Acoustic masking in marine ecosystems: intuitions, analysis, and implication

Abstract

Acoustic masking from anthropogenic noise is increasingly being considered as a threat to marine mammals, particularly low-frequency specialists such as baleen whales. Low-frequency ocean noise has increased in recent decades, often in habitats with seasonally resident populations of marine mammals, raising concerns that noise chronically influences life histories of individuals and populations. In contrast to physical harm from intense anthropogenic sources, which can have acute impacts on individuals, masking from chronic noise sources has been difficult to quantify at individual or population levels, and resulting effects have been even more difficult to assess. This paper presents an analytical paradigm to quantify changes in an animal's acoustic communication space as a result of spatial, spectral, and temporal changes in background noise, providing a functional definition of communication masking for free-ranging animals and a metric to quantify the potential for communication masking. We use the sonar equation, a combination of modeling and analytical techniques, and measurements from empirical data to calculate time-varying spatial maps of potential communication space for singing fin (Balaenoptera physalus), singing humpback (Megoptera novaeangliae), and calling right (Eubalaena glacialis) whales. These illustrate how the measured loss of communication space as a result of differing levels of noise is converted into a time-varying measure of communication masking. The proposed paradigm and mechanisms for measuring levels of communication masking can be applied to different species, contexts, acoustic habitats and ocean noise scenes to estimate the potential impacts of masking at the individual and population levels.

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

“…Scheduling ship transits close in time appears to create quiet periods that may have benefits to whale communication or behavior (Clark et al 2009) that would not be represented by the total CSEL metric. However, other vessel traffic (including tour vessels and small vessels) has the potential to create noise during any planned quiet period based solely on cruise ship scheduling adjustments, potentially re ducing the benefit of synchronizing cruise ship scheduling.…”

“…This temporary loss may impede their ability to communicate (after Clark et al 2009). Quantifying the biological effects of acoustic masking on whales is beyond the scope of this study, but the potential effects can be qualitatively described.…”

“…The impact of auditory masking of biologically relevant sounds by anthropogenic noise may be as great or greater than overt behavioral responses, constituting a transient and dynamic form of acoustic habitat loss (Clark et al 2009). Masking is the process by which the audibility of one sound is reduced by the presence of another sound (Moore 1982).…”

“…Masking is the process by which the audibility of one sound is reduced by the presence of another sound (Moore 1982). The effect can prevent listeners from recognizing or detecting biologically important sounds (Clark et al 2009, Barber et al 2010. The biological significance of masking almost certainly varies by species, behavioral context, population size and distribution, as well as other factors.…”

“…The biological significance of masking almost certainly varies by species, behavioral context, population size and distribution, as well as other factors. Nevertheless, vessel noise clearly has the potential to mask essential baleen whale communication signals and prevent whales from detecting potential predators (Hatch et al 2008, Tyack 2008, Clark et al 2009). The effect of noise on receivers is often assessed using acoustic propagation models that can predict the spatial pattern and extent of sound fields (e.g.…”