Niche partitioning within a population of seasnakes is constrained by ambient thermal homogeneity and small prey size

In many populations of terrestrial snakes, an individual’s phenotype (e.g.
body size, sex, colour) affects its habitat use. One cause for that link
is gape-limitation, which can result in larger snakes eating prey that are
found in different habitats. A second factor involves thermoregulatory
opportunities, whereby individuals select habitats based upon thermal
conditions. These ideas predict minimal intraspecific variation in habitat
use in a species that eats small prey and lives in a thermally uniform
habitat – such as the seasnake Emydocephalus annulatus, that feeds on tiny
fish eggs and lives in inshore coral-reefs. To test that prediction, we
gathered data on water depths and substrate attributes for 1475 sightings
of 128 free-ranging E. annulatus in a bay near Noumea, New Caledonia.
Habitat selection varied among individuals, but with a preference for
coral-dominated substrates. A snake’s body size and reproductive state
affected its detectability in deep water, but overall habitat use was not
linked to snake body size, colour morph, sex, or pregnancy. A lack of
ontogenetic shifts in habitat use allows extreme philopatry in E.
annulatus, thereby reducing gene flow among populations and potentially,
delaying recolonization after local extirpation events.