Haul-Out Behaviour of the World's Northernmost Population of Harbour Seals (Phoca vitulina) throughout the Year

Abstract

The harbour seal population in Svalbard occurs at the northernmost limit of the species' range. It experiences environmental extremes far beyond the norm for this species, including an extended period of polar night and extensive sea ice cover. In 2009 and 2010, 60 harbour seals (30 pups + 30 immature/mature seals) from this population were equipped with Satellite-Relay Data Loggers (SRDLs) to study their haul-out behaviour, with a special focus on the winter period. Using a combination of Generalized Additive Mixed Models and Cox Proportional Hazard models, the influences of sex, maturity, temporal, spatial and environmental factors on haul-out behaviour were explored. All of the seals continued to haul out even through the coldest periods during the polar night, though clear seasonality in the time spent hauled out daily was displayed by both immature and mature seals. Time spent hauled out daily decreased from ∼5.2 hrs in September to ∼1.2 hrs in February in these age groups, while pups displayed less seasonality (∼2.4 hrs/day throughout most of the year). The average at-sea period also exhibited seasonality, increasing to a maximum of ∼1.6 days in February (monthly maxima for individual animals ranged from 7 to 19 days). The seals showed a strong preference to haul out at low tide when hauling out on land but not when using sea ice as a haul-out platform. A diel rhythm in haul-out behaviour was present during the months with day–night cycling and midnight sun but not during the polar night. Haul-out behaviour was impacted to a greater extent by air pressure, through its effect on wind speed, than by absolute temperature values. The extreme environment in Svalbard likely causes some physiological challenges that might impact survival rates negatively, particularly among pups. Climate warming is likely to have positive effects on Svalbard's harbour seal population.

Dynamic habitat corridors for marine predators; intensive use of a coastal channel by harbour seals is modulated by tidal currents

“…These results support preliminary surveys in this area which observed that hauled-out seal numbers increased during the ebbing tide, with highest numbers observed from about 3.5 h before low tide until half an hour after (Cunningham et al 2010). So in addition to the in-water behaviour, the haul-out patterns appear relatively unusual and contrasts with the more traditional understanding that haul-out behaviour peaks at the transition of ebb and flood tides (Schneider and Payne 1983; Pauli and Terhune 1987); this adds to increasing evidence that haul-out patterns of harbour seals in some locations may not be driven by tide but by a complex interaction of environmental variables such as diel rhythms (Calambokidis et al 1987; Hamilton et al 2014), predation risk (London et al 2012) and weather conditions (Schneider and Payne 1983; Grellier et al 1996). …”

Harbour seal Phoca vitulina movement patterns in the high-Arctic archipelago of Svalbard, Norway

“…2000 animals (Merkel et al 2013) has low genetic diversity (Andersen et al 2011); it is Red-listed in Norway and hence protected from harvesting. The haul-out behaviour of this population has been studied intensively (Reder et al 2003), and concomittantly with the current stud (see Hamilton et al 2014), but the at-sea behaviour of adult harbor seals re mains largely undocumented. A few animals in this population were tracked through the fall and early winter period via satellite tag deployments in the early 1990s (Gjertz et al 2001) and 3 time-depth recorders (TDRs) were deployed for some weeks in the autumn of 1994 (Krafft et al 2002).…”

“…Gjertz et al (2001) suggested that harbour seals that disperse to other areas of Svalbard likely return to PKF for pupping, mating and possibly moulting. Identified terrestrial haul-out sites are certainly not limited to PKF; animals haul out along much of the west coast of Spitsbergen (Hamilton et al 2014), demonstrating that at least some individuals are not resident around PKF throughout the year. The large individual variations observed in movement metrics in this study suggest the existence of individual strategies, with part of the population staying close to PKF while other individuals disperse much more broadly, though members of this population remain tied to the west coast of Spitsbergen.…”

“…Hamilton et al (2014) have shown that harbour seals from Svalbard spend less time hauled out (and consequently more time in the water) during the winter compared to summer and suggested that it could be a strategy to avoid thermal stress when hauling out on ice in winter when air temperatures can drop below −30°C. However, the potential thermal challenges imposed by low winter temperatures are unlikely to be the only reason for the increased aquatic behaviour, since increased time spent in the water and increasing distances travelled per day occurred concomitantly.…”

Intrinsic and extrinsic drivers of activity budgets in sympatric grey and harbour seals

“…Although the proportion of time harbour seals rest overall (non diving) varied little with time of day, they showed significant preference to rest on land in the second half of the day. Harbour seals appear to be flexible in when they haul out, linked with availability of tidal haul out sites (Thompson et al , Hamilton et al ), disturbance (Brasseur et al ), predation pressure (London et al ) and environmental covariates (Watts ). In harbour seals, there is evidence of intra‐specific density dependent interactions on haul out sites (Neumann ) and at mixed haul out sites the smaller harbour seals could be competitively excluded by grey seals leading them to preferentially haul out at a different time of day to grey seals.…”