The Yellow-bellied Sea Snake (Pelamis platura)

Alyssa C. Albro

Biology Department, Frostburg State University

CLASSIFICATION

The most widely-used common name of this species is the yellow-bellied sea snake, scientific name being Pelamis platura (Linnӕus 1766). The scientific name Pelamis platurus was introduced by Ferdinand Stolička in 1872, and is still widely accepted by herpetologists today in spite of the grammatically incorrect use of the noun ending in –us rather than –a, as a feminine noun requires.

Other common names which the snake may be referred to by include pelagic sea snake, yellowbelly sea snake, serpent marin jaune (French), and serpiente marina amarilla (Spanish). Note that French and Spanish names literally translate to: “yellow sea snake”. The species got the name “yellow-bellied sea snake” due to the bright yellow belly it sports in contrast to the (usually dark) top half of its body, though there are some color morphs (as many as seven listed (Smith, 1926)) of the species, one of which is almost entirely yellow. The “pelagic sea snake” name was received due to the fact individuals are born, live, and die at sea – they are entirely pelagic, unlike other sea snakes which come to land periodically.

Pelamis platura belongs to the family Elapidae (meaning “sea-fish”; venomous snakes in tropical and subtropical regions of the world), subfamily Hydrophiinae (including coral reef snakes and sea snakes; venomous Elapid snakes inhabiting marine environments), genus Pelamis (meaning “tunny fish” in Ancient Greek, species platura (meaning “flat tail” in Ancient Greek; platys meaning “flat”, and oura meaning “tail”).

DISTRIBUTION

P. platura is the world’s most widely-distributed sea snake, as it is found in almost all coastal waters, the only exceptions being North America’s east coast (the Atlantic Ocean and the Caribbean Sea), and the Red Sea. Among the entirety of its distribution, the snake is most commonly found in the coastal waters of the Indian Ocean and Persian Gulf specifically, but is also a frequent sight in the waters of Southeast Asia.

This species is the only sea snake to reach the Hawaiian Islands (Liptow, 1999), and has also been reported around the shores of New Zealand, in the Agulhas Current around South Africa (Branch & Branch, 1981), though it is important to note that snakes do not migrate around the tip of South Africa, instead staying on either side of it.

Only two specimens have ever been found in Russia, both dead. One was found in southern Primorskij Territory, and one was near Vladivostok City. However, both were roughly along the coast of the Sea of Japan (Kharin, 2007).

The range map below was the most accurate available which correlated with information presented earlier in this section.

(from VAPAGuide, SEA-101. 2006.)

HISTORY OF THE SPECIES

Compared to other species of snake throughout the world, there is little to no information regarding this species’ history.

Man has had very little interference with P. platura, and most interaction between humans and this species has been either accidental or for the purpose of research. It is worth note that this snake would inhabit the Caribbean Sea and the Atlantic Ocean if the species had moved to that part of the world through Central America’s waterways prior to the formation of Panama’s land bridge forming approximately 3 million years ago.

Lastly, there are no known fossils of this species. All members of Hydrophiinae are of recent origin, arising no earlier than the late Oligocene period.

POPULATION NUMBERS

There are no specific population numbers on record on species, though it is assumed to be a stable species seeing as it is fairly common and widespread, estimated to contain 100,000 to >1,000,000 individuals, based on collection rates for research in specific areas in years past. Certain mating, feeding, and hygienic (skin-shedding, parasite-removing) rituals of the species are cause for hundreds or thousands of individuals to aggregate in a single location (Ernst & Ernst, 2001).

P. platura is listed as a species of Least Concern based on the ICUN Red List version 3.1 in 2010, and therefore is considered stable.

The species has no status listed under the ESA, CESA, BLM, USDA Forest Service, or California Department of Fish and Wildlife. Its status under the National Natureserve Conservation has been listed as both “Not Applicable” and G5-secure.

