Effects of seismic operations on bowhead whale behaviour: implications for distribution and abundance assessments.
Frances C. Robertson. 2014. University of British Columbia, Canada. 131pp.
Assessments of distribution and abundance are a common means of gauging impacts of anthropogenic activities on wildlife. However, the influence of behavioural responses on estimated numbers and distributions of animals is rarely considered within this context. I used behavioural data collected in the Beaufort Sea from 1980-2000 to investigate the effects of seismic operations on the distribution and abundance of bowhead whales (Balaena mysticetus). Bowhead whales are known to vary their dive and surface-respiration behaviour when exposed to seismic survey operations, although it is unknown whether these changes in behaviour differ by season, reproductive status and activity (feeding, socializing and travelling). Overall, I found that changes in behaviour of whales exposed to seismic operations were context dependent (i.e., they were contingent on the whale’s circumstance and activity). I then investigated the effects of these behaviour changes on the sightability of whales to aerial observers conducting line-transect surveys. I calculated and compared sightability correction factors specific to whales exposed and not exposed to seismic operations and found that whales in all circumstances were less available for detection when exposed to seismic sounds. In particular, non-calves were the least available to observers during autumn when exposed to seismic activities, regardless of activity state. I used line-transect distance sampling and spatial modeling methods to generate corrected density estimates for bowhead whales in an area of the southern Alaskan Beaufort Sea ensonified by seismic operations between late August and early October 2008 to investigate the extent to which density analyses were affected by changes in whale availability. The resultant density surface models revealed a wide-spread nearshore distribution of whales within the ensonified area with some spatial segregation related to activity state. Density estimates that accounted for variations in whale behaviour due to seismic operations were also 25–64 % higher than previous estimates. Collectively, these findings suggest that seismic activities may not have displaced bowhead whales as previously thought, but altered their dive behaviours instead ,making them less visible for counting. My research demonstrates the importance of accounting for behavioural reactions when assessing impacts of seismic operations on distributions and abundances of whales.