Yellow-bellied Sea Snake

The yellow-bellied sea snake (Hydrophis platurus) is a venomous species of snake from the subfamily Hydrophiinae found in tropical oceanic waters worldwide, excluding the Atlantic Ocean. It was previously classified in the monotypic genus Pelamis but has since been reclassified as part of the genus Hydrophis based on molecular evidence. It is also known by other common names such as yellowbelly sea snake or pelagic sea snake.

Sea snakes, including the yellow-bellied sea snake, are a monophyletic group that diverged from the Australasian venomous snakes (Elapidae) around 10 million years ago. The yellow-bellied sea snake is part of the rapidly radiating Hydrophis group.

This species has a distinct bicolor pattern with a yellow underbelly and brown back, making it easily distinguishable from other sea snake species. Yellow-bellied sea snakes are fully adapted to living at sea, engaging in mating, eating, and giving birth to live young (ovoviviparous). Adaptations to aquatic life include reduced ventral scale size, laterally compressed body and paddle-tail for swimming, valved nostrils and palatine seal for excluding seawater, and cutaneous gas exchange for prolonging dive times. They can obtain up to 33% of their oxygen requirements through their skin while diving and swimming at the water's surface. Sea snakes also possess a special salt gland in the lower jaw, initially believed to filter out salt from seawater, but it is now known that they only drink fresh water.

The yellow-bellied sea snake has a compressed body, with the posterior being less than half the diameter of the neck. The body scales are juxtaposed, subquadrangular in shape, and arranged in 23-47 rows around the thickest part of the body. Ventral scales, numbering between 264 and 406, are very small and may be indistinguishable from adjacent body scales. The head is narrow, with an elongated snout. The coloration of the snake can vary, but it is most commonly black above and yellow or brown below, with a sharp demarcation between the dorsal and ventral colors. Some individuals may have black spots or bars on the yellow or brown background, or the yellow may extend dorsally, resulting in a narrow middorsal black stripe or a series of black crossbars. Males can reach a total length of up to 720 mm (28 in), with a tail length of up to 80 mm (3.1 in), and females can reach a total length of up to 880 mm (35 in), with a tail length of up to 90 mm (3.5 in).

The yellow-bellied sea snake is widely distributed and primarily inhabits pelagic waters. It is often found on oceanic drift lines, utilizing surface currents and storms for movement. Its distribution is influenced by favorable water temperatures, oceanic currents, and the presence of land bridges that hinder further dispersal. The species can be found in the tropical Indo-Pacific, from 🇨🇷 Costa Rica to southern 🇺🇸 California and northern 🇵🇪 Peru. It is the only sea snake known to have reached the Hawaiian Islands. The species thrives in free-floating mats of sea kelp in the 🌊 Indian Ocean and is commonly found beached on the coast of Southwest 🇦🇺 Australia. It has also been reported in colder waters, such as the coasts of southern 🇺🇸 California, Tasmania, and 🇳🇿 New Zealand, although these occurrences are linked to El Niño events or severe storms. The yellow-bellied sea snake has even been found in limited circumstances in the Atlantic Ocean, although this is considered a dispersal from its native Pacific range. It has been documented along the eastern coast and eastern islands of Africa, as well as in the Colombian Caribbean. The species requires a minimum temperature of 16-18 °C (60.8 to 64.4 °F) for long-term survival.

Contrary to past beliefs, sea snakes require fresh water to survive, and the yellow-bellied sea snake drinks precipitation that forms on the surface of seawater. This species can survive severe dehydration for up to 7 months during seasonal drought. Yellow-bellied sea snakes breed in warm waters and have a gestation period of around 6 months. Females give birth to live young in tidal pools but move poorly on land due to their smaller belly scales. They are sometimes observed in large aggregations on the surface of the water, which is believed to aid in prey capture. They attract pelagic fish by floating on the water's surface, then capture prey through a backwards swimming motion and rapid lunge of the jaws. This species can swim backwards, which is an unusual characteristic. It is proposed that the snakes locate their prey by sensing vibrations generated by fish movement.

The venom of the yellow-bellied sea snake is highly potent, like that of other sea snakes. It contains various neurotoxins and other isotoxins. Sea snake venom can cause damage to skeletal muscle, resulting in myoglobinuria, neuromuscular paralysis, or direct renal damage. The venom of significant sea snake species, including the yellow-bellied sea snake, can be neutralized with antivenoms such as Enhydrina schistosa antivenom produced by Commonwealth Serum Laboratories Ltd. If this antivenom is unavailable, tiger snake or polyvalent antivenom should be used. No deaths from yellow-bellied sea snake bites have been recorded in 🇦🇺 Australian waters, where the Enhydrina schistosa antivenom has been tested and proven effective.

Overall, the yellow-bellied sea snake is a widely distributed and adaptable species that has evolved numerous anatomical and physiological adaptations for a fully aquatic lifestyle. With its highly potent venom, it serves as a unique and important member of the sea snake family.