Swim speed in a female northern elephant seal: metabolic and foraging implications

Abstract

The swim speed and dive pattern of an 8-year-old female northern elephant seal (Mirounga angustirostris) were recorded during the postlactation period at sea. A swim speed – distance meter and a time–depth recorder attached to the animal's back recorded the following synchronously and continuously for 29 days: swim speed, distance, depth, and duration of free-ranging dives. Mean swim speeds calculated as a function of time and distance ranged from 0.91 to 1.66 m/s. Mean descent velocities were 27% greater than ascent velocities and velocities at depth. Minimum and maximum speeds ranged from 0.4 to 3.0 m/s for most segments of all dives. There was no surface swimming. Angles of descent were less steep (30–56°) than angles of ascent (52–82°). Mean total horizontal distance traveled per dive ranged from 0.6 to 1.3 km, depending on dive type. From the above data and related information, each of four dive types, which accounted for the majority of dives in the record, were hypothesized to have one of the following principal functions: transit, foraging (pelagic and benthic), and process (serving rest, food processing, or anaerobic metabolite clearance).