- A male gharial, a critically endangered crocodilian, was found dead in Nepal’s Chitwan National Park, entangled in a fishing net and hook.
- Male gharials are vital for the survival of the species, which has a skewed sex ratio and faces threats from fishing, habitat loss and poaching.
- Park officials are trying to boost the male population by incubating eggs at a certain temperature, but critics question the effectiveness and sustainability of this approach.
On June 26, in Nepal’s Chitwan National Park, a male gharial, one of the world’s most endangered crocodilians, was found dead. A fishing net was found wrapped around the animal’s snout and a hook pierced its abdomen.
The death of the gharial (Gavialis gungeticus), a fish-eating crocodile with a long, narrow snout, is a major blow to the conservation of the species, which has only a few hundred individuals left in the wild. Male gharials are especially rare and vital for the survival of the population, as they mate with multiple females and fertilise their eggs.
“The natural sex ratio in gharials is already heavily skewed towards females with only a handful of males for a hundred females,” said conservationist Ashish Basyal. “Any unnatural death of a gharial is a serious threat for conservation, but the death of a male can have even severe consequences on the population.”
The gharial was discovered on the banks of the Budhi Rapti stream, a tributary of the Rapti river that flows through the park. According to Chitwan National Park officials, it was one of only four or five adult males in the Reu, Rapti and Narayani rivers, which are home to about 219 gharials. A 2019 survey of the Rapti river spotted 99 gharials, but only one was confirmed as an adult male.
Gharials were once abundant in the Ganges river and its tributaries that flow through the plains of Nepal and India. Their range is now limited to a handful of rivers and their survival is threatened by fishing, changes in river flow and poaching.
Male gharials are easily recognisable by their distinctive ghara, a large growth on their snout that resembles an earthen pot, locally called ghara. They use their gharas to vocalise and blow bubbles during mating displays. However, some researchers speculate that their ghara may have also made them more vulnerable to hunting or entanglement in fishing nets.
Another factor that may affect the sex ratio of gharials is temperature-dependent sex determination (TSD), a phenomenon in which the incubation temperature of the eggs determines whether they will hatch as males or females. A study at the Madras Crocodile Bank Trust and Centre for Herpetology in India found that when gharial eggs were incubated at 32.5°C, all the hatchlings were males, but when they were incubated at 33°C, only around 60% were males.
“There are indications that slight changes to the temperature during incubation could alter the sex of the offspring,” said Bashyal. “It is possible, although not confirmed, that rising global temperatures could have also tilted the balance in favour of females.”
The other problem is that it is impossible to tell the sex of gharials until they become adults and develop the ghara. “Even experienced gharial researchers have failed in ascertaining the sex of sub-adult gharials,” said Bed Khadka, who worked at the Gharial Breeding Centre in Chitwan for decades. “This further adds to the challenge of boosting male population.”
To address this challenge posed by scarcity of males, park officials have been using laboratory incubators for the last three years to hatch fertilised eggs at around 32°C in the hope that they turn out to be males. On June 7, authorities at the gharial breeding centre reported that all of the 20 fertile eggs in their laboratory incubator had hatched.
“We are glad that the eggs that we collected have hatched and hope that they turn out to be males,” said Ganesh Tiwari, information officer at Chitwan National Park.
However, critics argue that such incubation programs may not be sustainable or effective in the long run. “We don’t know how the hatchlings will turn out, and what will be their state of health when they grow up,” said Khadka.
He also questioned whether park officials had conducted proper surveys to assess how many males are needed in the river system. The sex ratio may have been skewed for a reason, he said. What happens if all the incubated eggs turn out to be males? Officials don’t have answers.
Meanwhile in Chitwan, as the monsoon rages on, officials have banned all types of fishing. But some people still risk breaking the law to catch fish in the swollen rivers. Critically endangered gharials pay the price.
Lang, J. W., & Andrews, H. V. (1994). Temperature-dependent sex determination in crocodilians. Journal of Experimental Zoology, 270(1), 28-44. https://doi.org/10.1002/jez.1402700105
Khadka, B., & Kandel, R. C. (2020). Translocation of male gharial (Gavialis gangeticus) from Babai River to Chitwan National Park, Nepal. Crocodile Specialist Group Newsletter, 39(3), 15-18. Retrieved from https://www.researchgate.net/publication/344578498_TRANSLOCATION_OF_MALE_GHARIAL_GAVIALISGANGETICUS_FROM_BABAI_RIVER_TO_CHITWAN_NATIONAL_PARK_NEPAL
Yadav, R. K., Lamichhane, S., Thanet, D. R., Rayamajhi, T., Bhattarai, S., Bashyal, A., & Lamichhane, B. R. (2022). Gharial (Gavialis gangeticus, Gmelin, 1789) abundance in the Rapti River, Chitwan National Park, Nepal. Ecology and Evolution. https://doi.org/10.1002/ece3.9425
This article was first published on Mongabay.com.
Banner image: A male gharial with its distinctive ghara. Photo by Bernard DUPONT/Wikimedia Commons.