First abundance estimate for white whales Delphinapterus leucas in Svalbard, Norway

J Vacquié-Garcia,M Andersen,Km Kovacs,C Lydersen,Ta Marques

doi:10.3354/esr01016

Abstract

The Svalbard Archipelago (Norway) is experiencing rapid declines in the seasonal duration and extent of sea-ice cover, and local tidewater glaciers are melting. These environmental changes represent a threat to ice-associated species in the region, including white whales Delphinapterus leucas. However, no estimates of stock size or trends are available for this stock. An aerial survey was conducted during the summer of 2018, covering the coastlines of all major islands in Svalbard, as well fjords and open ocean areas. A total count was attempted for the coastlines, while coverage of the fjords and open ocean areas was designed as distance-sampling line transects. In total, 265 white whales were detected in 22 groups along the 4965 km of coastline coverage. No whales were observed on fjord (1481 km) or open ocean transects (535 km). After correcting for surface availability using behavioural data from the same area (in summer) and making adjustments for small areas not flown during the survey, the stock size was estimated to be 549 individuals (95% CI: 436%%CONV_ERR%%723). This estimate is surprisingly low given that this species is one of the most frequently observed cetaceans in the area, but it confirms suspicions based on difficulties in finding animals when operating white whale tagging programmes over the past decade. This first population estimate is important in the context of the rapid environmental change taking place in the Arctic and for providing a baseline for comparison with future estimates.

Highlights

The Arctic has experienced a rapid reduction in sea ice over the last few decades, and in some areas tidewater glaciers are retracting onto land (Stroeve et al 2007, Lydersen et al 2014)
This study provides the first abundance estimate for white whales in the Svalbard Archipelago
The largest drawback of the design employed here was the large distance between independent transect lines in the OPEN OCEAN (i.e. 90 km), making it possible that some groups of animals might have been missed

Summary

Introduction

The Arctic has experienced a rapid reduction in sea ice over the last few decades, and in some areas tidewater glaciers are retracting onto land (Stroeve et al 2007, Lydersen et al 2014). Such changes represent direct loss of habitat for ice-associated marine mammals, which use these environments for breeding and foraging (Stirling 1997, Heide-Jørgensen & Laidre 2004, Lydersen et al 2014). One of the unknown stocks resides in the Svalbard Archipelago in the Norwegian High Arctic This region has been strongly affected by climate change, experiencing the greatest decrease in the seasonal duration of sea-ice cover within the circumpolar Arctic (Laidre et al 2015). The white whale stock in this region is genetically differentiated from the West Greenland stock to the west (O’Corry-Crowe et al 2010); its genetic relationship with white whales in Frans Josef Land to the east is currently unknown (Lønø & Øynes 1961, O’Corry-Crowe et al 2010), tracking data from Svalbard do not suggest routine movements between these archipelagos in recent decades (Lydersen et al 2001, Vacquié-Garcia et al 2018)

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Conclusion