Sonar causes (temporary) deafness in dolphins
One unlucky bottlenose
Exposure to military sonar may cause temporary hearing loss in bottlenose dolphins, scientists at the Hawaii Institute of Marine Biology have found.
Tests on a captive dolphin indicate exposure to sonar at high, prolonged levels can cause temporary deafness for as long as 20 to 40 minutes — but only if the dolphin stays close to the source of the sonar for several minutes.
In the past decade, numerous beachings of whales, dolphins, and porpoises have been blamed on navies pinging sound pulses into the oceans and listening for the echoes to detect enemy submarines and mines. In particular, mid-frequency active sonar has been fingered as injuring marine mammals and causing some to run aground.
A paper published in the Brit journal Biology Letters today, scientists have reported the first controlled study on the effects of sonar in dolphins.
One very lucky dolphin in an open-water pen was fitted with suction cup sensors to monitor its brainwaves as it was made to listen to recordings of real naval mid-frequency sonar played progressively louder.
When the pings reached 214 decibels underwater* and were repeated, the data showed the dolphin had become temporarily deaf. Other sensors showed the dolphin's breathing rose significantly when the sonar was switched on.
Hearing was typically restored after 20 minutes, but sometimes took as long as 40 minutes. Aran Mooney of the University of Hawaii said the deafening results are akin to a "rock-concert effect" for the mammal because the real-world equivalent of the results would require a dolphin to be just 40 meters from the source of the sonar and remain there for about 2.5 minutes. That's an unlikely scenario for a wild animal, the paper reports, unless there's some unusual conditions involved. For example, sound traps like underwater caverns on the sea bed or a layer of warm water at the oceans surface could cause sonar to bounce around a smaller area.
This could explain why dolphin beachings are relatively rare compared to how often mid-frequency sonar is used in military exercises.
The paper notes additional studies are needed to see how the sonar affects wild animals that aren't used to noise experiments. ®
*203dB above the water would instantly ruin your hearing at best. Under water, it's roughly the equivalent of 170dB in the air (like a gunshot 1 meter away — but that's still loud as hell).
"...scientists have reported the first controlled study on the effects of sonar in dolphins." ??? Hardly
"Temporary auditory threshold shift" or temporary hearing loss as a function of loud sonar sounds has been studied in dolphins and related species for over 15 years by the Navy and in other laboratories. This appears to be the first study wherein the measurements of that temporary loss was inferred by measurements of neural activity rather than by behavioral indicators that were used in the other studies. However, it's finding, regarding underwater sound level and duration of loss, are in line with those previous studies - but not original in that regard.
Further, the author's conversion of 203 dB in water to 170 dB in air is also in error and highly misleading. The conversion must take into account both the difference in reference level (20 microPascal for air v. 1 Micropascal for water) as well as differences in the acoustic impedance (rho x c) between air and water. The two together produce a difference of about 62.5 dB and not the 33 dB difference stated by the author. Previous research showed that, with that equivalence, susceptibility to temporary hearing loss and its duration, as a function of received energy, were in line with those observed in typical terrestrial mammals.
Where is the feckkin' "NO SHIT?" button?
Ok.... A little more.
Two things you say are things that realy get to me.
1) Companys and people saying how "green" they are, yet happily eating cod, not because of cost, but because they think its fine.
2) Passing on the costs and damage, not to great great grand children, but to there children. So many of the people you see campaining about green issues are people with time and money, who made this in the 70s and 80s. They expect there children to pay the costs, the ones with little time and money. The one example that most anoyes me is recycling. It is all build on the assumption that you have room for three bins, both in your garden and your kitchin, and that noone lives in a flat, yet we are forced to live in a small flat BECAUSE the same people who bang on about this are the ones with nice country homes who don't want any building near them, so we are stuck in a flat that costs more than my parants genaration paid for there house (alowing for inflation of course)