Prey‐mediated behavioral responses of feeding blue whales in controlled sound exposure experiments

Abstract

Behavioral response studies provide significant insights into the nature, magnitude, and consequences of changes in animal behavior in response to some external stimulus. Controlled exposure experiments (CEEs) to study behavioral response have faced challenges in quantifying the importance of and interaction among individual variability, exposure conditions, and environmental covariates. To investigate these complex parameters relative to blue whale behavior and how it may change as a function of certain sounds, we deployed multi-sensor acoustic tags and conducted CEEs using simulated mid-frequency active sonar (MFAS) and pseudo-random noise (PRN) stimuli, while collecting synoptic, quantitative prey measures. In contrast to previous approaches that lacked such prey data, our integrated approach explained substantially more variance in blue whale dive behavioral responses to mid-frequency sounds (r2 = 0.725 vs. 0.14 previously). Results demonstrate that deep-feeding whales respond more clearly and strongly to CEEs than those in other behavioral states, but this was only evident with the increased explanatory power provided by incorporating prey density and distribution as contextual covariates. Including contextual variables increases the ability to characterize behavioral variability and empirically strengthens previous findings that deep-feeding blue whales respond significantly to mid-frequency sound exposure. However, our results are only based on a single behavioral state with a limited sample size, and this analytical framework should be applied broadly across behavioral states. The increased capability to describe and account for individual response variability by including environmental variables, such as prey, that drive foraging behavior underscores the importance of integrating these and other relevant contextual parameters in experimental designs. Our results suggest the need to measure and account for the ecological dynamics of predator-prey interactions when studying the effects of anthropogenic disturbance in feeding animals.

Experimental field studies to measure behavioral responses of cetaceans to sonar

“…They then compared numerous dive parameters in intentionally unexposed Blainville's beaked whales to those in sonar CEEs using identical highresolution behavioral metrics. Similarly, studies of diving kinematics and feeding strategies of blue whales Balaenoptera musculus in relation to prey distribution have provided critical insight into the interpretation of responses of feeding whales during CEEs (Friedlaender et al 2016). Furthermore, baseline acoustic data from the tags have contributed to understanding the typical animal distribution in study areas before, during and after exposure to sound (McCarthy et al 2011, Tyack et al 2011, Yack et al 2013.…”

“…Additional methodological ad vances included using active fisheries acoustics to measure prey distribution for feeding baleen whales, resulting in key insights into baseline foraging ecology (e.g. Goldbogen et al 2013) and the context-dependent nature of behavioral responses (Friedlaender et al 2016). While some SOCAL-BRS data were still being collected and analyzed at the time of this review, many results were already published, notably for blue and beaked whales.…”

“…Friedlaender et al (2016) demonstrated a 5-fold increase in the ability to quantify variability in blue whale diving behavior when prey distribution and density variables were incorporated into across-individual analyses. These results provided the first integration of direct measures of prey distribution into the analyses of potential responses to sound exposure in feeding marine mammals and illustrated that responses evaluated without such measurements for foraging animals may be misleading.…”

“…These results provided the first integration of direct measures of prey distribution into the analyses of potential responses to sound exposure in feeding marine mammals and illustrated that responses evaluated without such measurements for foraging animals may be misleading. Additional studies are expanding on the findings of Goldbogen et al (2013) and Friedlaender et al (2016) behavioral state, environmental context, and spatial orientation and movement of sound sources relative to animals, particularly source−receiver range. These include studies of behavioral state-switching in blue whales using hidden Markov models (DeRuiter et al in press), as well as individual response analyses using structured expert severity scoring and quantitative change point statistical methods.…”

Predicting the acoustic exposure of humpback whales from cruise and tour vessel noise in Glacier Bay, Alaska, under different management strategies

“…For example, McKenna et al (2015) found that feeding blue whales exhibited a limited and inconsistent response repertoire during close approaches by large vessels near ship channels off the ports of Los Angeles and Long Beach. Likewise, deep-feeding blue whales showed stronger responses to presentation of anthropogenic noise than other behavioral states (Friedlaender et al 2016).…”