ALLEN ET AL.: EFFECT OF DISTURBANCE ON HARBOR SEALS 



be related to seal feeding habits as discussed by 

 Antonelis and Fiscus (1980) and Spalding (1964) 

 who noted that seals fed primarily in the late af- 

 ternoon. The weak inverse correlation between 

 tide level and seal numbers during the breeding 

 season is likely related to the tendency of females 

 with pups to haul out at irregular times to nurse. 



These patterns were interrupted by disturbance 

 from boats, pedestrians, dogs, and aircraft. People 

 in nonpower boats were the greatest source for 

 disturbance possibly because they are more 

 mobile than people in power boats or on foot. Dis- 

 tance of disturbance, however, rather than type or 

 season was the significant element at KI since at 

 distances >100 m seals tended not to leave the 

 hauling out site. The response of seals at distances 

 >100 m may have been precipitated by the nature 

 or unpredictability of the disturbance source. 

 For example, a boat advancing directly toward the 

 seals or lingering nearby caused flight more often 

 than a boat moving by. 



The source of current disturbances is a small but 

 stable resident and tourist human population; 

 however, a variety of changes in the seal's behavior 

 may be expected if disturbance levels increase. 

 Both Paulbitsky (1975) and Woodhouse 14 docu- 

 mented a change from diurnal to nocturnal haul- 

 ing out patterns in seals at Strawberry Spit, Tibu- 

 ron, and at Atascadero State Beach, Morro Bay, 

 Calif., which was believed to be a response to an 

 increase in the local human populations. The re- 

 sponse of seals to the prolonged activities of com- 

 mercial bait harvesters on Bolinas Lagoon is indic- 

 ative of the potential disruption of seal haul out 

 patterns. 



Excessive disturbance may also lead to in- 

 creased pup mortality. According to Kenyon 

 (1972), 7 of 18 Hawaiian monk seals, Monachus 

 schaunislandi, died before weaning on heavily 

 disturbed pupping grounds on Midway Atoll, 

 Hawaii. In contrast, for harbor seals at a relatively 

 undisturbed pupping ground in British Columbia, 

 Bigg ( 1969) estimated that pup mortality was only 

 12<7c . We do not know to what extent disturbance is 

 affecting pup mortality rates at Bolinas Lagoon. 

 In 1979, 3 of 12 pups were found dead; at least 1 of 

 those 3 was killed by a dog. 



Site abandonment is a third possible response to 

 increased disturbance. Newby (1971) attributed 

 harbor seal abandonment of a site in Puget Sound 



14 C. Woodhouse, Santa Barbara Museum of Natural History, 

 2559 Puesta del Sol, Santa Barbara, CA 93105, pers. commun. 

 May 1977. 



in part to increased disturbance from recreational 

 boating. Kenyon (1972) postulated for the monk 

 seal that site abandonment results in overall 

 population losses because other traditional haul 

 out sites probably cannot absorb the emigration. 

 The same could apply to harbor seal populations in 

 Marin County, if other sites are currently filled to 

 capacity. 



ACKNOWLEDGMENTS 



This study was funded by the Marine Mammal 

 Commission under Contract No. MMAC012, the 

 Marin County Department of Parks and Recre- 

 ation, and the Point Reyes Bird Observatory. 

 Special thanks are extended to L. and D. Roush 

 and D. and K. Beacock, who allowed us to place 

 cameras in their homes. We are also grateful to J. 

 Bausor, C. Hale, M. Rousch, B. Sorrie, L. Stenzel, 

 and S. Tallen for help in field observations. K. 

 and D. Reichard and R. Rains provided advice on 

 camera maintenance and operation. R. E. Jones of 

 Museum of Vertebrate Zoology, Berkeley, analyzed 

 pup carcasses and offered valuable advice and as- 

 sistance. 



LITERATURE CITED 



ANTONELIS, G. A., JR., AND C. H. FISCUS. 



1980. The pinnipeds of the California current. CalCOFI 

 Rep. XXL68-78. 



BIGG, M. A. 



1969. The harbour seal in British Columbia. Fish. Res. 

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1975. Discrete multivariate analysis: theory and practice. 

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1968. Distribution-free statistical tests. Prentice-Hall, 

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 BROWN, R. F, AND B. R. MATE. 



1983. Abundance, movements, and feeding habits of har- 

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FANCHER, L. E. 



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FlENBERG, S. E. 



1981. The analysis of cross-classified categorical data. 

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