The underwater locations and source levels of vocalizing harp seals in the Gulf of St. Lawrence

During the breeding season, harp seals are acoustically active under water and exhibit high calling rates. The underwater locations of seals in three dimensions were studied using a 4 hydrophone passive acoustic method near the Magdalen Islands, QC. Calibration tones determined the underwater transmission losses. Sound transmission was highly variable and reduced the ability of the array to localize calling seals beyond 20 m from the array. Most seals calls were located along the periphery of the ice floes and in open water, but not usually under large floes. Most calls were detected underneath the array. Source levels varied with call type (mean ranges 129 -151 dB re 1muPa --m) with the highest value being 180 dB re 1muPa --m. Monte Carlo models of communication ranges for the call types for a quiet sea indicated median distances of 526 to 5518 m (maximum 50 km). Median communication distances in the presence of other calling seals dropped to 129 to 153 m (maximum 5 km).