Long-term remote monitoring of the rookery of Eumetopias jubatus (Pinnipedia, Otariidae) on Matykil Island in the Magadan State Nature Reserve (Russia)

Abstract

The severe decline in the number of Eumetopias jubatus (hereinafter – Steller sea lion) almost throughout the entire range has drawn the public attention to monitor the abundance and increase in research activity of the species. In Russia, such a study has been conducted regularly since the early 2000s. It includes range-wide population surveys in the Russian Far East, marking newborn pups and monitoring their survival, movements, and reproduction success. In the first decade of the XXI century, observers conducted direct observations on rookeries during the breeding season. Since 2011 a novel survey method has been used, using custom-made autonomous high-resolution remote cameras, which have been taking images of the rookeries all year round. In 2013, six remote-camera units were installed in the Magadan State Nature Reserve (Russia) at the rookery of the Steller sea lion located on Matykil Island. The cameras gathered images during day time every 5–30 min. Maintenance of the photo recorders was carried out once per year in the summer period. A total of 721 927 photographs were collected during eight years of the surveys. Of them, 60 632 photographs were manually analysed in this research. It was found that the Steller sea lions use the rookery throughout the year, with the exception of March when a dense and wide ice cover in the study area prevents the Steller sea lions from reaching the shore of Matykil Island. During the year, two peaks of the Steller sea lion population abundance were observed, namely summer and, with a higher number of individuals, in autumn. In summer, females predominate on the rookery, while in the autumn-winter period, young animals (mainly males) and mature (8+ years) adults. In winter, the number of Steller sea lions was low on the shore. We have seen branded Steller sea lions on Matykil Island from all rookeries in the Russian Far East, with the exception of animals born on the Commander Islands. The highest number of migrant Steller sea lions appears in the autumn period, and it is represented mainly by young animals (1–3 years old) and semi-adults (males aged 4–7 years). In general, the data obtained from images collected by remote cameras during the entire year provided a detailed picture of the rookery used by Steller sea lions during the entire annual cycle of their life and monitored the seasonal population dynamics, the sex and age composition of animals on the shore, and the reproductive success of marked Steller sea lions. Currently, the use of autonomous remote cameras remains the only available method of year-round monitoring of the state and habitat use of hard-to-reach remote Steller sea lion’s rookeries.