AUSTRALIAN BIODIVERSITY RECORD - Calodema

Australian Biodiversity Record, 2007 (8): 1-124apparent conflict. Shelter sites are for short term use only (hours or days) and are regularlyabandoned for more suitable sites elsewhere on the reef - although on occasions a site maybe continuously occupied for 2 or 3 weeks by a large individual. When under cover, they donot seem to tongue flick or otherwise seek prey - they appear to be resting until suitableconditions for open active foraging occurs. One of the more interesting physiological traits ofAipysurus species (both laevis and pooleorum) concerns use of its tail - when sheltering, asnake will often leave its tail exposed - and this is done both during the day and night,although it appears to be more common at night. Physiologists have discovered that the tailhas a unique photoreceptor just anterior to the end, but its precise function is at presentunclear. It may be some sort of metabolic regulating mechanism to allow extended periods ofsubmergence during periods of darkness, or it is possibly used as a predator/prey detectiondevice. When in repose under cover, a snake will leave its tail exposed at the edge of theshelter, and when the light intensity changes suddenly the tail is moved instantly, and thesnake appears to investigate the source of the lighting change. Reproduction is highlyseasonal in this ovoviviparous species. Mating occurs between May and August and thegestation period is around 9 months. Males actively court receptive females with vigour duringthe mating season, and at this time this species can be particularly inclined to respondaggressively to divers who may disturb their courting or mating activities. By Spring(September to October females are carrying yolky follicles, and oviducal young are carriedfrom mid Spring through Summer to Autumn when they are born. Litter size is variable and iscorrelated with size - larger females tend to produce higher numbers of young. From 1 to 11young may be produced in a litter, although the average is only around 6-7 large young in abrood. At birth they juveniles are quite large, at around 300-350 mm in length. Growth is rapidfor the first few years, but slows upon attaining sexual maturity. Males attain sexual maturityat around 3 years of age, while females are not sexually mature until around 4 or 5 years old.It would appear that most females only reproduce every 2nd year, and a life-span of around15 years in attained. Major predators are sharks and sea eagles; parasitic nematodes havealso been found in their stomachs but their effects if any are unknown.Toxicity: Although often credited as being one of the more ‘aggressive’ species of sea snake,this is actually a very curious species that has been known to leave protective shelter or coveron becoming aware of a diver and swim towards them while rapidly flicking its tongue. Othersmay be very shy and rapidly flee to the protection of a crevice when approached by a diver,until they can assess the extent of the threat. During apparently exploratory or curious activity,an Olive Sea Snake may also just casually swim right up to human divers and proceed totouch arms, legs and body with its tongue or head. Naturally, this can be somewhatdisconcerting to the more inexperienced divers - particularly when some snakes vigorouslycoil around a diver's arm or leg during their ‘investigations’. Divers may be tempted to overreactto the snake by attempting to fend it off with a violent panic response of arm-waving oreven by directly hitting the snake by kicking and punching it. This often has the effect ofsufficiently harassing the snake to the point where it may actually attempt to bite, so cautionshould be exerted, because its venom is highly toxic to humans. On the other hand, duringthe breeding season in Autumn - Spring, males can become very nervous to any perceivedthreat, and may on rare occasions seek to bite a diver swimming too close. Indeed, suchlarge males can be quite belligerent and on occasions have forced divers from the water withtheir repeated lunges and determined attempts at biting. So how does one discriminatebetween a ‘curious’ sea snake and one that is intent on biting? An indication of the snake’sintentions is about the best one can hope for, so it’s best to give all sea snakes a fairly wideberth if possible. As a general rule - but this is not always the case - the swimming pattern ofan attacking sea snake usually leaves no doubt as to its intentions, as it is much faster andmore direct than that of a curious specimen. When a genuine ‘attack’ occurs, it may biterepeatedly and with determination if sufficiently aroused, and with its relatively large teeth, awet-suit should not be considered as adequate protection from penetration by the fangs of anadult specimen. Similarly, specimens landed on trawlers vigorously bite anything within range,including other snakes, fishes and fishing gear, and those handled by researchers readily tryto bite if restrained or handled roughly, so urgent medical attention should always be sought ifone is unfortunate enough to receive a bite from this species. Although there are no knownhuman fatalities associated with its bite, tests have shown that the venom is extremely toxic.6