Regional variability in diving physiology and behavior in a widely distributed air-breathing marine predator, the South American sea lionOtaria byronia

Abstract

Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Because of their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between massspecific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the shallowest and shortest duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals. Our study suggests that the physiology of airbreathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a 'training effect': as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath-holding capacity increases.

Intraspecific variation in feeding strategies of Galapagos sea lions: A case of trophic specialization

“…The variation in foraging patterns (pelagic/benthic) within a population has been associated with differences in body size or the biogeographic region where they live [ 1 , 22 , 58 ]. Australian ( Neophoca cinerea ) and South American sea lions ( Otaria flavescens ), are considered benthic foragers due to the extent and depth of the continental shelf around their rookeries [ 21 , 59 , 60 ].…”

“…Pinnipeds are high-trophic-level consumers that forage on a wide range of prey from different environments. Such environments may vary both geographically and over time [ 21 , 22 ]. However, this variability is more evident in tropical species that encounter greater uncertainty of marine productivity.…”

Sexual segregation in habitat use is smaller than expected in a highly dimorphic marine predator, the southern sea lion

“…Indeed, recent studies reveal that available habitat and individual foraging preferences influence whether individual-based limiting factors, such as diving capacity, constrain behaviour (Staniland & Robinson 2008, Sharples et al 2012, Kernaléguen et al 2015, Hückstädt et al 2016. For example, in harbour seals Phoca vitulina habitat is a more important determinant of foraging behaviour than sex, size and body condition (Sharples et al 2012).…”

“…Similarly, even though adult male northern elephant seals Mirounga angustirostris have greater diving ability than adult females (due to their significantly larger mass and oxygen stores), they do not necessarily dive deeper or for longer than adult females (Le Boeuf et al 2000). Finally, Hückstädt et al (2016), reviewing diving physiology in adult female SSL, conclude that environmental constraints, rather than body size, explain different oxygen storage capacities and diving capabilities between SSL at different breeding locations (Argentina, Chile, Falkland Islands and Uruguay).…”

Abundance and Population Trends of the South American Fur Seal (Arctocephalus australis) in Uruguay

“…Within Otariidae, populations of fur seals (Arctocephalinae) typically have higher abundance and growth rates than those of sea lions (Otariinae) (Costa et al, 2006), which may be related to the species' foraging strategies. Sea lions tend to be benthic feeders that frequently forage near their aerobic dive limit (Hückstadt et al, 2016) and, hence, spend more energy gathering food than fur seals that are predominantly pelagic feeders (Costa et al, 2001;Costa & Gales, 2003). Therefore, sea lions would have a smaller margin to increase their searching effort if food resources become scarce due to fishing pressure or climatic variation (Costa et al, 2001(Costa et al, , 2004.…”