Sharks and Sound at Port St Johns Second Beach

Sharks and Sound at Port St Johns Second Beach

Sharks and Sound at Port St Johns Second Beach: Second beach in Port St. John’s on the East Coast of South Africa has gained a reputation as being one of the world’s most notorious for shark attacks. Most of which are caused by bull sharks. In the last 14 years alone, these sea predators have claimed the lives of eight people.
Wikipedia records a total of 109 people having been killed by sharks in South African waters since records started being kept in 1852 ending at the beginning of 2018, a period of 165 years, or an average of 1.51 people having been killed annually.

I am not writing this article in an attempt to provide a reason as to why all these attacks and resultant deaths occurred in different times and places around the country. But rather to provide a possible answer to the sudden spike of shark-related deaths at Second Beach a few years back. A beautiful beach just south of the town of Port St Johns on the Wild Coast of South Africa.

The first recorded shark attacks and death that occurred in the Umzimvubu river near Port St Johns and Second Beach were those of Zangile a young local man in 1887, followed in 1895 by a man named Sombutize.

There is a gap of almost 110 years between the time when Sombutize was taken in 1895 and Sibulele Masiza being attacked and killed in Jan. 2007, and this is seriously puzzling as throughout this period Port St Johns, the only seaside town on the Wild Coast, remained a very popular tourist destination with thousands of people flocking there throughout the year. With Second Beach crowded with bathers and surfers, and during this period there were no shark attacks.

As tragic as this incident was, given the 110-year interval from the last recorded attack, it became accepted as an isolated incident and so beach usage continued as normal, with no further shark-related incidents.

And then 2009 happened, and at the beginning of that year Sikhanyiso Bangiliswe was attacked and killed in January followed by Luyolo Mangaliso in March and Bayuyile Dayimane being killed in March.

A further two years passed with no attacks, and then two occurred in 2011, the first in January with Zama Ndamase being killed in January and Tshintshekile Ndova being killed in December, with Lungisani Msungubani being killed weeks later in January 2012.

Further attacks then occurred annually with Fundile Nodumla becoming the only survivor of a shark attack in March 2013 after having been bitten on both arms

Liya Sibili was killed in December 2013, with Freidrich Burgstaller being killed in March 2014.

This sudden and alarming upsurge in shark attacks played havoc in the tourism industry and also attracted international attention resulting in Second Beach becoming labelled as the most dangerous beach in the world. This is an unfairgiven the location with the most recorded shark attacks is New Smyrna beach, Florida.

Being concerned for the safety of bathers, The Department of Environmental Affairs and Tourism and the OR Tambo District Municipality appointed the Natal Sharks Board team of experts to investigate possible causes of such attacks.

Their report considered factors or events presumed to be conducive to shark attacks and provided a number of recommendations to reduce the chances of them occurring again. Factors highlighted by them as being conducive to shark attacks include the proximity of the beach to the Umzimvubu River, a well-known nursery ground for Zambezi sharks. Newborn and juvenile Zambezi sharks have been captured in the river.

Another factor said to require careful investigation is the possible attraction of sharks through the disposal of blood and entrails from the ritual slaughtering of animals on this beach. Both Zambezi and tiger sharks are notorious scavengers and supposed would be attracted to this beach by the smell of blood and other animal remains. I personally dispute this as no large animals, with the possibility of the occasional sheep or goat, are slaughtered during these, and in any event, all parts of the animal are consumed with the exception of the bones which are burnt.

The possible result of sewerage entering the river or the sea is not likely to be a significant factor.

A shark monitoring program was initiated and is ongoing with radio transponders being implanted in sharks that had been caught and released, their transmissions, in turn, being recorded in monitors placed on the sea and river bed.

Angling records spanning from 1968 till 2007 were made available by Tony Oates, a longtime local angler who specialized in capturing sharks from the Gap, a rocky ledge bordering onto Second Beach. These records attest to the continuous presence of shark in the bay housing Second Beach.

The presence and volume of sharks along this coastline is well recorded and further vouched for by the off-shore scuba divers who flock to the Wild Coast annually to participate in diving during the annual sardine run.
Visual evidence also abounds in the underwater documentaries that have been aired worldwide by producers such as National Geographic, Discovery Chanel, to name but two.

We can therefore take it for granted that the sharks have always been there. And have co-existed alongside the bathers and surfers without attacking them. So what has caused or triggered this change in their behaviour?

