The Seasonal Variation of Ultrasonic Vocalizations Produced by Weddell Seals (Leptonychotes Weddellii) in Mcmurdo Sound, Antarctica with Ambient Illumination Levels

• Main Author: McCarthy, Ryan
• Other Authors: Lisa Munger, Richard Emlet, Carol Paty
• Format: Thesis
• Language: English
• Published: University of Oregon 2023
• Subjects: marine mammal biocoustics; Weddell seals; bioacoustics; Antarctica; vocalizations; Austral; McMurdo Sound; Weddell; Antarc*; Weddell Seals
• Online Access: https://scholarsbank.uoregon.edu/xmlui/handle/1794/28894

30 pages Weddell Seals (Leptonychotes weddellii) are a species of polar seal found circumpolar in the waters of Antarctica. This species, like all marine mammals, use highly complex vocalizations to communicate in aquatic environments over vast distances, and phocids as a group are thought to have exceptionally extensive vocal repertoires. Until last year it was believed that all phocids (seals) did not utilize vocalizations in the ultrasonic frequency range (>20 kHz) and only used sonic vocalizations. In a paper by Cziko et al., it was demonstrated that Weddell Seals frequently used ultrasonic vocalizations. The vocal repertoire of Weddell Seals is extensive, even for phocids, and it varies in the composition of unique call types throughout the year. The reason for these yearly variations is unknown and understudied but may fluctuate with abiotic factors in the Weddell Seal’s habitat, such as illumination. The aim of this study is to ascertain the purpose of ultrasonic vocalizations in the lives of Weddell Seals. Acoustic data were collected by the McMurdo Observation Station in McMurdo Sound, Antarctica (S 77.8510, E 166.6645) for 25 months. This data was analyzed by a human analyst with the acoustic analysis software, Raven, created by the Cornell Ornithology Lab. Ambient illumination levels were calculated using a Solar Elevation Calculator created by NOAA. There was a distinct peak in gross documented ultrasonic vocalizations in the austral winter, June, which is the darkest point of the year at this latitude. There were also variations in the predominant vocalization category of documented calls, the duration of specific calls, and the spectrographic signatures of some calls throughout the year. The reason for these variations is speculative as more specialized are needed.