11 Suryan FISH 97(2)

332 Abstract.–Disturbances to harbor seals, Phoca vitulina richardsi, during Variability in reactions of Pacific harbor seals, 1991 and 1992 pupping seasons were Phoca vitulina richardsi, to disturbance observed at Puffin Island, Clements Reef, and Skipjack Island in Washing- ton state. Harassment (≥ one seal en- Robert M. Suryan tering the water) of seals ashore was common (≥71% of survey days) and pri- James T. Harvey marily caused by powerboat operators Moss Landing Marine Laboratories approaching to observe seals. Recovery P.O. Box 450 (number of seals on a haul-out site re- Moss Landing, California 95039 turned to preharassment levels) follow- E-mail address (for R. M. Suryan): [email protected] ing a harassment was less at Puffin Is- Present address (for R. M. Suryan): Migratory Bird Management land (19%) than at Clements Reef (54%) U.S. Fish and Wildlife Service and Skipjack Island (45%). Addition- 1011 E. Tudor Rd. ally, seals were more vigilant (P<0.003) Anchorage, Alaska 99503 at Puffin Island than at the other two locations. These results indicated that seals at Puffin Island were less tolerant of disturbance than seals at other sites. This could possibly be attributed to a greater (P<0.05) percentage of pups In many locations, disturbance is an In addition to aircraft, sources of ashore (17%) than at Clements Reef important factor affecting the haul- disturbance include boats, seismic (3%) and Skipjack Island (3%). Because out patterns of harbor seals, Phoca exploration, pedestrians, kayakers, of this, we expected that powerboats vitulina. Disturbance is defined as and natural predators (Renouf et would disturb seals from greater dis- any activity that alters normal be- al., 1981; Laursen, 1982; Allen et al., tances at Puffin Island. To test this, we used a theodolite to determine distance havior. In the United States, distur- 1984; Terhune, 1985; Richardson et between seals and an approaching ves- bance of marine mammals by hu- al., 1995; Moss, 1992; Kroll, 1993; sel at Puffin Island and Clements Reef. mans is regulated by the Marine Johnson2; Murphy and Hoover3; There was, however, no significant Mammal Protection Act of 1972. In Calambokidis et al.4; and others). (P>0.05) difference in distances at contrast to pelagic marine mam- Allen et al. (1984) reported that which disturbances occurred. The most notable difference in distance of distur- mals, changes in the behavior of harbor seals on a haul-out site in bance was between initial and subse- pinnipeds on haul-out sites related Bolinas Lagoon, California were dis- quent harassments during a haul-out to disturbance is relatively simple turbed by humans on 71% of survey period. Those seals remaining or re- to measure. Long-term effects of days; most disturbances were caused turning to shore after a harassment disturbance, however, are often dif- by nonmotorized boats (primarily ca- were more tolerant of powerboats, al- lowing significantly (P<0.05) closer ap- ficult to assess. noes). Humans, primarily boat opera- proaches than those initially harassed. The effects of disturbance may be tors, were the most common cause of Seals detected (head raised and ori- quite mild or may cause displace- harassment to harbor seals on Pro- ented toward the potential disturbance) ment and even mortality. Bighorn a powerboat at a mean distance of 264 sheep (Ovis canadensis) and white- 1 m, and harassments occurred when Glockner-Ferrari, D. A., and M. J. Ferrari. boats approached, on average, to within tailed deer exposed to snowmobile 1985. Individual identification, behavior, traffic have shown increased heart reproduction, and distribution of hump- 144 m. Results of this study exemplify back whales, Megaptera novaeangliae, in the variability in reaction to distur- rate but no visible change in behav- Hawaii. Rep MMC-83/06 for Mar. Mamm. bance and the necessity for consider- ior (MacArthur et al., 1982; Moen Comm., 42 p. [NTIS PB85-200772.] ing these differences for minimizing et al., 1982). Humpback whale 2 Johnson, B. W. 1977. The effects of hu- disturbance. (Megaptera novaeangliae) female- man disturbance on a population of harbor seals. In Environmental assessment calf pairs in Hawaii have avoided of the Alaskan continental shelf, p. 422– nearshore areas of intense human 432. Annual. Rep. Princ. Invest., vol. 1. recreational activities (Salden, 1988; U.S. Dep. Commer., NOAA/OCSEAP, 708 p. 1 [NTIS PB-280934/1.] Glockner-Ferrari and Ferrari ). Dis- 3 Murphy, E. C., and A. A. Hoover. turbance-related mortality in har- 1981. Research study of the reactions of bor seals can result from stamped- wildlife to boating activity along Kenai fjords coastline. Final Rep. to Nat. Park ing and pup abandonment (John- Serv., Anchorage, AK, 125 p. 2 son ). Disturbance from low-flying 4 Calambokidis, J., G. H. Steiger, J. R. aircraft may have caused mortality Evans, and S. J. Jeffries. 