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

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.

Combining potential and realized distribution modeling of telemetry data for a bycatch risk assessment.

Establishing marine species distributions is essential for guiding management and can be estimated by identifying potential favorable habitat at a population level and incorporating individual-level information (e.g., movement constraints) to inform realized space use. In this research, we applied a combined modeling approach to tracking data of adult female and juvenile South American sea lions (Otaria flavescens; n = 9) from July to November 2011 to make habitat predictions for populations in northern Chile. We incorporated topographic and oceanographic predictors with sea lion locations and environmentally based pseudo-absences in a generalized linear model for estimating population-level distribution. For the individual approach, we used a generalized linear mixed-effects model with a negative exponential kernel variable to quantify distance-dependent movement from the colony. Spatial predictions from both approaches were combined in a bivariate color map to identify areas of agreement. We then used a GIS-based risk model to characterize bycatch risk in industrial and artisanal purse-seine fisheries based on fishing set data from scientific observers and artisanal fleet logs (2010-2015), the bivariate sea lion distribution map, and criteria ratings of interaction characteristics. Our results indicate population-level associations with productive, shallow, low slope waters, near to river-mouths, and with high eddy activity. Individual distribution was restricted to shallow slopes and cool waters. Variation between approaches may reflect intrinsic factors restricting use of otherwise favorable habitat; however, sample size was limited, and additional data are needed to establish the full range of individual-level distributions. Our bycatch risk outputs identified highest risk from industrial fisheries operating nearshore (within 5 NM) and risk was lower, overall, for the artisanal fleet. This research demonstrates the potential for integrating potential and realized distribution models within a spatial risk assessment and fills a gap in knowledge on this species' distribution, providing a basis for targeting bycatch mitigation outreach and interventions.

Foraging behaviour of the South American sea lion (Otaria byronia) in two disparate ecosystems assessed through blubber fatty acid analysis.

Fatty acids have been widely used as trophic biomarkers in marine mammals. However, for the South American sea lion, the most abundant otariid in the eastern South Pacific, there is no information about blubber fatty acids and their link to diet. Here, we compare fatty acid profiles of sea lions from two distinct oceanographic regions in northern and southern Chile. Their fatty acids vary greatly between regions, suggesting dietary differences at a spatial scale. The fatty acid C22:6ω3 was more abundant in sea lions from the northern region, likely associated with consumption of anchovy, cephalopods, and crustaceans, which are rich in that fatty acid, and have been reported as their main prey items. Sea lions from the southern region were richer in C22:1 and C20:1, characteristic of teleost fish, suggesting a piscivorous diet. Males displayed a more diverse fatty acid composition than females, suggesting a wider trophic niche. Few individual sea lions within the southern region had unusually high levels of C18:2ω6, commonly found in terrestrial environments. This suggests consumption of farmed salmon, whose diet is usually based on terrestrial sources. This demonstrates how human intervention is being reflected in the tissues of a top predator in a natural environment.