|
By Dr. A. J. Godknecht / Shark Info
The U.S. Marines and recently NATO have been testing a sonar system
which can detect submarines over long distances and which in the future
is expected to cover 75% of our oceans. The technology which makes this
possible is low frequency active sonar (LFAS) which works at an output
sound level of more than 215 decibels. A sound pressure level of 140
decibels, for example from a gunshot, can still be measured at a
distance of 380 km away. Such acoustic detonations, even if only brief,
are dangerous for living organisms and pose a threat not only to whales
and dolphins but also to sharks and bony fish.
|
The sonar system consists of the receiver
SURTASS (Surveillance Towed Array Sensor System), and the active LFAS
(Low Frequency Active Sonar) transmitter.
© Shark Info
|
|
Visibility in the oceans is usually limited. Sound, on the other hand,
moves through water about four times faster than through air, and lower
frequencies can travel longer distances than high ones. Biologists thus
agree that hearing is the most important locating sense over medium and
long distances for organisms living in the water. Hearing enables them
to locate prey or potential enemies, and also serves communication and
the identification of members of the same species. It is thus vital for
survival, especially for sharks, bony fish and sea mammals such as
whales and dolphins.
Sharks have excellent hearing (see box „The hearing of sharks”) which
functions optimally in the low frequency range around 100 hertz (Hz)
where, for example, oscillations are generated by injured fish.
The quieter a room, the more clearly and distinctly can sound waves
reach a listener. Or expressed in another way, can you imagine listening
to a piano concert from Chopin at a construction site?
What is valid on shore is just as valid for the oceans. Unfortunately
our once silent oceans are becoming louder from year to year, with the
natural background sounds of waves, wind, sand and rain becoming
secondary against the increasing noise pollution created by engines from
giant tankers, ferries, fishing boats and other watercraft. Almost all
such ships also generate permanent acoustic impulses (sonar) for depth
measurement. Additional noise emissions caused by man include blastings
for oil or drilling for natural gas, underwater work on oil platforms
and pipelines, construction work in ports and coastal regions, to
mention only a few. Added to this constant rise in environmental noise
pollution is LFA sonar with its explosive sound pulses which spread
across thousands of square kilometers.
|
The hearing of sharks
Sharks have no visible ears, yet their sense of hearing is vital for
hunting. Their inner ear is especially well developed and, as with man,
fulfills the two functions of maintaining equilibrium and hearing.
A shark’s two hearing organs are located directly over and behind the
eyes, embedded in the skull cartilage. Each is connected externally only
by an endolymphatic duct which ends in a tiny pore on top of the head.
Tests have shown that sharks not only perceive but also pinpoint noise
sources sent out by waves in the 100 Hz range at a distance of 250
meters away.
Each of the two hearing organs has three curved ducts which are
positioned at 90 degree angles to each other, and are thus capable of
registering three-dimensional information on equilibrium and location.
The actual sound receptors are found in a sack-like section which is
connected to the curved ducts.
|
For organisms living in the ocean which have adapted themselves to their
environment over millions of years, this massive increase in background
noise represents a severe impairment of their locating sense.
The LFA sonar system has two components: the SURTASS (Surveillance
Towed Array Sensor System) receiver and the active LFA transmitter. As
the name suggests, it transmits low frequency sound waves in the 100 to
500 Hz frequency range and, according to the Navy, at an actual output
of 215 decibels (dB). However, theoretically more than 235 dB are
reached, frequencies which lie exactly in the range where a) sound
distributes the farthest distance, b) sharks hear the best and thus c)
can cause the greatest damage to sharks’ hearing organs.
A decibel, by the way, is a logarithmic scale. In other words, 100 dB
are ten times louder than 90 dB, and 110 dB are 100 times louder than 90
dB.
LFA sonar emits so-called „pings“. When sound waves reach an object in
the water they are reflected and received by SURTASS. According to the
Navy, one such ping lasts about one minute. The Navy is planning to use
two ships, one in the Atlantic and one in the Pacific, each of which
will be under way 270 days per year and will emit high-energized pings
for about 20% of the time. Per ship this means that the oceans and its
marine life will be subjected to these sound waves 57 days per year and
this over an area covering 36 million square kilometers.
The U.S. Navy revealed that they have already invested millions of U.S.
dollars in environmental compatibility tests, based on which they claim,
for example, that LFAS pings amounting to 180 decibels do not disturb
whales. By comparison, one hundred and eighty decibels (180 dBs) are ten
times louder than a rocket launch (170 dB) and 100 times louder than a
gunshot (160 dB). However, other independent research shows that 120 dB
suffices to influence the behavior of whales.
Ships equipped with their own LFA sonar use a high frequency sonar
system designated HF/M3. This system was developed especially to locate
whales swimming in the vicinity of the LFA sonar ships to enable
immediate stoppage of LFAS use should they come too close. However, this
HF/M3 system was only developed to function in line with the Navy’s
self-defined 180 dB limit.
Unfortunately, the U.S. Navy neglected to include other marine life in
their investigations, considering that sharks and bony fish are just as
affected by LFAS as whales.
