DNOWS Header

Image Map

Sunday, July 8, 2012

Myths In The Open Water: Sharks vs. Dolphins

There is a certain amount of misinformation reported in the media about open water swimming. Open Water Source looked at the data in an attempt to distill fact from fiction, reality from rumor.

One issue that is commonly reported in the press is that "Dolphins protect swimmers from sharks."

This oft-used quote is a dramatic indication how scary it is to swim with sharks and how comforting it is to swim with dolphins.

But is it true?

Are open water swimmers truly and naturally protected from sharks by dolphins and porpoises as is commonly believed by many channel swimmers? There are a wide variety of opinions on this topic.

Many open water swimmers around the world, especially channel swimmers and marathon swimmers, often tell newcomers that when dolphins or porpoise are near them in the open water, there is no need to fear sharks. It is often said to be a sign of good luck and protection. The belief is that sharks fear dolphins and porpoises that can easily defend themselves against the apex predators - and will, in turn, protect swimmers, their mammalian friends.

Escort pilots of channel swimmers throughout the Pacific, from the Catalina Channel to the Hawaiian Islands, also share this opinion.

According to Peter Klimley and David Ainley who wrote a book Great White Sharks: The Biology of Carcharodon carcharias, Great white sharks attack dolphins and porpoises from above, behind or below to avoid being detected by the friendly mammal's echolocation. The targeted species include dusky dolphins, Risso's dolphins, bottlenose dolphins, Humpback dolphins, harbour porpoises, and Dall's porpoises.

Scientists like Michael Heithaus also raise possibilities that differ from the widely held beliefs of open water swimmers. He presented a study called Predator–prey and competitive interactions between sharks (order Selachii) and dolphins (suborder Odontoceti): a review, that shares findings similar to television programs like the Discovery Channel's Are Sharks Afraid of Dolphins?. He concluded that sharks remain the apex predator in the ocean and do not fear dolphins or porpoises, except perhaps when out-numbered.

His study in the Journal of Zoology (Cambridge University Press) stated, "White, tiger, bull and sevengill sharks are probably the major predators on nearshore cetaceans, but dusky sharks may also represent a risk. The risk that nearshore cetaceans face from sharks will vary with location. For example, the risk of shark predation is probably higher in tropical waters than in higher latitudes because of the diversity and abundance of large, predatory sharks in warm waters."

Richard Theiss of RTSea Productions believes what the scientific community has presented in published peer-review articles, but he also points out an important truth. "...what Michael had to say in his study is important: different species, different locations, different circumstances – all this makes it difficult to make a definitive statement. [In reference to the] Mythbusters video, there are errors in not making the distinction between a white shark’s role as an ambushing predator and that of a scavenger. Each generates different behavior patterns. As a scavenger, which is what it was doing with the floating tuna head, it can be easily put off by another large fish in the area (did it look like a dolphin or another shark?). It’s just looking for an easy meal and doesn’t want to have to compete for it. I’ve seen this many times with white sharks at Isla Guadalupe (see RTSea Productions video below).

So, sharks will kill dolphins on occasion – seeking a slow, sick, or aged fish, just like the Great white shark does in selecting a pinniped (seal or sea lion). What needs to be examined in a definitive study and not just through anecdotal storytelling is whether dolphins will show any aggressive tendencies towards sharks. It’s not so much as to whether sharks are scared of dolphins, but whether dolphins are fearless when it comes to sharks
."

Heithaus, who directs the Shark Bay Ecosystem Research Project in Shark Bay, Western Australia, encourages further study of the natural relationship between sharks and dolphins where more information and understanding about the nature of shark-dolphin interactions is needed.

A MythBusters episode on the Discovery Channel also explored this issue: Are Sharks Afraid of Dolphins?.





Other commonly held beliefs among open water swimmers include:

1. Most body heat escapes through your head in the water (read here).
2. Commercial jellyfish ointments will prevent jellyfish barbs from firing into the skin of open water swimmers.
3. Black wetsuits lead to shark attacks (read here).
4. Shark risks increase at dawn and dusk (read here).
5. More people have been in space than have swum across the English Channel (read here).

