The surfacing, respiration and diving (SRD) behavior of bowhead whales Balaena mysticetus changes upon exposure to seismic operations. However, it is unknown whether these changes differ by season, reproductive status (calves, mothers, and non-calves), and whale activity (traveling, foraging, or socializing). Such SRD behavioral responses to seismic operations might influence the detectability of whales during aerial surveys. We addressed these questions by applying non-parametric univariate tests and linear mixed models to behavioral data collected by aerial observation of bowheads in the Beaufort Sea from 1980 to 2000. Durations of surfacings decreased upon exposure to seismic operations, especially for traveling or socializing non-calf whales. The mixed models also indicated that dive durations were affected by the presence of seismic operations, but the effects depended on other variables such as season and whale activity. Overall, our results suggest that changes in the behavior exhibited by bowhead whales exposed to seismic operations are context-dependent (i.e. responses to seismic operations depend on both the circumstance and activity of the whale). The level of perceived threat may also be important based on similarities with behavioral changes observed in other air-breathing aquatic foragers facing dangers. We conclude that seismic-induced changes in bowhead SRD behaviors may affect the availability of bowhead whales for visual detection in some circumstances. This in turn means that estimates of abundance and distribution of bowhead whales near seismic surveys should be context-sensitive and incorporate correction factors that account for sound exposure, season, reproductive status, and whale activity.
The accuracy of estimates of cetacean density from line-transect survey data depends in large part on how visible the target species is to the observer. Behavioural data (i.e. surface and dive times) from government- and industry-funded aerial observation programmes (1980–2000) were used to calculate availability correction factors needed to estimate the number of bowhead whales (Balaena mysticetus) from aerial survey sighting data. Correction factors were calculated for bowhead whales exposed and not exposed to seismic operations. Travelling non-calf whales were found to be less likely to be available for detection than other whales, and their availability further declined in the presence of seismic operations. Noncalves were also less available to observers during autumn when exposed to seismic operations than when not exposed, regardless of activity (travelling or otherwise). Such differences in availability appear to reflect behavioural responses to the sound of seismic operations that alters the surfacing and diving patterns of bowhead whales. Localised abundance estimated from aerial surveys may range from 3% to as much as 63% higher in areas ensonified by seismic operations if correction factors are applied to account for differences in availability associated with the presence of seismic operations, compared to abundance estimates derived from assessments that only account for changes in availability of undisturbed whales. These results provide the first empirical estimates of availability for bowhead whales exposed to seismic operations and highlight the implications of not correcting for disturbance-related availability in density assessments in the vicinity of seismic operations.
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