Distance from shore as an indicator of disturbance of gray whales during a seismic survey off Sakhalin Island, Russia

Abstract

A seismic survey was conducted adjacent to the nearshore feeding ground of gray whales Eschrichtius robustus off northeastern Sakhalin Island, Russia. Scan surveys were conducted at 7 shore stations before, during and after the seismic survey. We investigated whether gray whales shifted their distribution with respect to distance from the shoreline in response to acoustic pulses from the seismic source. To do this, we used linear mixed effects modelling that included effects of detection, space and time. Data were tested for effects of magnitude and presence/absence of sound from seismic activity on whale distance from shore. Sound covariates were estimated over 3 temporal scales (8 h, 3 d and since the start of seismic activity) at locations 500 and 5000 m offshore each observation station. Sighting distance from shore was less in poor visibility and at earlier times of day. No significant effects of sound were identified, although data suggest that at most stations, sighting distance from shore increased slightly over the 2 wk of the seismic survey. The analysis was limited, however, by several factors that included low numbers of sightings throughout most of the study, non-availability of data on biomass of gray whale prey and sources of error that could not be accounted for in the model. Sensitivity to potential errors in sighting distance estimation was assessed using a correction factor based on known locations of vessels and gray whales when sighted. The model was refitted using distance-corrected sightings. Results were consistent with the original model.

Gray whale densities during a seismic survey off Sakhalin Island, Russia

“…Most sightings (~80%) were of individual gray whales. Average daily counts of whale sightings per scan at each station showed an increasing trend in numbers throughout the monitoring (Muir et al 2015a). Details of survey effort, number of gray whale sightings and individuals, and daily sighting maps are provided in Muir et al (2015a).…”

“…We conducted multiple shore-based surveys per day, weather permitting, to create a time series of density surfaces for analysis. As described in Muir et al (2015a), 2 'distribution' teams jointly conducted scans from 5 onshore stations (9 to 13; Fig. 1) so that a complete survey of the study area was performed in approximately 2 h. These surveys were timed to coincide with either the sailing of a line when airguns were fired ('on' sound), or a turn between lines when the airguns were shut down ('off' sound).…”

“…Sighting locations were calculated and mapped as described in Muir et al (2015a). The methodology to estimate density surfaces for shore-based scans is presented in Vladimirov et al (2011) and summarized here.…”

Cetacean sightings and acoustic detections during a seismic survey off Nicaragua and Costa Rica, November-December 2004

“…Localized and short-term behavioral responses such as movement toward or away from the sound source or a change in vocalization rates have been reported for some cetaceans during seismic surveys (Richardson et al, 1995;Gordon et al, 1998;Nowacek et al, 2007;Southall et al, 2007;Barry, Cucknell, & Clark, 2012;Castellote, Clark, & Lammers, 2012;Blackwell et al, 2013Blackwell et al, , 2015Thompson et al, 2013;Robertson et al, 2013;Cerchio, Strindberg, Collins, Bennett, & Rosenbaum, 2014;Pirotta, Brookes, Graham, & Thompson, 2014;Wole & Myade, 2014;Dunlop et al, 2015Dunlop et al, , 2016Muir et al, 2015Muir et al, , 2016Finneran et al, 2015;Gailey et al, 2016). However, the long-term consequences of airgun sounds on marine mammals are mostly unknown, and the effectiveness of mitigation measures are largely uncertain (Cato et al, 2013;Nowacek et al, 2013;Wright & Consentino, 2015).…”

Critical information gaps remain in understanding impacts of industrial seismic surveys on marine vertebrates

“…For example, targeted studies to examine pathology of stranded animals in areas with/without seismic activities could lend insights into physiological impacts of animals exposed to sound. All of these types of studies could be conducted in areas of recurring surveys, such as around Sakhalin Island, Russia (Bröker et al 2015, Muir et al 2015, West Africa (DeRuiter & Doukara 2012), and the Beaufort Sea (Richardson & Miller 2013, Robertson et al 2013, to name just a few places. Ideally, this type of information would be collected at an individual-and population-level setting to determine demographic consequences from surveys.…”