This article originally appeared in The Shark Tagger-1998 Annual Summary
The tiger shark is the easiest of the large coastal sharks to identify. The large head, with its short, blunt snout and wide mouth, makes this species stand out from most other requiem sharks. The curved teeth which are heavily serrated on both sides and have a distinct notch on their outer edge are one of their most diagnostic features. Small tigers are easily distinguished by their coloration, which varies from bluish to greenish gray to black above and from light gray to dirty yellow or white below. Sharks up to 4-5' FL also have a mottled appearance with their dorsal surface covered with dark spots. As tiger sharks grow, the spots fuse together to create vertical bars, hence their tiger-like appearance. In large tiger sharks, the bars tend to fade, but are usually visible upon close inspection. Approximately 2' FL at birth, tiger sharks are believed to reach a length exceeding 15' FL. In the western north Atlantic, the largest individual we have measured was 11' FL.
Adult tiger sharks occur worldwide in temperate and tropical coastal waters. In the North Atlantic they reside year round off the coast of Florida and seasonally migrate as far as Nova Scotia, Canada. Additionally, tiger sharks are known to make extensive movements throughout the North Atlantic, on occasion traveling to South America or Africa (see map). While considered to primarily inhabit coastal environments, it is clear from our recapture data that tiger sharks spend considerable time in the pelagic environment during part of their lives. Small tiger sharks appear to inhabit a different area than larger individuals, probably to avoid predation. Tagging and fishery data indicate that there is a nursery ground for tiger sharks on the continental shelf off the southeast coast of the U.S. This area extends from about Augusta, GA to Daytona, FL from shore, seaward to depths of 55 fathoms (fm). A similar area exists off the coast of North Carolina. In these nursery areas, tiger sharks ranging in size from birth to 4' FL are commonly caught. Larger individuals leave to occupy different habitats.
More has been written over the years about the food and feeding habits of the tiger shark than most other shark species, perhaps because their stomachs have reportedly contained an assortment of bizarre items. A partial list from popular and scientific accounts includes: a rubber tire, roll of tar paper, roil of chicken wire, bag of potatoes, sack of coal, rags, bottles, shoes, dogs, ladies pajamas, a can of Spam, and parts of sheep, cattle and horses. The latter three items occurred in areas where offal from slaughterhouses was once dumped into the coastal rivers or at sea. The head and forequarters of a crocodile were found in a 14' total length tiger shark captured off Durban, South Africa. Parts of dolphins, porpoises, and whales have been found by several investigators. The list goes on and is proof that the tiger shark is sometimes a scavenger. Despite this reputation, our studies show that their usual prey is more mundane, being comprised of various fishes, cephalopods (squid and octopus), crustaceans (crabs, lobsters, and shrimp), and sea turtles. The frequency with which certain items occur depends on how abundant they are and how much effort must be exerted to capture them. The tiger shark is most often associated with shallow depths (shore to 50 fm) around land masses and is usually considered a sluggish shark. Hence, its diet consists primarily of species found on the bottom, around reefs and outcroppings, or in the water column a fathom or so off the bottom.
Our studies of 51 tiger shark stomachs collected between Cape Hatteras and Georges Bank show that goosefish, searobins, sea ravens, lizard fish, and flounders occurred with the greatest regularity. Goosefish was the predominant species and occurred most often in stomachs examined at tournaments held along the New York and New Jersey coasts. The occurrence of these bottom dwelling species shows that the tiger shark regularly feeds on the bottom in this area. We also found remains of bluefish, mackerel and butterfish, but with less frequency, so it is evident that the tiger shark will feed on schooling prey when conditions are right. Sharks, skates and rays occurred in 23% of the stomachs we examined over the geographical range of our study, indicating that elasmobranchs are common prey.
Muscle and blubber from marine mammals were found in 24% of the stomachs we examined. Several species of sharks have been found with mammal remains in their stomachs, but the tiger shark with its cavernous mouth and large stomach capacity is particularly well adapted for devouring large prey. Because there is no evidence in the literature that tiger sharks successfully prey on healthy dolphins, porpoises, and whales, it is possible that these food items came from dead or moribund animals. Their large, blade-like teeth enable them to easily bite through bone and shells of large sea turtles. Although our data suggest that predation on sea turtles is relatively low north of Cape Hatteras, NC other studies have shown that in areas of higher turtle abundance (tropics and subtropics), turtle remains occur in tiger shark stomachs with much greater frequency (10-36%). The primary evidence of attacks on turtles is from the remains of shells and flippers found in shark stomachs. Some maimed turtles heal and survive, but an unknown percentage must surely die. Trash items we found in stomachs included small stones, sand, plastic bags, and assorted garbage such as pork chops, hot dogs, hamburgers, and beef bones. The small stones and sand were likely ingested along with bottom-dwelling prey. Overall, 46 stomachs (81%) contained some kind of food item.
Researchers in Hawaii have shown that there is a dietary shift throughout the lifetime of the tiger shark. Small sharks are nocturnal, bottom feeders with five major prey types: bony fish, birds, cephalopods, land mammals and crustaceans. Medium and large tiger sharks consume eight major prey types, the five listed above plus elasmobranchs, sea turtles and marine mammals. A dietary shift with increasing size is not uncommon in sharks and may be coupled with larger sharks being able to consume larger prey, an increase in hunting efficiency, or a change in geographic region inhabited.
Tiger sharks have been aged using two methods: bands on vertebral centra and tag/recapture data. Overall, the tiger shark is similar to other large carcharhinids in that it grows slowly and is relatively long-lived. Tag data indicate that tigers grow fast in their first few years, increasing by 74% from their size at birth during their first year of life (see figure). Since tiger sharks are rather awkward at birth, having a very large head and slender eel-shaped body, it is to their advantage to grow quickly through this stage to enhance their swimming capabilities for survival as both predator and potential prey.
The longevity of the tiger shark is difficult to estimate. The CSTP has received data on five tiger sharks at liberty between 6 and 11 years. The oldest of these fish would have been 3+ years at tagging and, therefore, 14+ years at recapture. Other authors have estimated maximum age at anywhere from 20 to 37 years.
The tiger shark is the only member of the family Carcharhinidae that is ovoviviparous. This means that the embryos develop inside the uterus but receive no placenta-like nutrition from the mother. It is also unusual for the relatively large number of young it produces, commonly from 35 to 55 with reports of as many as 82. Pups are born in the late spring and early summer. Gestation period is thought to be slightly over one year. In the Northwest Atlantic, both male and female tiger sharks mature at about 8.5' FL which corresponds to approximately 7 years of age. This suggests that females mature at 20 - 25% of their maximum age and may reproduce 10 times or more based on a two year reproductive cycle.
