Morphology, reproduction and diet of the greater sea snake, Hydrophis major (Elapidae, Hydrophiinae)

Although widespread, the large Hydrophiinae sea snake Hydrophis major is poorly known ecologically. We dissected 119 preserved specimens in museum collections to quantify body sizes and proportions, sexual dimorphism, reproductive biology and diet. The sexes mature at similar snout–vent lengths (SVLs, about 75 cm) and attain similar maximum sizes (females 123 cm vs. males 122 cm SVL), but females in our sample exhibited larger mean sizes than did males (means 98.8 vs. 93.1 cm SVL). The adult sex ratio in museum specimens was highly female-biased (64:30), and the high proportion of reproductive females during the austral summer suggests annual reproduction. At the same SVL, females had shorter tails and wider bodies than did males, but sex differences in other body proportions (e.g. tail shape, head dimensions, eye diameter) were minimal. Skin rugosity increased with SVL, was greater in males than females and was greater on the dorsal than the ventral surface of the body. Litter size averaged 4.9 offspring (range 2–10) and increased with maternal body size. Neonates were approximately 33 cm SVL. The only prey items found inside dissected snakes (and also, recorded as prey in free-ranging snakes in our New Caledonia field studies) were catfish (Plotosus lineatus), whereas previous studies have suggested a more diverse diet. Although H. major resembles its terrestrial relatives in some respects, other characteristics (such as scale rugosity, low proportion of juveniles in collections, frequent production of small litters of large offspring) may reflect adaptation to marine habitats.