Intense Ocean Noise: Effects on Fish
Fish use sounds to find food, avoid predators, and choose mates. Since hearing is essential for their survival it is important to understand how they are affected by underwater noise.
General Effects of Underwater Noise on Fish
No studies have addressed the long term effects of LFAS and other noise sources on fish, fish prey, life cycles, reproduction or essential habitats.
In an Office of Naval Research workshop on the effects of human-produced noise in the marine environment Cudahy et al. asked the pertinent question: "is chronic exposure to anthropogenic sound from any source or combination of sources, causing psychological or physiological stress that is reducing the average longevity or number of offspring produced by individual animals and thus causing a decrease in the productivity or size of the affected stock (e.g. by suppressing the immune systems…)?" These long term effects are unknown (Workshop on the Effects of Anthropogenic Noise in the Marine Environment, 1998).
Studies show harmful effects of even moderate noise on hearing in fish. (Myrberg, 1980)
As background noise increases, fish hearing decreases. (Myrberg, 1980)
Intense noise levels (180 dB) destroy the hair cells of the auditory maculae resulting in hearing loss. (Enger, 1981)
A broad band, 140 dB sound applied to fish tanks for 20 minutes a day influenced fat stores, growth and reproductive indices. (Meier and Horseman, 1977)
When marine fish were exposed to sound pressure levels 40-50 dB above that in their normal environment (at 40-1000 Hz) severe problems occurred; the viability of fish eggs was reduced and growth rates for fry were significantly reduced. (Banner and Hyatt, 1973)
Shrimp reared under sound levels 20-30 dB above ambient noise showed significantly reduced growth and reproductive rates, decreased food uptake and increased mortality. (Lagardere, 1982)
The above studies strongly suggest that increased noise levels may seriously impact production levels sought by aquaculture ventures. (Myrberg, 1990)
Specific Points on LFAS and Fish
In their Environmental Impact Statement (EIS) on LFAS the Navy concludes that LFAS is safe for fish up to exposure levels of 180 dB.
"Little or no data are available for fish exposed to sound between 149 and 180 dB. Thus more studies are needed to establish ‘safe’ levels of underwater sound at frequencies in the audible range of bony fishes. Given the existence of about 20,000 different species of bony fish, each with a unique inner ear, the problem is enormous." (Hastings, 1995)
In the EIS the Navy agrees with the above and states that "existing research on hearing responses in fish is limited to only a few species and there are almost no data that are useful in determining which sound pressure levels cause temporary or permanent injury." (EIS Executive Summary. p23)
Observations of fish being disoriented and fatigued when ensonified by dolphins indicates that sound pressure levels below 180 dB may cause damage. (Norris and Mohl, 1983)
Noise levels eliciting withdrawal and causing hearing problems in fish are similar to those causing avoidance in whales (about 115-120 dB). (Myrberg, 1990)
The EIS has only a one paragraph discussion of adverse nonauditory physiological impacts of LFAS on fish. The EIS states the larger pelagic fish (such as tuna) have swim bladders large enough to be resonated and damaged by LFAS, but they dismiss this concern by stating that their prime habitat is near the surface where sound transmission losses occur. Bluefin tuna do spend significant time at about 120 ft but tagging shows they routinely dive deeper than ˝ mile for more than an hour at a time.
Lutz (1995) cites evidence that fish can experience lethal gas bubble trauma (the "bends") making acoustically activated bubble growth a potential nonauditory impact from LFAS, not addressed in the EIS.
The National Research Council, in its recent report on low frequency sound and marine mammals, expressed concern about the potential effects of low frequency sound on marine life including zooplankton, fish and turtles. They noted that if the food chain is affected, all marine life will be adversely impacted.
The lack of empirical data on "which sound pressure levels cause temporary or permanent injury" in fish (EIS Executive Summary, p23) suggests that the Precautionary Principle be applied to decisions about acoustic activities to be conducted by the military and other institutions.
Prepared by Marsha L. Green, PhD – Ocean Mammal Institute
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