Department of Biological Sciences, California Polytechnic State University San Luis Obispo, 1 Grand Ave, San Luis Obispo, CA 93407, USA.
Department of Biology, Colorado State University, 1878 Campus Delivery, Fort Collins, CO 80523, USA.
J Exp Biol. 2024 Sep 1;227(17). doi: 10.1242/jeb.247134. Epub 2024 Sep 12.
Sea otters are extremely positively buoyant and spend most of their time resting at the water surface. It is understood that some of this buoyancy comes from the air layer that sea otters maintain in their pelage, with the lungs providing an additional source of positive buoyancy. Past studies have investigated the fur buoyant force in adult sea otters; however, little is known about the fur buoyant force in younger age classes. This study compared ontogenetic changes in the fur buoyant force of southern sea otter (Enhydra lutris nereis) pelage. We measured the fur buoyant force of pelt samples, scaled that to the whole animal, and calculated mass-specific fur buoyant force for six age classes: neonates (<1 month), small pups (1-2 months), large pups (3-5 months), juveniles (6 months-1 year), subadults (1-3 years) and adults (4-9 years). Each pelt sample was measured under three conditions: control, oiled and washed with Dawn® dish soap. Oiled and washed pelts had a lower fur buoyant force compared with the control pelts across all age classes. When oiled, the air layer of the pelt is ruined and no longer provides sufficient positive buoyancy. Pelts washed with Dawn® had higher variability in buoyant force compared with other conditions, and the air layer was not restored consistently. When we scaled up, we found that younger age classes were more buoyant because of their larger surface area to volume ratio. These differences in buoyancy may underlie variations in energetic costs and behavior among sea otters across development.
海獭具有极强的正浮力，大部分时间都在水面上休息。据了解，海獭皮毛中的气层和肺部都能提供额外的正浮力，这是其浮力的一部分来源。过去的研究已经调查了成年海獭的皮毛浮力；然而，对于年幼的海獭，人们知之甚少。本研究比较了南方海獭（Enhydra lutris nereis）皮毛浮力的个体发育变化。我们测量了皮毛样本的浮力，将其转化为整只动物的浮力，并计算了六个年龄组的单位质量皮毛浮力：新生儿（<1 个月）、小幼崽（1-2 个月）、大幼崽（3-5 个月）、幼崽（6 个月-1 岁）、亚成体（1-3 岁）和成年个体（4-9 岁）。每个皮毛样本在三种条件下进行测量：对照、涂油和用 Dawn®洗碗皂清洗。与对照皮毛相比，所有年龄组的涂油和用 Dawn®清洗的皮毛的浮力都较低。涂油后，皮毛的气层被破坏，不再提供足够的正浮力。与其他条件相比，用 Dawn®清洗的皮毛的浮力变化更大，而且气层不能始终恢复。当我们进行放大时，我们发现较小的年龄组具有更高的浮力，因为它们的表面积与体积比更大。这些浮力差异可能是海獭在发育过程中能量消耗和行为变化的基础。
