Diving behavior of juvenile northern elephant seals

Abstract

We describe and review the development of the diving and foraging pattern of northern elephant seals, Mirounga angustirostris, during migrations over the first 2 years of life. The diving pattern and migratory tracks of 23 juveniles, 9–27 months of age, from Año Nuevo and Piedras Blancas, California, were recorded with attached time–depth recorders and Argos satellite tags. The seals exhibited a general diving pattern like that of adults, diving deep (373 ± 77 m per dive (mean ± SD)), long (15.2 ± 2.6 min per dive), and continuously (88.7 ± 2.7% of the time submerged while at sea). Level of performance increased with age and experience up to 2 years of age, the end of the fourth migration, when modal diving performance was equal to that of adults. Juveniles migrated north to the waters west of Oregon, Washington, and British Columbia, moving more slowly and not as far as adults. By the third trip to sea, males began to exhibit more flat-bottomed dives than females, a sex difference observed in adults, suggesting that males supplement a diet of pelagic organisms with benthic prey. These data and related observations of elephant seals suggest that the greatest physiological changes enabling an animal to dive occur near the rookery following weaning, before the first trip to sea; transition to a pelagic existence is difficult, as reflected by high mortality during the first migration; improvement of diving skills continues up to 2 years of age; and sex differences in foraging behavior and foraging location, similar to those seen in adults, are evident before the seals reach 2 years of age.

Effects of forced diving on the spleen and hepatic sinus in northern elephant seal pups

“…Forced dive durations were slightly less than the mean dive durations reported for freely diving pups of a similar age class (17). Imaging the entire spleen required 28 -32 axial images.…”

Impact of El Niño on the foraging behavior of female northern elephant seals

“…Presumed foraging (Type D) dives exhibited the strong diel pattern in 1998 females that was evident in females from other years (Fig. 4) (Le Boeuf et al 1996) with the exception of 2 females ('Rai' and 'Sun'), who for part of their records spent significant parts of the day foraging higher in the water column than is typical. There was no obvious geographical variable correlated to this behavior, with one female foraging close to the coast (126°W, 'Rai') and another foraging much farther out in the pelagic environment (143°W, 'Sun').…”

“…Trip duration and rates of mass gain were compared with data from females that carried instruments on spring foraging migrations in 1983 to 1996 and in 1999 (n = 64) (Le Boeuf & Reiter 1991, Le Boeuf et al 1996, 2000.…”

Marine mammals and the community structure of the Estuary and Gulf of St Lawrence, Canada: evidence from stable isotope analysis

“…Many species of fishes become more piscivorous with age, which would increase their trophic position relative to juvenile conspecifics. In marine mammals, lower prey capture or handling skills and diving ability in young individuals (Le Boeuf et al 1996, Horning & Trillmich 1997, Lesage 1999 would promote feeding at lower trophic levels (e.g. Boulva & McLaren 1979, Lawson et al 1995, Proust 1995 and would reduce resource overlap with older animals.…”