Creature Feature: Great white shark

It all begins with an innocent evening dip. A woman runs down the beach, stripping off her outer garments and diving into the cold, dark water of the Atlantic Ocean. Her identity is barely relevant, because just days later, remnants of her corpse are washed ashore – she is just another victim of the leviathan of the deep.


 

The cover of Jaws, a book transformed into a cult film that dramatically affected the public’s view of sharks in the 1970s. [Source]


Though this scene is easily recognizable as the opening to the iconic thriller Jaws (1975), it is certainly not the first to capture our innate fear of the mysterious predators roaming the ocean. Since the dawn of human civilization, such animals have occupied a special place in our imaginations, through verbal stories, artwork, literature, and now the media. One in particular has taken center stage: the great white shark (Carcharadon carcharias). Of course, its reputation as a master killer is not entirely unwarranted. Take one look at the corpses of unlucky seals and sea lions that have suffered their fate as white shark prey and it is easy to understand why we react so strongly to this species. The epitome of an apex predator: massive in size, stealthy in manner, and armed with razor-sharp teeth. But a large part of their success as the monsters of the media likely stems from the fact that white sharks remain mysterious, even to the biologists who study them.

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Great white lurking in the depths of the open ocean in Mossel Bay, South Africa

Great white sharks are known more simply as white sharks, but even this name can be misleading. Like many other fish species, white sharks exhibit countershading, an evolutionary strategy enabling camouflage that occurs when an animal’s back (dorsal side) is dark while the underside (ventral side) is light. This allows the shark to hide when ambushing prey. From above, its dark back blends into the surrounding murky waters; from below, its light belly removes some of the contrast between its silhouette and the light from the sun. However, their name was coined when the sharks were seen dead, lying on their backs on fishermen’s boats1. Since then, white sharks have been observed in South Africa, Australia, California, and northeastern United States. Though often seen offshore in deeper coastal waters, they are also capable of migrating great distances through the open ocean. One recent study recorded a shark that had traveled from South Africa all the way to Australia2.


 

Researchers using bait to attract a white shark, to enable them to obtain photo IDs from its dorsal fin.


White sharks are among 503 of catalogued shark species that come in various shapes and sizes. Though it is not the largest shark—that title belongs to the whale shark, Rhincodon typus—the white shark can reach up to 6.4 meters in length (over 20 feet) and weigh up to 2,300 kg (or just under 5,000 lbs)3. Females tend to be larger than males and are ovoviviparous; that is, they give birth to pups that are hatched from eggs retained in the mother’s body but emerge live and fully-formed. Very little is known about the reproduction of this species, but they are thought to produce litters ranging from 2 to 10 pups4.  While it seems quite small, this litter size is indicative of their role as apex predators. Because the food chain can only support so many of them, apex predators generally tend to be slow-growing, are late to mature, and have low reproductive capacity. Imagine what it would take to feed an ocean overrun with white sharks: there simply aren’t enough fish, crustaceans, pinnipeds (seals/sea lions) or cetaceans (dolphins/porpoises), all of which currently serve as their prey.

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White sharks often leap out of the water to capture prey (Mossel Bay, South Africa)

Much of the reason that white sharks are able to feed on such a diversity of organisms is that they have an optimal hunting design. They have an amazing sense of smell, able to detect a single drop of blood floating in 10 billion drops of water3. Like other sharks, they also have ears, two small openings located just behind and above the eyes that can sense vibrations in the water. A lateral line, or a system of sense organs that run along the length of the shark’s body, allows them to detect both vibrations and larger movements in their surrounding environment. And contrary to popular belief, white sharks also have excellent eyesight and are capable of rolling their eyes back into their sockets when engaged in a violent encounter, such as during hunting. However, because of this mechanism, they tend to rely less on vision and more on electroreception while hunting. Specifically, a series of jelly-filled pores on the animal’s snout that are filled with electroreceptors allow them to sense electric fields in the water. An adaptation found on all sharks, these are known as ampullae of Lorenzini. But perhaps one of the most unique features of white sharks and their close relatives is their ability to regulate their body temperature. This species is regionally endothermic. That means that unlike other fish, they are able to maintain their core and other regions of the body (eyes and brain, swimming muscles, and certain organs) at a warmer temperature compared to the water that surrounds them5. This allows them to function efficiently and move quickly as they hunt in cooler waters.

