FELDKAMP ET AL.: NET ENTANGLEMENT ON NORTHERN FUR SEALS 



ably colder than that during the swimming trials. 

 For these reasons, this value should be viewed as 

 a minimum estimate of the energy required for sur- 

 vival by a juvenile fur seal entangled in a 200 g net. 



The elevated swimming costs associated with en- 

 tanglement and the resultant rise in food require- 

 ments suggest that northern fur seals enter a vicious 

 cycle when entangled in larger fragments. As swim- 

 ming costs increase, so will food demands. The need 

 to capture more prey requires more swimming. 

 Greater drag and perhaps reduced aquatic agility 

 will undoubtedly lower capture success. Under these 

 conditions, starvation would be a likely outcome. 



The observation that northern fur seals virtually 

 stopped swimming when entangled in 225 g nets is 

 consistent with this scenario. By reducing the time 

 spent swimming, fur seals should lower their ener- 

 getic expenditures and hence their energy require- 

 ments. However, ADMR measurements before and 

 during entanglement showed no significant differ- 

 ences. Since swimming activity declined by 75%, it 

 is possible that the costs of resting and grooming 

 were elevated by entanglement. A larger sample 

 size would be needed to verify these findings. None- 

 theless, grooming appeared to be much more vig- 

 orous and resting was not completely quiet. The fur 

 seals often rested with both foreflippers submerged 

 in the water, which may have elevated heat loss to 

 the environment and led to greater energy require- 

 ments. 



Fur seals were unable to free themselves from en- 

 tanglement during the 2-3 d periods (Table 5). These 

 results, however, must be interpreted with caution. 

 Because fur seals were confined to a round holding 

 tank with no haul-out areas provided, there were 

 no objects present that might have caught the net 

 and might have been used to remove it. From our 

 observations, it is doubtful that animals could have 

 freed themselves. However, Scordino (1985) has 

 documented several instances where wild fur seals 

 have lost their nets. It is possible that under natural 

 conditions, fur seals might snag the encumbering 

 fragment on rocks or other objects and be able to 

 pull free. 



The results of the present study show that juve- 

 nile northern fur seals are susceptible to, and 

 adversely impacted by entanglement. Our captive 

 fur seals were highly inquisitive and usually inves- 

 tigated and played with floating nets. Measurements 

 of their head, neck, and shoulder diameters indicated 

 that they were most susceptible to entanglement in 

 nets with mesh sizes of 23 cm or more. Observations 

 of actual entanglements substantiated this finding. 

 Once entangled, northern fur seals virtually stopped 



swimming and spent considerably more time rest- 

 ing. However, energy expenditure did not drop ac- 

 cordingly, suggesting that the energy expended for 

 grooming or resting may have been elevated by the 

 presence of a net. Direct measurements also showed 

 that at zero swimming speed, oxygen consumption 

 was slightly, though not significantly, elevated 

 because of the net. This elevation increased both 

 with the size of the net and with increasing swim- 

 ming speed. It is evident from these findings that 

 net fragments of 200 g or more can lead to signif- 

 icant behavioral changes in captive northern fin- 

 seals and greatly influence their energy require- 

 ments during swimming. 



ACKNOWLEDGMENTS 



We would like to thank B. Fadely, A. C. Huntley, 

 and D. Murnane for help in all phases of this work. 

 We are especially grateful to S. Beltramy, J. Burger, 

 D. Busch, J. Lajala, and P. Wolfe for their assistance 

 in feeding and maintaining the northern fur seals. 

 We also thank R. L. DeLong for help in the capture 

 and transport of the animals, R. L. Gentry and 2 

 anonymous reviewers for useful comments on the 

 manuscript, and D. Sims for technical assistance. 

 This work was supported by NOAA contract 85- 

 ABC-00185 from the National Marine Mammal 

 Laboratory. 



LITERATURE CITED 



Bartholomew, G. A. 



19T7. Energj' metabolism. In M. S. Gordon (editor). Animal 

 physiology: Principles and adaptations, p. 57-110. Macmil- 

 lan Publ. Co., N.Y. 



Costa, D. P., and R. L. Gentry. 



1986. Free-ranging energetics of northern fur seals, hi 

 R. L. Gentry and G. L. Kooyman (editors). Fur seals. Mater- 

 nal strategies on land and at sea, p. 79-101. Princeton 

 Univ. Press, Princeton, NJ. 



Fedak, M. a., L. Rome, and H. J. Seeherman. 



1981. One-step N2-dilution technique for calibrating open- 

 circuit VOj measuring systems. J. Appl. Physiol.: Respir. 

 Environ. E.xercise Physiol, 51:772-776. 



Feldkamp, S. D. 



1985. The effects of net entanglement on the drag and power 



output of a California sea lion. Zalopkus califomianus. 



Fish. Bull., U.S. 83:692-695. 

 Fowler. C. W, 



1982. Interactions of northern fur seals and commercial fish- 

 eries. Trans. N. Am. Wildl. Nat. Resour, Conf. 47:278-292. 



1985. An evaluation of the role of entanglement in the popu- 

 lation dynamics of northern fur seals on the Pribilof Islands. 

 In R. S. Shomura and H. 0. Yoshida (editors). Proceedings 

 of the workshop on the fate and impact of marine debris, 

 27-29 November 1984, Honolulu, Hawaii, p. 291-307. U.S. 

 Dep. Commer., NOAA Tech. Memo. NMFS. NOAA-TM- 



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