Copyright © 2012 by World Open Water Swimming Association

2 comments:

  1. It is known fact that as fast a dolphins and porpoises swim, a shark can swim more than twice as fast. So dolphins cannot outrun a shark if a shark attacks -- it would be like a human trying to outrun an attacking bear. It is also a known fact that dolphins and porpoises are social animals and are rarely found swimming alone. When dolphins hunt they follow techniques that depend on cooperation and highly coordinated efforts. On the other hand, sharks are not a social animal -- they are strictly loners who hunt alone. Sharks would never work cooperatively to attack a dolphin, but dolphins would work as a team in attacking a shark if threatened by a shark. And there is more than one instance where dolphins have killed sharks by battering them. It is not clear whether sharks fear dolphins or dolphins fear sharks (though it is more likely that the dolphins have fear because fear usually is a sign of intelligence and dolphins are far more intelligent that sharks), but one thing is sure -- you rarely see them together. Where you see sharks in numbers you do not see dolphins or porpoises and vice versa. So you can feel safer as a swimmer if you are in a region where dophins or porpoises are prevalent. Sharks are dim witted but very efficient hunters and killers and even without fear they may have instincts that tell them that dolphins or porpoises in groups are BAD news and something to avoid.

    ReplyDelete
    Replies
    1. Actually you are incorrect on a few statements. It has actually been shown that sharks do often coordinate attacks and are more social than we previously realized. Sharks also are far from dim witted, and while they are no where near as intelligent as dolphins they do posses a degree of intelligence.

      Delete

Thank you very much for your interest in the world of open water swimming.

The Staff of the World Open Water Swimming Association

A Thank You Gift from WOWSA


WOWSA is celebrating the
1-Year Anniversary of the monthly Open Water Swimming Magazine
by giving you a free copy of the anniversary issue.

Open Water Swimming Magazine Anniversary Issue
File Size: 13MB

FREE DOWNLOAD

INSTRUCTIONS:
Download the file to your computer, and then right-click to extract the magazine which is inside the zip folder. The magazine is in PDF format.

CLICK HERE to download your free copy now.

Open Water Swimming Magazine


Open Water Swimming Magazine

The Open Water Swimming Magazine is the monthly magazine entirely focused on open water swimming heroes and heroines of every age, ability, and background. Published by the World Open Water Swimming Association, the Open Water Swimming Magazine is a free benefit to WOWSA members.

WOWSA Member Benefits include 12 issues of the Open Water Swimming Magazine, the annual 276-page Open Water Swimming Almanac, a free listing in Sponsor My Swim, outstanding product discounts from FINIS, an entry in Openwaterpedia and more...
LEARN MORE

The Other Shore


The Other Shore follows world record holder and legendary swimmer Diana Nyad as she comes out of a thirty-year retirement to re-attempt an elusive dream: swimming 103 miles non-stop from Cuba to Florida without the use of a shark cage. Her past and present collide in her obsession with a feat that nobody has ever accomplished. At the edge of The Devil’s Triangle, tropical storms, sharks, venomous jellyfish, and one of the strongest ocean currents in the world, all prove to be life-threatening realities. Timothy Wheeler’s documentary brings Diana Nyad’s extraordinary adventure to life as Diana sets out to prove that will and determination are all you need to make the unimaginable possible.
LEARN MORE...

2014 Open Water Swimming Almanac



An Almanac for Open Water Swimming

An almanac is essentially a body of knowledge which is so complete that it enables people in different fields to make predictions about the future of their respective industries.

This, for example, was the purpose of the traditional farmers almanacs. It enabled farmers to determine as accurately as possible which crops to plant for the greatest harvests in a given year.

But the farmers almanac was just one example among many.
There are, of course, many different kinds of almanacs.

In fact, there is even one for open water swimming...

Preview the Open Water Swimming Almanac:
https://www.worldopenwaterswimmingassociation.com/preview-open-water-swimming-almanac


The trends are very clear.
The tide is rising for open water swimming.

SponsorMySwim.com

Open Water Swimming Event Sanctioning

World Professional Marathon Swimming Federation

Open Water Race Calendar

Coaches Education Program