A New Context‐Based Approach to Assess Marine Mammal Behavioral Responses to Anthropogenic Sounds

Abstract

Acute effects of anthropogenic sounds on marine mammals, such as from military sonars, energy development, and offshore construction, have received considerable international attention from scientists, regulators, and industry. Moreover, there has been increasing recognition and concern about the potential chronic effects of human activities (e.g., shipping). It has been demonstrated that increases in human activity and background noise can alter habitats of marine animals and potentially mask communications for species that rely on sound to mate, feed, avoid predators, and navigate. Without exception, regulatory agencies required to assess and manage the effects of noise on marine mammals have addressed only the acute effects of noise on hearing and behavior. Furthermore, they have relied on a single exposure metric to assess acute effects: the absolute sound level received by the animal. There is compelling evidence that factors other than received sound level, including the activity state of animals exposed to different sounds, the nature and novelty of a sound, and spatial relations between sound source and receiving animals (i.e., the exposure context) strongly affect the probability of a behavioral response. A more comprehensive assessment method is needed that accounts for the fact that multiple contextual factors can affect how animals respond to both acute and chronic noise. We propose a three-part approach. The first includes measurement and evaluation of context-based behavioral responses of marine mammals exposed to various sounds. The second includes new assessment metrics that emphasize relative sound levels (i.e., ratio of signal to background noise and level above hearing threshold). The third considers the effects of chronic and acute noise exposure. All three aspects of sound exposure (context, relative sound level, and chronic noise) mediate behavioral response, and we suggest they be integrated into ecosystem-level management and the spatial planning of human offshore activities.

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

“…These metrics were introduced because the duration of a noise may affect an individual's behavioral response (Ellison et al 2012). To calculate these metrics, each whale's sound exposure history was plotted over time.…”

“…The primary reason that avoidance responses were not included in these simulations was because real-world animal response to noise is not well understood and likely occurs as a function of social context in addition to sound level (Ellison et al 2012). By omitting unnecessary speculation about whale avoidance responses, the current work focuses on determining the relative effectiveness of different vessel management options.…”

“…Recent efforts to quantify and classify disturbing acoustic stimuli indicate that baleen whales rarely respond to received sound pressure levels at 90 to 120 dB re 1 µPa, but show an increasing probability of avoidance and other behavioral reactions to sound in the 120 to 160 dB re 1 µPa range (Southall et al 2007). However, baleen whale response may vary depending on be havioral context, sound source proximity, novelty, and sound pressure level (Ellison et al 2012). 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.…”

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

“…We have insufficient data to confirm these hypotheses at present, but extension of our modelling approach to areas with greater telemetry data overlap would allow greater exploration of these possibilities. Our approach may allow us to examine whether seals avoid specific depths after sound exposure, and whether they show heading changes or alter dive characteristics in response to parameters including received sound, given time of year and activity and/or physiological state (Ellison et al, 2011). This requires the simultaneous modelling of sound produced by all ships in the region at any given time, ambient noise caused by waves and wind and the inclusion of data from multiple seals.…”

“…Although the long-term or chronic effects from shipping noise on marine life are still largely unknown and have not yet been incorporated into management decisions (Ellison, et al, 2011), there is increasing concern about the detrimental impacts in chronically exposed areas.…”