Date of Award
Doctor of Philosophy (PhD)
Susan E. Parks
acoustics, animal behavior, animal communication, anthropogenic noise, harbor seals, marine mammals
Harbor seals (Phoca vitulina) are a widely distributed pinniped species that mate underwater. Similar to other aquatically mating pinnipeds, male harbor seals produce vocalizations during the breeding season that function in male-male interactions and possibly as an attractant for females. I investigated multiple aspects of these reproductive advertisement displays in a population of harbor seals in Glacier Bay National Park and Preserve, Alaska. First, I looked at vocal production as a function of environmental variables, including season, daylight, and tidal state. Vocalizations were highly seasonal and detection of these vocalizations peaked in June and July, which correspond with the estimated time of breeding. Vocalizations also varied with light, with the lowest probability of detection during the day and the highest probability of detection at night. The high probability of detection corresponded to when females are known to forage. These results are similar to the vocal behavior of previously studied populations. However, unlike previously studied populations, the detection of harbor seal breeding vocalizations did not vary with tidal state. This is likely due to the location of the hydrophone, as it was not near the haul out and depth was therefore not significantly influenced by changes in tidal height. I also investigated the source levels and call parameters of vocalizations, as well as call rate and territoriality. The average source level of harbor seal breeding vocalizations was 144 dB re 1 μPa at 1 m and measurements ranged from 129 to 149 dB re 1 μPa. Analysis of call parameters indicated that vocalizations of harbor seals in Glacier Bay were similar in duration to other populations, but were much lower in frequency. During the breeding season, there were two discrete calling areas that likely represent two individual males; the average call rate in these display areas was approximately 1 call per minute. The harbor seal breeding season also overlaps with peak tourism in Glacier Bay, and the majority of tourists visit the park on a motorized vessel. Because of this overlap, I investigated the impacts of vessel noise on the vocal behavior of individual males. In the presence of vessel noise, male harbor seals increase the amplitude of their vocalizations, decrease the duration, and increase the minimum frequency. These vocal shifts are similar to studies of noise impacts on other species across taxa, but it is unknown how this could impact the reproductive success of male harbor seals. Finally, I looked at the role of female preference for male vocalizations. Using playbacks of male vocalizations to captive female harbor seals, I found that females have a higher response to vocalizations that correspond to dominant males. Females were less responsive to subordinate male vocalizations, which had a shorter duration and a higher frequency. Given that male harbor seals decrease the duration and increase the frequency of vocalizations in the presence of noise, it is possible that these vocalizations become less attractive in noise.
Matthews, Leanna, "Harbor Seal (Phoca vitulina) Reproductive Advertisement Behavior And The Effects Of Vessel Noise" (2017). Dissertations - ALL. 718.