Masking effects of marine vibrator (MV) sources on seals and other marine mammals

Acoustic modeling efforts indicate that MV sources, although longer in duration, may provide improved acoustic conditions for marine mammals relative to air guns due to their lower source levels and lower frequency content.  While it is possible to model the potential behavioral and auditory effects of MV sources on marine mammals based on these assumptions (Category 1 desktop study), in the absence of field measurements, the accuracy of such predictions is unknown. This work builds upon previously completed JIP work on this topic (Category 1 desktop study) and evaluates potential auditory and behavioral impacts of prototype MV device output signals on pinnipeds. The most pervasive auditory effect of MV noise is likely to be masking, in which an animal’s ability to hear and respond to a signal of interest is reduced by the presence of overlapping noise.  This work assesses the degree to which masking occurs in bearded seals in the presence of MV signals.

Objectives and methods

• Extend available knowledge of hearing and masking in marine mammals to the very low frequencies at which MV sources will operate
• Obtain robust measures of masking for bearded seals in the presence of noise sources within controlled, well-measured laboratory conditions
• Integrate measured auditory parameters to develop a modified power spectrum model to predict masking probabilities for seals in the presence of MV noise sources with different operational parameters
• Identify general masking patterns that should be common to other marine mammals

Importance

As MV sources are developed for marine applications and approach operational testing and deployment stages, information concerning their possible environmental effects, specifically the impact to marine mammals, is needed. It is not currently possible to estimate masking from industry sources for large whales, due to the absence of direct information about their hearing ability; however, well-controlled laboratory studies with seals as surrogate species can be used to quantify low-frequency masking potential under controlled conditions. Project results contribute to the understanding of masking by MV sources in seals, and will also provide insight into masking in other presumed low-frequency specialists, including many whales requiring high levels of protection due to their threatened or endangered conservation status.  Implications of the project results will inform the selection and application of MV operational parameters to minimize environmental impacts for other marine mammal species with presumed sensitive low-frequency hearing, including large whales and support informed decision-making regarding the development and implementation of new seismic technologies.

Links to other research

1. Determining the Environmental Impact of Marine Vibrator Technology
2. Marine Vibroseis Field Behavioural Response Study

Institutions/PIs

• Long Marine Lab, University of California Santa Cruz (Colleen Reichmuth and Jillian Sills)
• Southall Environmental Associates, Inc. (Brandon Southall)