Drift Diving by Hooded Seals (Cystophora cristata) in the Northwest Atlantic Ocean

Abstract

Many pinniped species perform a specific dive type, referred to as a ‘drift dive’, where they drift passively through the water column. This dive type has been suggested to function as a resting/sleeping or food processing dive, and can be used as an indication of feeding success by calculating the daily change in vertical drift rates over time, which reflects the relative fluctuations in buoyancy of the animal as the proportion of lipids in the body change. Northwest Atlantic hooded seals perform drift dives at regular intervals throughout their annual migration across the Northwest Atlantic Ocean. We found that the daily change in drift rate varied with geographic location and the time of year and that this differed between sexes. Positive changes in buoyancy (reflecting increased lipid stores) were evident throughout their migration range and although overlapping somewhat, they were not statistically associated with high use areas as indicated by First Passage Time (FPT). Differences in the seasonal fluctuations of buoyancy between males and females suggest that they experience a difference in patterns of energy gain and loss during winter and spring, associated with breeding. The fluctuations in buoyancy around the moulting period were similar between sexes.

Drift dives and prolonged surfacing periods in Baikal seals: resting strategies in open waters?

“…crabeater seal) throughout the year, and no drift dives have been detected in the diving records of these species (Bengtson and Stewart, 1992;Lesage et al, 1999;Davis et al, 2003). Therefore, our finding, together with those of the previous studies (Hindell et al, 1991;Crocker et al, 1997;Page et al, 2005;Andersen et al, 2014), indicates that drift diving is an option for pinnipeds to rest or process food when there are no places to haul out.…”

“…Given that the function of prolonged surfacing periods is similar to that of drift dives, our results agree with those for elephant seals, which exhibit drift dives most frequently in the morning after a long series of forging dives at night (Crocker et al, 1997). Drift dives of Baikal seals are observed during the daytime, which is inconsistent with findings for hooded seals (Andersen et al, 2014) and New Zealand fur seals (Page et al, 2005), which exhibit drift dives at night-time.…”

“…Among the 34 extant pinniped species, Baikal seals are now the fifth species that has been confirmed to perform drift dives, together with northern and southern elephant seals, hooded seals and New Zealand fur seals (Hindell et al, 1991;Crocker et al, 1997;Page et al, 2005;Andersen et al, 2014). A common feature of the five species showing drift dives is that they spend, during a certain time of the year, a considerable amount of time in open waters, without nearby land or ice that can be used for hauling out.…”

“…Based on these observations, it is currently accepted that drift dives represent resting or food processing by the seals (Crocker et al, 1997;Mitani et al, 2010), although it is difficult to determine whether the seals sleep during drift dives. Drift dives have also been reported for hooded seals, Cystophora cristata (Andersen et al, 2014), and New Zealand fur seals, Arctocephalus forsteri (Page et al, 2005), and an additional function of predator avoidance was proposed. That is, repeating drift dives might be safer for seals than resting at the surface in the presence of predators such as white sharks, Carcharodon carcharias (Page et al, 2005).…”

Inferring prey size variation from mandible acceleration in northern elephant seals

“…We implemented a random effect by using the “re” smoother option, as suggested that it is appropriate for simple, independent random effects (Wood , Andersen et al . ). We used AIC to select the most parsimonious model among null and full models.…”