New publication:
Baird, R.W., D.L. Webster, G.S. Schorr, D.J.
McSweeney and J. Barlow. 2008. Diel variation in beaked whale diving behavior.
Marine Mammal Science 24:630-642.
Abstract
We investigate diel variation in beaked whale
diving behavior using data from time-depth recorders deployed on six
Blainville's (Mesoplodon densirostris) (255 h) and two Cuvier's (Ziphius
cavirostris) (34 h) beaked whales. Deep foraging dives (>800 m) occurred at
similar rates during the day and night for Blainville's beaked whales, and there
were no significant diel differences in ascent rates, descent rates, or mean or
maximum depths or durations for deep dives. Dive to mid-water depths (100-600 m)
occurred significantly more often during the day (mean = 1.59/h) than at night
(mean= 0.26/h). Series of progressively shallower "bounce" dives were only
documented to follow the deep, long dives made during the day; at night whales
spent more time in shallow (<100 m) depths. Significantly slower ascent rates
than descent rates were found following deep foraging dives both during the day
and night. Similar patterns were found for the Cuvier's beaked whales. Our
results suggest that the so-called "bounce" dives do not serve a physiological
function, although the slow ascents may. This diel variation in behavior
suggests that beaked whales may spend less time in surface waters during the day
to avoid near-surface, visually oriented predators such as large sharks or
killer whales (Orcinus orca).
Robin