1991. Cen- of more than 200 (10%) harbor seal suses and disturbance of harbor seals at Woodard Bay and recommendations for Manuscript accepted 26 may 1998. pups on Tugidak Island, Alaska, in protection. Final report to Washington Fish. Bull. 97: 332–339 (1999). 1976 (Johnson2). Dep. Nat. Resources, Olympia, WA, 45 p. Suryan and Harvey: Variability in reaction to disturbance among Phoca vitulina richardsi 333 tection Island (Kroll, 1993) and Woodard Bay (Calambokidis et al.4), Washington. Sources of disturbance to harbor seals ashore at Gertrude Island, Washington, were mainly unidentifiable; however, of detectable causes, human activities and coyotes were the most common (Moss, 1992). Reaction to disturbance may vary among harbor seal groups within an area (Terhune and Almon, 1983) and according to disturbance sources (e.g. powerboats vs. canoes and kayaks; Calambokidis et al.4). This variability may be attributed to dif- ferent levels of tolerance among age, sex, or reproductive status of harbor seals. Reaction to dif- ferent causes of disturbance may vary with exposure to particular sources, eventually resulting in greater avoidance or tolerance. In Figure 1 any case, results of previous stud- Locations (★) of harbor seal haul-out sites observed at Clements Reef, Puffin Island, and ies indicate that reaction to dis- Skipjack Island during 1991 and 1992 pupping seasons in the San Juan Islands, Wash- ington. Dots (•) indicate other haul-out sites in the area. turbances vary within and among regions, although little quantita- tive evidence exists. typically are used by fewer than 100 animals. During In this study, we collected data to evaluate the this study, observations were conducted at Clements extent of disturbance to harbor seals at haul-out sites Reef, Puffin Island, and Skipjack Island (Fig. 1). in the northern San Juan Islands. Our objectives were to determine 1) if human-related activities were Observations of haul-out sites the primary source of disturbance; 2) if recovery varied between flood and ebb tides and was similar Ground-based surveys of harbor seals were conducted among the three haul-out sites (one location was a at Clements Reef (n=13), Puffin Island (n=9), and pupping area); 3) if vigilance characteristics differed Skipjack Island (n=8) from 2 July to 19 August 1991. among haul-out sites; 4) if the response to harass- In 1992, surveys were conducted between 24 June ment was similar for pups and for adults and sub- and 10 September 1992 at Clements Reef (n=21) and adults; and 5) if the mean distance between harbor Puffin Island (n=18). Skipjack Island was not surveyed seals and a boat causing a disturbance varied within during 1992 to allow increased sampling effort at the and among haul-out sites and, if so, to determine other two sites. Seals at each location were observed at potential causes of this variability. least twice a week (one observer per site). Seals at Clements Reef were viewed from Ewing Island (Fig. 1), approximately 0.55 km away. Seals on the north- Methods west end of Puffin Island were viewed from the south- east corner of Matia Island, 0.38 km away (Fig. 1). Study area Observer heights above zero tide level were 10 m at Clements Reef and 13 m at Matia Island. The observa- The study area was located in the northern San Juan tion point on the northeast side of Skipjack Island was Islands, Washington (Fig. 1). This area is character- directly above (23 m) the haul-out site (Fig. 1). ized by numerous islands, a tidal range of 3.6 m, strong Observations of harbor seals began one to three currents (maximum of 7.7 km/h), and a rocky shore- hours before low tide and ended three to seven hours line. Haul-out sites of harbor seals, which include reefs after low tide (when <50% of the maximum number of and rocky intertidal zones of islands, are numerous but seals counted during that tide cycle remained ashore). 334 Fishery Bulletin 97(2), 1999 Seals were viewed with 22× and 15–60× spotting Positions of an approaching vessel were monitored scopes. Scan surveys (Altmann, 1974) were conducted by using a Nikon NT2A or Pentax TH20D theodo- at ten minute intervals throughout the observation lite. Bearings to the approaching vessel and seals period. During each half-hour period, the first scan exhibiting disturbance reactions were recorded. The was a count of all seals, the second scan included distance from theodolite to vessel or seal was calcu- size structure (number of harbor seal pups and sub- lated by using the tangent of the vertical angle from adults and adults), and the third scan was used to the theodolite and height of the theodolite above the quantify vigilance of seals (head up, alert but not water. The distance between vessel and seals was oriented toward a disturbance source) and sources calculated by using the Law of Cosines that incorpo- of disturbance (within 1.0 km of the haul-out site).

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