Richard Gaëtan, Vacquié-Garcia Jade, Jouma'a Joffrey, Picard Baptiste, Génin Alexandre, Arnould John P Y, Bailleul Frédéric, Guinet Christophe
CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC 3125, Australia.
J Exp Biol. 2014 Jul 15;217(Pt 14):2609-19. doi: 10.1242/jeb.088542. Epub 2014 May 6.
Mature female southern elephant seals (Mirounga leonina) come ashore only in October to breed and in January to moult, spending the rest of the year foraging at sea. Mature females may lose as much as 50% of their body mass, mostly in lipid stores, during the breeding season due to fasting and lactation. When departing to sea, post-breeding females are negatively buoyant, and the relative change in body condition (i.e. density) during the foraging trip has previously been assessed by monitoring the descent rate during drift dives. However, relatively few drift dives are performed, resulting in low resolution of the temporal reconstruction of body condition change. In this study, six post-breeding females were equipped with time-depth recorders and accelerometers to investigate whether changes in active swimming effort and speed could be used as an alternative method of monitoring density variations throughout the foraging trip. In addition, we assessed the consequences of density change on the swimming efforts of individuals while diving and investigated the effects on dive duration. Both descent swimming speed and ascent swimming effort were found to be strongly correlated to descent rate during drift dives, enabling the fine-scale monitoring of seal density change over the whole trip. Negatively buoyant seals minimized swimming effort during descents, gliding down at slower speeds, and reduced their ascent swimming effort to maintain a nearly constant swimming speed as their buoyancy increased. One per cent of seal density variation over time was found to induce a 20% variation in swimming effort during dives with direct consequences on dive duration.
成年雌性南象海豹（Mirounga leonina）仅在10月上岸繁殖，1月上岸换毛，一年中的其余时间都在海上觅食。在繁殖季节，由于禁食和哺乳，成年雌性象海豹可能会损失高达其体重50%的重量，主要是脂质储备。繁殖后离开前往大海时，雌性象海豹处于负浮力状态，之前通过监测漂流潜水期间的下降速度来评估觅食之旅中身体状况（即密度）的相对变化。然而，进行的漂流潜水相对较少，导致身体状况变化的时间重建分辨率较低。在本研究中，六只繁殖后的雌性象海豹配备了时间深度记录仪和加速度计，以研究主动游泳努力和速度的变化是否可以作为监测整个觅食之旅中密度变化的替代方法。此外，我们评估了密度变化对个体潜水时游泳努力的影响，并研究了对潜水持续时间的影响。研究发现，下降游泳速度和上升游泳努力都与漂流潜水期间的下降速度密切相关，从而能够对整个旅程中海豹密度变化进行精细监测。负浮力的海豹在下降过程中尽量减少游泳努力，以较慢的速度下滑，并随着浮力增加减少上升游泳努力以保持几乎恒定的游泳速度。研究发现，随着时间的推移，海豹密度变化1%会导致潜水时游泳努力变化20%，这对潜水持续时间有直接影响。