On October 31, 2002, the Natural Resources Defense Council (NRDC) in San
Francisco reported that a preliminary court injunction temporarily
prevented the U.S. Navy from using SURTASS LFA sonar. Judge LaPorte came
to the conclusion that the American National Marine Fisheries Service
(NMFS) gave the U.S. Navy a permit which contradicts various federal
laws, including the Marine Mammal Protection Act (MMPA) and the
Endangered Species Act (ESA).
In addition, based on the motto „if they have it, we want it too“, NATO
and the English Royal Navy are also testing the usage of high-powered
sonar systems. In this connection, the death of 15 Cuvier beaked whales
(Ziphius cavirostris) was, for example, linked to NATO tests organized
by the Spanish marines under the name “Neo Tapon 2002”. Meanwhile,
representatives of the English fishing industry have blamed the
reduction of certain fish populations on LFAS tests performed by the
Royal Navy.
No investigations have been made so far on the cumulative effect of LFAS
system usage by the U.S. Navy and NATO. Should NATO and the U.S. Navy
implement such systems, it will probably not be long before Russia,
China and other countries would want to follow suit.
A sound level of 120 dB suffices to clearly influence the behavior of
various whale species, driving away bowhead whales (Balaena mysticetus)
and gray whales (Eschrichtius robustus).
Humpback whales (Megaptera
novaeangliae) stop singing at 155 dB, and a sound level of 140 dB has
been found to disturb communication between large whales, directly
influencing their reproductive and migratory behavior.
At the end of September 2002, 15 beaked whales, nine of which were dead,
stranded on the Canary Islands. Examination of the dead animals revealed
that they had suffered from severe cerebral hemorrhaging caused by high
sound pressures such as those resulting from military LFAS application.
These strandings occurred at the same time as NATO tests were being
performed in the region using LFA sonar ships (Neo Tapon 2002).
Sonar-induced whale strandings have also been noticed in the
Mediterranean.
|
|
|
Schallpegel
|
| 170 dB | rocket launch |
| 160 dB | automatic rifle |
| 150 dB | takeoff of a jet aircraft |
| 130 dB | pain threshold (man) |
| 100 dB | chain saw |
| 90 dB | discotheque |
| 70 dB | road traffic |
| 50 dB | office |
| 20 dB | bedroom |
| 10 dB | radio studio |
| 0 dB | lower threshold of hearing (man) |
The Swiss Federal Office for Public Health
prohibits any events which produce a noise level over 125 dB and prescribes the distribution of
earplugs to protect hearing. |
Studies on LFAS only included its effects on whales, ignoring sharks or
other ocean inhabitants. Yet scientific investigations on the effects of
high sound levels on bony fish and sharks allow the conclusion that LFAS
also seriously disturbs or even injures these animals. The subjection of
various fish to sound levels of 140 to 150 dB over several hours have
led to a loss of their hearing over many weeks.
Investigations with silky sharks (Carcharhinus falciformis), lemon
sharks (Negaprion brevirostris) and oceanic whitetip sharks (C.
longimanus) show that these shark species are scared off by a suddenly
occurring sound which was only 40 dB higher than background noises.
In reply to our inquiry about LFAS, Professor Arthur Myrberg from the
University of Miami – an accepted specialist on acoustics with fish and
sharks – said: “Noise intensities 30 to 100 times higher than those
which only scare off animals will most likely cause injuries (Editor’s
note: to the sharks).” According to Dr. Myrberg, the critical value for
sharks is around 180 dB. In this range we can assume that long-term
injuries, especially to the inner ear, will result. This underlines the
importance of scientifically examining the influence of such noise
levels on sharks and fish.
Professor Samuel Gruber, a renowned international shark specialist, also
confirmed the danger of permanent injuries to sharks’ hearing organs
when these animals are confronted with sound levels to the extent as
those generated by LFAS.
The Swiss Marine Mammal Protection (ASMS) has worked out a petition
which calls for NATO to have a global environmental assessment made on
the effects of LFA and other high-powered sonar systems on life in the
oceans, including the possible cumulative and synergetic effects
resulting from the application of such technology by several nations.
Shark Info and the Shark Foundation join forces with the “European
Coalition for Silent Oceans” with our own petition whose wording has
been extended to also include sharks and bony fish which in the end will
also help the sharks. This petition is attached and is also available on
the www.sharkinfo.ch and
www.shark.ch websites in PDF format for
downloading purposes (German only).
We kindly ask you to collect as many signatures as possible and return
the signed petition to Shark Info or the Shark Foundation (Blütenstrasse
4, CH-8057 Zurich, Switzerland) at the latest by the end of May 2003.
For bibliographic references and additional information please feel free
to contact the Shark Info office.
*
Dr. Alexander J. Godknecht is a biologist and President of the Shark
Foundation and a member of the Shark Info editorial staff. He works with
the information technology services at Zurich University.
May be published only by indicating the source: Shark Info / Dr. A. J. Godknecht / Shark Info
|
top |
|
last change: 06-04-2016 11:48
|
|
|
|
|
