Marine acoustic testing as a deterrent
to marine wildlife has been studied for decades. Since the late 1970’s researches
have been conducting sound tests underwater and recorded specific species
responses to sounds. In 1974 and 1975 studies were conducted to test the
effectiveness of sound to deter seals from salmon netting station in River
Tweed, Scotland. A wide variety of sounds were used, including the calls of
killer whales, with the frequencies of the entire hearing range utilized with
no sound consistently scaring seals from the nets(1). In 1978,
scientists from the University of Miami studied silky sharks (Carcharhinus
falciformis) in the Straits of Florida and the Tongue of the Ocean (TOTO),
Bahamas demonstrating a rapid withdrawal from sound when it was abruptly
increased or changed and especially if it was from the screams of an Orca whale(2). A year later,
in 1979, similar tests were applied on lemon sharks (Negaprion brevirostris) with
similar results, indicating that withdrawal from sound is not species specific
(3). Two caveats must
be noted here about the experiments. One: they noted that responses to sound
diminished when chum was present in the water (sharks) and two: all species rapidly habituated to such signals.
There are several ideas at play here
that have led scientists to research acoustic testing as a deterrent. First is the knowledge that sounds travels
faster, farther and is louder in water than in air. Sound travels approximately
1560 m/s in salt water vs dry air 343 m/s, but that all depends on pressure
(depth), temperature, and salinity of the water (4).
Because of the depth, temperature and salinity differences in the
ocean, sounds in the ocean are reverberated and propagated in surface layers of
the ocean allowing sound to travel hundreds of miles from the source. Also, lower
frequency sound dissipates slower than higher frequencies allowing us to hear
some sounds from across the ocean (5).
How loud a sound is determined by the medium with which it is
traveling through, when sound travels through water, which is much denser than
air, it not only can be heard, but felt as a vibration (6). The second
idea at play is bio-mimicry, which is the biological resemblance of an organism
for the purposes of gaining benefits of mistaken identity and/or to appear
unpalatable or harmful (hence the use of killer whale calls). Mimicry is seen
across the animal kingdom for these purposes and modern day bio-mimicry is the scientific
study of biological systems to find solutions to complex human problems (7). The third idea is the need to deter species of
marine wildlife from becoming by-catch, from interfering with our modern
technology (estuarine
power stations), and from interfering with commercial fishing operations.
Acoustic
deterrent studies seemed to take a hiatus during the 1980’s only to resurface
in the 1990’s. In 1993, acoustic fish deterrents were tested in the laboratory
with positive results (10). Concern over reducing
fish species of commercial value by water intakes of nuclear, fossil-fuelled
and tidal electric generating stations was the impetus of the study. Despite this, the majority of published papers
in the area of acoustic deterrents focused on deterring marine mammals from
fishing gear. Several patents appeared
during this period for the use of separating dolphins from tuna by using the
sound of killer whales, ‘digitized, edited and enhanced to produce digitally
synthesized killer whale sounds’(8), though it
seems that those devices are still patent pending and not on market. However,
the concern for cetacean’s incidental mortality in commercial fisheries became
an international matter, as it is still today. Acoustic alarm devices showed
promise as an effective by-catch mitigation method in a study published in 1997
that helped bottlenose dolphins detect gillnet-like structures (9). The idea here
was based on noise makers developed to curtail humpback whale collisions with
static nets and traps. The acoustic alarm devices, later called ‘pingers’, not
only showed lower rates of bottlenose, but reduced number of all by-catch
species in gillnets attached with them in studies conducted off the coast of
California, USA. ‘The pinger experiment
ended when regulations were enacted to make pingers mandatory in this fishery’(11).
In 2003, 2004, and 2005 data was collected off the coast of North Carolina, USA
on whether or not acoustic devices on gillnets deterred fish as well as
cetaceans, which they found they did not, demonstrating a positive correlation
of use for cetacean mitigation for the gillnet fishery (12).
Unfortunately, the device utilized in these experiments (SaveWave) was not
hardy enough to be used regularly within the fishery.
Cetaceans are not the only predator or
species of concern with regard to commercial fishing activity. In Scotland’s Atlantic salmon rivers
competition between salmon rod fisheries and seals occur, often with negative
impacts on the protected populations of seals which are managed by shooting the
seals who make it upstream to feast on the salmon. A means of non-lethal
mitigation technique is then highly sought after. Trails of an acoustic
deterrent device (ADD) were tested between January and May 2006 and between
October 2007 and February 2008 on two separate rivers in northeast Scotland. While there was not significant decrease of
overall abundance of seals in study area, a 50% reduction in seals movement
upstream in both rivers were noted (13). This shows to
be a potential tool for non-lethal mitigation of seals in estuaries and rivers
of the Atlantic salmon Rivers.
Sea turtles are another species of
concern with regard to commercial fishing. The longline fisheries often have
interactions with protected and endangered sea turtles becoming by-catch. In an
attempt to reduce these interactions one approach was to develop gear that ‘is
less attractive, not-detectable, or even repellent to sea turtles’(14). Some
initial studies using seismic airguns underwater (250 -1000Hrz range) to deter
loggerhead sea turtles from intake canals of nuclear power plants in Florida
showed that turtles kept a 30m perimeter from the sound source. The feasibility
of using such a device for longlines was dismissed since it would most likely
scare the target species (the fish) away as well (14).
