332 



Abstract.— Disturbances to harbor 

 seals. Phoca vitulina richardsi, during 

 1991 and 1992 pupping seasons were 

 observed at Puffin Island, Clements 

 Reef, and Skipjack Island in Washing- 

 ton state. Harassment (> one seal en- 

 tering the water) of seals ashore was 

 common (>71'r of survey days) and pri- 

 marily caused by powerboat operators 

 approaching to observe seals. Recovery 

 (number of seals on a haul-out site re- 

 turned to preharassment levels ) follow- 

 ing a harassment was less at Puffin Is- 

 land ( 19^* ) than at Clements Reef (54'7f ) 

 and Skipjack Island (459^). Addition- 

 ally, seals were more vigilant (P<0.003) 

 at Puffin Island than at the other two 

 locations. These results indicated that 

 seals at Puffin Island were less toler- 

 ant of disturbance than seals at other 

 sites. This could possibly be attributed 

 to a greater (P<0. 05) percentage of pups 

 ashore (IVJ) than at Clements Reef 

 (39^ ) and Skipjack Island (3'7, ). Because 

 of this, we expected that powerboats 

 would disturb seals from greater dis- 

 tances at Puffin Island. To test this, we 

 used a theodolite to determine distance 

 between seals and an approaching ves- 

 sel at Puffin Island and Clements Reef 

 There was, however, no significant 

 (P>0.05) difference in distances at 

 which disturbances occurred. The most 

 notable difference in distance of distur- 

 bance was between initial and subse- 

 quent harassments during a haul-out 

 period. Those seals remaining or re- 

 turning to shore after a harassment 

 were more tolerant of powerboats, al- 

 lowing significantly (P<0.05 ) closer ap- 

 proaches than those initially harassed. 

 Seals detected (head raised and ori- 

 ented toward the potential disturbance) 

 a powerboat at a mean distance of 264 

 m, and harassments occurred when 

 boats approached, on average, to within 

 144 m. Results of this study exemplify 

 the variability in reaction to distur- 

 bance and the necessity for consider- 

 ing these differences for minimizing 

 disturbance. 



Variability in reactions of Pacific harbor seals, 

 Phoca vitulina richiardsi, to disturbance 



Robert M. Suryan 



James T. Harvey 



Moss Landing Marine Laboratories 



PO, Box 450 



Moss Landing, California 95039 



E-mail address (for R M Suryan) roberlsuryan li mail fws gov 



Present address (for R. M. Suryan): Migratory Bird Management 



U.S Fish and Wildlife Service 

 101 1 E Tudor Rd 

 Anchorage, Alaska 99503 



Manuscript accepted 26 may 1998. 

 Fish. Bull. 97: 332-;«9 ( 1999). 



In many locations, disturbance is an 

 important factor affecting the haul- 

 out patterns of harbor seals, Phoca 

 vitulina. Disturbance is defined as 

 any activity that alters normal be- 

 havior. In the United States, distur- 

 bance of marine mammals by hu- 

 mans is regulated by the Marine 

 Mammal Protection Act of 1972. In 

 contrast to pelagic marine mam- 

 mals, changes in the behavior of 

 pinnipeds on haul-out sites related 

 to distLU'bance is relatively simple 

 to measure. Long-term effects of 

 disturbance, however, are often dif- 

 ficult to assess. 



The effects of disturbance may be 

 quite mild or may cause displace- 

 ment and even mortality. Bighorn 

 sheep (Ovis canadensis) and white- 

 tailed deer exposed to snowmobile 

 traffic have shown increased heart 

 rate but no visible change in behav- 

 ior (MacArthur et al., 1982; Moen 

 et al., 1982). Humpback whale 

 (Megaptera novaeangUae) female- 

 calf pairs in Hawaii have avoided 

 nearshore areas of intense human 

 recreational activities (Salden, 1988; 

 Glockner-Ferrari and FenariM, Dis- 

 turbance-related mortality in har- 

 bor seals can result from stamped- 

 ing and pup abandonment (John- 

 son'^). Disturbance from low-flying 

 aircraft may have caused mortality 

 of more than 200 ( IG'fi ) harbor seal 

 pups on Tugidak Island, Alaska, in 

 1976 (Johnson-). 



In addition to aircraft, sources of 

 disturbance include boats, seismic 

 exploration, pedestrians, kayakers, 

 and natural predators (Renouf et 

 al, 1981; Laursen, 1982; Allen etal., 

 1984; Terhune, 1985; Richardson et 

 al., 1995; Moss, 1992; Kroll, 1993; 

 Johnson-; Murphy and Hoover^; 

 Calambokidis et al."'; and others). 

 Allen et al. (1984) reported that 

 harbor seals on a haul-out site in 

 Bolinas Lagoon, California were dis- 

 turbed by humans on 71'7f of survey 

 days; most disturbances were caused 

 by nonmotorized boats ( primarily ca- 

 noes ). Humans, primarily boat opera- 

 tors, were the most common cause of 

 harassment to harbor seals on Pro- 



' Glockner-Ferrari, D. A., and M. J. Ferrari. 

 198.5. Individual identification, behavior, 

 reproduction, and distribution of hump- 

 back whales, Megaptera novacangliae, in 

 Hawaii. Rep MMC-8.3/06 for Mar Mamni. 

 Comm., 42 p. |NTIS PB85-200772.J 



- Johnson, B. W. 1977. The effects of hu- 

 man disturbance on a population of har- 

 bor seals. In Environmental assessment 

 of the Alaskan continental shelf p. 422- 

 432. Annual Rep. Princ. Invest., vol. 1. 

 U.S. Dep. Commer, NOAA/OCSEAP, 708 p. 

 INTISPB-280934/l.l 



' Murphy, E. C, and A. A. Hoover. 

 1981. Research study of the reactions of 

 wildlife to boating activity along Kenai 

 fjords coastline. Final Rep. to Nat. Park 

 Serv., Anchorage, AK. 12,5 p. 



^ Calambokidis, J., G. H. Steiger, J. R. 

 Evans, and S. J. Jeffries. 1991. Cen- 

 suses and disturbance of harbor seals at 

 Woodard Bay and recommendations for 

 protection. Final report to Washington 

 Dep. Nat. Resources, Olympia. WA. 45 p. 



