AUSTRALIAN BIODIVERSITY RECORD - Calodema

Australian Biodiversity Record, 2007 (8): 1-124Description: This is a very small species of sea snake, with a short, deep head that is notdistinct from the neck, and a moderately robust body-form. The head is usually brownish, withor without darker brown flecking. The base body colour is variable from one region to another,and may be cream to pinkish-brown, with prominent darker banding along the entire body.The series of broad transverse bands are black or dark slaty grey, and these bands may taperto a point at the ventrolateral margin, or extend partly onto the ventrals. In the paleinterspaces between the dark bands, the scales may be either faintly edged with black, ormore solidly marked with short black streaks, or on occasions blackish blotches; thesesmaller markings are usually more intense along the lower flanks. The venter is usually darkgrey to black, with the median area being darkest; on occasions specimens may have a darkcreamish venter. Some significant features of this species' morphology are: head shieldsenlarged and symmetrical; nasals contacting; prefrontals present; 1 preocular; 2 postoculars;temporals small; primary temporals 1-3; supralabials 6; body scales smooth, imbricate and in17 rows at mid-body (males and females have the same mid-body scale count); ventrals 125-165 (females have a higher ventral count than males); ventrals about three times the width ofadjacent body scales, and each with a shallow keel in the centre; the ventrals usually lacknotching on the posterior edge, but if present it is shallow; anal divided; subcaudals 23-34(males have slightly more subcaudals than females). Attains a maximum total length of onlyaround 90 cm., and a snout-vent length of about 80 cm., but the average adult total lengththough only rarely exceeds 50 cm. Females are sexually mature at 47 cm SVL. Variation inmorphology suggest that this species is composite.Distribution: Largely confined to tropical Australian seas, being found off the coasts ofQueensland, Northern Territory and Western Australia. Also widely known in South-EastAsian waters from about Vietnam to New Guinea.Habitat: Often associated with inshore areas of strong current or muddy conditions incontinental shelf waters. It can be particularly common around major river deltas, muddybottomed bays and estuaries of fairly shallow water depths ranging from about 3m. to 22 m. Itis also known from deeper waters of around 30 to 50 metres depth as well, and has beenobserved even living in the upper reaches of major tidal rivers - up to 10 or more kilometresfrom the coast. It has mainly been observed in association with muddy bottoms, and hasseldom been observed with other substrates.Biology/Ecology: This is mainly a diurnal species that feeds only on the eggs of fishes,although there is a record of an eel being taken. It is ovoviviparous, with gravid specimensbeing found in Australian waters during the middle of the year (May-August, Dry Season) incontrast to most other sea snakes that tend to be gravid during the Wet Season. In variousparts of Asia there is variation in the timing of reproduction, with gravid females being found inJanuary to April (late winter Monsoon Season) in the Straits of Malacca, but with none gravidin April in the South China Sea. In Australia, litter sizes range from 1 to 9, with the averagebeing about 4 relatively large living young being produced at a time, and larger females tendto produce larger litters. Litter sizes in Asia however, appear to be slightly higher (up to 12,but with a similar average of only about 4 or 5), which could indicate that Asian populationsmay attain a slightly larger maximum size. In Australia, there is some evidence to suggest thatfemales significantly outnumber males.Toxicity: Although this species is most reluctant to bite, it does actually possess smallfunctional venom glands, so caution should be exerted when handling this species. Despitethe fact that there are no known human fatalities due to the bite of this species - possiblybecause of the rudimentary nature of its venom apparatus - medical assistance should besought in the event of a bite as a precaution.Survival Status: Protected under the Qld Nature Conservation Act (1992), the Territory Parksand Wildlife Conservation Act (1998) and the WA Wildlife Conservation Act 1950 (asamended). Listed as a Marine Protected Species under the Australian EnvironmentalProtection and Biodiversity Conservation Act (1999). Probably not under threat, but itsrestricted distribution in Australian waters could potentially make it vulnerable in some parts ofits range.17