Creatures of habit: foraging habitat fidelity of adult female Australian sea lions

Steller sea lion ( Eumetopias jubatus (Schreber, 1776)) populations have had differing dynamics in different regions of Alaska over the past 30 years. The western population (west of 144°W, near Cape Suckling) declined by approximately 85% between the 1970s and 2000, while the eastern population has increased at a rate of over 3%/year. Past research has indicated that the decline in the western population likely resulted from decreased juvenile survival and smaller declines in adult female survival and reproduction. Based on repeated observations (1987–2003) of sea lions branded as pups at Marmot Island (58.216°N, 151.840°W; western population; branded in 1987–1988) and at the Forrester Island rookery complex (54.859°N, 133.539°W; eastern population; branded in 1994–1995), we used mark–resight analyses to estimate age-specific survival probabilities. Juvenile sea lion survival probability at Marmot Island from 1988 to 1991 was lower than survival estimates at that location in the 1970s (assumed stable population) and lower than juvenile survival at Forrester Island from 1995 to 1998 (increasing population). Adult female survival at Marmot Island from 1992 to 2003 was only slightly reduced compared with that in the 1970s but was substantially lower than that at Forrester Island (1999–2003). In addition, and contrary to the typical pattern (e.g., Forrester Island), adult female survival probabilities at Marmot Island were indistinguishable from adult male survival probabilities. This suggests that regardless of which factors altered the dynamics of the western Steller sea lion population, they differentially affected females.

Download Full-text

Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru

Canadian Journal of Zoology ◽

10.1139/z93-273 ◽

1993 ◽

Vol 71 (9) ◽

pp. 1908-1911 ◽

Cited By ~ 17

Author(s):

Robert Harcourt

Keyword(s):

Adult Female ◽

Individual Variation ◽

Small Proportion ◽

South American ◽

Adult Males ◽

Sea Lion ◽

Subadult Male ◽

Sea Lions ◽

Hunting Success ◽

Fur Seals

Southern sea lions (Otaria byronia) were observed to prey on juvenile and adult female South American fur seals (Arctocephalus australis) at Punta San Juan, Peru (15°22′S, 75°12′W) between October 1987 and December 1988. Over the course of the study there were 165 attacks on fur seals with 33 seals killed. While both adult male and subadult male sea lions captured and killed fur seals, adult female and juvenile sea lions never acted aggressively towards fur seals. Adult males attacked fur seals on 82.4% of the occasions when they were present at the rookery, subadults on 52% of occasions. Distinctive pelage characteristics allowed some of the male sea lions to be individually identified, and differences in hunting success were observed between adults and subadults, and between five identifiable adults who hunted on at least five occasions. Motivation for attacks differed for subadults and adults, with subadult males using captured fur seals as female sea lion substitutes, guarding them from others and copulating with them, whilst adult sea lions hunted fur seals as food. However, only a small proportion of adult sea lions hunted fur seals, and with differing rates of success.

Download Full-text

Habitat selection by adult female eastern grey kangaroos

Wildlife Research ◽

10.1071/wr01057 ◽

2002 ◽

Vol 29 (5) ◽

pp. 439 ◽

Cited By ~ 27

Author(s):

Benjamin D. Moore ◽

Graeme Coulson ◽

Sarah Way

Keyword(s):

Habitat Selection ◽

Adult Female ◽

Compositional Analysis ◽

Home Range Size ◽

Radio Tracking ◽

Foraging Habitat ◽

Habitat Types ◽

Spring Period ◽

Night And Day ◽

Selection Of

We determined patterns of habitat selection in the winter–spring period by adult female eastern grey kangaroos (Macropus giganteus) at Yan Yean Reservoir Catchment near Melbourne, Victoria, during 1994–95. We assessed habitat selection at two levels by radio-tracking 11 adult female kangaroos. The 95% isopleth harmonic mean home-range size (mean = 62.3 ha) was the smallest recorded for female eastern grey kangaroos. No range encompassed all of the habitat types available in the study area, and the mix and rankings of habitats selected at this level varied amongst individuals when compared by compositional analysis with available habitats. Selection of habitats at the within-range level also varied among individuals and differed between night and day for many individuals, but not for the population mean. Individuals selected strongly for good foraging habitat within their ranges. In particular, grassy clearings were used by all individuals and were selected strongly by day, night or at both times.

