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Fishery Bulletin 97(2), 1999 



nent. Although we also observed certain groups of 

 harbor seals (often small-size groups) entering the 

 water well before others during a harassment, there 

 was no significant trend. Terhune and Almon (1983) 

 also noted that not all groups of harbor seals reacted 

 to disturbances in the same manner. 



The most notable difference in distance of distur- 

 bance was the decrease between initial and subse- 

 quent harassments. There are two plausible expla- 

 nations for this: 1) seals became more tolerant of 

 powerboat approaches; or 2) seals that were less tol- 

 erant of disturbance did not return to the haul-out 

 site after the initial harassment. Based on lack of 

 full recovery following initial harassments, our re- 

 sults support the latter possibility. 



Allen et al. (1984) reported that boats advancing 

 toward, or remaining near, harbor seals ashore at 

 Bolinas Lagoon, California, caused seals to leave the 

 haul-out site more often than a boat simply moving 

 past seals. Boats that traveled slowly, parallel to the 

 haul-out site, and made no abrupt move or changes 

 in speed approached harbor seals at Clements Reef 

 and Puffin Island with minimal disturbance. Greater 

 sample sizes probably would have resulted in sig- 

 nificant differences among distances of disturbance 

 for various approach speeds and angles recorded 

 during this study. 



Additional potential factors affecting the distance 

 at which seals were disturbed included time of day 

 for haul-out period or location of haul-out site. Har- 

 bor seals may more readily enter the water toward 

 the end of the haul-out period, if air temperature is 

 high (Watts, 1992), or during rain. These consider- 

 ations were not addressed in this study Harbor seals 

 also may become accustomed to close approaches ( < 15 

 m) by boats in areas of high boat traffic (authors' 

 pers. obs.). In Woodard Bay, Calambokidis et al."* re- 

 ported powerboats were able to approach to an aver- 

 age of 40 m before harbor seals entered the water. 

 This area near Seattle, Washington, undoubtedly 

 gets more year-around recreational traffic than the 

 northern San Juan Islands which may explain why 

 disturbance distances were over a third less than 

 those observed during our study 



Most harassments in our study were caused by 

 people approaching to view harbor seals. It is impor- 

 tant therefore to distribute information and guide- 

 lines for wildlife viewing to the general public. An 

 effective solution may be to include information with 

 vessel registration. 



Direct mortality of harbor seals or long-term aban- 

 donment of haul-out sites (greater than one haul- 

 out period) because of harassment by humans was 

 not obsen-'ed during this study. Long-term impacts 

 of harassment of harbor seal populations, however. 



are difficult to assess. Cases where marine mammals 

 remain in heavily disturbed areas are easy to detect; 

 therefore, cases of partial or complete abandonment 

 of disturbed areas may be more common than evi- 

 dence indicates (Richardson et al., 1995). Harass- 

 ments increase energy expenditure of harbor seals 

 by decreasing duration of haul-out period. Increased 

 energy requirements likely have the greatest impact 

 on harbor seal pups during nursing and on adult and 

 subadult harbor seals during molt when access to 

 haul-out sites is important. Brasseur et al. (1996), 

 however, demonstrated that captive harbor seals may 

 need to haul-out even outside these "critical" peri- 

 ods. Richardson et al. (1995) noted that occasional 

 disturbance probably has little effect on harbor seal 

 populations; repeated disturbance, however, may 

 have significant negative effects especially at haul- 

 out sites used for pup rearing. 



Results of this study quantify the variability in 

 response to disturbance among individuals and lo- 

 cations. We also demonstrated the potential bias in 

 sampling animals that remain after an initial dis- 

 turbance, or in areas of regular boat traffic. Distance 

 at which powerboats caused harassment were vari- 

 able, ranging from 28 m to 260 m. Boating regula- 

 tions near harbor seal haul-out sites should address 

 activity of vessel (speed and approach angle) in ad- 

 dition to distance from harbor seals. Boating precau- 

 tions are particularly important near harbor seal 

 pupping areas such as Puffin Island. 



Acknowledgments 



We thank Birgit Kriete with The Whale Museum and 

 Robert DeLong with the National Marine Mammal 

 Laboratory for providing initial assistance and ac- 

 quiring funding to conduct field work in 1991. Steve 

 Jeffries and Harriet Huber provided equipment and 

 assistance during both field seasons. Kim Raum- 

 Suryan was instrumental in data collection and lo- 

 gistics for conducting field work. For assistance in 

 the field we thank Karen Russell, Tomo Eguchi, and 

 Doug Huddle. Additional assistance was provided by 

 Steve Osmek and David Rugh. Robert DeLong, 

 Michael Foster, and two anonymous reviewers pro- 

 vided critical review of early versions of this manu- 

 script. John Calambokidis and Peter Watts provided 

 helpful discussions on studying disturbance of har- 

 bor seals. Primary funding was provided by the Wash- 

 ington Department of Wildlife and the National 

 Marine Mammal Laboratory. Additional funding was 

 provided by the Earl H. and Ethel M. Myers' Oceano- 

 graphic and Marine Biology Trust "Save the Whales, 

 Inc.," and the Packard Foundation. This study was 



