Return of Featured Species Friday: Tiger Shark (Galeocerdo cuvier)

Easily one of the most recognizable, charismatic, and notorious shark species is the tiger shark (Galeocerdo cuvier). Growing to nearly 20 feet (6 m) in length and weighing up to 1,300 lbs (590 kg), the tiger shark is one of the largest species of shark (Parker, 2008). And with it’s large, blunt head, tiger-like stripes, and unique tooth shape, the tiger shark is hard to mistake for any other species.

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Botelho, D. (Photographer). (2014). Distinct Tiger Shark Stripes [Digital Image]. Retrieved from https://www.epicdiving.com/

The stripes of each tiger shark are unique, much like your finger print, and can be used to identify an individual. When the shark is born, the stripes are dark and highly pronounced, but as the shark ages, the stripes often fade and sometimes disappear completely by adulthood (Tricas, et al, 1997). As with other species with unique patterns, such as whale sharks and zebra sharks, it is possible to use photo identification techniques to monitor and track individuals and populations for long periods of time without using invasive techniques.  The Milisen Photography Tiger Shark Project is based in Hawaii and has been using photo identification to track the tiger sharks in Honokohau Harbor for several years. If you’ve been lucky enough to encounter a tiger shark in Hawaiian waters and photograph it, you can even contribute to the project by submitting your encounter. Check out the project for more information.

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Seale, A. (Photographer). (2013). Juvenile Tiger Shark [Digital Image]. Retrieved from www.artesub.com

Tiger sharks are incredible apex predators that are known to eat just about anything. They are often referred to as “swimming garbage cans” (Skomal, 2016).  Tiger sharks have been found with a variety of food items in their stomachs including sea turtles,  marine mammals, other sharks, large variety of fish species, sea birds, and even a variety of non natural food items like fast food wrappers, car tires, and license plates (Tricas, et al, 1997; Parker, 2008; Skomal, 2016). One amazing adaptation they have that allows them to so successfully hunt and scavenge such a wide variety of prey items is their unique tooth shape. Species that feed on marine mammals or turtles, like the tiger shark, have teeth that feature serrated edges that are ideal for piercing, cutting, and tearing away large sections of flesh away at a time (Parker, 2008). The tiger shark’s uniquely shaped tooth features a hook and serrated arch. This acts as a two pronged attack, both stabilizing the prey by piercing in, and when the jaw swings side to side, slicing through. In effect, the tiger shark has a built in knife and fork in a single tooth.

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Left: Ryan, P. (Photographer). (n.d.). Tiger Shark [Digital Image] Retrieved from http://www.fossilguy.com/ Center: Kuhn, S. (Photographer). (25 August 2006). Tiger Shark Teeth [Digital Image] Retrieved from https://en.wikipedia.org/ Right: Skerry, B. (Photographer). (17 May, 2016). Face to Face with Tiger Shark [Digital Image]. Retrieved from http://www.epicdiving.com/

Tiger sharks are also highly opportunistic predators. They spend their days off shore in deeper waters and in towards shallower, inshore waters at night to feed (Parker, 2008). They typically stalk their prey from below and are capable of sudden great bursts of speed of nearly 20 mph (32 km/h), however they cannot sustain this speed for more than the few seconds it takes to surprise their prey (Parker, 2008). Their retinas are specially adapted to their deep water stalking method. Their visual streaks, or the area of highest acuity in the retina, are positioned on the ventral surface of the retina, giving them a better spatial resolution in the upper visual field when they are looking up towards the surface (Klimley, 2013). This means when the tiger shark is near the sea floor, their vision is acute when fixed on the surface looking for their next meal… like a helpless fledgling albatross. Yum!

 

BBC Earth (2012 October 10). Tiger Shark Attack \Benedict Cumberbatch Narrates South Pacific | BBC Earth [Video Clip]. Retrieved from https://www.youtube.com/

 

The tiger shark often gets a bad reputation. Because of their biology and their preferred habitats in tropical and seasonally warm temperate waters, they often overlap with waters humans prefer. And as tiger sharks grow, they eat larger and larger prey items, which sometimes has meant encounters with humans (Skomal, 2016). But we have to remember the scope and context of these encounters. According to the International Shark Attack Files, tiger sharks have been implicated in more any attacks than any other species except the great white shark. From 1580 to 2014, there have been only 111 unprovoked tiger shark attacks on humans (Skomal, 2016).  That’s 111 unprovoked attacks in 434 years, that’s an average of 1 every 4 years. Now consider the millions of people every year that enter the water and never encounter a shark, especially a tiger. I have been to Hawaii. The only tiger shark I saw was at the Maui Ocean Center (and yes I was disappointed I didn’t see one in its natural environment but I may be a little crazy).  Tiger sharks are currently considered Near Threatened by the IUCN Red List (Simpfendorfer, 2009). In some areas they are considered common, however further investigation into population estimates is still required and their status may change at their next assessment.

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Flannery, A. (Photographer). (2017 May 12). Juvenile Tiger Shark at Maui Ocean Center [Digital Image].

Shark Stats

Authority: Péron & Lesueur, 1822

Family: Carcharhinidae; 59+ species

Length: A maximum of 20 feet (6.09 m)

Weight: Up to 1,300 lbs (590 kg)

Habitat: Coral atolls and lagoons, river estuaries, and shallow coastal waters to surface waters of the open ocean

Depth: Down to 1,000 feet (305 m) during the day, moving into shallow inshore waters at night

Reproduction: Ovoviviparous

Gestation: 12 months

Litter Range: 10 – 80 pups

Home Range: Worldwide distribution in warm tropical warms and through seasonally warm temperate waters.

Diet: Varies widely. Known as a swimming garbage can. Known to eat fishes, other sharks, sea birds, sea snakes, marine mammals, and garbage.

IUCN Status: Near Threatened. Common in some places, however population estimates are unknown.

(Parker, 2008; Simpfendorfer, 2009; Skomal, 2016)

Thanks for checking out the fantastic tiger shark this week! Thank you for bearing with me the past few months while I took some time away for graduate school. If you missed the new study published about the angular rough shark, I highly recommend that you check it out. It’s incredibly rare that these sharks are encountered, especially in Malta, and the footage is just fantastic!

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Remember you can make a difference for marine ecosystems by contacting your Congress man or woman and telling them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.

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Featured Image Source

Oliphant, J. (Photographer). (2018 January 19). Tiger Shark [Digital Image]. Retrieved from https://www.instagram.com/p/BeJ8LR3jWzg/?taken-by=juansharks

Literature Cited

Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Simpfendorfer, C. 2009. Galeocerdo cuvier. The IUCN Red List of Threatened Species 2009: e.T39378A10220026. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T39378A10220026.en

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

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Daddy on the Outside, Mommy on the Inside: Evidence of Hermaphroditism in Sharks

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