Abundance, behavior, and movement patterns of western gray whales in relation to a 3-D seismic survey, Northeast Sakhalin Island, Russia

Abstract

A geophysical seismic survey was conducted in the summer of 2001 off the northeastern coast of Sakhalin Island, Russia. The area of seismic exploration was immediately adjacent to the Piltun feeding grounds of the endangered western gray whale (Eschrichtius robustus). This study investigates relative abundance, behavior, and movement patterns of gray whales in relation to occurrence and proximity to the seismic survey by employing scan sampling, focal follow, and theodolite tracking methodologies. These data were analyzed in relation to temporal, environmental, and seismic related variables to evaluate potential disturbance reactions of gray whales to the seismic survey. The relative numbers of whales and pods recorded from five shore-based stations were not significantly different during periods when seismic surveys were occurring compared to periods when no seismic surveys were occurring and to the post-seismic period. Univariate analyses indicated no significant statistical correlation between seismic survey variables and any of the eleven movement and behavior variables. Multiple regression analyses indicated that, after accounting for temporal and environmental variables, 6 of 11 movement and behavior variables (linearity, acceleration, mean direction, blows per surfacing, and surface-dive blow rate) were not significantly associated with seismic survey variables, and 5 of 11 variables (leg speed, reorientation rate, distancefrom-shore, blow interval, and dive time) were significantly associated with seismic survey variables. In summary, after accounting for environmental variables, no correlation was found between seismic survey variables and the linearity of whale movements, changes in whale swimming speed between theodolite fixes, mean direction of whale movement, mean number of whale exhalations per minute at the surface, mean time at the surface, and mean number of exhalations per minute during a whales surfaceto-dive cycle. In contrast, at higher received sound energy exposure levels, whales traveled faster, changed directions of movement less, were recorded further from shore, and stayed under water longer between respirations.

Monitoring and impact mitigation during a 4D seismic survey near a population of gray whales off Sakhalin Island, Russia

“…Apart from monitoring the A-zone for the presence of whales during acquisition of A-lines, a second objective of the behavioural teams was to determine if seismic activity and/or vessel proximity affected the behaviour of animals within the A-zone (Gailey et al in press). Consistent with previous behavioural monitoring during industrial activities in the Piltun area, univariate and multivariate analyses were conducted to assess the null hypothesis of no behavioural effects caused by continuous and/or pulse sounds and/or proximity of vessels during the 4D seismic survey (Gailey et al 2007a,b, in press, Johnson et al 2007). The 2 behavioural teams conducted 3 types of observations: (1) regular scans to determine distribution and abundance of gray whales, (2) focal-animal follows to monitor respiration patterns and (3) theodolite tracking to obtain geographic positions of the whales over time.…”

“…Approximately 10% of the animals interrupted feeding at received pulse levels of 163 dB re 1 μPa rms. Despite the application of mitigation criteria based on these thresholds, be havioural responses and changes in distribution, including changes in swim speed, reorientation rate, distance from shore, blow interval and dive time were observed in gray whales during a 3D seismic survey off Sakhalin in 2001 (Gailey et al 2007a). Although localized displacement was ob served, the whales remained within the feeding area throughout that survey.…”

Delineation of a coastal gray whale feeding area using opportunistic and systematic survey effort

“…Seismic surveys produce underwater sound that can cause hearing injury and behavioural changes in marine mammals (Richardson et al 1995, Nowacek et al 2007). Documented effects of acoustic disturbance on baleen whales range from minor changes in surfacing behaviour and respiration rates to displacement from areas closest to the sound source (Reeves et al 1984, Richardson et al 1986, 1999, Ljungblad et al 1988, McCauley et al 2000, Gailey et al 2007a). In particular, Malme et al (1986) found 10% of gray whales stopped feeding and moved away from pulsed airgun sounds exceeding 163 dB re µPa rms.…”

Seismic operations have variable effects on dive-cycle behavior of bowhead whales in the Beaufort Sea

“…This was in sharp contrast to migrating whales that appeared to avoid seismic operations by distances of 20−30 km , Manly et al 2007. Gray whales Eschrichtius robustus (Gailey et al 2007, Yazvenko et al 2007) and sperm whales Physeter macrocephalus (Madsen et al 2002, Miller et al 2009) have also been observed foraging near seismic operations, but there is less in formation for those species about their relative response to seismic during foraging vs. migration. Our findings further suggest that traveling bowhead whales may not avoid ensonified areas to quite the extent reported in previous aerial-studies (e.g.…”

“…Gray whales sometimes avoid airgun operations (e.g. Malme et al 1984) and also change their movement patterns and dive durations as exposure to seismic sound increases (Gailey et al 2007). However, cetaceans may also show little if any behavioral response to a human activity in some circumstances, as reported for humpback whales exposed to blasting (Todd et al 1996) or sperm whales exposed to distant explosions (Madsen & Møhl 2000).…”