Social Behaviour in Zoo Bachelor Groups: A Case Study of Related South American Fur Seals

Simple Summary

Appropriate management of social groups is one of the greatest challenges that face zoos and aquaria worldwide. All-male social groups provide an opportunity for facilities to house surplus males in groups which optimise their welfare whilst they are being retained for future use in breeding programmes. Here, we investigated social behaviour in a relatively poorly studied species, the South American fur seal (SAFS). Four individuals housed in a related group were studied over a 6-month period. The results showed that their social relationships changed over time, although the individuals always engaged in more positive than negative interactions. We recommend establishing baseline social behaviour profiles of individuals to enable long-term monitoring of SAFS social groups, as has been recommended in other species. This will enable enhanced understanding of South American fur seals and will contribute to the development of evidence-based social management guidelines for this species.

Abstract

Appropriate management of social groups is one of the greatest challenges that face zoos and aquaria worldwide. To facilitate breeding programmes, particularly in polygynous species, there is a need to house surplus males in bachelor groups, yet for pinnipeds, the social impact of this management strategy is unknown. The aim of this research was to enhance understanding of sociality in South American fur seals (SAFSs), with a particular focus on social dynamics in a related bachelor group, and consider implications for evidence-based management of this species in zoos. The subjects were four related male seals housed at Bristol Zoo Gardens. Social interaction and nearest neighbour data were collected between February and July 2019. Individuals engaged in both positive and negative social interactions. Positive interactions were more frequent than negative interactions, and no excessive negative interactions were observed. Temporal dynamics were observed in social relationships, and negative interactions did not increase with the onset of the breeding season. Reciprocity in dyadic relationships was variable across the study months, and nearest neighbours were not necessarily reflective of social partners. This research highlights the importance of longitudinal monitoring of social relationships and establishment of baseline social behaviour profiles to support evidence-based species management. We advocate that this research is extended, to further develop our understanding of SAFS social needs within zoo environments, to understand the differences between single-sex and mixed-sex groups and to identify the degree to which the extensive research conducted in other polygynous species (e.g., gorillas) is applicable in the social management of South American fur seals moving forwards.

The northernmost haulout site of South American sea lions and fur seals in the western South Atlantic

We present estimates of the seasonal and spatial occupation by pinnipeds of the Wildlife Refuge of Ilha dos Lobos (WRIL), based on aerial photographic censuses. Twenty aerial photographic censuses were analysed between July 2010 and November 2018. To assess monthly differences in the numbers of pinnipeds in the WRIL we used a Generalized Linear Mixed Model. Spatial analysis was carried out using Kernel density analysis of the pinnipeds on a grid plotted along the WRIL. Subadult male South American sea lions (Otaria flavescens) were the most abundant pinniped in the WRIL. Potential females of this species were also recorded during half of the census. The maximum number of pinnipeds observed in the WRIL was 304 in September 2018, including an unexpected individual southern elephant seal (Mirounga leonina), and a high number of South American fur seal yearlings (Arctocephalus australis). However, there was no statistically significant difference in counts between months. In all months analysed, pinnipeds were most often found concentrated in the northern portion of the island, with the highest abundances reported in September. This study confirms the importance of the WRIL as a haulout site for pinnipeds in Brazil, recommends that land research and recreational activities occur in months when no pinnipeds are present, and encourages a regulated marine mammal-based tourism during winter and spring months.

Sex beyond species: the first genetically analyzed case of intergeneric fertile hybridization in pinnipeds

A species, according to the biological concept, is a natural group of potentially interbreeding individuals isolated by diverse mechanisms. Hybridization is considered the production of offspring resulting from the interbreeding of two genetically distinct taxa. It has been documented in over 10% of wild animals, and at least in 34 cases for Artic marine mammals. In Otariids, intergeneric hybridization has been reported though neither confirming it through genetic analyses nor presenting evidence of fertile offspring. In this study, we report the finding of a hybrid adult female between a South American fur seal (Arctocephalus australis) and a South American sea lion (Otaria byronia), and its offspring, a male pup, in Uruguay. Further based on morphological constraints and breeding seasons, sex-biased hybridization between the two species is hypothesized. Morphological and genetic (nuclear and mitochondrial) results confirm de hybrid nature of the female-pup pair. Here we discuss a genetic dilution effect, considering other hybridization events must be occurring, and how isolation mechanisms could be circumvented. Moreover, the results obtained from stable isotope analysis suggest feeding habits may be a trait transmitted maternally, leading to consider broader issues regarding hybridization as an evolutionary innovation phenomenon.

Parturition process in an amphibian mammal species: new evidences in South American fur seal (Arctocephalus australis)

In mammals, the transition from a terrestrial to an aquatic environment has implied a great number of adaptations. While in terrestrial mammals the presentation of the foetus at birth is typically cephalic, in strictly aquatic mammals as cetaceans and sirenians the presentation of the foetus is mainly breech. The order Pinnipedia is the most recently evolved group of marine mammals and has an amphibian lifestyle. We document, for the first time, the parturition process in the largest breeding colony of the South American fur seal Arctocephalus australis in Uruguay and compare our results with the scarce information available for other species. The analysis of the parturition processes shows that the cephalic/breech birth ratio was 1. In this species, the presentation of the foetus did not affect the total duration of the parturition process, but the cephalic presentation implied a significantly lower duration of the stage 1 of birth, a trend that is also observed in other Otariid species. Phylogenetic reconstructions suggest that O. flavescens and E. jubatus are older than the Arctocephalus genus, having their most recent common ancestor dated between 5-5.8 mybp. Within the Arctocephalus genus, A. australis would be the most recent species (0.7 mybp). In this light, the skewed ratios of breech presentation in older otariids species may suggest a convergent adaptation toward the aquatic life. We hope this finding will promote an increase of studies aiming for a more detailed examination on the adaptive processes involved in the selection of both types of fetal presentations, and their potential effect on the survival of the pup.