Estimating the number of walruses in Svalbard from aerial surveys and behavioural data from satellite telemetry

ABSTRACT. All known terrestrial haul-out sites for walruses in Svalbard (n = 79) were surveyed during the period 1–3 August 2006, and sites that were in use (n = 17) were documented using digital photography. A total of 657 walruses were counted on land in the resultant images. An extensive behavioural data set from walruses equipped with satellite relay data loggers, covering August 2002 to August 2005, was used to account for walruses that were in the water. The proportion of walruses at sea during the survey was calculated to be 0.750 on the basis of 28 thirty-day periods from 23 male walruses. Time of day and wind chill did not significantly affect haul-out behaviour. However, a logistic regression model revealed both a correlation among haul-out patterns of individuals within years, and a year effect (χ2 = 6.42, df = 2, p = 0.04). Because the survey was not flown in a year when satellite tags were deployed, the interannual variance was retained in a model (with no other explanatory variables). The over-dispersion parameter from this model was 2.02 (deviance = 28.33, df = 14). Thus, variance in proportions of time individuals spent at sea was multiplied by this parameter to achieve a corrected SE around the estimate. The 95 % CI based on this SE corresponded to a proportion of walruses at sea during the survey between 0.717 and 0.781, resulting in an estimated total number of walruse

Ringed seal (Pusa hispida) diet on the west coast of Spitsbergen, Svalbard, Norway: during a time of ecosystem change

Global warming is causing Atlantification of water masses and concomitant changes in food webs in the Barents Sea region. To determine whether changes that have been documented at lower trophic levels are impacting the diet of ringed seals (Pusa hispida) gastrointestinal tracts (GITs) from 99 coastal-feeding ringed seals, collected in western Spitsbergen, Svalbard, were analysed via identification of hard-parts. The study animals were shot in spring (n = 30; April–July) or autumn (n = 69; August–October) during four consecutive years (2014–2017). Thirty different prey types were identified, but most seals (55.6%) had consumed between 2 and 4 different types of prey. Polar cod (Boreogadus saida) dominated the diet of the ringed seals in terms of relative biomass (Bi = 60.0%) and frequency of occurrence (FOi = 86.9%), followed by pricklebacks (Stichaeidae; Bi = 23.4%; FOi = 79.8%). Redundancy analysis (RDA) revealed that year was the only significant predictor explaining variance in autumn diet composition (RDA, F3 = 4.96, AIC = − 76.49, p ≤ 0.0050; blubber content and maturity/sex group were not significant). Blue whiting (Micromesistius poutassou) occurred in the diet in small quantities; this Atlantic fish species has not previously been documented in the ringed seals’ diet. Atlantic cod (Gadus morhua) had the highest Bi (9.2%) among Atlantic prey types. However, despite major changes in the last decade in the fish and zooplankton community in western Svalbard, and consumption of a few Atlantic prey types, the ringed seals’ diet in Svalbard continues to be dominated by Arctic prey, especially polar cod.publishedVersio