Haul-out patterns and effects of vessel disturbance on harbor seals (Phoca vitulina) on glacial ice in Tracy Arm, Alaska

Abstract

Tidewater glacial fjords provide important habitat for breeding harbor seals (Phoca vitulina) that rest, give birth, and nurse pups on icebergs. These fjords also attract tourist vessels that potentially disturb seals. In May and June during 2001–2006, we documented seal abundance, pupping phenology, and seal–vessel interactions in Tracy Arm, a glacial fjord in southeastern Alaska. We used randomized observations to determine the frequency at which seals entered the water in the presence and absence of vessels, and we estimated the reaction distances of seals to approaching vessels. Mean daily vessel counts varied from 10.2 (2001) to 2.0 (2006) (range: 1–33). Tour and power vessels were the most common types of vessels, but seals were most sensitive to cruise ships and kayaks. The odds of a seal entering the water were higher when vessels were present (>2 times) or within 100 m (3.7 times), and when a pup was present (1.3 times). The baseline, undisturbed, rate of seals entering the water was 0.06 (95% CI: 0.05–0.08) per 10 min. Seal births occurred during 30 May–25 June and peaked (4–8 per day) during 7–13 June. The maximum pup count (408) was observed on 24 June. Harbor seal fitness in Tracy Arm may be reduced by vessel disturbances during breeding and pupping.