Scientific and commercial collecting have documented high levels of abundance among several species of marine snakes. Estimates of first-year mortality in populations of marine snakes range from 40 to 90%. The primary cause of this mortality is unknown. Storms, currents, sun exposure, dehydration and fire are abiotic factors that may control populations of marine and amphibious snakes. Disease, malnutrition and predation are biotic factors known to affect populations. In the literature there are isolated reports of predation by marine mammals, birds of prey, fish and invertebrates. Sharks in Australian waters are known to be predators on sea snakes. Our studies show that in the estuaries, intertidal mangrove creeks and mud flats of southeast Asia decapod crustaceans are important snake predators. Microhabitat overlap, exoskeleton armour and a respiratory advantage in an underwater standoff argue for their potential as potent predators. Field observations, a survey of crab stomach contents and encounters between snakes and crabs under laboratory conditions support this hypothesis. –

Stomach contents of 845 wild-captured elasmobranchs (representing 21 species of more than 13 genera) from the Yaeyama area, southern Ryukyus, were examined for the elapid sea snakes. These specimens included 496 tiger sharks Galeocerdo cuvier, of which 343 had prey remains and 48 had sea snakes. Of the others, one of the 29 nurse sharks Nebrius concolor (including 23 with some items in stomachs) and the one smooth hammerhead shark Sphyrna zygaena also had sea snakes, whereas the remainder, including 187 with some prey remains in stomachs, had no sea snakes. Six of the seven sea snake species hitherto recorded from the Yaeyama area, including Pelamis platura, for which very little is known about its predator, were found from the tiger shark stomachs.