The land and sea conditions in and around Port St Johns have not changed to any degree over the years, and neither has an infrastructure or commercial enterprise been created that could cause pollution, so that can be ruled out.
Looking at the dates on which the attacks occurred a pattern emerges, and that is that they all fall into the time of holiday seasons when the beaches are crowded, but then they were crowded like that in the years before, the difference being the volume of motor vehicles that park along the beachfront and shoreline are now more prolific, as is the volume of rhythmic sub-sonic sound generated by numerous taxies and other motor vehicles all playing loud music through their heavily amplified sound system.

I must make it clear that its not the number of vehicles that causes the problem, but rather the sound that is being generated and transmitted.

Sub-sonic sound transmits easily through seemingly solid items such as motor-car tyres and soils and water to make its presence felt in the surrounding ocean, and as water is denser than air, with greater elasticity, sound travels farther underwater than it does on land – in fact it travels about four times faster in water than through air, with sound waves of frequencies below 500 hertz traveling thousands of miles through the ocean without diminishing greatly in energy.

The overall consensus of all the studies is that sharks can detect and react to low frequency hydrodynamic sounds, using these to their advantage.

Googling detection of subsonic sounds by sharks produces numerous results such as the paper written by AA Myrburg, detailing the effects of subsonic sound on sharks, and published by the Rosenstiel School of Marine and Atmospheric Science in 1979.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a078642.pdf

by AA Myrberg Jr · 1979 · Related articles

and more such as

The Acoustic World of Sharks – Pure API – The University of …
api.research-repository.uwa.edu.au › files › THESIS_DO…
PDF. Differences in the reactions of sharks towards sounds are consistent with the differences in inner ear … unlikely these studies represent a comprehensive analysis of sound detection in sharks. … Acoustic Signals in the Near-Subsonic Range.
by L Chapuis · Cited by 4 ·

A more detailed article on the varying behaviour of sharks and their reaction to subsonic sound appeared in Nature the groundbreaking Global Science Research Magazine.

UNDERWATER SOUNDS AND ITS EFFECTS ON SHARKS

https://www.nature.com/articles/s41598-019-43078-w

The article also highlights that the broadcast sound of Orca calls tends to scare certain species of sharks causing them to leave the locality, and in addition lists numerous studies done by various persons in this field.

The following article written by Josh Clark and published in How Stuff Works (and mildly edited for brevity), gives a simple yet excellent overview of the effect of subsonic sounds on sharks as also their reaction to these.

https://animals.howstuffworks.com/fish/sharks/shark-yummy-hum1.htm

A yummy Hum ——- a low-frequency sound that lets sharks know their order’s up — is based on the fact that sharks pick up on plenty of infrasonic noises (ones too low for us to hear) and use them to their advantage. It’s possible because lots of oceanic sounds operate at this level. Dying fish, for example, emit infra-sounds as they flop around in the water, so needless to say it’s a noise to which sharks are reportedly attracted: Once they hear the yummy hum, it’s dinner time. Homing in on this yummy hum helps them to locate an injured fish — guaranteed weak prey.

But don’t get confused. Sharks don’t go crazy for actual humming. They prefer rapid pulsing sounds as opposed to steady continuous hums. Specifically, studies of sharks have shown that they respond most to low-frequency pulsing sounds, including those well below the threshold of human hearing.

The first test to demonstrate this was conducted by shark researchers from the University of Miami in 1963. The researchers found that sharks didn’t respond to low-frequency continuous sounds or any kind of high-frequency sounds [source: Nelson and Gruber]. Later tests determined that sharks hear frequencies ranging between approximately 10 and 800 hertz [source: Shark Trust]. (Humans, by contrast, hear frequencies between about 20 and 20,000 hertz [source: Britannica].)

Sound behaves differently underwater than it does traveling through the air. Water is denser than air, but because of its greater elasticity, sound travels farther underwater than it does on land — and it travels about four times faster in water than through air [source: FAS]. What’s more, sound waves of low frequencies below 500 hertz can travel thousands of miles through the ocean without losing much steam [source: McGraw-Hill].

So sharks have adapted to tuning in on low-frequency pulsing sounds. But how do they hear? Unlike humans, who have a pair of inner, middle and outer ears, sharks have only inner ears. Each ear consists of three D-shaped, fluid-filled canals that allow the shark to orient and balance itself (like your inner ears do), and tiny hair-like structures that sense the vibrations of sound waves [source: ReefQuest].

