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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