Individual variability in diving, movement and activity patterns of adult bearded seals in Svalbard, Norway

Abstract

Bearded seals are one of the least studied Arctic marine mammals, despite their circumpolar distribution and importance as a resource to Inuit communities. In this study, adult bearded seals (Erignathus barbatus) were equipped with GPS-Argos-CTD-SRDLs in Svalbard, Norway (2011–2012, n = 7) to document their diving, activity and movement patterns in a region where their habitat is changing rapidly. Five seals transmitted for > 8 months, sending 21,738 GPS-positions and 17,866 dives between July and April. The seals spent little time hauled out (≤ 5%). Diving, which occupied 74 ± 3% of their time, was generally shallow (24 ± 7 m, max: 391 m) and of short duration (6.6 ± 1.5 min, max: 24 min) with deeper, longer dives in winter/spring compared to summer. All seals occupied shallow, coastal areas and relatively small 50% home ranges (10–32 km2). However, individuals exhibited high degrees of specialization in their habitat use and diving behaviour, differing markedly with respect to proportions of benthic vs pelagic dives (range: 51–95% benthic dives), distance to glacier fronts (range: 3–22 km) and in the time spent at the bottom of dives (range: 43–77%). Having specialized strategies within a generalist population may help bearded seals adapt in a rapidly changing Arctic ecosystem.

Behavioural ontogeny of bearded seals Erignathus barbatus through the first year of life

“…Svalbard's isolated location and its narrow shelf might be defining regional characteristics de termining these choices by this benthic-feeding seal species. Bearded seals of all ages are quite sedentary in Svalbard, largely remaining in shallow, coastal areas (this study, Gjertz et al 2000, Krafft et al 2000, Hamilton et al 2018. Similar to the pups in this study, adults were found in coastal areas with low sea-ice concentrations (″10%) in the summer and early autumn, and preferred intermediate sea-ice concentrations (10− 70%) in the late-autumn and winter, according to Hamilton et al (2018).…”

“…The number of pups transmitting data is shown above (a) lower total body oxygen stores of pups compared to adults do not provide a large constraint due to the large size of bearded seal pups and the fact that they forage on shallow-dwelling benthos (infauna, epifauna and benthically distributed fishes; Lowry et al 1980. Pups did dive to greater depths than adult bearded seals in Svalbard until they were 180 d old, when diving depths became shallower (this study, Hamilton et al 2018). Pups likely dove to deeper depths than adults in an ex ploratory manner, be fore they learned that food is found at shallow depths.…”

“…Bearded seals of all ages are quite sedentary in Svalbard, largely remaining in shallow, coastal areas (this study, Gjertz et al 2000, Krafft et al 2000, Hamilton et al 2018. Similar to the pups in this study, adults were found in coastal areas with low sea-ice concentrations (″10%) in the summer and early autumn, and preferred intermediate sea-ice concentrations (10− 70%) in the late-autumn and winter, according to Hamilton et al (2018). In contrast, juvenile bearded seals in the Bering Sea move south with the advancing sea ice, selecting areas near the ice edge and occupying areas with moderate to high ice concentrations; adult bearded seals in this same re gion have a similar migration, though they re main in areas further north than young animals where sea-ice concentrations are heavier (Ca meron et al 2018).…”

“…Weaned pups of many pinniped species compensate for short dive durations by making more dives to foraging depths or spending a greater proportion of time diving compared to adults (Burns 1999, Fowler et al 2006, Vacquie-Garcia et al 2017. In contrast, bearded seal pups spent less time diving than adults throughout the tracking period, and dove a similar number of times per day compared to adults from the time of weaning until pups were ~180 d of age (this study, Hamilton et al 2018). This is likely because the Fig.…”

“…Ontogenetic changes in (a) distance travelled (mean ± SE; no error bars shown when only 1 pup was transmitting data) and (b) 95% home range size (mean ± 95% CI) over the first year of life for 13 bearded seal Erignathus barbatus pups equipped with satellite relay data loggers in 2005 and 2006 in Svalbard, Norway. The number of pups transmitting data is shown at the bottom of (b) the highly individualistic foraging patterns seen in adult bearded seals (see Hamilton et al 2018; 1 yr old pups are 35 to 50% of the asymptotic mass of adults, Andersen et al 1999).…”