Regional variability in diving physiology and behavior in a widely distributed air-breathing marine predator, the South American sea lion (Otaria byronia).

Rachael A Orben,Michael S Tift,Macarena Santos,Luis A Hückstädt,Valentina Franco-Trecu,Alastair M M Baylis,John P Y Arnould,Federico Riet-Sapriza,Daniel P Costa,Jennifer M Burns,Maritza Sepulveda

doi:10.1242/jeb.138677

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 mass-specific 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 air-breathing 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.

Highlights

Many marine top predators have undergone declines in their abundance, mostly as a consequence of human exploitation (Casini et al, 2009; Heithaus et al, 2008)
As the estimation of total body oxygen stores requires sampling and handling of animals, our knowledge is biased towards amphibious species that can be handled on land, or small cetaceans and sirenians that can be sampled in captivity or post mortem (Noren et al, 2002; Noren and Williams, 2000)
To evaluate the influence of total body oxygen stores on the diving behavior of South American sea lions, we examined the relationship between the third quartile of both diving depth and diving duration of each animal versus their respective mass-specific total body oxygen stores

Summary

Introduction

Many marine top predators have undergone declines in their abundance, mostly as a consequence of human exploitation (Casini et al, 2009; Heithaus et al, 2008) Their ability to recover after cessation of exploitation varies widely, and the reasons for such disparities in their recovery are poorly understood, often because of inadequate knowledge of their ecology, physiology and interactions with human activities (Lotze et al, 2011). The estimation of the total body oxygen stored in the lungs, blood and muscle can provide insight into how these species operate in their respective environments (Costa, 2007; Kooyman, 1989; Kooyman and Ponganis, 1998). While the differences in oxygen stores and diving physiology caused by intrinsic factors, such as age, size and gender have been examined (Fowler et al, 2007; Hassrick et al, 2010; MacArthur et al, 2001; Ponganis et al, 1999; Richmond et al, 2006; Weise and Costa, 2007), the role of the extrinsic environmental changes on diving physiology has only recently been considered (Costa et al, 2004; Maekawa and Kato, 2015; Thometz et al, 2015; Villegas-Amtmann et al, 2012)

Methods

Results

Conclusion