Exploring the Hearing of Freshwater Fish
Water is a carrier for many forms of sound. Some sounds vary in frequency; others have a range of volume measured in decibels (intensity and power). When one travels one cannot help but ask the question, “What impact does the boating equipment I own make?”
Dr. Arthur Popper, who is the Professor of Biology at the University of Maryland, forwarded some articles to me to learn more about acoustics in water. These articles were studies on mid-frequency sonar, pile driving, and air guns, focusing on the impacts of sound on salmon, striped bass, rainbow trout, and catfish. Dr. Popper explained that the impacts of sound levels on fish range from mortality, injury to tissues, disruption of physiological state, damage to the auditory system, masking other sounds, and behavioral changes. Other factors, such as water temperature when the season cools off, may influence the natural threshold of hearing, in particular with catfish. The minimal sound exposure to cause disruption to the physiological state of a salmon was 204 dB.
A study on fathead minnows stated the sound pressure level of a boat motor could be 142 dB. As well, small boats with large outboard motors have been reported to produce sound pressure levels of 175 dB. The sounds from boat motors are low frequency and are easy for fish to hear. A small vessel with a 4 blade prop runs 10-11 Hz. Also, sounds formed in the vacuums from spinning props range from 0.1 to 1.0 KHz. These boat motor sound tests were completed after 2 hours of sound exposure in a lab. Yet the conclusions of the fathead minnow study were made without the wide range of sounds found in the wild. Therefore any evidence of harm gathered in data about sounds is inconclusive. At worst, a more sharp sound from an explosive stick of dynamite (which fishermen used to do) might result in a temporary threshold of hearing shift (TTS), and rarely worse, fish mortality. Permanent damage from sound exposure will vary by fish species. This is unlikely for salmon since they heal those cells within a short period of time, possibly within a day, according to one of Dr. Popper’s articles. As for minnows, a span of temporary hearing loss is possible. However again, information was gathered in a lab so how permanent the harm to a minnow’s hearing may be inconclusive.
Dr. Popper stated that a fish finder would be unnoticed due to the high frequency above fish hearing, typically at most 3,000 Hz (my fish finder runs at 200 kHz to 455 kHz). One article Dr. Popper gave me states that there are 32,000 fish species, and only about 100 species have thresholds known to researchers. Some of those species known include tuna, cod, salmon and goldfish. It may be safe to say that the sounds from our boats are not causing any physiological harm. Yet continuously produced sounds may interfere with natural fish behaviors and may mask those sounds important to fish behavior. Another scholarly article I found focused entirely on anthropogenic (human) noise increasing fish mortality by predation. This was due to sounds masking those acoustics cues that signal flight from an approaching fish. The loud masking noise from boat motors is important to consider when baitfish are the focus of game fish anglers pursue. Loud noise may also mask cues for the behaviors of fish related to predators, prey items and finding potential mates.
Much of the research on marine sounds that does exist needs to be expanded upon. Dr. Popper says the concern is in sound pressure levels when it comes to boat motors. Some answers out there may still be in the realm of speculation, even misinformed, and need more research to establish correctness. There is more to learn about sound at Discovery of Sound in the Sea.
(See this link at DOSITS in regards to fish hearing)
B. Halvorsena and David G. Zeddiesb, William T. Ellison, David R. Chicoine, and Arthur N. Popper. 2011. Effects of mid-frequency active sonar on hearing in fish. Accepted October Michele Obtained by request from ResearchGate Online.
Stephen D. Simpson, et al. Published February 2016. Anthropogenic Noise Increases Fish Mortality by Predation.
John Neporadny Jr. July 2013. Which Sounds Spook Fish?
Anthony D. Hawkins and Arthur N. Popper. 2016. Developing Sound Exposure Criteria for Fishes, Chapter 51. (currently incomplete). Obtained by request.
Arthur N. Popper, et al. 2014. Does Man-Made Sound Harm Fishes? Journal of Ocean Technology.
Obtained by request.
Amy R. Scholik and Han Y.Yan. 2002. The Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas. Environmental Biology of Fishes.