An AMAR to study harbour seal calls

Kat Nikolich, a Western Washington University (WWU) graduate research student, is collaborating with JASCO Applied Sciences to deploy one of its Autonomous Multichannel Acoustic Recorders (AMARs) this summer to measure the vocal repertoires of harbour seals (Phoca vitulina) breeding in the northern Strait of Georgia, BC. Nikolich, who is completing a master’s degree in biology, will work with JASCO bioacoustics expert and pinniped specialist Dr. Héloïse Frouin-Mouy.

The specialized acoustic recorder will be anchored to the seabed near one of the largest seal haul-outs in the region, on the south shore of Hornby Island. The device will record sounds continuously from June through September, spanning the full breeding season of the seals. At the same time, a research team from WWU, comprised of a dedicated team of undergraduate students led by Nikolich, will observe the seals’ activity from the shore nearby.

Harbour seals are a common sight in the Strait of Georgia, the waterway separating Vancouver Island from the lower mainland of British Columbia. These puppy-faced pinnipeds are often seen lounging on rocks and logs near shore, but also visit marinas and harbours for gifts of fish heads, bait, and other handouts. Compared to the other common pinnipeds in the area—California (Zalophus californianus) and Steller (Eumetopias jubatus) sea lions—harbour seals are relatively silent both above and below the water, with one notable exception: during the breeding season, males produce low rumbling calls known as roars. These roars are near the lower limit of human hearing; to us, they sound like a distant airplane.

These roars appear to serve the same purpose as humpback whale songs: to establish male dominance hierarchy, with the largest and toughest males trying to reach the top. The superior seals have their choice of territory during the breeding season, giving them better access to females. Subordinate males must stake out sub-prime territories, but they still try to attract females with vocal displays and rolling and splashing at the water’s surface. It is unclear how female harbour seals choose mates, and whether or not the vocal prowess of the males influences this choice. What we do know is that the calls are a learned behaviour, and like those from other marine mammal species, harbour seal vocalizations differ slightly between populations. So the first step in determining how vocal displays affect mate choice is to understand the males’ regional dialect and if it changes over time. Whereas this has been documented in many populations, it has not yet been investigated in British Columbian waters.

The study will also record background noise from sources such as recreational boats and commercial fishing vessels. Hornby Island is a popular recreational area in summer. Boat traffic peaks in mid to late summer, at the same time as the harbour seals’ breeding season. If male vocal communication is as essential to breeding success as it appears, boat noise could interfere by masking these breeding displays. The shore-based team will simultaneously observe seal behaviours and vessel traffic in the area. This information will then be combined with the underwater noise recordings by the AMAR to determine if seal behaviours are affected by vessel noise.

Harbour seal pup being held by JASCO's Dr. Héloïse Frouin-Mouy during a program of biological measurements.

A harbour seal in the Strait of Georgia.

Underwater view of an AMAR recording sound near the south shore of Hornby Island.