HABITAT

P. platura, as mentioned earlier, is an entirely pelagic species, living in the uppermost layers of the ocean for the duration of its life, typically staying above 10m (Cogger, 2007) in depth. It is found in the open ocean, and is less frequently found around coral reefs and coastlines than its relative sea snakes. Occasionally, it may wind up in inter-tidal habitats (Minton, 1966) after being caught in currents.

The species can most commonly be found in tropical and subtropical waters of the Pacific and Indian Oceans, especially on the east coast of Africa north of the Arabian Gulf, and east of the Asian coast on the Indo-Pacific border, and northward to Japan. Seeing as it primarily lives in the tropics, with some variation north and south of tropical waters, survivable temperatures are recorded in a wide range between 11.7-36°C (Shabnam, 2014), or as narrow a temperature range as 16-18°C has been recorded as a necessity for long-term survival (Dunson & Ehlert, 1971), which is why they do not migrate around the southernmost tips of South Africa or South America – the water gets too cold.

As a whole, the species does not show trends in migration with the changes in season, though some select populations may do so depending on where they were located prior to migration. Occasionally, P. platura is washed ashore (dead and alive) with rough weather and currents forcing it to land. Patterns of distribution appear to be largely clumped (Dunson & Ehlert, 1971), especially during breeding season.

(from Effects of Temperature, Salinity, and Surface Water Flow in Distribution of the Sea Snake Pelamis (Dunson & Ehlert, 1971))

This snake is incapable of tolerating fresh water (and for this reason they are not found in the Atlantic Ocean or the Caribbean Sea, as individuals would need to cross through the Panama Canal post-land bridge-formation otherwise), though specimens have been caught by the dozen per hour at the Pacific entrance of the Canal (Kropach, 1972). In addition, they are incapable of tolerating high levels of salinity (for this reason, they are not found in the Red Sea), and are not the only species of sea snake with this intolerance. Research has suggested that there is a negative correlation between mean annual salinity in oceans and sea snake species richness (Brischoux et al., 2012).

FOOD AND FEEDING BEHAVIORS

P. platura is an entirely carnivorous species, specifically speaking, they are strictly piscivorous (fish eaters, preying on small fish). Their diet is not recorded to vary between sexes or age groups, and individuals typically forage during the day when they do forage. Foraging and feeding can take place regularly, or even in intervals of weeks at a time (Visser, 1967).

When foraging, massive groups of the species aggregate (Ernst & Ernst, 2001), and the snakes take part in a behavior called “knotting”. Dozens, or even hundreds, of snakes group up and intertwine their bodies loosely with others after feeding, interlocking with those surrounding

it, and the formation has the rough appearance of a “knot”. Foraging and knotting both occur in ocean slicks (Kropach, 1975), which is an area where sea currents diverge and debris accumulates.

P. platura is an ambush predator, lying in wait in these slicks (and giving the appearance of floating debris) until fish swim by. They do not chase their prey. If a strike misses, they will resume floating to try again (Ernst & Ernst, 2011). Once the prey is grabbed, the snake swims backward through the ocean (effectively drowning the fish if the snake has it by the tail), and may “chew” (without fully letting go) two or three times to sufficiently inject venom, which is a potent neurotoxin which blocks acetylcholine receptors (Tu, 1991), before swallowing prey whole headfirst. This species’ fangs are hollow and nonmovable, only located in the back of their mouth.

As for drinking, this species may wait for months until the next rainy season comes. When it does, P. platura sits atop the water to drink the freshest rainwater which falls. The fresh rainwater has a lesser concentration of salt than seawater (Lillywhite et al., 2014). P. platura cannot drink seawater, either, as their bodies are unable to handle (and sufficiently filter out) the increased amount of sodium.

BEHAVIORS AND SOCIAL RELATIONSHIPS

Although a species of sea snake, P. platura breathe air just like any other species of snake, having one lung in their bodies instead of gills similar to fish. However, in order to cope with their lifestyle, the species has developed an adaptation for holding their breath over long periods of time. In each breath held, the amount of air in the snake’s body is enough to keep it neutrally buoyant up to 30m (Vogel, 2003). Individuals have been recorded to hold their breath up to 213 minutes, though they typically do not exceed breath holding periods over 90 minutes (Rubinoff et al., 1986). Toward the end of the breath-holding limit, P. platura gradually begin ascending as the amount of gases in its lung has decreased. Their natural cycle of breathing, diving, and resurfacing can take as long as three hours (Graham, 1987b), as indicated by the maximum amount of time snakes can hold their breath.

