Seismic operations have variable effects on dive-cycle behavior of bowhead whales in the Beaufort Sea (original) (raw)
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Marine Ecology Progress Series, 2016
Aerial surveys are sometimes used to assess the densities of wide-ranging whales, as well as changes in their distributions in response to human activity. Such surveys also provide data used to estimate numbers of animals exposed to different received levels of seismic sound, as required by regulators. However, estimates of abundance are often biased because they fail to account for the effects of seismic operations on the surfacing and diving behavior of whales. Our objective was to determine the extent to which analyses of the distribution of bowhead whales Balaena mysticetus are affected by changes in visual 'availability' caused by seismic operations. We used aerial survey data collected during seismic operations in the Alaskan Beaufort Sea from late August to early October 2008 and fit spatial density surface models to bowhead sighting data to predict whale density in an ensonified area. We also incorporated availability correction factors to determine the sensitivity of density estimates to changes in surfacing and diving behavior caused by seismic operations. The influence of altered whale behavior was then evaluated by comparing a series of realistic simulated scenarios in which models incorporated undisturbed or seismic disturbance-related correction factors. Results suggest that the numbers of bowhead whales present in the vicinity of seismic operations during the bowhead autumn migration are underestimated if the behavioral effects of seismic operations on whales are ignored. Our study highlights the importance of accounting for changes in whale behavior that can affect sightability when estimating numbers and distribution of whales in the vicinity of industrial activity.
2014
Assessments of distribution and abundance are a common means of gauging impacts of anthropogenic activities on wildlife. However, the influence of behavioural responses on estimated numbers and distributions of animals is rarely considered within this context. I used behavioural data collected in the Beaufort Sea from 1980-2000 to investigate the effects of seismic operations on the distribution and abundance of bowhead whales (Balaena mysticetus). Bowhead whales are known to vary their dive and surface-respiration behaviour when exposed to seismic survey operations, although it is unknown whether these changes in behaviour differ by season, reproductive status and activity (feeding, socializing and travelling). Overall, I found that changes in behaviour of whales exposed to seismic operations were context dependent (i.e., they were contingent on the whale's circumstance and activity). I then investigated the effects of these behaviour changes on the sightability of whales to aerial observers conducting line-transect surveys. I calculated and compared sightability correction factors specific to whales exposed and not exposed to seismic operations and found that whales in all circumstances were less available for detection when exposed to seismic sounds. In particular, non-calves were the least available to observers during autumn when exposed to seismic activities, regardless of activity state. I used line-transect distance sampling and spatial modeling methods to generate corrected density estimates for bowhead whales in an area of the southern Alaskan Beaufort Sea ensonified by seismic operations between late August and early October 2008 to investigate the extent to which density analyses were affected by changes in whale availability. The resultant density surface models revealed a widespread nearshore distribution of whales within the ensonified area with some spatial segregation related to activity state. Density estimates that accounted for variations in whale behaviour due to seismic operations were also 25-64 % higher than previous estimates. Collectively, these findings suggest that seismic activities may not have displaced bowhead whales as previously thought, but altered their dive behaviours instead ,making them less visible for counting. My research demonstrates the importance of accounting for behavioural reactions when assessing impacts of seismic operations on distributions and abundances of whales
J. Cetacean Res. Manage.
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 operatio...
Western gray whale behavioral response to seismic surveys during their foraging season
Environmental Monitoring and Assessment
Gray whales utilizing their foraging grounds off northeastern Sakhalin Island, Russia, have been increasingly exposed to anthropogenic activities related to oil and gas development over the past two decades. In 2015, four seismic vessels, contracted by two operators, conducted surveys near and within the gray whale feeding grounds. Mitigation and monitoring plans were developed prior to the survey and implemented in the field, with real-time data transfers to assist the implementation of measures aimed at minimizing impacts of acoustic exposure. This study examined the behavioral response of gray whales relative to vessel proximities and sounds generated during seismic exploration. Five shore-based teams monitored gray whale behavior from 1 June to 30 September using theodolite tracking and focal follow methodologies. Behavioral data were combined with acoustic and benthic information from studies conducted during the same period. A total of 1270 tracks (mean duration = 0.9 h) and 4...
Effects of airgun sounds on bowhead whale calling rates: evidence for two behavioral thresholds
PloS one, 2015
In proximity to seismic operations, bowhead whales (Balaena mysticetus) decrease their calling rates. Here, we investigate the transition from normal calling behavior to decreased calling and identify two threshold levels of received sound from airgun pulses at which calling behavior changes. Data were collected in August-October 2007-2010, during the westward autumn migration in the Alaskan Beaufort Sea. Up to 40 directional acoustic recorders (DASARs) were deployed at five sites offshore of the Alaskan North Slope. Using triangulation, whale calls localized within 2 km of each DASAR were identified and tallied every 10 minutes each season, so that the detected call rate could be interpreted as the actual call production rate. Moreover, airgun pulses were identified on each DASAR, analyzed, and a cumulative sound exposure level was computed for each 10-min period each season (CSEL10-min). A Poisson regression model was used to examine the relationship between the received CSEL10-mi...
