Yeates Laura C, Williams Terrie M, Fink Traci L
Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95060, USA.
J Exp Biol. 2007 Jun;210(Pt 11):1960-70. doi: 10.1242/jeb.02767.
As the smallest and one of the most recently evolved marine mammals, sea otters face physiological challenges rarely encountered by larger, more derived aquatic species. To examine the effect of these challenges on foraging costs and resultant daily energy budgets, we measured the energetics of resting, grooming, diving and foraging for adult, male sea otters. The energy expended for these different behaviors as determined from open flow respirometry was then standardized across activity budgets measured for wild sea otters to estimate field metabolic rates (FMR). We found that the metabolic rate of captive otters performing single dives ranging in duration from 40 to 192 s was 17.6+/-0.5 ml O(2) kg(-1) min(-1) and only 1.3 times resting rates. This rate increased significantly if the animals foraged during submergence. The cost of a foraging dive for sea otters was nearly twice that predicted for phocid seals, which was attributed in part to elevated locomotor costs associated with buoyancy and swimming style. Our behavioral studies indicate that wild sea otters spend the greatest proportion of the day feeding and resting, with the largest daily energy expenditure (6.1+/-1.1 MJ day(-1)) associated with foraging. The resulting mean FMR for wild sea otters based on the energy expended for all behaviors was 15.7+/-2.7 MJ day(-1) and matched predicted FMR values based upon a regression of known FMR values for other marine mammals across a range of body sizes. This was achieved by counterbalancing elevated foraging costs with prolonged periods of rest on the water surface.
作为最小且进化时间最晚的海洋哺乳动物之一，海獭面临着大型、进化程度更高的水生物种很少遇到的生理挑战。为了研究这些挑战对觅食成本及由此产生的每日能量预算的影响，我们测量了成年雄性海獭休息、梳理毛发、潜水和觅食时的能量消耗情况。通过开放式流动呼吸测定法确定的这些不同行为所消耗的能量，随后根据对野生海獭测量的活动预算进行标准化，以估算野外代谢率（FMR）。我们发现，圈养海獭单次潜水持续时间在40至192秒之间时，其代谢率为17.6±0.5毫升氧气·千克⁻¹·分钟⁻¹，仅为休息时代谢率的1.3倍。如果动物在潜水时觅食，这个代谢率会显著提高。海獭觅食潜水的成本几乎是髯海豹预测成本的两倍，这部分归因于与浮力和游泳方式相关的运动成本增加。我们的行为研究表明，野生海獭一天中花费在进食和休息上的时间比例最大，与觅食相关的每日能量消耗最大（6.1±1.1兆焦耳·天⁻¹）。基于所有行为所消耗的能量得出的野生海獭的平均FMR为15.7±2.7兆焦耳·天⁻¹，与根据其他海洋哺乳动物已知FMR值在一系列体型范围内进行回归预测的FMR值相符。这是通过在水面长时间休息来平衡增加的觅食成本实现的。
