Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Posts from the ‘Marine Mysteries’ category

The Creature Below the Floathouse?

How I enjoyed receiving the following mystery this week.

Be sure to have your sound on when you read and listen to the clip below.

Yes, it’s a male Pacific Harbour Seal! So many people do not realize that the male Harbour Seals establish and defend territory in the water (unlike species of sea lion and elephant seal who defend territory on land).

From Discovery of Sounds in the Sea . “Harbor seals were thought to be the least vocal of the pinnipeds. Recent studies have shown, however, that males produce underwater vocalizations during the mating season to attract females or to compete with other males. Males establish territories in the waters offshore of haul-out sites. Using underwater vocalizations, they defend their territories against other males and display to females traveling through the area. Their underwater vocalization is described as a roar with a peak frequency at approximately 1.2 kHz. Harbor seals also produce a wide variety of in-air vocalizations, including short barks, tonal honks, grunts, growls, roars, moans, and pup contact calls.”

It is remarkable isn’t it that these sounds were not known to be made by male Harbour Seals until ~1994.? This is the most common marine mammal on so many coasts and yet . . . we know so little.

Note: The person who sent me the mystery preferred to remain anonymous and that the location of the recordings not be provided. I can share that it was in the Sunshine Coast area of British Columbia. However, this underwater sound could be from ANYWHERE male Pacific or Atlantic Harbour Seals wish to pass on their genes. 🙂

See below for some of the research into Harbour Seal vocalizations.


From the research of Leanna Matthews:

“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.


Click here for Harbour Seal vocal samples from Discovery of Sound in the Sea.

Sources:

Discovery of Sound in the Sea (DOSITS) – Harbor Seal Sounds (Phoca vitulina).

Hanggi, E. B., & Schusterman, R. J. (1994). Underwater acoustic displays and individual variation in male harbour seals, Phoca vitulina. Animal Behaviour, 48(6), 1275–1283. 

Matthews, Leanna. (2017). Harbor Seal (Phoca vitulina) Reproductive Advertisement Behavior And The Effects Of Vessel Noise. SURFACE.

Nicholson, T. E. (2000). Social structure and underwater behavior of harbor seals in southern Monterey Bay, California.

Sabinsky, P. F., Larsen, O. N., Wahlberg, M., & Tougaard, J. (January 01, 2017). Temporal and spatial variation in harbor seal (Phoca vitulina L.) roar calls from southern Scandinavia. The Journal of the Acoustical Society of America, 141, 3.)

Van, P. S. M., Corkeron, P. J., Harvey, J., Hayes, S. A., Mellinger, D. K., Rouget, P. A., Thompson, P. M., … Kovacs, K. M. (January 01, 2003). Patterns in the vocalizations of male harbor seals. The Journal of the Acoustical Society of America, 113, 6, 3403-10.