The diving pattern of this species is recorded to have four phases, listed in order. The snake begins its dive with a nearly vertical descent, before slowing down and descending with a more buoyant bobbing motion every two minutes until the individual reaches a depth where they have attained neutral buoyancy (neither sinking nor rising), followed by a gradual descent without bobbing, and lastly a rapid descent (3-4m per minute) concludes the pattern which snakes follow to dive (up to 10m, as stated earlier) (Priede, 1990). To ascend, the snake rises gradually through the water, and this surfacing process takes approximately 82% of the time spent between breaths. Diffusion gradients in the body of P. platura remove nitrogen gases built up in the bloodstream, in order to increase oxygen intake (Seymour, 1974). This is an effective method of the snake avoiding “the bends”, as SCUBA divers may suffer if they ascend from a dive too quickly.

Furthermore, the snake’s skin acts as a membrane to filter out carbon dioxide and nitrogen after it is removed from the blood (Graham, 1987a).

To swim, P. platura undulate its flattened tail, along with its entire body, laterally in order to propel itself through the water. This species prefers to move by drifting with the current, and it does not swim actively for long distances. Due to the fact this species is so well-adapted for ocean life, it is helpless and awkward on land. If washed ashore, individuals can quickly die of heat exhaustion and/or dehydration if they are unable to squirm back into the water.

Based on observations, P. platura appears to be primarily diurnal, though some nocturnal activity has been reported (Myers, 1945). This snake often sleeps closer to the ocean floor, only resurfacing every few hours to breathe.

P. platura appears to be a silent species, with no vocalizations or other sounds, including hissing.

Hygiene is maintained by shedding its skin by “knotting”. Although the snake is capable of knotting itself, it is more commonly observed to “knot” with others of its species, typically when grouped to hunt.

Lastly, the species is often alert to its surroundings, though rarely reacts aggressively when approached, preferring to swim away rather than engage in conflict. Due to this behavior, they can easily be caught. Furthermore, it is very reluctant to strike, and often does not inject venom unless it is hunting.

YEARLY CYCLE AND BREEDING BIOLOGY

Unfortunately, there is little information known about the specifics on breeding biology of P. platura compared to other species, and further, serious research is needed (Ernst & Ernst, 2011). From what is known, the most basic information is as follows: the species is ovoviviparous with internal fertilization, mated pairs practice knotting during their mating ritual, and gestation lasts roughly six months (Dunson, 1971).

There are 1-10 young per brood, with some correlation between mother length and clutch size (Vallarino & Weldon, 1996). Young are birthed tail-first or head-first, and no negative impacts have been reported from either method. Females bear young in tidal pools where there is no current, with temperatures of 20°C or higher, and even in swamps or brackish estuaries (Schmidt & Davis, 1941). The offspring are fully developed when born, having the appearance of miniature adults (22-26cm) with brighter coloration. Outside of the female protecting her young during their first few days of life, there is no other parental care offered (Rose, 1950).

No set “breeding season” has been noted, either, as P. platura seems capable of breeding throughout the year, though studies have suggested it prefers winter months (Dunson & Ehlert, 1971). Newborn snakes have been observed in waters more than 20°C every month of the year in certain locations (Gulf of Panama (Kropach, 1975), South Africa, and the Philippines (Visser, 1967)).

Young snakes grow quickly within their first year of life, though male growth rate slows after the individual reaches roughly 50cm in length. Sexual maturity is reached at this point, while females reach sexual maturity around 62.5cm (which is roughly 2-3 years of age).

