FISHERY BULLETIN: VOL. 87, NO. I 



RESULTS 



Measurements of the northern fur seals' length, 

 mass, and body diameters as a function of age are 

 presented in Table 1. 



Table 1.— Age', weight, length, and body diameters of the 

 three northern fur seals used in this study. Means ( + SD) 

 are given. 



'Age based on estimated birth date of July 1 



Energetic Measurements 



During the winter swimming trials, mean water 

 temperature ( ± SD) was 14.9 ( ± 0.2) °C. Mean body 

 mass of the three northern fur seals was 14. 1 ( + 0.6) 

 kg. At zero water flow, fur seals expended a mean 

 of 6.95 (±1.02) W/kg; at 0.75 m/s it was slightly, 

 though not significantly, lower and averaged 6.89 

 ( ± 0.45) W/kg (Table 2). The greater metabolic rate 

 at zero flow was due to uncontrolled activity (swim- 

 ming and grooming) inside the chamber. At 0.75 m/s 

 the animals swam steadily and did not groom. 



At zero water flow, the presence of a net also 

 slightly increased each fur seal's metabolic rate (Fig. 

 1). Although there was no evidence of any behav- 



ioral change, the net may have caused slight stress 

 and led to an elevated 0^ consumption. Additional- 

 ly, there may have been a loss of air from the pelage 

 in the region of the net allowing the infiltration of 

 cold water. This rise was noted both in the winter 

 and spring experiments (Table 2). 



At the relatively slow speed of 0.75 m/s, small net 

 fragments did not significantly elevate mean meta- 

 bolic rates (Fig. lb). In fact, metabolism was 3.5% 

 lower with a 61 g net at 0.75 m/s than at zero flow 

 (Table 2). While a slight elevation did occur with the 

 100 g net at 0.75 m/s, this was not significantly 

 greater than at zero flow with a 100 g net or than 

 at 0.75 m/s with no net (Fig. lb). 



During the spring experiments, water tempera- 

 ture had increased to a mean of 16.6 ( + 0.5) °C, and 

 the fur seals had increased in weight to 16.4 ( + 0.5) 

 kg (Table 2). As a result, each animal's routine 

 energy consumption, determined at zero flow and 

 without a net, had declined to a mean of 5.22 ( + 0.21) 

 W/kg. This decline was also evident when the results 

 of the winter and spring experiments at 0.75 m/s 

 and with 100 g net fragments were compared (Table 

 2). 



As noted during the winter trials, animals with 

 100 g nets did not expend greater amounts of energy 

 at 0.75 m/s than during unentangled swimming at 

 this speed. At 1.1 m/s, however, a 100 g net caused 

 a significant 40% increase in metabolic rate (^test; 

 P < 0.05) (Fig. Ic). The 200 g fragments caused 

 significant metabolic increases at both flume speeds. 

 When entangled in a fragment of this size, fur seals 

 expended 66% more energy at 0.75 m/s than at zero 

 flow speed. At 1.1 m/s, mean metabolic rate was 

 elevated 2.1 times that measured for unentangled 



Table 2.— Mean ( + SD) rate of energy utilization (W//kg) for the three northern fur seals during the 

 winter and spring swimming experiments. Means were determined by combining data from all animals. 

 The sample size for each animal (FS1. FS2. FS3) is given in parentheses (n,, n^, and n^. respec- 

 tively). Body mass and water temperature averaged 14.1 ( + 0.55) and 14.9 ( + 0.2) °C in the winter, 

 and 16.4 (±0.5) kg and 16.6 (±0.5) °C in the spring. 



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