FELDKAMP ET AL.: NET ENTANGLEMENT ON NORTHERN FUR SEALS 



introduced, and this time it was completely ig- 

 nored. After 8 hours, the net was removed from the 

 tank. 



In contrast to FSl's apparent increased wariness 

 to floating nets after its first entanglement, FS3 

 became entangled almost immediately on every net 

 presentation (Table 5). Upon encountering the first 

 net, FS3 played with it constantly, exhibiting similar 

 behaviors as shown by FSl. Within 20 minutes FS3 

 had entangled itself. This net was left on for 2 days 

 without the animal freeing itself and was then 

 removed by hand. 



Approximately one week later, FSB was presented 

 with a second, smaller net, and it quickly became 

 entangled. Rather than remove this net, another 

 small net was introduced into the tank. Within 30 

 minutes, FS3 became entangled in this as well. The 

 tank was subsequently drained and both nets were 



Table 5- — Entanglement observations of two captive northern fur 

 seals held In a 7,6 m diameter, 1 m deep circular holding tank. 

 The net used had a 23 cm stretched mesh size. 



'First presentation of a net, 



^Net left floating in water over nigfit 



3Net left on animal when next one was introduced into the tank 



removed. The tank was then refilled and a net im- 

 mediately placed in the water. Within 10 minutes 

 the animal became entangled. Two additional nets 

 were then placed in the water. Within 1 hour, FS3 

 had become entangled in these as well. All three nets 

 were then removed from the animal's neck. 



From these and from subsequent observations 

 (Table 5), it is unclear whether net fragment size 

 influences the probability of entanglement. FS3 

 became entangled almost immediately following 

 every net presentation, regardless of the net's size. 

 FSl, however, seemed to be wary of nets following 

 its first entanglement. This wariness appeared to 

 subside after several days without encountering a 

 net. 



Video recordings made of FS3 documented the 

 behaviors preceding and following an entanglement. 

 While playing with the net, FS3 approached from 

 below and began to inspect it. After several seconds, 

 FS3 pushed its nose up through a mesh opening in 

 an apparent attempt to breathe. Immediately upon 

 sensing the net around its muzzle, FS3 attempted 

 to free itself by quickly shaking its head from side 

 to side. This served to pull the net further down its 

 head and, within several seconds, meshes were 

 tightly wrapped around the animal's neck. During 

 this time, and immediately following, FS3 became 

 extremely agitated. It continued its quick and vio- 

 lent headshaking, but also began to swim rapidly 

 around the tank, porpoising frequently. This action 

 undoubtedly caused the net to be pulled even fur- 

 ther down its neck. After approximately 2 minutes, 

 swimming slowed, but FS3 continued to stop and 

 shake its head violently. Approximately 5 minutes 

 later, FS3 had several meshes looped over its head 

 and neck. 



FS3's eating ability was not impaired by the net, 

 and so it was left on for 2 days. There was never 

 any indication that the animal would be able to free 

 itself and the net was finally removed. Although the 

 net was so tightly wrapped around the animal's neck 

 that it had to be cut off, there was no evidence of 

 abrasions or lacerations. 



DISCUSSION 



In a recent review. Fowler (1987) suggested that 

 younger northern fur seals are more prone to en- 

 tanglement related mortality than are older animals. 

 Results from the present study help to shed light 

 on possible reasons for these apparent age related 

 discrepancies. Small physical size and the inquisi- 

 tive nature of juvenile animals are likely to be the 

 two important factors leading to a higher mortal- 

 ity from entanglement. Naive animals may become 

 entangled with greater frequency than older, per- 

 haps less inquisitive animals, and smaller animals 

 have the potential to become entangled in a greater 

 range of mesh sizes. Moreover, once entangled, 

 relative swimming costs will be higher for smaller 

 animals (Feldkamp 1985). 



The majority of nets found on two Alaskan islands 

 (St. George and Amchitka) had stretched mesh sizes 

 of 20 cm or less, with a mode of 10-15 cm (Fowler 

 1987). If this is representative of material adrift at 

 sea, then most fragments have a small mesh size. 

 It seems reasonable to conclude, therefore, that 

 relative to larger animals, a greater number of frag- 

 ments exist that are potentially hazardous to smaller 



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