The Tiger Shark – a Formidable and Essential Predator

posted in: Marine Life | 0

My first encounter with sharks was in the Bahamas 12 years ago and, to this day I remember how my heart accelerated when I met the mighty tiger shark, Galeocerdo cuvier. A large, stunning female swam slowly around us, acting as if she owned the place. I was taken back by her elegance and confidence.

Text & Photo | Vanessa Mignon

After that first observation I found myself aching for more time with this apex predator and scanned the waters hoping to see their very recognisable silhouette.

Tiger sharks have wide blunt snouts, slender bodies and long, powerful tails that provide speed and agility. They owe their name to the dark spots and vertical stripes lining the sides of their bodies. These stripes are most noticeable in juveniles and tend to fade or even disappear as the shark gets older, so they cannot be used as a feature to identify an individual shark. It is believed that the patterns and colouring serve as camouflage; indeed the young usually stay close to the water surface and their stripes and spots resemble the shadows of waves in the water.

Tiger sharks are a member of the largest order of sharks known as Carcharhiniformes (ground sharks), and characterized by the presence of a nictitating membrane over the eyes, two dorsal fins, an anal fin, and five gill slits.

Tigers are one of the largest shark species. They commonly reach 3 to 4.2 meters in length and weigh between 385 kgs and 635 kgs. There have been records of large specimens measuring over 5.5 meters.

They can be found world-wide in tropical and warm temperate oceans. Although they tend to live in shallow coastal waters, they can also swim to deep, open ocean environments. Satellite telemetry work has found individual tiger sharks are capable of undertaking long migrations. For example, a study led by scientists James Lea and Brad Wetherbee that used up to three years of Argos satellite tracking data revealed that the 24 tiger sharks studied travelled nearly 7,500 km/year on average, from the Caribbean Islands where they spend the winter to the North Atlantic where they spend the summer. Another shark tagged by BioPixelTV scientists was found to swim close to 6500 kms across the Indian Ocean in 7 months.

Tiger sharks are indiscriminate scavengers, armed with a sophisticated sensory system, great eyesight, excellent sense of smell and a unique dentition designed to tear apart tough preys. They have sharp, serrated teeth with a sideways-pointing tip that are continually replaced by rows of new teeth throughout the shark’s life. Their powerful jaws are strong enough to crack clams and sea turtles shells. Their diet is believed to be the most varied among all sharks and usually includes marine mammals, sea turtles, birds, rays, other sharks and fish, but they will eat nearly anything they can find, edible or not! There has been reports of old tires, license plates, plastic items and other man made items being found in their stomachs!

Tiger sharks are usually solitary animals however they will gather in areas where food is abundant such as turtles and seabirds rookery, or during mating season.

It is a sexually dimorphic species where females are larger than males. Females reach sexual maturity between 2.5m and 3.3 m (7-12 years old) and males mature at about 2.3–2.9 m (6-8 years old). Females typically breed every 3 years and the gestation period is 13 to 16 months. When tiger sharks mate, the male usually bites the female on her back and fins to hold her in place while he inserts a clasper into her to release sperm. Pregnant females carry fertilised eggs within their body, each egg containing an embryo which feeds on its own egg-yolk. Then, the embryos hatch inside their mothers body and continue to develop internally before being born live. Litter sizes of tiger sharks vary from 10 to 80, with an average number of 30 to 40 pups. At birth, tiger sharks are 50 to 75 cm in length, are fully formed and fully independent. They are already a natural predator, feeding mostly on coastal fishes and invertebrates.

Their lifespan in the wild is believed to be between 20 and 50 years.

Tiger Sharks play a crucial role in maintaining healthy marine ecosystems. They help to regulate the populations of other predatory fish and prevent the spread of disease across a broad range of species by preying on the old and sick. In sea grass environments it has been shown that tigers reduce grazing by preying on herbivores such as dugong and turtles. This allows the sea grass to rest, bounce back and store more carbon. It is also believed they can act as carbon sinks where the carbon they consumed at the surface is then transferred to the deep ocean via their poo and eventually, one day, their dead body.

Tiger sharks are considered dangerous to people as their large size and sharp teeth can inflict substantial injuries. Furthermore, their presence in shallow, coastal waters means that they are more likely to encounter people compared to pelagic shark species. Tiger sharks are actually listed by several sources as second only to great whites in the number of recorded accidents on humans. However, those accidents remain extremely rare, and sharks are more at risk from humans than the other way round; Indeed, tiger sharks face many threats: They are fished for their fins, skin, flesh and liver oil, which is rich in vitamin A. They are also victims of bycatch, sport fishing, and in some countries they are targeted by shark control programs. Those menaces, along with their slow growth and reproduction rate, are detrimental to the species. Tiger sharks are currently listed as Near Threatened on the IUCN red list and it is assessed that the overall population is decreasing.

I do hope that this negative trend can be reversed and that the mighty tiger will continue to roam the oceans in abundance.