Listening to whales: tying acoustics to ecology
Date
2018-12-04
Authors
Burnham, Rianna Elizabeth
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Abstract
The acoustic sense is vital to all life processes for whales. It defines their ‘active space’, and the extent and nature of interactions with their surroundings. Yet, we are still learning the basics of most species’ acoustic behaviours and vocal repertoires.
The ecology of gray whales (Eschrichtius robustus) is well known, however vocal behaviours are not well described outside of breeding lagoons. Bottom-stationed acoustic monitoring devices were deployed in Clayoquot Sound, west coast Vancouver Island to explore acoustics use outside of these areas. During migration the use of low frequency moan calls are prevalent, perhaps for group cohesion, with lead whales guiding followers. During the summer more inter-group calls (knocks, upsweeps) are employed. Here I explored the use of ‘motherese’ calls between cow-calf pairs, and how this may mirror the weaning process. Photoperiod, increased ambient noise, threat perception, and vessel and aircraft presence elicited acoustic responses. Calling was also altered by social, behavioural, and physiological state. These results begin to show gray whales to be acoustically sensitive, with highly nuanced vocalising behaviours.
Acoustic methods afford monitoring at times and in places that would otherwise be impossible, and lends themselves to the study of rare or cryptic species. Ocean gliders with passive acoustic capacity were used to explore deep-coastal and shelf-break waters for large whale species. Humpback whales (Megaptera novaeangliae) were common on the shelf, whereas calls from fin (Balaenoptera physalus), blue (Balaenoptera musculus), sperm (Physeter macrocephalus), and possibly sei whales (Balaenoptera borealis) were heard in more offshore locations. Concurrent habitat data steams help establish area use and importance to these species. The surveys focus on submarine canyons that are thought to aggregate prey. Calls denote whale presence, whereas call type may suggest behaviour and habitat use. Calls described for feeding and breeding were heard for fin and blue whales, with distinct temporal distribution.
Acoustic techniques complement other ecological methods and can fill existing knowledge gaps in whale life histories. It can also help quantify the effect of human activities on whale populations and ocean soundscapes. These findings will inform management actions. I provide examples of management links to acoustic-ecological research.
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Keywords
whales, acoustics, soundscape, anthropogenic noise, passive acousitc monitoring, Canadian Pacific, management, conservation, call repertoire, 'active space'