Movements and location at sea of South American sea lions (Otaria flavescens)

Abstract

This study examined the foraging locations of lactating female and pre-breeding adult male South American sea lions Otaria¯avescens in the Patagonian continental shelf, south-west Atlantic ocean. Research on females included the diving pattern, and was conducted during the 1994±98 breeding seasons in ®ve northern and central Patagonian rookeries. Twenty females were satellite-tracked using the Argos system and yielded 1558 locations at sea. Satellite transmitters were also deployed on two adult males tracked for a total of 94 days (n = 364 locations) before the onset of the 1999 breeding season. Foraging trips for both sexes were con®ned to the temperate waters of the Patagonian continental shelf although males travelled greater distances than females, and arrived close (c. 80 km) to the edge of the shelf. Females from the same rookery dispersed widely and locations at sea often overlapped. Individual differences were apparent between coastal and pelagic animals. Trips lasted a mean of 3.4 days (sd = 1.3, n = 115 trips). Mean travel distance per trip was 206 km (sd = 117 km, maximum 864 km, n = 115 trips). Females reached further distances by travelling faster rather than by extending the duration of trips. Consistent with the shallow continental shelf, 65% of 75 087 dives recorded for nine animals were in the range of 2±30 m. Males alternated periods on the coast with trips to sea lasting a mean of 5.7 days (sd = 3.0, n = 8 trips). Mean travel distance exceeded 591 km (1 sd = 301 km, n = 8 trips). Results are consistent with sex differences reported from diet studies. Locations overlap with the summer operation of shelf ®sheries targeting species that are also part of the sea lion diet.

Change in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia) after parturition

“…On the contrary, shifting to coastal, benthic prey after parturition may result in a reduction in the foraging trip duration of females, which in turn may result in a decrease in the pup mortality rate. This hypothesis is supported by the results of a telemetry study demonstrating that in northern Patagonia the trip length of lactating females was significantly correlated with the distance travelled, although females travelling off-shore swam faster than those feeding on-shore (Campagna et al, 2001). Furthermore, a positive correlation between the foraging trip length of lactating South American sea lion females and the pup mortality rate has also been reported off Peru (Soto et al, 2004(Soto et al, , 2006.…”

“…Twenty-six one-week-old pups (11 males and 15 females) were captured at random using a noose pole (Gentry and Holt, 1982) and about 2-5 ml of blood was extracted from the caudal gluteal vein in the lumbar region (Geraci and Lounsbury, 1993). Pups were also sexed, bleach-marked (Campagna et al, 2001) and finally released close to their mothers. The entire operation took about 10-15 min for each pup.…”

“…The South American sea lion (Otaria flavescens) exploits an ample range of coastal and off-shore prey in the southwestern Atlantic, foraging close to both the sea bed and the surface of the water column (Werner and Campagna, 1995;Thompson et al, 1998;Koen Alonso et al, 2000;Campagna et al, 2001). Stable isotope analysis has revealed that off northern Patagonia adult females consume more pelagic prey than adult males throughout the year (Drago et al, 2009a).…”

Summer foraging areas for lactating New Zealand sea lions Phocarctos hookeri

“…Lactating female Antarctic, New Zealand and Australian fur seals Arctocephalus gazella, A. forsteri and A. pusillus doriferus, respectively; and Australian and California sea lions Neophoca cinerea and Zalophus californianus, respectively, also forage over continental shelves or in relation to the edge of the shelves, close to breeding sites (Harcourt et al 1995, Gales & Costa 1997, Arnould & Hindell 2001. The geographic preference for foraging in shallower shelf waters and at shelf edges displayed by otariids usually results in foraging occurring within 100 km of breeding sites (A. gazella, Boyd et al 2002, Guinet et al 2001; South American sea lions Otaria flavescens, Campagna et al 2001, Thompson et al 1998A. forsteri, Harcourt et al 1995A.…”

“…The NZ sea lion's total foraging distances are, however, high (423 ± 43.9 km, present study; and 321.4 ± 59.7 km, Costa & Gales 2000) relative to other otariids. For comparison, O. flavescens make foraging trips of 206 ± 117 km, yet have similar maximum foraging site to colony distances (mean = 103 km, Campagna et al 2001). This suggests that female NZ sea lions are covering a greater area and distance in a single foraging trip than other otariids, which may indicate high prey heterogeneity, patchiness and/or low prey abundance.…”