Habitat selection by sea kraits (Laticauda spp.) at coastal sites of Orchid Island, Taiwan.

Three species of amphibious sea kraits (Laticauda spp.) spend variable time at sea and require fresh water for water balance. Both the rate of cutaneous evaporative water loss and the extent of terrestriality are known to differ among them. Laticauda semifasciata has the greatest rate of water loss and the least extent of terrestriality, whereas L. colubrina exhibits the reverse and L. laticaudata is intermediate. These sea kraits tend to be more abundant at places where there are sources of fresh water, but other factors also influence their distribution. To further clarify the habitat requirements, we investigated the abundance of each species of sea krait at six different habitats and the availability of each type of habitat on Orchid Island, Taiwan. The six habitats were high coral reef without fresh water (HR) and with fresh water (HRF); low coral reef without fresh water (LR) and with fresh water (LRF); sand or gravel coast, which has no coral reef, without fresh water (NR) and with fresh water (NRF). The extent of safety judged from the relative availability of retreat sites, from high to low, was HR, LR, and NR among these habitats. More than 75% of individuals counted for each species were found in HRF. We found no sea kraits in NRF and NR. The most available habitat was LR, but no L. laticaudata or L. semifasciata were found in this habitat. We found 3.3% and 16.7% of L. colubrina in LR and HR, respectively. For L. colubrina, the second abundant habitat was HR, whereas for L. laticaudata and L. semifasciata, the second abundant habitat was LRF. We conclude that both safety (availability of retreat sites) and fresh water are important to the habitat selection of sea kraits. Compared with other species, L. colubrina is characterized by a greater extent of terrestrial habit and possibly greater variety of access to sources of fresh water.