Anti-masking strategies and communication ranges of polar seal underwater vocalizations

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My research investigates the production, transmission and reception of underwater vocalizations of polar seals.  Underwater calls of harp seals from the Gulf of St. Lawrence and Weddell seals from Antarctica will be analyzed to determine if they have evolved to overcome jamming (masking) by other seal calls.  Two students will overwinter in Antarctica to determine if monitoring seal calls can index population numbers and find out more about the sound generation abilities of Weddell seals. Under optimal conditions, some underwater Weddell seal calls can be heard up to 25 km away while others would only travel 100 metres.  Harp seal calling rates can exceed 130 calls per minute thus producing loud backkground noises.  This is similar to the "cocktail party" effect encountered by humans at social functions.  We will determine if Weddell seals, like harp seals, follow the "courtesy rule" and call so that they do not mask a neighbour's vocalizations.  Cracking ice, waves, industrial noises of ships and underwater construction also have the potential to block the acoustic communication channel of seals. Underwater calls are studied using hydrophones (underwater microphones) lowered under the sea ice.  Because so many calls overlap, there are no automated analysis possibilities and the analyses of the tape recordings is very time consuming.  We will examine the variability of both natural and human noises and determine the extent to which the fine structure of the noises will impact the seal calling behaviours.  By relating information on the physical and behavioural aspects of seal calls to their hearing abilities and life history needs, we will gain a better understanding of the importance of sound communication in these polar seals.  A practical aspect of this research is that it will provide information which is necessary to assess the potential environmental impacts of noises generated by ice-breaking ships in the Arctic on seals and other marine mammals.