| dc.description.abstract | I used video and movement data obtained from animal-borne video and data recorders (VDRs) and histological data obtained from vibrissal pads of elephant seals to address the questions: When, where, how, and on what prey do female southern elephant seals forage? Although the annual cycle of southern elephant seals for breeding, molting, and foraging is well known, there is little information about their foraging strategies, hunting tactics, habitat-associations and sensory biology at sea. I deployed VDRs and satellite telemeters on eight female southern elephant seals from Península Valdés, Argentina, during their two-month post-breeding migration. I identified three distinct dive types and their functions (foraging, resting and transiting) in the deep waters of the Patagonian continental slope and Argentine Basin. Compared to resting and transit dives, foraging dives were deeper and less linear with bursts of speed, steeper descent and ascent angles, longer two-dimensional and three-dimensional dive paths, and greater variation in speed, descent angle, and vertical head movements. The primary prey identified on video included herring smelt (Argentinidae) and myctophids (Myctophidae). Seals foraged at a mean maximum depth of 469 m with a mean water temperature of 3.7°C and mean salinity of 33.8 psu associated with Sub-Antarctic Mode Water, Antarctic Intermediate Water and Upper Circumpolar Deep Water. These habitat associations were similar to those for elephant seals from other colonies. Compared to foraging and transit dives, resting dives were longer in duration with shorter two-dimensional dive paths, lower stroking rates and speeds, and greater variation in pitch and roll angle during descent. Transit dives were shallower and more linear with higher swim speeds and stroking rates, shorter durations, shallower ascent angles, and farthest straight-line distances traveled. I provide evidence that elephant seal vibrissae have similar microstructure and innervation to other seals, adding to the growing body of evidence that species in the family Phocidae, and perhaps all pinnipeds, possess highly sensitive vibrissae that form a sensory system for prey detection and capture.
In summary, female southern elephant seals from Península Valdés immediately depart the coast after breeding and travel to the continental slope while making shallow transit dives with little variation in easterly heading. Once beyond the continental shelf, they begin making deep foraging dives along the continental slope and Argentine Basin in cold water that arises from southern polar regions. While at sea for 75 days, they travel an average horizontal distance of 6,080 km and make 2,815 foraging dives. Their primary prey are small fish, some of which are bioluminescent, that they detect and capture in total darkness using vision and the tactile sensory system in their vibrissae. Between bouts of foraging dives, they make transit dives to new foraging areas or rest and probably sleep at an average maximum depth of 375 m. Of the 26 species of seals in the family Phocidae, southern elephant seals are the deepest diving and most pelagic, spending 10 months per year at sea and 89% of their time submerged while transiting, hunting and resting at depth. | en |
