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Guest Post! The Right Stuff: What It Takes To Be The Ocean’s Top Predator

The views expressed are those of the author and are not necessarily those of Scientific American.


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Editor’s Note: While I’m on vacation, I’ve arranged a series of guest posts from other writers who routinely cover animal behavior and cognition. Today’s post, about attack behavior and social communication in great white sharks, comes from David Manly, who blogs at The Definitive Host. Follow him on twitter: @davidmanly.

In 1975, Steven Spielberg’s thriller Jaws erupted into theatres and convinced an entire generation to despise and even fear sharks. The sad fact is while some sharks can attack and kill humans from time to time, they are the minority. In fact, out of the over 350 shark species in the world, only a few have ever attacked people. But, those few have tarnished the reputation of these amazing creatures.

Scientists around the world are fighting to change that from one of fear to one of respect, and one of the ways they can do that is by understanding why sharks do what they do.

One fact that is undeniable about sharks is that they have had millions of years to perfect their behavior and physical attributes to become some of nature’s greatest hunters. But what makes sharks, especially the most famous: the great white (Carcharodon carcharias), so efficient a predator?

While the movie Jaws reinforced people’s negative stereotypes of great whites, Pixar’s Finding Nemo tried to paint them in a more positive light. The character of Bruce was a vegetarian, but still maintained his killer instincts. It may work in the movies, but we must remember that as it has been for millions of years, sharks are at the top of the ocean food chain … not us.

If you’re talking about sharks, easily the most striking feature they possess is an abundance of teeth. Great whites have rows and rows (and yes, even more rows because a shark replenishes them over its lifetime) of sharpened and serrated teeth, structured similarly to steak knives.

The serrations help rip and tear the flesh from prey while the sharks whip their heads back and forth over and over again in the water. They behave like this because their prey is often larger than their mouths, and since they have no limbs to help cut the prey into smaller pieces, they have to generate the force to do it themselves. The teeth are also curved inward to hold the prey in its jaws, almost prehensile like, to prevent the prey from fleeing and helping shred meat from bone.

It is like being held in place by a serrated vice and being shaken back and forth like you’re paint being mixed, all while in the water. You can understand why people get so scared of sharks!

So that’s the business end of a shark, but while it is important to have the tools, how do they put it into practice?

Large sharks like tiger or great whites, often feed by ram feeding, which involves swimming directly towards a stationary or moving prey at a high speed and engulfing it completely. But, what if the prey is too big (like a seal) to nab in one bite?

Well, that is when things get interesting.

In 2005, R. Martin and colleagues investigated just that in a paper called “Predatory behavior of white sharks (Carcharodon carcharias) at Seal Island, South Africa.” Using observations of how sharks attacked both live seals and seal-shaped decoys, the researchers identified a remarkable diversity of behaviors.

They noticed that the sharks utilized 20 different attack patterns, and postulated that the sharks changed their behaviors based solely on the prey’s location and speed. The researchers determined that each attack consisted of four phases: the initial strike, secondary pursuit, prey capture, and finally, feeding.

Most commonly, the sharks began with a Polaris Breach [A in the figure below], where the shark leap out of the water with or without the prey in its mouth, followed by a surface lunge [E], where only the animal’s dorsal area is out of the water. Ending the attack is usually accomplished via a lateral snap [I], where the shark laterally captures the prey within its jaws before consuming its prize [as shown in M-O].

That is how sharks attack their prey, but catching it unaware is a completely different and fascinating story.

Wesley R. Strong Junior and colleagues used two different decoy shapes, and found that most sharks approach their prey from a steep 90-degree underwater angle. They hypothesized in the figure below that this allows an increased amount of light to enter the shark’s eye for the attack (c), while subsequently reducing the available escape routes of the sea lion (eliminating escape route d).

By attacking in this way, the shark minimizes the risk to itself, as well as the loss of the prey. The attack itself can go one of two ways; either the shark will persist with its attack, or employ the “bite, release, and wait” method. It is very simple and yet highly effective attack method that is used by a whole host of species in the animal kingdom.

If a shark employs this method, it may bite the prey item and then subsequently release it, waiting for the prey to die from shock or blood loss, all the while avoiding potential injury. There are drawbacks to both methods, as attacking and pursuing could yield bigger prey, but costs more energy and risks injury. However, if by using the attack and wait strategy, there is a risk of losing the prey item to other predators or scavengers.

Since sharks do not have hands to slap usurpers away or vocalizations to show dominance, they had to evolve their own method of social interaction: tail slapping and breaching.

Tail slapping involves a shark jumping out of the water and hitting its tail upon re-entry, splashing the other sharks. Breaching, on the other hand, is akin to what whales do: propelling two-thirds of their bodies out of the water and landing flat. These interactions do not usually last very long, as one shark will eventually submit to the other and leave, allowing the victor to consume their prize.

Bet you didn’t know that sharks communicated to one another like that, did you?

Sharks, especially those known as “man-eaters” are just animals. There is nothing evil about them, no motive to their ferocity … it is just how they experience the world and interact with it. So, keep that in mind next time you go into the ocean.

After all, sharks and all other animals out there are just doing what they need to survive. If you were in that position, you would be doing the exact same thing.

Martin, R., Hammerschlag, N., Collier, R., & Fallows, C. (2005). Predatory behaviour of white sharks ( Carcharodon carcharias ) at Seal Island, South Africa Journal of the Marine Biological Association of the UK, 85 (05) DOI: 10.1017/S002531540501218X

Strong, WR Jr. (1996). Shape discrimination and visual predatory tactics in white sharks. In: Klimley, AP & Ainley, AD (eds). Great white sharks: the biology of Carcharodon carcharias. Academic Press, New York, pp 229-240.

Shark image: Flickr/kqedquest. Shark attack photo series: Martin et al., (2005). Shark attack schematic: Strong Jr., et al. (1996).

David Manly is a Canadian freelance science journalist who holds degrees in Biology and Zoology, as well as a Masters of Journalism. Currently, he writes about the ecology, physiology and behavior of all animals (from sharks to flatworms and everything in between), as well as how to improve science communication and interaction between professionals and the general public. You can find David’s work on his Lab Spaces blog, as well on his own blog The Definitive Host and on twitter: @davidmanly.

Jason G. Goldman About the Author: Dr. Jason G. Goldman received his Ph.D. in Developmental Psychology at the University of Southern California, where he studied the evolutionary and developmental origins of the mind in humans and non-human animals. Jason is also an editor at ScienceSeeker and Editor of Open Lab 2010. He lives in Los Angeles, CA. Follow on . Follow on Twitter @jgold85.

The views expressed are those of the author and are not necessarily those of Scientific American.





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