Andrew D. Lowther

Post-breeding at-sea movements of three central-place foragers in relation to submesoscale fronts in the Southern Ocean around Bouvetøya

Abstract At-sea behaviour of central-place foraging fur seals and penguins in the Southern Ocean is understudied during the latter stages of parental care and the subsequent pre-moulting period. This biologically important period is costly to investigate due to the risk (or certainty) of losing tracking instruments when the animals moult. Early in this period, parents must meet the increasing demands of larger, more mobile offspring that are still nutritionally dependent and then the parents must recover lost body condition prior to the onset of their annual moult. This study reports late-season, at-sea movement patterns of macaroni penguins, chinstrap penguins and adult female Antarctic fur seals from the subantarctic island Bouvetøya, in relation to remotely-sensed oceanographic features. Foraging trips differing significantly in direction and distance travelled compared to those performed earlier in the breeding season, coincide with the time when offspring would be expected to become independent. On these trips, macaroni penguins moved towards the Polar Front while chinstrap penguins and Antarctic fur seals moved southward. Individuals from all three species appeared to target submesoscale ocean features once they were presumed to have been released from the constraints of feeding their young and were able to travel greater distances from the colony.

Maternal strategies of the Australian sea lion (Neophoca cinerea) at Dangerous Reef, South Australia

Maternal strategies of otariid seals reflect the optimisation between resource exploitation and offspring provisioning driven across spatially separated foraging and nursing grounds. Intercolony variation in the expression of maternal strategies may represent temporal and spatial differences in resource availability, intraspecies competition or differences in life-history traits. The current study describes maternal strategies of the Australian sea lion at the largest breeding colony of the species (Dangerous Reef) and a comparative analysis was performed with data collected 16 years earlier at Seal Bay (Kangaroo Island). Significant differences in maternal strategies were characterised by lower milk lipid content (21.0 versus 28.9%), abbreviated periods onshore (0.93 versus 1.63 days) and slower pup growth rates (0.09–0.12 kg day–1) at Dangerous Reef. These data suggest flexibility in the expression of maternal investment between breeding sites and support the hypothesis of localised adaptation

The Limits of Dispersal: Fine Scale Spatial Genetic Structure in Australian Sea Lions

Describing patterns of connectivity throughout a species range is critical to conservation management. In common with other mammals, pinnipeds typically display male-biased dispersal. Earlier studies using mitochondrial DNA showed that the endangered Australian sea lion (Neophoca cinerea) exhibits extreme matrilineal structure throughout its range. If male dispersal were similarly restricted, most breeding colonies may not receive sufficient levels of new genetic variation to buffer against risks associated with inbreeding and environmental change. To address these concerns we used 16 microsatellite loci to obtain a more highly resolving measure of genetic structure among colonies and determine whether dispersal is male-biased. We found that both male and female Australian sea lions are highly philopatric with limited dispersal. Within those constraints, when animals disperse between close colonies (<110 km) there is a tendency for males to move further than females. Our findings are intriguing considering the dispersal potential of Australian sea lions and the unique asynchronous breeding opportunities that might be expected to provide an incentive for male reproductive movements between geographically close colonies.

The Argos-CLS Kalman Filter: Error Structures and State-Space Modelling Relative to Fastloc GPS Data

Understanding how an animal utilises its surroundings requires its movements through space to be described accurately. Satellite telemetry is the only means of acquiring movement data for many species however data are prone to varying amounts of spatial error; the recent application of state-space models (SSMs) to the location estimation problem have provided a means to incorporate spatial errors when characterising animal movements. The predominant platform for collecting satellite telemetry data on free-ranging animals, Service Argos, recently provided an alternative Doppler location estimation algorithm that is purported to be more accurate and generate a greater number of locations that its predecessor. We provide a comprehensive assessment of this new estimation process performance on data from free-ranging animals relative to concurrently collected Fastloc GPS data. Additionally, we test the efficacy of three readily-available SSM in predicting the movement of two focal animals. Raw Argos location estimates generated by the new algorithm were greatly improved compared to the old system. Approximately twice as many Argos locations were derived compared to GPS on the devices used. Root Mean Square Errors (RMSE) for each optimal SSM were less than 4.25km with some producing RMSE of less than 2.50km. Differences in the biological plausibility of the tracks between the two focal animals used to investigate the utility of SSM highlights the importance of considering animal behaviour in movement studies. The ability to reprocess Argos data collected since 2008 with the new algorithm should permit questions of animal movement to be revisited at a finer resolution.

