Abstract
Large numbers of harbor seals (Phoca vitulina) use habitat in tidewater glaciers in Alaska for pupping, breeding, and molting. Glacial fjords are also popular tourist destinations; however, visitation by numerous vessels can result in disturbance of seals during critical life-history phases. We explored factors affecting haul-out behavior of harbor seals at a glacial site frequented by tourism vessels. In 2008-10, we deployed VHF transmitters on 107 seals in Endicott Arm, Alaska. We remotely monitored presence and haul-out behavior of tagged seals and documented vessel presence with time-lapse cameras. We evaluated the influence of environmental and physical factors on the probability of being hauled out, duration of haul-out bouts, and as factors associated with the start and end of a haulout. Location, season, hour, and interactions of location by year, season, hour, and sex significantly influenced haul-out probability, as did ice, weather, and vessels. Seals were more likely to be hauled out with greater ice availability during the middle of the day, and less likely to be hauled out if vessels were present. Cruise ships had the strongest negative effect; however, most vessel types negatively affected haul-out probability. Haul-out duration was longest in association with starting on incoming tides, clear skies, no precipitation, occurring in the middle of the day, and ending in the late afternoon or evening. End of haulouts was associated with increasing cloud cover, low ice availability, and vessel presence; large-sized tourism vessels or all-vessel-types combined were significant predictors of ending a haul-out bout. Probability of being hauled out was highest in June, during pupping season. Potential disturbances of harbor seals could be reduced, enabling longer resting times for seals and fewer interruptions for nursing pups, if vessels focused the majority of visits to glacial habitat to before or after the hours of 08:00-17:00 or, less optimally, 09:00-16:00.
Highlights
Scenic fjords filled with icebergs calved from tidewater glaciers are popular tourism destinations in Alaska [1,2,3,4]
Mitigation to reduce the potential for vessel disturbance of harbor seals in glacial habitat may be especially important during these critical life-history phases
Ours is the first study to provide empirical data on the haul-out behavior of large numbers of individually-marked harbor seals in glacial habitat over a period of several months, while tourism vessels were present in that habitat
Summary
Scenic fjords filled with icebergs calved from tidewater glaciers are popular tourism destinations in Alaska [1,2,3,4]. Many of those sites are important habitat for pupping, breeding, and molting harbor seals (Phoca vitulina richardii), seasonally supporting disproportionately large numbers of mothers and pups relative to the total number of seals in the area [5, 6]. Noise generated by vessels may result in displacement or avoidance [13], increased stress, changes in swim-speed, foraging and diving behavior, and stranding of marine mammals (studies reviewed by [14]), and may disrupt communication [15]. Common dolphins (Delphinus spp) disrupted foraging and resting bouts [19] in the presence of vessels, while humpback whales (Megaptera novaeangliae) spent more time submerged, and pods with calves were more sensitive to vessel presence than those without calves [20]
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