There are only two stages in a male snake’s testicular cycle: germ cell recrudescence and proliferation, and lumina becoming lined with spermatozoa. Smaller females have been reported to have inactive ovaries in February, whereas larger females had eggs in her oviduct. By May, smaller females had eggs in her oviduct, and larger females’ eggs had developed into embryos (Goldberg, 2004).

MORTALITY AND DISEASE

Most threats to P. platura are from natural occurrences. That said, there are no major threats to the species listed.

There is only sparse data on parasites which impact the species, and no data on diseases. Parasites include Torticaecum nipponicum and Paraheterotyphlum austral (both species of nematodes) (Sprent, 1978), marine invertebrates encrusting the body surface (including, but not limited to, barnacles and bryozoan ectoprocts). External parasites can negatively impact swimming ability and courtship behavior, though they can easily be scraped off by knotting, coiling, or shedding skin. Turbulent seas caused by bad weather often result in snakes being washed ashore, most of which die.

Threats from humans are not excluded, as there are a handful. Occasionally snakes are harmed by boating activities, along with bycatch in squid fisheries, ghost fishing nets, and pollution (Guinea et al., 2010).

Lastly, it should be noted that this species does not do well in captivity, typically only surviving 2 years, 3 maximum, when wild-caught and moved to aquariums or zoos (Snider & Bowler, 1992). The cause for this is unsure.

MANAGEMENT

There is no species-specific conservation regulations in effect due to the ICUN and CITES statuses (both of which declare P. platura species of least concern in spite of the potential change in stability in coming years due to global warming and ocean pollution increasing). This snake is not considered a nuisance species, either, so no attempts to control it have been made.

Populations are not closely monitored, though as stated they are occasionally bycatch in fishing operations (Ward, 1996).

Although this snake’s fangs are located in the back of its mouth, there is still some risk to humans. They are venomous, but no fatalities have ever been reported.

LITERATURE CITED

Branch, M., and Branch, G. 1981. Seasnakes. Pp. 130-131. The Living Shores of Southern Africa. Struik Publishers, South Africa.

Brishoux, F., Tingley, R., Shine, R., and Lillywhite, H.B. 2012. Salinity influence and the distribution of marine snakes: implications for evolutionary transitions to marine life. Ecography 35: 994-1003.

Dunson, W.A. 1971. The sea snakes are coming. Natural History 80: 52-60.

Dunson, W.A., and Ehlert, G.W. 1971. Effects of temperature, salinity, and surface water flow on distribution of sea snake Pelamis. Limnology and Oceanography 16: 845-853.

Ernst, C.H., and Ernst, E.M. 2011. Yellow-bellied Seansakes (Serpeiente del Mar). Pp. 135-148. Venemous Reptiles of the United States, Canada, and northern Mexico. The Johns Hopkins University Press, USA.

Ernst, C.H., and Ernst, E.M. 2001. Snakes of the United States and Canada. Smithsonian Books, USA.

Graham, J.B., Gee, J.H., Motta, J., and Rubinoff, I. 1987a. Subsurface buoyance regulation by the sea snake Pelamis platurus. Physiological Zoology 60: 251-261.

Garahm, J.B., Lowell W.R., Rubinoff, I., and Motta, J. 1987b. Surface and subsurface swimming of the sea snake Pelamis platurus. Journal of Experimental Biology 127: 27-44.

Goldberg, S.R. 2004. Note on reproduction of the yellowbelly sea snake Pelamis platurus (Serpentes: Elapidae) from Costa Rica. Maryland Herpetological Society 40: 91-93.

Guinea, M., Lukoschek, V., Cogger, H., Rasmussen, A., Murphy, J., Lane, A., Sanders, K., Lobo, A., Gatus, J., Limpus, C., Milton, D., Courney, T., Read, M., Fletcher, E., Marsh, D., White, M.D., Heatwole, H., Alcala, A., Voris, H., and Karns, D. 2010. Pelamis platura: an online reference available at http://www.icunredlist.org/details/176738/0. Archived by WebCite at http://www.webcitation.org/6XNUSkER0 on 28 March 2015.