Characterization of 12 novel microsatellite loci and cross-amplification of four loci in the endangered Australian sea lion (Neophoca cinerea)

We describe a microsatellite panel of 12 newly developed and four cross-amplification loci for the endangered Australian sea lion, Neophoca cinerea. Next-generation 454 sequencing was used to obtain species-specific partial genomic library. We genotyped 28 individuals sampled from a single breeding colony to characterize these 16 polymorphic loci. Number of alleles per locus ranged from three to seven, and observed and expected heterozygosites from 0.333 to 0.852 and from 0.377 to 0.787, respectively. These markers will be used to examine genetic diversity, genetic connectivity among colonies and the mating system of Australian sea lions.

Convergence of marine megafauna movement patterns in coastal and open oceans

Significance Understanding the key drivers of animal movement is crucial to assist in mitigating adverse impacts of anthropogenic activities on marine megafauna. We found that movement patterns of marine megafauna are mostly independent of their evolutionary histories, differing significantly from patterns for terrestrial animals. We detected a remarkable convergence in the distribution of speed and turning angles across organisms ranging from whales to turtles (epitome for the slowest animals on land but not at sea). Marine megafauna show a prevalence of movement patterns dominated by search behavior in coastal habitats compared with more directed, ballistic movement patterns when the animals move across the open ocean. The habitats through which they move will therefore need to be considered for effective conservation. The extent of increasing anthropogenic impacts on large marine vertebrates partly depends on the animals’ movement patterns. Effective conservation requires identification of the key drivers of movement including intrinsic properties and extrinsic constraints associated with the dynamic nature of the environments the animals inhabit. However, the relative importance of intrinsic versus extrinsic factors remains elusive. We analyze a global dataset of ∼2.8 million locations from >2,600 tracked individuals across 50 marine vertebrates evolutionarily separated by millions of years and using different locomotion modes (fly, swim, walk/paddle). Strikingly, movement patterns show a remarkable convergence, being strongly conserved across species and independent of body length and mass, despite these traits ranging over 10 orders of magnitude among the species studied. This represents a fundamental difference between marine and terrestrial vertebrates not previously identified, likely linked to the reduced costs of locomotion in water. Movement patterns were primarily explained by the interaction between species-specific traits and the habitat(s) they move through, resulting in complex movement patterns when moving close to coasts compared with more predictable patterns when moving in open oceans. This distinct difference may be associated with greater complexity within coastal microhabitats, highlighting a critical role of preferred habitat in shaping marine vertebrate global movements. Efforts to develop understanding of the characteristics of vertebrate movement should consider the habitat(s) through which they move to identify how movement patterns will alter with forecasted severe ocean changes, such as reduced Arctic sea ice cover, sea level rise, and declining oxygen content.

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

Abstract 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.

Temporal shift in the isotopic niche of female Antarctic fur seals from Bouvetøya

