Researchers have created an inventory of India’s marine snakes. They report a total of 26 species from India’s seas and coasts.

Being caught as bycatch is one of the biggest threats to sea snakes. Instances of mass bycatch death have been reported.

Many marine snakes are venomous and hence pose a threat to fishermen.

They are neither well-known nor well-studied. Now a documentation of India’s sea snakes hopes to stimulate further research interest and bring focus on the conservation of these marine creatures.

In a new study published recently in Journal of Threatened Taxa, scientists from the Chennai Snake Park and the National Centre for Sustainable Coastal Management (NCSM), Chennai, created an inventory of India’s marine snakes. The researchers report a total of 26 species from India. Many of these species are under threat of bycatch deaths caused during fishing.

Broadly speaking, marine snakes are of two kinds; one that spend their entire lives in the sea and are called true sea snakes. The other variety consists of snakes that prefer estuaries and mud-flats. All true sea snakes have front fangs, are venomous and have an oar-shaped tail.

“The inventory is a part of NCSM’s effort to create annotated lists for almost all marine life in India,” said S.R. Ganesh, deputy director, Chennai Snake Park, who was part of the project. The report is a “state of the art compilation of information” on the subject, he said. “Not only scientists, but also others interested in sea snakes will find our work useful,” he added.

The most common sea snake, along the Indian coast, is the hook-nosed sea snake (Hydrophis schistosa). Then come two other species, the annulated sea snake (H. cyanocinctus) and Malacca sea snake (H. caerulescens), said Vivek Sharma, who runs the website, indiansnakes.org. In the other category of marine snakes (that are not true sea snakes), the dog-faced water snake and glossy marsh snake are most widespread along India’s coast and even in the islands.

“Lastly, the file snake, which is a lookalike of the sea snake, but is a harmless marine snake, is without a doubt the most common in many places along the western coast. On any given day, you can count 30 to 40 of these, with fishermen, off the Konkan coast,” said Sharma.

Chetan Rao, a researcher with conservation and natural resource management non-government organisation Dakshin Foundation, has been studying sea snakes in Sindhudurg in Maharashtra along the western coast of India. Rao agrees that the hook-nosed sea snake is the most common in India. On board fishing trawlers during his research work, Rao has seen many sea snakes getting caught in nets. Being caught as bycatch during fishing is one of the biggest threats to sea snakes.

“Mortality due to fishing varies among species – some species are more affected than others. But most deaths do happen due to physical injuries (trapped under the weight of the catch) or cases of drowning (because sea snakes are air-breathing),” said Rao.

Instances of mass bycatch death have also been reported. In one incident in Goa, 81 hook-nosed sea snakes were found dead over a 20 to 30-metre stretch on the beach. A couple of days later, 69 snakes were found dead again on the same stretch of beach.

The authors of the present study say that such mass bycatch deaths are caused due to shore seines used by fishermen. Seine fishing uses a net called a seine that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Prawn trawlers and boat seine nets are also among the top threats for sea snakes.

In countries like Australia, people have experimented with bycatch reduction devices and have seen a 30 percent reduction in sea snake catch, said Rao. “However, these gears may not be suited for our seas as fishing practices, policies, number of vessels and variations in fisheries management across states are very different in both countries. We may have to experiment with different gear to see what causes least harm to snakes,” he added.

Another challenge is that fishermen along the Indian coast are not interested in sea snakes as they don’t hold any economic value. They are also aware that sea snakes are venomous. So, according to Rao, although a fisherman doesn’t go looking for sea snakes, they are exposed to sea snake bites, especially when they are sorting their catch.

“This happens as the snakes are often trapped near the head region and they have to be physically removed. Since sea snakes have [small] fangs, using thick gloves onboard the trawler or while sorting fish from nets could protect fishermen from getting bitten,” said Rao.

Such precautionary measures are especially essential because there is no antidote available specifically for sea snake venom. “Due to the lack of adequate information on sea snake ecology, any comprehensive plan to develop an antidote becomes futile as populations tend to show variation and venom potencies vary geographically,” said Rao.

Although there isn’t enough data on the number of sea snake bites in India, both Rao and Sharma agree that the numbers are low, despite the frequent encounters between fishermen and sea snakes. “This is probably because the fishermen have some idea about how to deal with them,” said Sharma, adding, “Many fishermen simply return them back to the sea while others kill them. We definitely need to educate fishermen to advocate for a ‘no killing by hand’ mindset.”

Although marine snakes are protected under schedule IV of Indian Wildlife (Protection) Act, 1972, they are threatened by human activities and changing marine environment. In addition, there are hardly any studies in India that have looked at the environmental impacts of these threats on sea snakes. The authors of the present study say that a “long-term bycatch monitoring programme to obtain baseline evidence on the abundance of the sea snake species” is needed. Also, finding areas of “high biodiversity and the distribution of threatened (sea snake) species” will be fundamental for their conservation.

CITATION:

Ganesh, S. R., Nandhini, T., Samuel, V. D., Sreeraj, C. R., Abhilash, K. R., Purvaja, R., & Ramesh, R. (2019). Marine snakes of Indian coasts: historical resume, systematic checklist, toxinology, status, and identification key. Journal of Threatened Taxa, 11(1), 13132-13150.

Banner image: A close-up of a Shaw’s sea snake. Photo by Chetan Rao.