Download Full-text

Foraging behavior of adult female and young-of-the-year Steller sea lions in Alaskan waters

Canadian Journal of Zoology ◽

10.1139/z97-099 ◽

1997 ◽

Vol 75 (5) ◽

pp. 776-786 ◽

Cited By ~ 135

Author(s):

Richard L. Merrick ◽

Thomas R. Loughlin

Keyword(s):

Adult Female ◽

Prey Availability ◽

Gulf Of Alaska ◽

First Year ◽

Home Ranges ◽

Steller Sea Lions ◽

Foraging Effort ◽

Sea Lions ◽

Adult Females ◽

Young Of The Year

One explanation for recent declines in the Alaskan Steller sea lion (Eumetopias jubatus) population is that the availability of preferred prey has changed. Part of our evaluation of this hypothesis involved the use of conventional radio and satellite-linked time–depth recorder transmitters to compare summer and winter foraging of adult female and young-of-the-year Steller sea lions in Alaska waters. Foraging effort was not significantly different seasonally for postpartum adult females, though females with dependent young in winter may increase their foraging effort. In winter, all adult females made longer trips over larger home ranges and dove deeper. Young sea lions exerted less foraging effort, had the shallowest and briefest dives, and had home ranges intermediate in size to the two groups of adult females. Their foraging ability appears to develop throughout the first year. We conclude that adult female sea lions can exploit prey throughout the Gulf of Alaska and Bering Sea, and are constrained only by their reproductive status and seasonal changes in prey availability. Young sea lions' diving is more limited because their physiological and behavioral development constrains them from diving like an adult. Perhaps most important, dives remain shallow through the first year. Consequently, young sea lions could be more easily food-limited by changes in prey distribution.

Download Full-text

Foraging behavior of adult female Steller sea lions during the breeding season in Southeast Alaska

Marine Mammal Science ◽

10.1111/j.1748-7692.2008.00278.x ◽

2009 ◽

Vol 25 (3) ◽

pp. 588-604 ◽

Cited By ~ 15

Author(s):

M. J. Rehberg ◽

R. D. Andrews ◽

U. G. Swain ◽

D. G. Calkins

Keyword(s):

Foraging Behavior ◽

Breeding Season ◽

Adult Female ◽

Steller Sea Lions ◽

Southeast Alaska ◽

Sea Lions

Download Full-text

Specialized foraging habits of adult female California sea lions Zalophus californianus

Marine Mammal Science ◽

10.1111/mms.12603 ◽

2019 ◽

Vol 35 (4) ◽

pp. 1463-1488 ◽

Cited By ~ 1

Author(s):

Martha P. Rosas‐Hernández ◽

David Aurioles‐Gamboa ◽

Claudia J. Hernández‐Camacho

Keyword(s):

Adult Female ◽

Zalophus Californianus ◽

California Sea Lions ◽

Sea Lions

Download Full-text

Regional variation in trophic ecology of adult female Australian sea lions inferred from stable isotopes in whiskers

Wildlife Research ◽

10.1071/wr12181 ◽

2013 ◽

Vol 40 (4) ◽

pp. 303 ◽

Cited By ~ 3

Author(s):

A. D. Lowther ◽

R. G. Harcourt ◽

S. D. Goldsworthy

Keyword(s):

