Yellow-bellied Sea Snake, Hydrophis platurus
Yellow-bellied Sea Snake, Hydrophis platurus. Beach wash-up found in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.
Phylogeny: The Yellow-bellied Sea Snake, Hydrophis platurus (Linnaeus, 1766), is a member of the Elapidae Family of Sea Snakes. The Hydrophis genus is one of thirty-five genera in the Elapidae family and there are thirty-nine species in the Hydrophis genus. This species is also known as the Pelagic Sea Snake and in Mexico as Serpiente Marina Amarilla. There is one accepted subspecies, Hydophis platurus xanthos, which is smaller, all yellow, and limited to the Golfo Dulce, Costa Rica. The genus name Hydrophis comes from the Greek word for “water snake”. The species name platurus is also Greek and means “flat tail”.
Morphology: The Yellow-bellied Sea Snake is a marine snake that has a compressed body that tapers toward the tail. They are uniquely adapted to ocean survival with small scales, a paddle-like tail, valved nostrils, a palatine seal to exclude sea water, and they are capable of cutaneous gas exchange that affords prolonged dive times. They vary in color, being dark brown to black dorsally and bright yellow to pale yellow ventrally. The tail has black spots or bars. They have a narrow elongated flattened triangular head with an elongated snout and nostrils set high on top of the head They have small fangs at the front of the upper jaw. They are sexually dimorphic with females being larger than males. Yellow-bellied Sea Snakes reach a maximum of 1.14 m (3 feet 9 inches) in length.
Habitat and Distribution: The Yellow-bellied Sea Snake is found in warm ocean waters from within a few miles of shore to far out at sea. They live primarily near the surface and at depths up to 9 m (30 feet). They are at the whim of oceanic currents but require water temperatures above 16oC (61oF) for long term survival. Their optimal temperature range is 28oC (82oF) to 32oC (90oF). They collect along drift lines of floating debris in tranquil waters in schools that number into the thousands which affords them an abundant food source. They are diurnal and live their entire life at sea. They are able to swim both forward and backwards. They obtain the water they need for survival from either coastal fresh-water sources or from fresh rainfalls; they can survive for up to 7 months without access to fresh water. They can remain submerged for up to three hours and spend as much as 87% of their time underwater having the ability to obtain up to 33% of their oxygen requirement through the skin from the oceanic water. The Yellow-bellied Sea Snake is probably the most widely distributed snake in the world, inhabiting tropical ocean waters in the Indian and Pacific Oceans, including the coasts of Africa, Asia, Australia, Mexico, and Central America. The Yellow-bellied Sea Snake is found in all Mexican coastal waters of the Pacific Ocean. It is the only sea snake found in Mexican oceanic waters. They have also been observed in Southern California waters but only during warm water episodes.
Diet: Yellow-bellied Sea Snakes are lie-in-wait ambush predators that feed in the first 3 m (10 feet) of the water column and consume a wide variety of small fishes and eels, many of which mistakenly seek shelter beneath the motionless snake that resembles drifting wood. The Yellow-bellied Sea Snake injects a neurotoxin into their prey which they swallow whole.
Predators: There is no documentation of any animal preying on a Yellow-bellied Sea Snake. Perhaps other biological factors such as food shortages, parasitism or illness, or physical events such as storms pushing them ashore or into cold water are sufficient to keep population levels in check. When they wash ashore they die fairly quickly.
Reproduction: Yellow-bellied Sea Snakes are gonochoric (male or female for life). Reproduction is sexual, with internal fertilization. Mating only occurs when water temperatures exceed of 20oC (68oF). Females are ovoviviparous, meaning that her eggs hatch internally and she gives birth to fully formed snakes. The gestation period is 6 months and 1 to 8 juveniles are hatched. Newly born Yellow-bellied Sea Snakes are 22 cm (8.7 inches) in length.
Ecosystem Interactions: Yellow-bellied Sea Snakes provide habitat for other species such as barnacles, crabs and fish. These interactions don’t appear to harm the snakes, and the other species benefit by having structure to cling to, or hide in, in an otherwise vacant pelagic environment. In some populations, about 19% of these snakes are colonized by these epibionts. If the epibionts become a problem, they have the interesting ability to tie themselves into a knot and then move the knot from one end of the body to the other removing foreign items such as algae, barnacles and miscellaneous growths. They can also shed their skin on a regular basis to rid themselves from pests. Yellow-bellied Sea Snakes are also known to host internal parasites such as round worms and tape worms.
Human Interactions: Human interactions with Yellow-bellied Sea Snakes are limited. Sea snakes are not targeted as a fishery and they have limited impact on fisheries. Yellow-bellied Sea Snakes are considered to be Venomous and Potentially Dangerous, however, they are not considered to be a threat to swimmers, with no reported fatalities from bites recorded. They are non-aggressive, reluctant to strike and often strike without injecting venom. Most bites occur when fishermen find them in their fishing nets. The venom of this species is highly potent, with a subcutaneous LD50 of 0.067 mg per kg with 1.0 mg to 4.0 mg delivered with each bite. There are anti-venom’s commercially available that effectively neutralize their venom. From a conservation perspective the Yellow-bellied Sea Snake is considered to be of Least Concern with stable, widely distributed populations.
Synonyms: Anguis platura and Pelamus platurus.