Western Gray Whale (Eschrichtius robustus) Mother and Calf Ecology Off Sakhalin Island

The western population of gray whales (Eschrichtius robustus) is endangered with approximately 130 individuals remaining. Many individuals return annually to the same feeding sites off northeastern Sakhalin Island, indicating a site-specific dependence to this geographic area. This apparently critically important habitat is especially vital for nursing females and their calves, as female energetic requirements are increased during lactation, and calves need to be ready to separate and begin to feed on their own. This study focuses on movements, respirations and behavioral patterns of mother/calf pairs on their feeding ground, with data collected during summer-autumn of 2002-2009. Shore-based observations included three methods: theodolite tracking, focal-animal behavior sampling, and photo-identification. Whales were categorized as three groups of individuals: mother/calf pairs, weaned calves, and other individuals. Analyses were performed to assess differences between groups of individuals, and in relation to their behavior. The null hypothesis of the study was that there were no differences in movement/respiration/behavioral patterns and habitat use between different groups of individuals. Results did not support this hypothesis. Significant differences in movements and respirations were found for certain groups of individuals. These differences also varied in relation to the whales' behavioral activity (feeding, feeding/traveling, and traveling). The shore-based photography was used to obtain additional information on individuals (especially mother/calf pairs) and their sightings, as well as to evaluate the success of this approach. A total of 144 individuals, including 10 females (sighted with calves) and 31 calves were identified during 2004-2009. The shore-based photo-identification approach was successful, and due to being a non-invasive technique, is recommended as a supplemental approach to vessel-based photo-ID efforts. Reproductive success and survival of western gray whales are concern especially due to the presence of industrial activity in the area, as well as recently increased mortalities of female gray whales off Japan. Therefore, the results of this study indicate the importance of considering differences in needs and habitat utilization of different groups of individuals for basic science information as well as for management purposes of protection of western gray whales

Site-fidelity and spatial movements of western North Pacific gray whales on their summer range off Sakhalin, Russia

The Western North-Pacific (WNP) gray whale feeding grounds are off the northeastern coast of Sakhalin Island, Russia and is comprised of a nearshore and offshore component that can be distinguished by both depth and location. Spatial movements of gray whales within their foraging grounds were examined based on 13 years of opportunistic vessel and shore-based photo-identification surveys. Site fidelity was assessed by examining annual return and resighting rates. Lagged Identification Rates (LIR) analyses were conducted to estimate the residency and transitional movement patterns within the two components of their feeding grounds. In total 243 individuals were identified from 2002-2014, among these were 94 calves. The annual return rate over the period 2002-2014 was 72%, excluding 35 calves only seen one year. Approximately 20% of the individuals identified from 2002-2010 were seen every year after their initial sighting (including eight individuals that returned for 13 consecutive years). The majority (239) of the WNP whales were observed in the nearshore area while only half (122) were found in the deeper offshore area. Within a foraging season, there was a significantly higher probability of gray whales moving from the nearshore to the offshore area. No mother-calf pairs, calves or yearlings were observed in the offshore area, which was increasingly used by mature animals. The annual return rates, and population growth rates that are primarily a result of calf production with little evidence of immigration, suggest that this population is demographically self-contained and that both the nearshore and offshore Sakhalin feeding grounds are critically important areas for their summer annual foraging activities. The nearshore habitat is also important for mother-calf pairs, younger individuals, and recently weaned calves. Nearshore feeding could also be energetically less costly compared to foraging in the deeper offshore habitat and provide more protection from predators, such as killer whales

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

Gray whale habitat use and reproductive success during seismic surveys near their feeding grounds: comparing state-dependent life history models and field data

We used a stochastic dynamic programming (SDP) model to quantify the consequences of disturbance on pregnant western gray whales during one foraging season. The SDP model has a firm basis in bioenergetics, but detailed knowledge of minimum reproductive length of females (Lmin) and the relationship between length and reproductive success (Rfit) was lacking. We varied model assumptions to determine their effects on predictions of habitat use, proportion of animals disturbed, reproductive success, and the effects of disturbance. Smaller Lmin values led to higher predicted nearshore habitat use. Changes in Lmin and Rfit had little effect on predictions of the effect of disturbance. Reproductive success increased with increased Lmin and with higher probability of reproductive success by length. Multiple seismic surveys were conducted in 2015 off the northeast coast of Sakhalin Island, with concomitant benthic prey surveys, photo-identification studies, and whale distribution sampling, thus providing a unique opportunity to compare output from SDP models with empirical observations. SDP model predictions of reproductive success and habitat use were similar with and without acoustic disturbance, and SDP predictions of reproductive success and large-scale habitat use were generally similar to values and trends in the data. However, empirical estimates of the proportion of pregnant females nearshore were much higher than SDP model predictions (a large effect, measured by Cohen’s d) during the first week, and the SDP model overestimated whale density in the south and underestimated density around the mouth of Piltun Bay. Such differences in nearshore habitat use would not affect SDP predictions of reproductive success or survival under the current seismic air gun disturbance scenario.publishedVersio