Behavioural responses of western gray whales to a 4-D seismic survey off northeastern Sakhalin Island, Russia

A seismic survey was conducted off the northeastern coast of Sakhalin Island, Russia in 2010. The survey area was adjacent to the only known near-shore feeding ground of the Critically Endangered population of western gray whales Eschrichtius robustus in the western Pacific south of the Aleutian Islands. This study examined the effectiveness of efforts to minimize the behavioural responses of the whales to vessel proximity and sound during the survey. Two shore-based behavioural observation teams monitored whale movements and respirations pre-, during and post-seismic survey. Theodolite tracking and focal-animal follow methods were used to collect behavioural data. Mixed linear models were used to examine deviations from 'normal' patterns in 10 movement and 7 respiration response variables in relation to vessel proximity, vessel/ whale relative orientations and 8 received sound metrics to examine if seismic survey sound and/or vessel activity influenced the whales' behaviour. Behavioural state and water depth were the best 'natural' predictors of whale movements and respiration. After considering natural variation, none of the response variables were significantly associated with seismic survey or vessel sounds. A whale's distance from shore and its orientation relative to the closest vessel were found to be significantly influenced by vessel proximity, which suggested some non-sound related disturbance. The lack of evidence that the whales responded to seismic survey sound and vessel traffic by changing either their movement or respiration patterns could indicate that the current mitigation strategy is effective. However, power analyses suggest that our sample sizes were too small to detect subtle to moderate changes in gray whale behaviour

Model based sound level estimation and in-field adjustment for real-time mitigation of behavioural impacts from a seismic survey and post-event evaluation of sound exposure for individual whales

ABSTRACT While it is common practice to use sound propagation modelling to estimate the safety shutdown radius around a seismic survey source, only rarely are numerical estimation methods applied to the real-time mitigation of behavioural effects that occur at much greater ranges. For a seismic survey in 2010 near a critically endangered whale population on their feeding grounds, a strategy was implemented for the prediction and field calibration of behavioural safety boundaries that were used for shutdown decisions by shore and vessel based observers equipped with ranging instruments and geo-referencing software. This summary paper describes the steps involved in the estimation, selection and validation of the noise boundaries for different survey lines and under variable propagation conditions. Results of post-event analyses to estimate sound exposure levels and other acoustic parameters of the received seismic pulses along the paths of visually tracked whales are also presented