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Standard metabolic rate at the surface and during trained submersions in adult California sea lions (Zalophus californianus)

Jenifer A. Hurley^* and Daniel P. Costa

Department of Biology and Institute of Marine Sciences, University of California, Santa Cruz, CA 95064 USA

View larger version (12K): [in a new window]   Fig. 1. Mean mass versus maximum submersion duration for all subjects (P=0.08). The solid line represents the least-squares linear relationship.

View larger version (31K): [in a new window]   Fig. 2. Sample single-dive MR (rate of oxygen uptake) calculation using a 5 min dive trial with M1. Oxygen consumption was sampled every 10 s. Horizontal line A represents the baseline MR calculated from the area under the metabolic curve divided by the duration; A=5.12 ml O2 min–1 kg–1. Horizontal line B represents the post-recovery MR calculated from the area under the metabolic curve divided by the duration; B=5.09 ml O2 min–1 kg–1. The recovery interval contains all the post-dive O2 debt, including 3 min of post-recovery MR, to ensure that all the O2 debt has been included; recovery=46.18 ml O2 kg–1 and covers a 4.67 min period. The average baseline rate is (A+B)/2=5.11 ml O2 min–1 kg–1. The portion of the recovery period MR which is accounted for by the baseline MR is 4.67 minx5.11 ml O2 min–1 kg–1=23.86 ml O2 kg–1. Therefore, the O2 debt from the dive is 46.18 ml O2 kg–1–23.86 ml O2 kg–1= 22.32 ml O2 kg–1, and the dive MR is 22.32 ml O2 kg–1/5.0 min=4.46 ml O2 kg–1min–1.

View larger version (17K): [in a new window]   Fig. 3. Submersion MR versus dive duration for (A) males and (B) females. Solid lines represent least-squares linear relationships (M1: r2=0.78, P=0.02; M2: r2=0.96, P=0.01; F1: r2=0.5, P=0.001; F2: r2=0.45, P=0.02). Values are means ±1 S.D. The sample size is given in parentheses. Dotted horizontal lines represent standard MR for each animal for comparison.

View larger version (21K): [in a new window]   Fig. 4. An example of how the measurement period affects variation in oxygen consumption measurements in sea lions. The results of three analytical methods are shown. The dotted line shows the variability when a 10-second average is used, the bold line depicts a 10-minute running average and the flat line represents the regression of the entire data set (r2=0.0001, P=0.84).