Junghanss, T., and Bodio, M. PhD. 2006. Seasnakes: an online reference available at: http://www.vapaguide.info/catalogue/SEA-101. Archived by WebCite at: http://www.webcitation.org/6XN14F9n5 on 28 March 2015.

Kharin, V.E. 2007. On the second record of Yellow-bellied sea snake Pelamis platurus (Linnӕus, 1776) from Russia. Russian Journal of Herpetology 14: 45-49.

Kropach, C. 1972. Pelamis platurus as a potential colonizer of the Caribbean Sea. Biological Society of Washington 2: 267-269.

Kropach, C. 1975. The yellow-bellied sea snake, Pelamis, in the eastern Pacific. Pp. 185-213 in W.A. Dunson (ed.), The Biology of Sea Snakes. University Park Press, USA.

Lillywhite, H.B., Sheehy, C.M., Brishoux, F., and Grech, A. 2014. Pelagic sea snakes dehydrate at sea: an online reference available at: http://rspb.royalsocietypublishing.org/content/281/1782/20140119. Archived by WebCite at: http://www.webcitation.org/GXNL69BFi on 28 March 2015.

Liptow, J. 1999. Pelamis platura; Yellowbelly Sea Snake, Pelagic Sea Snake: an online reference available at http://animaldiversity.org/accounts/Pelamis_platura/. Archived by WebCite at: http://www.webcitation.org/6XMzwKKuF on 28 March 2015.

Minton, S.A. Jr. 1966. A contribution to the herpetology of west Pakistan. Bulletin of the American Museum of Natural History 134: 76-77.

Myers, G.S. 1945. Noctornal observations on sea=snakes in Bahia Honda, Panama. Herpetologica 3: 22-23.

Priede, M. 1990. The sea snakes are coming. New Scientist 128: 29-33.

Rose, W. 1950. The reptiles and amphibians of South Africa. Maskew Miller, South Africa.

Rubinoff, I., Graham, J.B., and Motta, J. 1986. Diving of the sea snake Pelamis platurus in the Gulf of Panamá. Marine Biology 91: 181-191.

Seymour, R.S. 1974. How sea snakes may avoid the bends. Nature (London) 250: 489-490.

Shabnam, M. 2014. Pelamis platura: an online reference available at http://eol.org/pages/791184/details. Archived by WebCite at: http://www.webcitation.org/6XNVkH0i7 on 28 March 2015.

Snider, A.T., and Bowler, J.K. 1992. Longevity of reptiles and amphibians in North American collections. Society for the Study of Amphibians and Reptiles Herpetological Circular 21: 1-40.

Sprent, J.F.A. 1978. Ascaridoid nematodes of amphibians and reptiles: Paraheterophlum. Journal of Helminthology 52: 163-170.

Tu, A.T. 1976. Investigation of the sea snake, Pelamis platurus (Reptilia, Serpentes, Hydrophiidae), on the Pacific Coast of Coasta Rica, Central America. Journal of Herpetology 10: 13-18.

Tu, A.T. 1991. Primary structure of the sea-snake neurotoxins and their modes of attachment to acetylcholine receptors. Pp. 87-95 in M.F. Thompson, R. Sarojini, and R. Nagabhushanam (eds.), Bioactive Compounds from Marine Organisms: With Emphasis on the Indian Ocean. An Indo-United States Symphosium, Oxford and IBH Publishers, New Delhi.

Vallarino, O., and Weldon, P.J. 1996. Reproduction in the yellow-bellied sea snake (Pelamis platurus) from Panama: field and laboratory observations. Zoo Biology 15: 309-314.

Visser, J. 1967. Color varieties, brood size, and food of South African Pelamis platurus (Ophidia: Hydrophiidae). Copeia 1967: 219.

Vogel, S. 2003. Comparative Biomechanics: Life’s Physical World. Princeton University Press, USA.

Ward, T.M. 1996. Sea snake by-catch of prawn trawlers on the northern Australian continental shelf. Marine and Freshwater Research 47: 631-635.