FISHERY BULLETIN: VOL. 87, NO. 1 



swimming at this speed, and 2.7 times that mea- 

 sured at zero flow (Fig. Ic). All animals with 200 

 g nets struggled against the flow at 1.1 m/s. 



Behavioral and Energetic Changes 

 Associated with Entanglement 



Before entanglement, swimming was the predom- 

 inate behavior of the northern fur seals (Table 3). 

 Grooming was the next most frequent activity, while 

 resting accounted for 18% of the total activity. After 

 entanglement in a 225 g fragment, the fur seals' 

 behavior was substantially altered. Time spent 

 swimming declined by roughly 75% from control 

 measurements, while the percent time spent resting 

 increased by a factor of 2.4. Time spent grooming, 

 however, was not significantly altered; fur seals con- 

 tinued to spend approximately 1/3 of their daylight 

 hours engaged in this activity (Table 3). 



Table 3.— Percentage of time spent by three northern tur seals 

 at swimming, resting, grooming, or in other activities over 6 d 

 intervals before and during entanglement in a 225 g net. 



Before entanglement 



During entanglement 



ment was slightly greater than in the control experi- 

 ment, although this difference was not significant. 

 While mean ADMR increased by 16% after en- 

 tanglement (Table 4), this increase was primarily 

 due to one animal (FS2). FS2 swam more than either 

 of the other two animals both before and during en- 

 tanglement (Table 3), and this undoubtedly led to 

 a higher ADMR. 



No consistent trend was observed for FSl and 

 FS3 with respect to altered energetic expenditures 

 associated with entanglement. FSl's metabolic rate 

 increased 1 W/kg above the control measurement. 

 FS3 showed a decrease of roughly the same amount 

 (Table 4). FSl exhibited an increased ADMR even 

 though it spent less time swimming and grooming 

 during the entanglement period. While FS3 showed 

 similar behavioral trends, its ADMR decreased dur- 

 ing entanglement. 



Table 4.— CO^ Production fVCOj in L COj h ' kg " ') and rate 

 of three northern fur seals' energy expenditure' (W/kg) determined 

 by the doubly labeled water method. Measurements were made 

 over 6 d intervals before and during entanglement in a 225 g net. 



Before 



During 



'CalculatecJ using an RQ of 80 



The nature of the resting and grooming behaviors 

 of fur seals appeared to change as a result of en- 

 tanglement. Unentangled fur seals typically rested 

 quietly on the surface in a "jug-handle" position with 

 one foreflipper and both rear flippers held out of the 

 water. Entangled fur seals most often rested with 

 their ventral surfaces down and both fore- and rear 

 flippers submerged. In this position, they had to lift 

 their heads to breathe. Resting was also not com- 

 pletely quiet. Unlike before, fur seals changed posi- 

 tions frequently and were always alert in the pres- 

 ence of observers. 



When grooming, fur seals spent more time vio- 

 lently shaking their heads and scratching at the net 

 vdth both their rear and foreflippers than before en- 

 tanglement. Grooming was less vigorous in the 

 absence of a net. More time was spent slowly roll- 

 ing around in the water, or passively moving about 

 (Table 3). 



The rate of energy expenditure during entangle- 



Entanglement Observations 



Individual variations in behavior were the most 

 important factors influencing whether entanglement 

 occurred (Table 5). For example, FSl became en- 

 tangled 1 hour and 45 minutes after it was first 

 presented with a 6 x 4 mesh net (0.9 m x 0.6 m). 

 From presentation to entanglement, the net was the 

 focus of the animal's attention. FSl bit and pulled 

 at it, laid beneath it, and often rested on top of it. 

 Once entangled, FSl became quite agitated and 

 swam around vigorously while violently shaking its 

 head. The holding tank was drained after 1 hour and 

 the net was removed from its neck. Another net (4 

 X 4 meshes; 0.6 m x 0.6 m) was then introduced 

 into the holding tank and FSl ignored it complete- 

 ly throughout the rest of the day. By the following 

 morning, FSl had become entangled again. This net 

 was left on the animal for 2 days. At no time did 

 it appear that FSl could free itself, and the net 

 was subsequently removed. Another net was then 



90 