Adult Female ◽

Regional Variation ◽

Foraging Ecology ◽

Isotope Ratios ◽

Western Coast ◽

Sea Lion ◽

Δ13c Values ◽

Sea Lions ◽

Australian Sea Lion ◽

Δ15n And Δ13c

Context The primary selective forces responsible for shaping life-history traits come from the physical and biological environment in which a species resides. Consequently, the limits of a species range may provide a useful measure of adaptive potential to environmental change. The proximity of foraging grounds to terrestrial nursing habitat constrains central-place foragers such as otariid seals in selecting breeding locations. The Australian sea lion (Neophoca cinerea) is an endangered otariid endemic to Australia, whose northern-range extent occurs at a temperate–tropical transition zone on the western coast of Western Australia (WA). Aims Currently, there is a complete absence of data on the foraging ecology of Australian sea lions in WA. We sought to address this critical knowledge gap and provide data on the foraging ecology of adult female Australian sea lions at three isolated breeding colonies in western WA. Methods We used stable-isotope ratios of carbon (δ13C) and nitrogen (δ15N) in the whiskers of pups as proxies to characterise feeding behaviour of 10–28% of all adult female Australian sea lions at each colony. We then compared these geographic data to (1) conspecifics at similar latitude in South Australia (SA) and (2) isotopic data collated from other studies on seabirds that inhabit the region, to place foraging behaviour of adult female Australian sea lions into context. Key results At the southernmost colonies in WA, individual animals were members of one of two distinct isotopic clusters that could be described by differences in δ15N and δ13C values. Individuals at the northernmost colony displayed δ15N values similar to those of seabirds in the same region. Across the study, isotope ratios of adult female Australian sea lions in western WA were between 3‰ and 5‰ lower than those observed at a colony at similar latitude in SA. Conclusions Gross differences in the physical oceanography between WA and SA may in part explain the differences in isotope ratios of individuals between the regions, with lower δ15N and δ13C values in WA probably reflecting the relatively depauperate conditions of the Leeuwin Current. Implications Potential regional differences in trophic structure should be considered when developing appropriate management plans for Australian sea lions and regional variation in the diet of Australian sea lion warrants further investigation.

Download Full-text

Body Weights and Dimensions of Adult Female Australian Sea Lions, Neophoca cinerea

Journal of Mammalogy ◽

10.2307/1379986 ◽

1980 ◽

Vol 61 (1) ◽

pp. 164-165

Author(s):

G. E. Walker ◽

J. K. Ling

Keyword(s):

Adult Female ◽

Sea Lions ◽

Neophoca Cinerea ◽

Body Weights

Download Full-text

Intraspecific comparison of diet of California sea lions (Zalophus californianus) assessed using fecal and stable isotope analyses

Canadian Journal of Zoology ◽

10.1139/z10-101 ◽

2011 ◽

Vol 89 (2) ◽

pp. 109-122 ◽

Cited By ~ 17

Author(s):

A. J. Orr ◽

G. R. VanBlaricom ◽

R. L. DeLong ◽

V. H. Cruz-Escalona ◽

S. D. Newsome

Keyword(s):

Stable Isotope ◽

Adult Female ◽

Age Groups ◽

Zalophus Californianus ◽

California Sea Lions ◽

Stable Isotope Analyses ◽

Merluccius Productus ◽

Sea Lions ◽

Adult Females ◽

Isotope Analyses

The diet of juvenile and adult female California sea lions ( Zalophus californianus (Lesson, 1828)) at San Miguel Island, California, was estimated and compared using fecal and stable isotope analyses to determine dietary differences by age. Fecal samples were collected during 2002–2006 and prey remains were identified. Stable carbon (δ13C) and stable nitrogen (δ15N) isotope values were determined from plasma and fur obtained from yearlings, 2- to 3-year-old juveniles, and adult females during 2005 and 2006. Juveniles ate more than 15 prey taxa, whereas adult females consumed more than 33 taxa. Relative importance of prey was determined using percent frequency of occurrence (%FO). Engraulis mordax Girard, 1854, Sardinops sagax (Jenyns, 1842), Merluccius productus (Ayres, 1855), genus Sebastes Cuvier, 1829, and Loligo opalescens Berry, 1911 were the most frequently occurring (%FO > 10%) prey in the feces of both juvenile and adult female sea lions, although their importance varied between age groups. Only yearlings had significantly different isotopic values than older conspecifics, indicating that older juveniles were feeding at a similar trophic level and in similar habitats as adult females. Whereas each method had biases, combining the two provided a better understanding of the diet of California sea lions and intraspecific differences.

Download Full-text