Lost and Found: Reassessing Ringed Seal Abundance in a Key Fjord System in Svalbard After a 20-Year Hiatus

Abstract

Ringed seals (Pusa hispida) in Svalbard, Norway, are thought to be declining due to the impacts of climate change in the region, particularly due to a significant reduction in the extent of landfast sea ice that they rely on for breeding. The only available survey of ringed seals in Svalbard took place in 2002, so is now over twenty years old. Here, we address this data gap by conducting UAV aerial surveys throughout the Isfjorden fjord system on the island of Spitsbergen, Svalbard, during the moulting season in 2023. We also provide the first aerial-based assessment of size/age structure of the ringed seal population within Isfjorden using body length measured from the UAV images. From a total 7,042 images collected along 2,159 km of transects we covered an area of 132 km² of landfast sea ice. We show a decrease of 77% in landfast sea ice and concomitant decline in ringed seal abundance in Isfjorden of approximately 46% since 2002. We show that the declines in landfast sea ice and ringed seal abundance have led to an increase in the density of seals, from 1.86 seals/km2 in 2002 to 2.41 seals/km2 in 2023. Length-based estimates of age suggest that 65% of the contemporary population consists of immature individuals. Together, the results from this updated population survey underscore the urgent need for more frequent monitoring of ringed seals in Svalbard to better understand the drivers of population decline and highlights the broader implications of environmental changes on Arctic marine biodiversity. The innovative use of UAV technology in this study demonstrates its utility in wildlife research, offering a less invasive, cost-effective, and efficient method for collecting aerial images of ringed seals and their environment that enable a wide variety of studies that will be useful to inform management and climate change mitigation.