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

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.诸多鳍足目（Pinniped）动物会执行一类被称为"漂移潜水（drift dive）"的特定潜水行为，即被动地在水层中随流漂移。这类潜水行为被认为可用于休息、睡眠或食物消化，还可通过计算随时间推移的垂直漂移速率日变化量，反映动物的摄食成功率：该速率变化会随体内脂质占比改变，进而体现动物浮力的相对波动情况。西北大西洋冠海豹（Northwest Atlantic hooded seals）在横跨西北大西洋的年度洄游过程中，会定期开展漂移潜水行为。本研究发现，漂移速率的日变化会随地理位置与季节时序发生变化，且该变化存在显著性别差异。在其整个洄游分布范围内，均观测到浮力正向变化（对应脂质储备增加）；尽管该变化与高频使用海域存在一定重叠，但基于首次通过时间（First Passage Time，FPT）的统计分析显示，二者并无显著关联。雌雄个体间浮力季节波动的差异表明，二者在冬季与春季的能量收支模式存在差异，该差异与繁殖活动相关。而换毛期前后的浮力波动模式则不存在性别差异。