scholarly journals Fish prey of the sympatric Galápagos fur seals and sea lions: seasonal variation and niche separation

1999 ◽  
Vol 77 (8) ◽  
pp. 1204-1216 ◽  
Author(s):  
Thomas Dellinger ◽  
Fritz Trillmich
Keyword(s):  
El Niño ◽  
El Nino ◽  
Warm Season ◽  
Niche Overlap ◽  
Sympatric Species ◽  
Niche Separation ◽  
Fish Prey ◽  
Sea Lions ◽  
Fur Seals ◽  
Fur Seal

Analysis of fish otoliths in scats and vomits of Galápagos fur seals (Arctocephalus galapagoensis) and Galápagos sea lions (Zalophus californianus wollebaeki) was used to determine the numerical composition of the diets for the post-El Niño year 1983, the cold seasons in 1984 and 1985, and the warm season in 1986. Between 84 and 99% of all otoliths in fur seal scats were from myctophids and bathylagids. The fur seals' diet included 26 species. Only 3 species contributed more than 1% of otoliths. No seasonal differences in diet were found. Sea lion samples contained a mean of 14 otoliths. Sardines (Sardinops sagax) contributed 75-85% of otoliths. Sea lions preyed on 24 species, but only 3 surpassed 1% abundance. Seasonality was not reflected in the sea lions' diet. After the 1982-1983 El Niño, the diets of both species deviated from those in all other years of the study. Food-niche overlap between the two sympatric species was almost non-existent. This is hard to understand, based on our knowledge of the diving capabilities of the two species, but reflects the fact that Galápagos fur seals are nighttime foragers and sea lions are daytime foragers.

Long term population changes of fur seals Arctocephalus gazella and Arctocephalus tropicalis on subantarctic (Crozet) and subtropical (St. Paul and Amsterdam) islands and their possible relationship to El Niño Southern Oscillation

1994 ◽  
Vol 6 (4) ◽  
pp. 473-478 ◽  
Author(s):  
C. Guinet ◽  
P. Jouventin ◽  
J-Y. Georges
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Enso Events ◽  
Fur Seals ◽  
Fur Seal ◽  
Arctocephalus Tropicalis

The population trend over the last decade for subantarctic fur seals (Arctocephalus tropicalis) on Amsterdam and St. Paul islands and on Possession Island (Crozet Archipelago) and Antarctic fur seals (A. gazella) on Possession Island are analysed. At Amsterdam Island, based on pup counts, the subantarctic fur seal population appears to have stabilized after a period of rapid growth. At Possession Island subantarctic fur seal and Antarctic fur seal, with respective annual growth rates of 19.2 and 17.4%, are reaching the maximum growth rate for the genus Arctocephalus. Annual pup censuses at Possession Island since 1978 indicate important variations from year to year with pup production for A. gazella significantly lower the year after an El Niño Southern Oscillation (ENSO) event, but with no such relationship for A. tropicalis. Several other long term demographic studies of seabirds and marine mammals at different breeding locations in the Southern Ocean indicate that the breeding success of several of these predators appears to be widely affected in years which appear to be related to the ENSO events. To clarify this, it is necessary to analyse in more detail the demographic data obtained for the different subantarctic and Antarctic locations where long term monitoring programmes are conducted.

scholarly journals Impact of the 2015 El Niño-Southern Oscillation on the Abundance and Foraging Habits of Guadalupe Fur Seals and California Sea Lions from the San Benito Archipelago, Mexico

PLoS ONE ◽  
2016 ◽  
Vol 11 (5) ◽  
pp. e0155034 ◽  
Author(s):  
Fernando R. Elorriaga-Verplancken ◽  
Gema E. Sierra-Rodríguez ◽  
Hiram Rosales-Nanduca ◽  
Karina Acevedo-Whitehouse ◽  
Julieta Sandoval-Sierra
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
California Sea Lions ◽  
Sea Lions ◽  
Fur Seals

Evidence of a genetic bottleneck in an El Niño affected population of South American fur seals, Arctocephalus australis

2009 ◽  
Vol 89 (8) ◽  
pp. 1717-1725 ◽  
Author(s):  
Larissa Rosa de Oliveira ◽  
Diogo Meyer ◽  
Joseph Hoffman ◽  
Patricia Majluf ◽  
João S. Morgante
Keyword(s):  
Population Size ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Genetic Bottleneck ◽  
South American ◽  
Enso Events ◽  
Fur Seals ◽  
The Pacific ◽  
Fur Seal

