maryland, 2003).
Noise is irregular fluctuations of sounds that accompany a transmitted electrical signal but are not part of it and tend to obscure it. So noise is a masking agent where the detection of one signal is impaired by another, and covers up relevant sounds or distracts or disrupts the hearing processes of the intended recipient. The frequency of sound that a hearing generalist fish, such as the pumpkinseed sunfish Lepomis gibbosus, can hear is between 100-4000 Hz, so noise to pumpkinseed sunfish would have to fall in that range (Wysocki & Ladich, 2005). The sound frequency range of most freshwater boat motors is between 1000-5000 Hz, and would be considered as noise to many fish. Studies have demonstrated that sunfish are substantially less affected by the same amount of background noise (because of their lower hearing sensitivity) than goldfish Carassius auratus, although there is only a small difference in the threshold to noise ratio of these two species (Wysocki & Ladich, 2005).
© Association for Research
in Otolaryngology 2005
Audiograms (solid lines) and appropriate cepstrum-smoothed noise spectra (dashed lines) of A. Carassius auratus, B. Platydoras costatus and C. Lepomis gibbosus. –○– Hearing thresholds obtained under normal laboratory conditions, –▵– hearing thresholds under masking noise of 110 dB, –▿– hearing thresholds under masking noise of 130 dB. At a masking noise level of 110 dB LLeq, the mean hearing thresholds (average of all individuals at a particular frequency) of C. auratus increased by up to 20 dB and by up to 44 dB at a noise level of 130 dB (Fig. 2A). The amount of threshold shift differed between frequencies, being more pronounced in the most sensitive hearing range (500 and 1 kHz). At 130 dB, the whole audiogram became relatively flat. Paired t-tests showed significant differences between baseline and masked thresholds for both noise levels at all frequencies except 4 kHz (Fig. 3A), (Wysocki & Ladich, 2005).
One challenge that noise can present to certain fish is the reduction of predator detection, evasion, and avoidance. This reduction puts the fish under more stress and could even lead to greater mortality rates in a certain species, if the noise has a greater effect on that species than that of its predators. Another challenge in living in a noisy environment is the affects on prey detection and capture rates of predator species. If noise decreases the amount of successful detections and capture rates of prey this could lead to slower growth and development, elevated stress, reduced fitness, and increased mortality rates (Slabbekoorn et al. 2010). Fitness can be reduced as a result of impacts on reproductive success, arising from incorrect assessment of the quality of rivals or the receptiveness of potential mates (Radford et al. 2014).
Loss of energy gains by noise avoidance can have effects on survival and fitness as well. The simplest method of avoiding the potential impacts of anthropogenic noise is to move away from the source. However, this is not always possible if the source dominates certain frequencies, as is the case with low-frequency boat motor noise, or if an entire area is affected, as might occur in certain lakes and estuaries subjected to large amounts of commercial and recreational activities. Also, if a species is dependent on a particular area because of crucial resources, such as food or nesting sites, or is restricted by the geography of the region, then there may be no option but to remain despite the noise (Radford et al. 2014).
We know that fish can still hear in certain noisy environments, and that these noises are masking agents that can directly affect fish health and fitness, but there is still a lot we do not know. Some of these issues are, the direct effect on fish communities and how noise might affect individual species ability for adaptation. More research is needed to discover the entire direct effects of noisy environments on fish.
Radford, Andrew N., Kerridge E., Simpson, S.D.; Acoustic communication in a noisy world: can fish compete with anthropogenic noise?. Behav Ecol 2014; 25 (5): 1022-1030. doi: 10.1093/beheco/aru029
Slabbekoorn, Hans., Bouton N., Opzeeland I., Coers , A., Carel C., Popper A. N. A noisy spring: the impact of globally rising underwater sound levels on fish DOI: http://dx.doi.org/10.1016/j.tree.2010.04.05
University of Maryland, College Park. "Loud Noise Can Injure Fish Hearing." ScienceDaily. ScienceDaily, 10 February 2003.
Wysocki, L. E., & Ladich, F. (2005). Hearing in Fishes under Noise Conditions. JARO: Journal of the Association for Research in Otolaryngology, 6(1), 28–36. http://doi.org/10.1007/s10162-004-4043-4