Tiger Sharks, Galeocerdo cuvier
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Description & Behavior
Tiger sharks, Galeocerdo cuvier (Péron and Lesueur in Lesueur, 1822), are one of the largest sharks in the world. Adults commonly reach lengths of 3.3-4.3 m and weigh between 385-635 kg [View 4.3 m, 544 kg tiger shark caught in Kaneohe Bay, Oahu in 1966]. Length at birth varies from 51-76 cm. Males reach sexual maturity at 2.3-2.9 m, while females mature at 2.5-3.5 m. The largest adult tiger sharks are believed to attain a length of over 7.4 m and weigh over 900 kg. Tiger sharks are gray in color with vertical tiger-stripe markings which usually fade or disappear in adults. They can also be identified by their characteristic sickle-shaped teeth that are similar in both the upper and lower jaw.
This species is a requiem shark (Family Carcharhinidae) with a short, blunt snout, labial furrows, and large head. Spiraculi are also present. Tigers have a slender body behind the pectoral fins and low keels on their caudal peduncle, and slender and long caudal fins.
World Range & Habitat
Tiger sharks are found worldwide in temperate and tropical seas.
Western Atlantic: Massachusetts to Uruguay, Gulf of Mexico, Bahamas, Caribbean.
Eastern Atlantic: Iceland and possibly the UK (due to the warm Gulf Stream), Morocco, Canary Islands, possibly the Mediterranean, Senegal to Ivory Coast.
Indian Ocean: South Africa to the Red Sea, Pakistan, India, Sri Lanka, Maldives, Thailand, Vietnam.
Western Pacific: Southern China, Japan, Philippines, Indonesia, Australia, New Zealand, New Caledonia. Western central Pacific: Palau, Solomon Islands, Marshall Islands, Tahiti, and Hawaii. Eastern Pacific: Southern California, Peru, Galapagos.
This species lives in coastal and pelagic waters, from the surface to depths of about 350 m. The tiger shark has a wide tolerance for different marine habitats, but seems to prefer turbid waters on or adjacent to the continental and insular shelves. It is often found in river estuaries, close inshore, in coral atolls and lagoons. These solitary hunters are nocturnal and move inshore into shallow waters at night to feed and then move back to deeper waters in the daytime.
Research by the Hawaii Institute of Marine Biology has shown that tiger sharks have very large home ranges. Tiger sharks with surgically implanted ultrasonic transmitters all swam more than 16 km within one day of their release, and it took between two weeks and 9 months for them to revisit the area where they were released.
Feeding Behavior (Ecology)
Tiger sharks likely have the widest variety in their diet out of all shark species. These sharks are predatory animals primarily known for their voracious appetites. They seem to be indiscriminate in their food selection and are known to eat: fishes, other sharks, sea turtles, mollusks, and seabirds. They are also known scavengers. Examination of tiger shark stomach contents revealed such diverse items as animal antlers and ship garbage. This wide spectrum of food selection has often been interpreted as these sharks being indiscriminate feeders, however their feeding habits may indicate a highly specialized adaptation to their biology in that they are extremely large animals and need a lot of food. Their uniquely shaped teeth are highly evolved and allow them to feed on a variety of food items, which helps prevent food shortages that might arise in more selective feeders.
Tiger sharks are ovoviviparous bearing between 10-82 pups per litter. Pups at birth measure between 0.5-1.05 m. The pups are very slender with clearly defined vertical stripes which fade as they become adults. They grow quite slowly, which makes them vulnerable to declines in population due to overfishing.
Ovoviviparous: eggs are retained within the body of the female in a brood chamber where the embryo develops, receiving nourishment from a yolk sac. This is the method of reproduction for the "live-bearing" fishes where pups hatch from egg capsules inside the mother's uterus and are born soon afterward. Also known as aplacental viviparous.
Conservation Status & Comments
Tiger sharks are second only to the great white shark in the number of reported attacks on humans. Fortunately though, attacks are rare. In Hawaii, although tiger sharks were responsible for several fatalities in the 1990s, there is an average of one shark attack there per year. A low number considering the average number of drownings is 40. Its large size and voracious appetite make the tiger shark an apex predator of the ocean. Because of their indiscriminate appetite, tiger sharks can be curious and aggressive towards humans in the water and therefore must be treated with extreme caution.
Both commercial and recreational fishing catch rates for this species in the mid-Atlantic region have declined since the mid-1980s as the size of the population declined due to fishing pressure. In contrast, relative abundance and catch rates for this species noted by commercial fisheries observers, especially for juveniles, are much higher than in previous fishery-independent and fishery-dependent surveys.
Tiger sharks, Galeocerdo cuvier, are now listed as Near Threatened (NT) on the IUCN Red List of Threatened Species due to:
"This large (>550 cm), omnivorous shark is common world wide in tropical and warm-temperate coastal waters. It is a relatively fast growing and fecund species. The Tiger Shark is caught regularly in target and non-target fisheries. There is evidence of declines for several populations where they have been heavily fished, but in general they do not face a high risk of extinction. However, continued demand, especially for fins, may result in further declines in the future."
NEAR THREATENED (NT)
A taxon is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
References & Further Research
[ECHENG.COM] Tiger Shark photos - Wetpixel Bahamas Sharks & Dolphins 2004
[ECHENG.COM] Shark videos - Tiger sharks!
Tiger shark (Galeocerdo cuvier) - Shark Foundation
NOVA Online - Island of the Sharks
Shark Research Progam - Florida Museum of Natural History
Lars Kirchhoff [Web Journal] - Bahamas Trip
Elasmodiver.com - image database of sharks, skates, rays, and chimaera's from around the world by Andy Murch
Simpfendorfer, C. 2005. Galeocerdo cuvier. In: IUCN 2009. IUCN Red List of Threatened Species
Research Galeocerdo cuvier » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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