The South American fur seal, Arctocephalus australis, was one of the earliest otariid seals to be exploited by humans: at least 6000 years ago on the Atlantic coast and 4000 on the Pacific coast of South America. More than 750,000 fur seals were killed in Uruguay until 1991. However, a climatological phenomenon—the severe 1997–1998 El Niño Southern Oscillation (ENSO)—was responsible for the decline of 72% of the Peruvian fur seal population due to starvation as a consequence of warming of sea-surface temperatures and primary productivity reduction. Currently, there is no precise information on global population size or on the species' conservation status. The present study includes the first bottleneck test for the Pacific and Atlantic populations of A. australis based on the analysis of seven microsatellite loci. Genetic bottleneck compromises the evolutionary potential of a population to respond to environmental changes. The perspective becomes even more alarming due to current global warming models that predict stronger and more frequent ENSO events in the future. Our analysis found moderate support for deviation from neutrality–equilibrium for the Pacific population of fur seals and none for the Atlantic population. This difference among population reflects different demographic histories, and is consistent with a greater reduction in population size in the Pacific. Such an event could be a result of the synergic effects of recurrent ENSO events and the anthropogenic impact (sealing and prey overfishing) on this population.

Fur Seals and Sea Lions

2013 ◽  
Author(s):  
Roger Kirkwood ◽  
Simon Goldsworthy
Keyword(s):  
Evolutionary Ecology ◽  
Conservation Status ◽  
Sea Lions ◽  
Australian Sea Lion ◽  
Fur Seals ◽  
Fur Seal ◽  
History Of ◽  
Near Shore ◽  
New Zealand Fur Seal ◽  
Near Extinction

Fur seals and sea lions are charismatic, large carnivores that engage us with both their skill and playful antics. Although all species in Australian waters were harvested to near extinction 200 years ago, fur seals are recovering and are now common in near-shore waters across southern Australia. Sea lions, however, are endangered. Their populations appear not to have recovered like fur seals and are declining at some locations. Fur seals and sea lions are important top level predators and play an important role in Australia’s temperate marine ecosystems. Key threats they currently face relate to human activities, particularly interactions with fisheries. This book outlines the comparative evolutionary ecology, biology, life-history, behaviour, conservation status, threats, history of human interactions and latest research on the three species of otariids that live in the waters of southern Australia: the Australian fur seal, New Zealand fur seal and Australian sea lion. It also includes brief descriptions of Antarctic and Subantarctic seals that occupy the Antarctic pack-ice and remote Australian territories of Macquarie Island and Heard Island.

scholarly journals Fur seals do, but sea lions don't — cross taxa insights into exhalation during ascent from dives

2021 ◽  
Vol 376 (1830) ◽  
pp. 20200219 ◽  
Author(s):  
Sascha K. Hooker ◽  
Russel D. Andrews ◽  
John P. Y. Arnould ◽  
Marthán N. Bester ◽  
Randall W. Davis ◽  
...  
Keyword(s):  
Shallow Water ◽  
Decompression Sickness ◽  
Mammal Species ◽  
Free Living ◽  
Video Cameras ◽  
Sea Lions ◽  
Fur Seals ◽  
Fur Seal ◽  
The Antarctic ◽  
Management Issues

Management of gases during diving is not well understood across marine mammal species. Prior to diving, phocid (true) seals generally exhale, a behaviour thought to assist with the prevention of decompression sickness. Otariid seals (fur seals and sea lions) have a greater reliance on their lung oxygen stores, and inhale prior to diving. One otariid, the Antarctic fur seal ( Arctocephalus gazella ), then exhales during the final 50–85% of the return to the surface, which may prevent another gas management issue: shallow-water blackout. Here, we compare data collected from animal-attached tags (video cameras, hydrophones and conductivity sensors) deployed on a suite of otariid seal species to examine the ubiquity of ascent exhalations for this group. We find evidence for ascent exhalations across four fur seal species, but that such exhalations are absent for three sea lion species. Fur seals and sea lions are no longer genetically separated into distinct subfamilies, but are morphologically distinguished by the thick underfur layer of fur seals. Together with their smaller size and energetic dives, we suggest their air-filled fur might underlie the need to perform these exhalations, although whether to reduce buoyancy and ascent speed, for the avoidance of shallow-water blackout or to prevent other cardiovascular management issues in their diving remains unclear. This article is part of the theme issue ‘Measuring physiology in free-living animals (Part I)’.

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