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Specialized network of electroreceptors (ampullae of Lorenzini) functions as a sensory organ in sharks. [Source]
Yet while their evolutionary toolkit is certainly impressive, the question remains whether white sharks take advantage of these features to seek out a different source of prey: the humans that venture into their territory. According to the International Shark Attack File (ISAF), there have been 153 unprovoked white shark attacks on humans between 1990 and 2013, of which 118 were fatal6. That’s approximately 6.5 attacks worldwide per year. These facts may seem daunting in themselves, but let’s consider the context. In a single year in 1996 in the United States alone, more people were injured by toilets (43,000), buckets and pails (11,000), and even room fresheners (2,600) than by any shark (13) – much less by a white shark6. So, the next time you are considering whether to get in the water for your own ocean dip, try to shake the Jaws theme song from your head. Like all animals, we are programmed to fear danger, and white sharks deserve a healthy respect and awareness, as do all predators. But the odds are very slim that you will ever meet the leviathan, unintentionally, face to fin.

[By: Alexandra McInturf]


References:

[Unless otherwise specified, photographs/video featured in this article were taken by the author Alexandra McInturf. More photographs and general information on shark research by the author can be found here.]

1Klimley, A. P., & Ainley, D. G. (Eds.). (1998). Great white sharks: the biology of Carcharodon carcharias. Academic Press.

2Bonfil, R., Meÿer, M., Scholl, M. C., Johnson, R., O’brien, S., Oosthuizen, H., … & Paterson, M. (2005). Transoceanic migration, spatial dynamics, and population linkages of white sharks. Science310(5745), 100-103.

3The Smithsonian Institute: http://ocean.si.edu/great-white-shark

4Proposals for amendment of Appendices I and II (CITES) – Thirteenth meeting of the Conference of the Parties: Bangkok (Thailand), 2-14 October 2004 (June, 2006)
http://www.cites.org/eng/cop/13/prop/E13-P32.pdf

5Bernal, D., Carlson, J. K., Goldman, K. J., & Lowe, C. G. (2012). Energetics, metabolism, and endothermy in sharks and rays. Biology of sharks and their relatives. 2nd edition, CRC Press, Boca Raton, 211-237.

6For more information on shark attack statistics, check out the following links:

http://natgeotv.com/ca/human-shark-bait/facts

https://www.floridamuseum.ufl.edu/fish/isaf/contributing-factors/highlight-white-sharks/attack-statistics

Featured image [Source].


For more information on what’s going on in white shark research, take a look at these other scientific publications:

Anderson SD, Chapple TK, Jorgensen SJ, Klimley AP, Block BA (2011) Long-term individual identification and site fidelity of white sharks, Carcharodon carcharias, off California using dorsal fins. Marine Biology 158:1233-1237

Chapman BK, McPhee D (2016) Global shark attack hotspots: Identifying underlying factors behind increased unprovoked shark bite incidence. Ocean & Coastal Management 133:72-84

Jewell OJ, Wcisel MA, Towner AV, Chivell W, van der Merwe L, Bester MN (2014) Core habitat use of an apex predator in a complex marine landscape. Marine Ecology Progress Series 506:231-242

Jorgensen SJ, Reeb CA, Chapple TK, Anderson S, Perle C, Van Sommeran SR, Fritz-Cope C, Brown AC, Klimley AP, Block BA (2010) Philopatry and migration of Pacific white sharks. Proceedings of the Royal Society of London B: Biological Sciences:rspb20091155

Klimley AP, Ainley DG (1996) White shark research in the past: a perspective. Academic Press

Klimley AP, Le Boeuf BJ, Cantara KM, Richert JE, Davis SF, Van Sommeran S, Kelly JT (2001b) The hunting strategy of white sharks (Carcharodon carcharias) near a seal colony. Marine Biology 138:617-636

Martin RA, Rossmo DK, Hammerschlag N (2009) Hunting patterns and geographic profiling of white shark predation. Journal of Zoology 279:111-118

McCosker JE (1987) The white shark, Carcharodon carcharias, has a warm stomach. Copeia:195-197

Philpott R (2002) Why sharks may have nothing to fear more than fear itself: An analysis of the effect of human attitudes on the conservation of the Great White Shark. Colorado Journal of International Environmental Language and Policy 13:445

Towner AV, Leos‐Barajas V, Langrock R, Schick RS, Smale MJ, Kaschke T, Jewell OJD, Papastamatiou YP (2016) Sex‐specific and individual preferences for hunting strategies in white sharks. Functional Ecology 30:1397-1407

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