Sound is simply a wave of energy that causes air particles to vibrate rapidly (at high frequency) or slowly (low frequency). And sharks have developed another means — called the lateral line — to sense low-frequency sound vibrations. Lateral lines are a series of fluid-filled tubes that crisscross the shark’s body just beneath the surface of its skin [source: Shark Trust]. These tubes detect faint changes in pressure, including those made by the vibrations of sound waves.

The lateral lines and inner ears of the shark are used to locate prey, including injured fish as far away as around 800 feet (roughly 250 m) [source: Sea World]. Studies have shown that the flapping sounds injured fish make attract sharks. Sharks have been observed to respond to audio recordings of flapping fish broadcast underwater [source: Shark Trust]. and considering they have only an inner ear to work with sharks detection abilities are astute

In Australia in the first test, reefs with sound collected 325 fish, compared with 108 in silent reefs. A second experiment had high-frequency noise, low-frequency noise and silent reefs. Reefs with high-frequency sounds attracted 1,118 fish, the low-frequency reefs 1,171 and the silent reefs 657.

The researchers say their finding raises the possibility there may be damaging effects from human-caused noise, such as that from shipping and drilling. In addition, however, the discovery may show fishery managers a new way to attract fish to restock depleted areas.

At ordinary sound pressure levels (SPL), most humans can hear down to about 20 Hz.[1] Woofers are generally used to cover the lowest octaves of a loudspeaker’s frequency range. In two-way loudspeaker systems, the drivers handling the lower frequencies are also obliged to cover a substantial part of the midrange, often as high as 2000 to 5000 Hz; such drivers are commonly termed mid woofers. Since the 1990s, a type of woofer (termed subwoofer), which is designed for very low frequencies only, has come to be commonly used in home theatre and PA systems to augment the bass response; they usually handle the very lowest two or three octaves (i.e., from as low as 20 to perhaps 80 or 120 Hz).

Australian Geographic published the following during 2011

Great white sharks attracted by AC/DC hits

BY ANGELA CASE |JUNE 02, 2011
A shark cage tour operator has found that great white sharks are attracted to music by Aussie band AC/DC.

SHARKS ENTHUSIASTS HAVE USED fish guts to attract great white sharks for years, but it seems the fearsome creatures may be attracted to something more pleasing to their ears: music from Australian rock band AC/DC.

Matt Waller, a tour operator in South Australia’s Neptune Bay, has observed that when sharks hear the band’s hits, especially Shook Me All Night Long and Back in Black, they are drawn to the source of the music.

Matt’s research was inspired by dive operators on Guadalupe Island, who discovered playing music underwater for clients also caused changes in shark behaviour. He and his company, Adventure Bay Charters, decided to do some experimenting of their own.

Using underwater speakers attached to diving cages, they pumped Australian rock hits through the water. Most of Matt’s tunes had no effect, but when the great whites heard the AC/DC songs, they swam up and rubbed their faces against the source of the music.

Sharks react to music
Matt acknowledges he is no expert on the minds of sharks and doesn’t know exactly why they find the ’80s rock band’s music so appealing.

“Sharks don’t have ears, they don’t have long hair, and they don’t head bang past the cage doing the air guitar,” he told Australian Geographic.

The sharks are probably drawn to the low frequencies found in AC/DC’s music, and Matt wants to test out this theory. “Once we’ve got a range of songs, we can electronically identify a common characteristic between those songs,” he says.

Led Zeppelin is next on Matt’s playlist, but his children are convinced that the sharks will be fans of the White Stripes and Wolfmother.

Matt’s findings could help cage-diving operations become more environmentally sustainable by reducing the amount of berley used on tours. He says Adventure Bay Charters is currently the only company in the world that uses music, not bait, to attract sharks, but predicts other operators will soon follow his lead.

https://www.nationalgeographic.com/news/2018/05/sharks-jazz-music-food-animals-spd/

The above leaves little doubt as to the attractive effect that certain sounds have on sharks and their behaviour, but to date the deterrent effect of sounds is only recently begun to be studied.

This will prove to be highly complex as attention would have to be given to a sound that would repulse sharks only without disturbing all marine creatures, and if this could be determined it would become an effective shark barrier for areas now relying on nets and drumlines.

Copyright John M Costello

Editors note: I caught this little guy in the Umzimkulu – with a boatload of tourists making such a racket!