Gharial Biology

Introduction and Etymology

The earliest ancestors of Crocodilians date back over 200 million years, and there was an incredible diversity of now-extinct prehistoric crocodilians. Today, there are three crocodilian family groups that surivive:the Alligatoridae, Crocodylidae and Gavialidae. These families currently consist of 25 species found throughout the world in the tropics and subtropics.

The family Gavialidae contains just two species: the gharial and the tomistoma, however the two species diverged at least 20 million years ago – so not all that closely related! The two species diverged from the crocodiles 40 million years ago, so they represent a huge amount of unique evolutionary history.Because the gharial is very evolutionarily distinct, and also critically endangered, it is an EDGE species.

The Gharial (Gavialis gangeticus) is a monotypic genus (i.e. having only one species in that genus). The gharial is a unique species of crocodilian, characterized by its long, thin snout and the bulbous growth at the end of the snout of adult males called the “ghara”. The ghara is only found on adult males, making the gharial the only sexually dimorphic crocodilian, which helps in identifying mature males from females. This is all how the gharial got its name: from the Hindi word “ghara”, which means pot. The “ghara” is a bulbous blob that starts to grow on the nostrils at the tip of the snout as soon as the males reach maturity. This unique and distinctive growth turns the hissing noise commonly made by crocodilians into a buzzing noise, as air is forced through the nasal passage. It may also act as a sound amplifier, carrying the produced “Popping” sound for great distances across water.

Physical Characteristics Of Gharial

Long, very slender snout, vertically flattened tail, and webbed back feet. Body covered with heavy non-overlapping scales. Over 100 very sharp teeth.

Body Length:

Males: 5 – 6 m (16 – 20 ft);

Females: 3.5 – 4.5 m (11.5 – 13 ft)

Hatchlings: 32.5 -37.5 cm (12.8 – 14.8 in)

Body Weight (Average): 159 – 181 kg (350 – 400 lbs)

Ecology:

Gharial live in deep, fast-moving rivers. They are the most aquatic of all crocodilians, spending most of their time in the water and coming out onto land only to lay eggs and to bask. They are social and can be found in aggregations along a river system. Their hierarchy is very interesting with one male and many females: the females choose the strongest male to join their group.

The gharial’s form is highly adapted to the riverine habitat; they have a long slender and streamlined appearance, with highly specialized scales on their body which contain small nerve centres called Dome Pressure Receptors (DPR) which helps them detect movement underwater and also gauge depth. These receptors are used to locate prey underwater. Gharial have a slender snout which equips them to hunt fast and slippery fish. They employ a very specialized hunting technique to capture fish; they shake their head side to side and seize fish which stray close to their jaws underwater. They come up to the surface to swallow that meal. Gharial are probably the most specialised fish-eaters (piscivorous) among crocodilians, but will also take other aquatic prey, including amphibians, invertebrates and occasional turtles!

Gharial are naturally intelligent, migrating to different river systems to find better feeding grounds and also to accesswater year-round. They are proficient at swimming through the river and they may move up to 200 kms in a season.

Reproductive Ecology:

Gharial are seasonal breeders, with courtship and breeding starting in the February and continuing till March. After mating, female gharial search for high banks to lay they eggs. Although gharial lack strong limbs, they climb steep banks to ensure the nests are high enough above the water level to avoid flooding, as this is vital to protect their eggs from drowning. They are known to nest communally, with up to 40 females nesting on the same bank. Females compete for nesting space and younger females may be forced to nest on other banks. Females nest between the 4th week of March and 2nd week of April.

Gharial are known to lay between 35 to 40 eggs in a clutch. The few experienced nesting females constantly guard their nests as a community. By the end of May, after approximately 60 days (depending on the temperature of the nests: in cooler years the eggs take longer to hatch),eggs from all the nests begin to hatch; thousands of hatchlings can be found in a creche along the banks of the river. Males are known to take part in parental care, however the male need not be a parent of the hatchlings. In some instances, a male who is not the biological fatherwill take care of all the hatchlings, which is an interesting example of alloparenting. For the next 3 to 4 weeks there is always an adult around the creche guarding the new hatchlings: this is key to protect them from the large variety of animals that will predate small gharial, including wading birds, birds of prey, mongooses and other crocodilians. Then, with the onset of monsoon during July, the adults are forced to move from their nesting grounds due to rising water levels in the rivers. Adult females will then travel along the river systems in search of food, before making their journey back to the nesting grounds for the next breeding season. For some females, this will be a journey of up to 200km!We predict that on average every year monsoon claims up to 90% of all the hatchlings from that year.

Photo of nesting, eggs and hatchlings

Did you know?

Gharial eggs are the heaviest of all crocodilians, weighing between 200 grams and 250 grams, with females laying up to 40 eggs, these eggs will weigh up to 10 kgs. Gharial are also the longest crocodilian hatchlings when they hatch out of their eggs!