The Yellow-lipped sea krait is a highly venomous sea snake that occurs in tropical Indo-Pacific oceanic waters. The head of these snakes is black, with lateral nostrils and an undivided rostral scale. The upper lip and snout are characteristically colored yellow, and the yellow color extends backward on each side of the head above the eye. The upper surface of their body is typically a shade of blueish gray, while the belly is yellowish, with wide ventral scales. Black rings of about uniform width are present throughout the length of the snake, but the rings narrow or are interrupted at the belly. The tail of these snakes is paddle-shaped and adapted to swimming. Yellow-lipped sea kraits have very potent neurotoxic venom which they use to prey on eels and small fish. Because of their affinity to land, banded sea kraits often encounter humans, but the snakes are not aggressive and only attack when feeling threatened.
Yellow-lipped sea kraits are widespread throughout the eastern Indian Ocean and Western Pacific. They can be found from the eastern coast of India, along the coast of the Bay of Bengal in Bangladesh, Myanmar and other parts of Southeast Asia, to the Malay Archipelago and to some parts of southern China, Taiwan, and the Ryukyu Islands of Japan. These snakes are also common on Fiji and other Pacific islands within their range. Vagrant individuals have been recorded in Australia, New Caledonia, and New Zealand. Yellow-lipped sea kraits lie in the open ocean, shallow coastal waters, coral islands, coral reefs, and in mangrove areas. On land, they often hide in vegetation, under beach rocks, or in small crevices and caves.
Yellow-lipped sea kraits are semiaquatic snakes; they spend much of their time underwater in order to hunt but return to land to digest their prey, to rest, and reproduce. Juveniles stay in the water and on the adjacent coast, but adults are able to move further inland and spend half their time on land and half in the ocean. Adult males are more active on land during mating and hunt in shallower water. On the other hand, adult females are less active on land during mating and hunt in deeper water. Because males are smaller, they crawl and swim faster than females. Body adaptations, especially a paddle-like tail, help these sea kraits to swim. On dry land, they can still move, but, not as fast as in the water. When hunting, Yellow-lipped sea kraits frequently head into deep water far from land, but always return to their specific home islands. They usually hunt alone, but may also do so in large numbers in the company of hunting parties of Giant trevally and goatfish. During this cooperative hunting sea kraits flush out prey from narrow crevices and holes, and the trevally and goatfish feed on fleeing prey. While probing crevices with their head, sea kraits are unable to observe approaching predators and can be vulnerable. The snakes can deter predators, such as larger fish, sharks, and birds, by fooling them into thinking that their tail is their head because the color and movement of the tail are similar to that of the snake's head.
Yellow-lipped sea kraits are carnivores (piscivores). They primarily feed on varieties of eels, but also eat small fish. Adult females, which are significantly larger than males, prefer to hunt in deeper water for larger conger eels, while adult males hunt in shallower water for smaller moray eels.
Yellow-lipped sea kraits have a polyandrous mating system in which females have more than one partner in a single breeding season. These snakes are oviparous, meaning they lay eggs that develop outside of the body. Each year during the warmer months of September through December, males gather on land and in the water around gently sloping areas at high tide. When a male detects a female, it chases the female and begins a courtship. Females are larger and slower than males, and many males will escort and intertwine around a single female. The males then align their bodies with the female and the resulting mass of snakes can remain nearly motionless for several days. After mating the female then lay as many as 10 eggs per clutch. The eggs are deposited in crevices where they remain until hatching. Little information is known regarding the hatchling of baby sea kraits. The eggs are very rarely found in the wild and only two nests have been definitively reported throughout the entire range of the species. It is known that females become reproductively mature when they are 1.5-2.5 years old while reach maturity at the age of 1.5 years.
Yellow-lipped sea kraits are threatened by the habitat loss which they require for laying eggs and digesting prey; this happens due to destruction and coastal development. They are also attracted to light and can be distracted by artificial sources of light, including hotels and other buildings, on coasts. In the Philippines, Yellow-lipped sea kraits are caught for their skin and meat; the meat is smoked and exported for use in Japanese cuisine.
According to IUCN, the Yellow-lipped sea krait is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
Yellow-lipped sea kraits prey mainly on eels and control its populations, thus playing an important in the ecosystems they inhabit.