Sea snakes and file snakes commonly voluntarily submerge (or if on the surface, hold their breath) for periods of 5 to 30 min but may do so for up to about 1 1/2 to 2 h. There is great variability in submergence time, and short apneic periods (several seconds to a few minutes) are not unusual, at least in captivity. Voluntary submergence time is reduced by activity and increased temperature but, if the effects of these two variables are considered, there is no consistent effect of phase of the diel cycle.