Frontiers in Physiology, 2012
Anthropogenic underwater sound in the environment might potentially affect the behavior of marine mammals enough to have an impact on their reproduction and survival. Diving behavior of four killer whales (Orcinus orca), seven long-finned pilot whales (Globicephala melas), and four sperm whales (Physeter macrocephalus) was studied during controlled exposures to naval sonar [low frequency active sonar (LFAS): 1-2 kHz and mid frequency active sonar (MFAS): 6-7 kHz] during three field seasons (2006)(2007)(2008)(2009). Diving behavior was monitored before, during and after sonar exposure using an archival tag placed on the animal with suction cups. The tag recorded the animal's vertical movement, and additional data on horizontal movement and vocalizations were used to determine behavioral modes. Killer whales that were conducting deep dives at sonar onset changed abruptly to shallow diving (ShD) during LFAS, while killer whales conducting deep dives at the onset of MFAS did not alter dive mode. When in ShD mode at sonar onset, killer whales did not change their diving behavior. Pilot and sperm whales performed normal deep dives (NDD) during MFAS exposure. During LFAS exposures, long-finned pilot whales mostly performed fewer deep dives and some sperm whales performed shallower and shorter dives. Acoustic recording data presented previously indicates that deep diving (DD) is associated with feeding. Therefore, the observed changes in dive behavior of the three species could potentially reduce the foraging efficiency of the affected animals.
Journal of Zoology, 2006
Johnstone Strait provides important summer habitat for the northern resident killer whales Orcinus orca of British Columbia. The site is also an active whale-watching area. A voluntary code of conduct requests that boats do not approach whales closer than 100 m to address perceived, rather than demonstrated, effects of boat traf®c on killer whales. The purpose of the study was to test the relevance of this distance guideline. Relationships between boat traf®c and whale behaviour were studied in 1995 and 1996 by shorebased theodolite tracking of 25 identi®able focal animals from the population of 209 whales. Individual killer whales were repeatedly tracked in the absence of boats and during approaches by a 5.2 m motorboat that paralleled each whale at 100 m. In addition, whales were tracked opportunistically, when no effort was made to manipulate boat traf®c. Dive times, swim speeds, and surface-active behaviours such as breaching and spy-hopping were recorded. On average, male killer whales swam signi®cantly faster than females. Whales responded to experimental approaches by adopting a less predictable path than observed during the preceding, no-boat period, although males and females used subtly different avoidance tactics. Females responded by swimming faster and increasing the angle between successive dives, whereas males maintained their speed and chose a smooth, but less direct, path. Canonical correlations between whale behaviour and vessel proximity are consistent with these conclusions, which suggest that weakening whalewatching guidelines, or not enforcing them, would result in higher levels of disturbance. High variability in whale behaviour underscores the importance of large sample size and extensive experimentation when assessing the impacts of human activity on killer whales.
Foraging is likely the most biologically significant activity for sperm whales that are the focus of whale-watching at Kaikoura. Foraging success is therefore a key behaviour to monitor changes that have direct impact on the whales' fitness in the area. We are now able to measure foraging effort and prey detection rates using passive acoustics. In this chapter, we measure the acoustic foraging behaviour of whales before, during and after viewing by different numbers and types of whale-watching vessels. We found no differences in parameters that we believe are most closely related to prey encounter rates and feeding success that could be attributed to vessel interactions. There were slight changes to the initial search pattern of dives following whale-watching boat encounters: whales delayed their first click and descended for longer before stopping for their first silence, which was also extended. However, the effects appeared small relative to high individual variability and we...
2016
Monitoring of a 2010 seismic survey near the feeding grounds of gray whales (Eschrichtius robustus) off Sakhalin Island, Russia, yielded underwater sound recordings and visual observations of nearshore distribution and behavior during the whales' early summer feeding season. These data along with temporal, spatial and environmental non-acoustic impact variables were used in multivariate analyses (MVAs) to investigate effects of sound on i) whale distance from shore, ii) occupancy/abundance and iii) behavioral responses. Sound metrics were estimated through modelling on a grid of density surface cells and on individual whale paths. Acoustic recordings provided refinement factors for modelling results. Distance from shore analyses found no evidence that seismic pulses resulted in a distributional shift. Density MVAs found no significant changes in whale occupancy associated with seismic sound exposure, but found a weak association between decreased densities and a rise-fall pattern of sound exposure over the previous 3 days. These MVAs were limited by sample sizes, and shifts could also reflect changes in prey distribution (not monitored). Behavioral analyses found no significant association between response variables and noise covariates including sound from vessels; however, power analyses on behavioral data found sample sizes to be insufficient to detect small to moderate changes.
Meta-analyses of whalewatching impact studies: comparisons of cetacean responses to disturbance
Marine Ecology Progress Series, 2015
Whale-watching activities can induce behavioral changes that may negatively affect cetacean populations. However, these changes may vary depending on species, populations and environmental features. It is important to determine inter-specific variation in cetacean responses to stressors in order to identify the best metrics for evaluation of consequences of anthropogenic disturbance. We used meta-analyses to assess the consistency of cetacean responses to whalewatching vessels across a pool of suitable studies covering a variety of species and sites. We analyzed several metrics to capture cetacean heterogeneous responses and to explore their reliability across species. We found disruptions of activity budget and of path directionality as the most consistent responses towards whale-watching vessels. In a similar manner across species, animals were more likely to travel and less likely to rest and forage in the presence of vessels. Cetaceans also showed a tendency to increase path sinuosity (deviation index) and decrease path linearity (directness index) during boat interactions. We also explored the influence of socio-ecological factors on behavioral response but found no consistent results among studies. Further population-specific studies should address the potential long-term consequences of these behavioral responses to inform management of the whale-watching industry.