The Antarctic fur seal (Arctocephalus gazella) is a key marine predator in the Southern Ocean, a region that has recently started to show changes as a result of global climate change. Here, carbon (δ13C) and nitrogen (δ15N) stable isotope analyses on whole blood and plasma samples were used to examine the isotopic niche of lactating female Antarctic fur seals. Using recently developed Bayesian approaches to determine changes in isotopic niche, a significant increase in δ13C and δ15N was found between 1997 and 2015; this change occurred at an average rate of 0.067‰ (δ13C) and 0.072‰ (δ15N) per year over this period. This suggests that a marked isotopic niche shift has occurred over this period, which very likely corresponds to a shift in diet towards prey at a higher trophic level, such as fish (replacing krill). Although our sampling design prevented us from exploring a seasonal trend in a conclusive manner, our data suggest that concurrent increases in δ13C and δ15N might occur as the breeding season progresses. At a seasonal scale, an average decrease of −0.7‰ per month (95% confidence interval=[−0.9; −0.6]) in δ13C might have occurred, concurrently with an average increase of 1.1‰ per month in δ15N. The results of this study constitute the first isotopic assessment for female Antarctic fur seals from Bouvetøya and provide a baseline for the use of this predator species as a sentinel of the marine trophic system in one of the least studied areas within this species’ distributional range.

When were the weaners weaned? Identifying the onset of Australian sea lion nutritional independence

Weaning in mammals is typically thought of as the transition from reliance on maternal milk to feeding independently. Current theory suggests a complex process involving mothers imparting enough resources to offspring as to ensure survival without compromising both prior and future reproductive efforts, and the demands of offspring whose primary concern is survival. Otariid seals are a suitable group to study this given the morphological and behavioral similarities across species of the primary care giver, adult females. At higher latitudes, the duration of maternal care is short and tightly linked to seasonal productivity of the marine environment, punctuated by a predictable migration of mothers away from breeding sites. In contrast, nonmigratory temperate latitude otariid species have a much wider range of lactation periods, with mothers prolonging maternal support in relation to seasonal unpredictability of food resource. Prolonging care into the subsequent reproductive effort will likely have profound effects on the survival of the younger offspring. The Australian sea lion Neophoca cinerea has broken the phylogenetic constraint of a 12-month breeding cycle, which may reflect an alternate strategy to reduce the fitness costs of prolonged support by providing up to 18 months nutritional support to offspring. We use stable isotope analysis of temporally matched whisker sections combined with telemetry data on nutritionally dependent Australian sea lion pups to determine the weaning process and characterize the transition to nutritional independence. Using changes in isotopic nitrogen (δ15N) over time, pups undergo a gradual transition to independent foraging during a 3- to 6-month period before the onset of the next reproductive effort. Telemetry data supported this conclusion, indicating benthic foraging of weaned pups in areas consistent with adult female foraging.

A sum greater than its parts: merging multi‐predator tracking studies to increase ecological understanding

Understanding how animals find prey in heterogeneous environments is a central goal of ecology. Placing this process in an environmental context requires a lot of information regarding the characteristics of both the habitat selected by the animal and its surroundings. In high-latitude marine systems, information about subsurface habitats of marine predators is often very limited. Animal-borne oceanographic instruments have added a new modality to improve our understanding of marine predators and their habitats. While these instruments do not collect environmental information beyond that experienced by the animals carrying them, our study makes use of an oceanographic dataset collected by southern elephant seals (Mirounga leonina; N = 15), to provide environmental context for two sympatrically foraging penguin species in the waters close to the subantarctic island of Bouvetoya. The seals collected 154 CTD profiles during the study period, averaging 4.9 (±3.67) profiles per day, documenting the stratification of the upper water layer in terms of both seawater density and temperature. Using these data, we quantitatively describe the relationship between the diving behavior of the penguins (N = 3,745 dives) and the hydrographic properties of the three-dimensional area in which they were foraging. Both penguin species appeared to favor water characterized by a shallow mixed layer. The chinstrap penguins (Pygoscelis antarctica) dove within a shallow, unstable body of water close to the colony, whereas macaroni penguins (Eudyptes chrysolophus) exploited the bottom of the surface mixed layer further offshore. The hydrographic properties preferred by the penguins match closely those that describe the highest densities of their preferred prey, krill (Euphausia superba), identified during a temporally and spatially concurrent study. We demonstrate how merging multiple telemetric data streams from animals can shed new light on aspects of foraging behavior beyond simply relating movements to two-dimensional, remotely sensed measurements of the environment.