species report

1. 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.

2. 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.

3.  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.

4. (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

5. 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.

6. 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).

7. 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.

8.  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.

9.  LITERATURE CITED
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