Effects of Intense Sounds on the Ear of Fishes
Over the past several years there has been considerable interest
generated in the impact of human-generated (anthropogenic) sounds
on the ears of animals. It is widely known that intense sounds and
certain drugs will damage the sensory cells of the ears of mammalian
species, and the concern is that similar sounds will impair hearing
in wild animals. Related to this is the increase in the presence
of anthropogenic sounds in the environment. This has been of particular
interest for its impact on marine mammals, where the concern is
that human-generated sounds from a variety of underwater activities
may impair the survival of a number of species (see NRC 2000).
While the major interest in the impact of anthropogenic sounds
in the marine environment concerns mammals, it is now appreciated
that these sounds may also impact the lives of fishes and other
organisms as well as marine mammals. However, the extent of data
on the effects of intense sounds on fishes is only poorly known.
At the same time, several results from the Popper lab are germane
to the topic.
One of the very few direct studies on the impact of intense sounds
on the ear of fishes was done in collaboration between the Popper
lab and the lab of Dr. Mardi Hastings at the Ohio State University.
In this study (Hastings,
M.C., Popper, A.N., Finneran, J.J., and Lanford, P.J. (1996). Effect
of low frequency underwater sound on hair cells of the inner ear and
lateral line of the teleost fish Astronotus ocellatus. J.
Acoust. Soc. Am. 99:1759-1766.) we investigated the effect
of high intensity on the ears of the oscar, Astronotus oscellatus.
We found that sounds that were lower than 180 dB (re 1 µPa)
and sounds that were not on continuously had no apparent impact
on the sensory cells of the ear. However, when we subjected fish
to 180 dB signals 300-Hz pure tones for four continuous hours, and
then examined the ears after four days, there was some damage to
the sensory cells of the lagena. This is shown in the figure to
the right. In this scanning electron micrograph from the lagena,
the top figure shows a low power view of the whole macula. The area
within the square is shown in the lower SEM. The lower picture shows
that there has been some loss of ciliary bundles resulting from
the high acoustic stimulation.
While damage was found in a number of specimens, it did not show
up unless the animals were allowed to live for several days, suggesting
that damage takes a while to be visible. While these data are highly
suggestive that damage may result from long-term intense sounds,
there are several caveats on these data. First, it is not known
if data from this freshwater fish can be extrapolated to other species.
Second, how significant is this damage in terms of sound detection,
and would damage of this low magnitude impact the survival of a
fish? Third, it is important to note that the fish in this study
were kept close to the sound source, and it is unlikely that fish
in the wild would be exposed to four-hours of continuous sound and
stay in the vicinity of the sound for the full time. Another significant
question is whether the hair cells that are damaged would regenerate.
As we have shown in other studies, sensory cells in the ears of
fish do regenerate after treatment with ototoxic drugs, and this
might mean that the hair cells in fishes would also regenerate after
damage by intense sounds. Thus, while there may be some damage shortly
after sound stimulation, will this have a long-term impact on fish?
Of course, during the time that damage is present, and before any
regeneration, fishes may be at a disadvantage in terms of detecting
predators and prey, and so their survival may be impacted.