Effects of Low and Mid-Frequency Active Sonar on Fishes
We conducted studies to test the effects of high intensity naval sonars on fishes. These studies, which tested the effects of actual Low-Frequency or Mid-Frequency active sonar elements, examined the changes in hearing capabilities, structure of the ear, and the effects on many other organ systems including the swim bladder and brain. (The header to the page shows the spectrum of the low frequency signal over time.)
The results of the study have now been published in four papers.
Popper, A. N., Halvorsen, M. B., Kane, E., Miller, D. D., Smith, M. E., Stein, P., and Wysocki, L. E. (2007). The effects of high-intensity, low-frequency active sonar on rainbow trout. J. Acoust. Soc. Am., 122:623-635.
Kane, A. S., Song., J., Halvorsen, M. B., Miller, D. L., Salierno, J. D., Wysocki, L. E., Zeddies, D., Popper, A. N. (2010). Exposure of fish to high intensity sonar does not induce acute pathology. J. Fish Biol., 76:1825-1840.Link
Halvorsen, M. B., Zeddies, D. G., Ellison, W. T., Chicoine, D. R., and Popper, A. N. (2012). Effects of mid-frequency active sonar on fish hearing. J. Acoust. Soc. Am., 131:599-607. Link
Halvorsen, M. B., Zeddies, D. G., Chicoine, D., and Popper, A. N. (2013). Effects of low frequency naval sonar exposure on three species of fish. JASA Express Letters, 134(2), EL206-210. Link
The studies were done on a U.S. Navy barge in Seneca Lake in upstate New York. The barge, which is part of a U.S. Navy test facility enabled us to test the effects of actual mid and low frequency active sonar sources on fish in very deep water.
Barge on which study was conducted.
Fish were placed into a tank and lowered from the barge. At the same time, the sound source was also lowered. TV cameras (on the white arms) were used to monitor the fish and several hydrophones were in the test tank. Once the camber was lowered to depth, the surrounding plexiglas shell was lowered further, leaving the fish in a net pen. After exposure, the shell was raised to support the net and then the whole unit was returned to the barge.
Scanning electron microscopic studies of inner ear sensory tissue (as this from a catfish) showed no damage to hair cels in saccule (top row), lagena (middle row), or utricle (bottom row).
The studies demonstrated that the high intensity sounds from both low frequency active sonar (around 300-500 Hz) and mid-frequency sonar (in our case 2,500 to about 4,000 Hz) did not result in mortality or damage to either the sensory cells of the ear or to non-auditory tissues (e.g., Kane et al., 2010). Low frequency sonar resulted in some hearing loss by both channel catfish and rainbow trout, but less in several additional species (data being prepared for publication now). However, and most interestingly, not all rainbow trout showed a hearing loss. The results suggest strongly that some aspects of genetic background or development may have an impact on the susceptibility of fish to effects of high intensity sounds. All catfish, and most rainbow trout, recovered from hearing loss.
Detailed histopathology, as shown here, showed no damage to any internal tissues in any species tested.
The mid-frequency active sonar studies showed some temporary hearing loss in channel catfish at around 2,500 Hz, but not at other frequencies. There was no hearing loss in rainbow trout, which is not surprising considering that this species does not hear sounds above perhaps 1,000 Hz.
The sound levels used in these experiments approached those that fish would encounter close to an active LFA or MF source. However, the exposure during experiments were far more substantial than any a fish would encounter in that we exposed fish to multiple replicates of very intense sounds, whereas any fishes in the wild would encounter sounds from a moving source, and successive emissions from the source would decrease intensity as the ship moved away from exposed fish.