FELDKAMP ET AL.: NET ENTANGLEMENT ON NORTHERN FUR SEALS 



animals to reach a steady state and then VOg mea- 

 surements were made for 20-30 minutes. The sec- 

 ond pump was then activated, creating a water 

 speed of 1.1 m/s, and VO2 was monitored as de- 

 scribed above. Only those trials where steady swim- 

 ming occurred were used in the final calculations 

 of metabolism. Experiments that reversed the order 

 of swimming speeds revealed no differences in 

 VO2 that could be attributed to the effects of order- 

 ing. 



Each fur seal was run once per day over a 2 wk 

 period until baseline values were established. Fur 

 seals were then entangled in small net fragments 

 and the measurements were repeated. All three ani- 

 mals were run daily, and trials with one net size 

 were completed before beginning the next size. For 

 each net size, experimental trials lasted approx- 

 imately 2 weeks. 



Nets were attached by placing the fur seal's head 

 through a wire ring, 15 cm in diameter, sewn into 

 the center of each fragment. Three sizes of net were 

 used in the following order: 61, 100, and 200 g with 

 dimensions of 4 x 4 meshes (0.6 m x 0.6 m), 7 x 

 4 meshes (1.2 m x 0.6 m), and 7x7 meshes (1.2 

 m X 1.2 m), respectively. Nets were folded over 

 once (100 g), or twice (200 g) to prevent fouling of 

 the foreflippers, and were removed after each 

 session. 



Experiments were run both in the winter and 

 spring. Winter experiments were conducted at a 

 single flume speed of 0.75 m/s using 61 g and 100 

 g nets. During the spring, 100 g and 200 g nets were 

 used at flume speeds of 0.75 m/s and 1.1 m/s. At 

 the completion of the spring trials, baseline values 

 were again established through daily runs conducted 

 without nets. 



Behavioral and Energetic Changes 

 Associated with Entanglement 



In this study, the effect of entanglement on the 

 northern fur seals' behavior and average daily meta- 

 bolic rate (ADMR) was measured. The fur seals were 

 14 months old and weighed an average ( ± SD) of 

 19.1 (±1.0) kg. They were kept in a circular hold- 

 ing tank, 7.6 m in diameter and 1 m deep with no 

 haul-out provided. 



Two experiments were undertaken. First, free- 

 swimming fur seals were monitored over a 6 d 

 period. They were then entangled in 225 g net frag- 

 ments and the measurements were taken for 

 another 6 days. A nylon dog collar, sewn into the 

 middle of each fragment, was used to fasten the net 

 around the animal's neck. 



The ADMR of each fur seal was determined before 

 and during entanglement using isotopic tracers 

 (Nagy 1980; Schoeller and van Santen 1982; Costa 

 and Gentry 1986). Prior to each experiment, blood 

 samples were taken, and then the animals were in- 

 jected interperitoneally with 5.5 mL of 0.66 mCi 

 tritium (HTO) per mL and 2.5 g of Hji^O at 95 

 atoms percent. After equilibration (3 hours), a 10 

 cc blood sample was taken from a flipper vein and 

 the animal was released into the tank. After the 6 

 d measurement period, fur seals were removed from 

 the holding tank, and final blood samples were 

 taken. 



Tritium specific-activity in water that was vaccum 

 distilled from blood samples was determined by 

 liquid scintillation spectrometry. Oxygen-18 levels 

 were measured by isotope mass ratio spectrometry 

 in a commercial laboratory (Global Geochemistry, 

 Canoga Park, CA). Rates of CO, production (VCO2) 

 were calculated using equation 2 in Nagy (1980), and 

 water flux rates determined using equation 4 in 

 Nagy and Costa (1980). We assumed an RQ of 0.80 

 to calculate energy consumption. 



The northern fur seals' behavior over the course 

 of each study period was quantified using a discon- 

 tinuous time sampling method (Tyler 1979). Every 

 hour, from 0800 to 2000, the fur seals were observed 

 for 10 minutes. At exactly 1 min intervals during 

 this period, the behavior displayed by each fur seal 

 was noted. Behaviors were broken into four cate- 

 gories: swimming, grooming, resting, and other ac- 

 tivities. Animals were considered to be swimming 

 when they were actively stroking or gliding between 

 strokes. Grooming was defined as scratching, rub- 

 bing the fur, or shaking the head. Animals at rest 

 were lying quietly, often holding their flippers out 

 of the water. Activities such as rolling, nuzzling one 

 another, or other slow movements were placed in 

 the "other" category. 



Entanglement Observations 



The reactions of northern fur seals to the pres- 

 ence of floating nets, their ability to free themselves 

 after entanglement, and the likelihood of entangle- 

 ment in net fragments of various sizes were inves- 

 tigated. Two fur seals were placed in a 7.6 m diam- 

 eter holding tank, 1 m deep, along with floating net 

 fragments of various sizes, and were denied access 

 to haul-out areas during this time. The time from 

 net presentation to entanglement was recorded and 

 correlated with fragment size. Once entangled, nets 

 were left on for periods ranging from several hours 

 to several days. 



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