Like last weeks Blacktip reef shark, many sharks are targeted by recreational fisherman. After the film “Jaws” it became cool and manly to catch “man-eating” sharks as big-game fish, either alone or in tournaments. Rarely they are of use after (unlike in artisanal fisheries) – it is only for the thrill. And the kill, even if some tournaments try a catch-and-release-approach (if the shark survives the injuries and stress, and even the pull-up can be dangerous for example for deep sea sharks or highly pregnant females). Since the Tiger shark (Galeocerdo cuvier) has the reputation of a man-eating killer machine, it is a main target. As pointed out here, this results in many killings. In California alone, tiger sharks caught recreationally outnumbered the commercial side 6-to-1. Commercially, they are taken as bycatch or targeted for their fins, meat (the mercury content of this shark’s flesh is lower than in other large requiem shark species due to their diet), skin, cartilage and liver oil.
Yes, sharks can bite. And due to its size (females up to 16 ft 5 in – over 5 m- and males up to 13 ft 1 in – 4 m- length), power and dentition, an adult Tiger shark can cause significant harm -its serrated teeth are able to slice through turtle shells, after all. According to the ISAF, it is second only to the White shark in number of reported attacks on humans, many of them fatal. But if you watch this video, they seems rather docile and sluggish. They are big, curious and potentially dangerous, but no evil killing machines.
Tiger sharks live in tropical and subtropical waters all around the world and undergo a long-distance seasonal migration. As opportunistic feeders they prey mostly on fish, cephalopods, crabs, sea snakes, sea birds and carrion, but also with age more and more on seals, turtles, dugongs, dolphins and injured whales. As Neil Burnie said: “Tiger sharks like the dead, the dying and the dumb” (I would add dump, since they sometimes eat garbage, too), because they can’t be picky. To grow to such a size in relatively nutrient-poor warm waters is no mean feat (White sharks inhabit mostly cooler waters).
Tiger sharks are unique among their family. Firstly, they have got spiracles and a capacious stomach with a muscular wall that is proportionately three times thicker than that of any other requiem shark. Also unlike any other requiem shark, the female Tiger shark is ovoviviparous and not viviparous. That means the pups hatch in the uterus, but are not feed by a placental connection after the yolk supply is depleted. During the gestations period of up to 16 months the mother does provide unfertilized eggs (oophagy) and the one or other sibling to nibble on (in-utero cannibalism). But, other than in the Sandtiger shark, many survive, resulting in big litter sizes of 10 to 80 pups (unlike almost all other requiem sharks).
The 20 to 30 in -51 to 76 cm- long newborn Tiger sharks stay in their shallow nursery areas and grow fast. That is necessary, since their slender and delicately built bodies with over-sized fins and unique tail structure (an elongate upper caudal lobe) condemns them to an eel-like wriggle, an inefficient swimming style that renders them extremely susceptible to predators like bigger sharks (even other Tiger sharks). They do not outgrow their ‘awkward stage’ until they reach a length of about 8 feet -2.4 metres- at about four years of age. After that, their powerful build and fins make them successful predators with startling speed bursts.
Like the Blacktip reef shark, the Tiger shark has got large eyes with a reflective tapetum lucidum like a cat for nightly hunting. Normally they enter shallow, coastal waters at night and spend the day offshore in deeper water. But if their prey, like the Hawaiian Monk Seals, remains near shore during daylight hours and forages in deeper waters under cover of darkness, the Tiger Sharks adapt and revers their usual day-night pattern, remaining inshore during the day and moving offshore at night.
Tiger sharks are considered “near threatened” by the IUCN due to fishing pressure and questionable shark control programmes. But their widespread distribution and high growth and reproductive rates give reason to hope. It has been discovered that juvenile survivorship increases where adult Tiger Shark populations have been depleted by fisheries and hence predation of young is lessened.
Sources: here, here and here