AUSTRALIAN BIODIVERSITY RECORD - Calodema

Australian Biodiversity Record, 2007 (8): 1-124temperate waters through drift in major currents is thought to result in it temporarily occupyingnon-feeding and non-reproductive habitats such as southern Australia, Africa and NewZealand, but observations also suggest the possibility that this species can have a long-termpresence in such southern waters. At the broader global scale, it ranges from the southernCape of Africa throughout the Indian Ocean to India and across most of Asia and Australasia.It is widespread throughout the Pacific Ocean and although it occurs in both hemispheres, it isapparently more successful south of the Equator. In the Northern Hemisphere it has beenrecorded as far north as Possiet Bay, Russia in the western Pacific Ocean. The distributionextends right across to the western coasts of the Americas where it has been recorded fromabout as far north as California in the USA, and south to about Ecuador. In the south Pacific itoccurs in the Solomon Islands, Vanuatu, New Caledonia, Fiji and numerous other reefs andisland territories and states, to as far south as New Zealand.Habitat: This is a pelagic, or surface-dwelling species, well-known from open seas andoceans in tropical, subtropical and even temperate areas. It drifts worldwide amongst theflotsam of debris and seaweeds that gather along major current lines and most wouldprobably spend all of their lives on the open sea. Such drifts represent a unique marinehabitat for fishes and other marine life which utilise the debris fields as shelter and as asource of pelagic micro-organisms. Generally their presence in continental shelf waters isunusual, and probably the result of storms or unusual currents in their primary open-seahabitat.Biology/Ecology: Essentially a nocturnal species that drifts beneath or amongst flotsam suchas drifting seaweed where they lay in wait for surface-dwelling fishes. Although they tend tobe far less active than other sea snakes (indeed, they can lay motionless on the surface forhours at a time) for the most part they just go with the flow unless they are disturbed. Ifnecessary, they swim quite quickly by powerful lateral undulations and can also swim inreverse if necessary. Pelamis are essentially float-and-wait foragers, ambushing a variety ofsmall pelagic fishes by swimming backwards to seize fish that have been unknowingly usingthe snakes’ body as shelter. They will also actively chase fishes and seize them either headonor by a quick sideways lunge. In captivity they will eat fish that alive or dead, as well aspieces of fish and a captive Pelamis can get quite excited during feeding, rapidly lunging andbiting even other snakes in the frenzy to secure a fish; frogs have also been taken by captivespecimens as well. Specimens have lived just over 2 years in captivity, but their lifespan isunknown. The reproductive biology of Pelamis is poorly known, and varies somewhat acrossits range. It produces from 2 to 6 young in a brood (usually about 3), following a 6-8 monthgestation period. The size of young at birth range from 220mm. to 280mm in total length, andcan feed on small fish on the same day they are born. Apparently the number of offspring isnot related to female body-length. In Australian waters (New South Wales) it reproducesduring the winter months (May-July) in contrast to the pattern elsewhere over the species’range. Whereas near Costa Rica in the Eastern Pacific gravid females are found during theDry Season (December-April), with births appearing to occur around March (in nearbyPanama). In Asia (Sri Lanka) gravid females have been found in March (during the intermonsoonperiod). Off Africa in the Indian Ocean gravid females have been recorded from lateAutumn through Winter to Spring (May to October). Huge populations can accumulate inareas of converging currents, and on occasions thousands of snakes have been observedsheltering amongst the flotsam over many kilometres of drift. This species can also beoccasionally found stranded on beaches following periods of strong onshore winds. As suchlarge populations of Yellow-bellied Sea Snakes drift with flotsam in the major sea currents, itcan be expected that many are washed ashore during severe storms. When such eventsoccur, they appear to be able to temporarily seek shelter on the land in stormy weather, andon occasions can be found sheltering under debris above the high tide mark along beachesand mangroves. Their capacity for temporary survival out of water is in marked contrast tomost other sea snakes where it can be very quickly fatal. This probably indicates that thelower pressure of surface-dwelling or pelagic habits of Pelamis have resulted in a blood-flowphysiology less sensitive to otherwise hazardous terrestrial air pressure conditions. However,their extreme laterally-compressed body-form makes movement land extremely difficult, withthe snake being forced to crawl on its sides (laterally rather than ventrally). One of thepossible reasons for this species’ abundance could be its toxic flesh - which would make itpotentially unpalatable or even dangerous to most carnivores - although sharks, some large58