Recently research into acoustic
deterrents for sharks has come back around as a popular field of study. In an
attempt to deter feeding of target fish species from commercial fishing lines
and to reduce sharks as by-catch several varieties of shark repellents were
tested; chemical, electric, as well as sound. Sharks have the same five senses
we do, but also an extra sixth sense we don’t possess. All elasmobranchs have
what’s called the Ampullae of
Lorenzini,
which is a network of fluid filled pores on the nose and head of sharks and
rays that detect electromagnetic pulses, like your heart beat. This last sense
has spurred shark deterrent research to the area of electric and magnetic
devices. Chemical repellants are based on the sharks’ sense of smell, while
sound is of course based on sharks’ sense of hearing.
Acoustic studies on sharks during the
early 1970’s support the theory that sharks ‘are low frequency specialist’ (15) , meaning their
hearing range lies within the lower frequencies of sound. In fact, free ranging
silky sharks (Carcharinus falciformis)
and oceanic white-tip sharks (Carcharinus
longimanis) were drawn to low frequency sound (25-1000Hz), with heightened
interest in lower frequencies (16). The most
attractive of frequency pulses were the irregular ones, which mimic the sounds
caused by struggling prey (17). The most
immediate and rapid withdrawal from both species was observed from abrupt
transmission of high intensity sound at close range (17) (14).
Chemical shark deterrents were studies by the U.S. Navy during World War II and then later
again in the early 1970’s. A discovery of pardaxin, secreted by the Red Sea
Moses sole (Pardachirus marmoratus),
an alkyl sulfate that is hydrophobic in nature was an effective chemical shark
repellent, but ‘is only practical as a directional repellent such as in a
squirt application’ (18).
This did not meet the Navy’s requirement of
a ‘non-directional surround-cloud type repellent’, or buffer for short.
In
2008, laboratory research studied the effect of rare earth metals and magnets
on spiny dogfish (Squalus acanthius)
and Pacific halibut (Hippoglossus
stenolepis). The impetus here was to decrease the elasmobranch by-catch in
the north pacific halibut fishery. Using cerium mischmetal and magnets,
scientists observed the reactions of both species. Dogfish appeared to be
disturbed by both the mischmetal and magnets, but the magnets afforded no
protection for baited lines in the experiments. Halibut were unresponsive to
both the mischmetal and magnets. This suggests mishmetal could be utilized in
reducing the amount of spiny dogfish as by-catch in the pacific halibut fishery
by attaching it to fishing gear. A concern on cerium mishmetal is that it
undergoes accelerated hydrolysis in seawater (19).
In
2009 it was reported that electropositive metals placed within ~10cm of hooks
on longline fishing gear reduced the catch of sandbar sharks (Carcharuhinus plumbeus) by around two
thirds. This research is based on sharks sixth sense, the ampullae of
lorenzini, with the idea that the electropositive metals disturbs sharks enough
to deter them from being caught as by-catch in commercial fishing operations (20). The use
of electropositive metals is then seen as a positive shark deterrent for
longline fisheries.
The
need to deter non-target species from harm in our fisheries is a highly sought
after endeavor. With declining populations of sea turtles, pinnipeds,
cetaceans, and sharks worldwide the need to protect these vulnerable species is
beneficial to a rich biodiverse and healthy ecosystem with which we depend.
Sharks, in particular, are in need of our attention. Pelagic longline fisheries
often catch more sharks than their target species of tuna and swordfish, with
the global by-catch in all commercial fisheries estimated to be 260,000 –
300,000 metric tons annually (11.6 – 12.7 million individual sharks) (20).
With the negative media attention sharks receive, these numbers often go unnoticed,
while their image is constantly tarnished by the few human deaths that occur
globally each year (569 fatalities reported since 1580) (21). This makes protecting them against reactionary responses
to human shark incidents difficult. As seen recently in Western Australia,
where the majority of shark fatalities have occurred, the government instituted
a three month long shark culling program directed at decreasing shark numbers
in the off chance that might decrease human fatalities from sharks (22).
In
defense of Western Australia’s government, they have also instituted a full
range of research programs, most non-lethal, aimed at deterring sharks from
popular beaches, one such tactic returns to the use of sound to deter them (23). In January trails began by broadcasting
replicated sounds of killer whales underwater after attracting tiger sharks (Galeocerdo cuvier) and great white
sharks (Carcharodon carcharias) to
the area. If successful, new technology will be developed as a shark deterrent
off Perth beaches. In recent news, a
Maui based technology company, No Bite Technologies, has developed a personal
sonic camouflage apparatus based on the same idea. To learn more about this
device, sharks and sharks natural predator, the killer whale, visit their
kickstarter campaign at ORCAv1.
“It’s
not about removing sharks. It’s about coexisting with sharks.” – NoBiteTechnologies.
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