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

Natália Procksch,Rodrigo Machado,Marcelo Zagonel,Maurício Veronez,Paulo Henrique Ott,Enrique A Crespo,Karina Groch,Paulo A C Flores,Guido Pavez,Larissa Rosa De Oliveira,M Florencia Grandi,Murilo Guimarães

doi:10.1038/s41598-020-76755-2

Abstract

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.

Highlights

Every year hundreds of pinnipeds of various species are found along the southern Brazilian coast, most of which are South American fur seals (Arctocephalus australis) and South American sea lions (Otaria flavescens)[1,2,3,4]
The abundance of the pinnipeds in the Wildlife Refuge of Ilha dos Lobos (WRIL) was best explained by the intercept-only model which performed better than the model that included month as a predictor of abundance for both South American sea lions (χ2 = 5.77, df = 3, p = 0.12) and South American fur seals (χ2 = 5.32, df = 3, p = 0.15; Table 1)
Our data confirms the hypotheses of male bias in abundance for both species and a difference in the spatial occupation of the WRIL by South American fur seals and sea lions, with occupation mainly occurring on the northern portion of the island

Summary

Introduction

Every year hundreds of pinnipeds of various species are found along the southern Brazilian coast, most of which are South American fur seals (Arctocephalus australis) and South American sea lions (Otaria flavescens)[1,2,3,4]. The two species have similar reproductive periods during the austral summer, with South American sea lions breeding from December to early February[11], and South American fur seals breeding from late November to mid-January[12,13]. Males of both species do not provide paternal care and once the breeding period ends, they move away from their rookeries to return in the breeding season. For the coast of Argentina there is an increasing trend in the population numbers, including breeding and non-breeding colonies, with the total population estimated at about 123,200 individuals[20]

Methods

Results

Conclusion