Most people recall the mass beached whale incident discovered in Washington State in 2004. This event marked the shift in attention to how sonar testing can cause acute biological damage to whales, to the point of death. Studies on the effect of high intensity underwater noise have focused on the short term effects on whale behavior and activity. Even though human-induced underwater noise has been addressed and studied for some 40 years, less is known about the long-term effects of lower-intensity ambient noise, which could have a larger spatial and temporal effect.
Baleen whales are endangered in most international waters and communicate via calling sounds that can travel for tens or hundreds of kilometers underwater. Their calls are hypothesized to be important for mating, feeding, navigation, threat detection, and individual identification. The large area necessary to communicate is known as their acoustic habitat or “communication space,” and has been disrupted by noise from large commercial vessels. Due to increased transportation of ships on open seas, this noise has cumulated into ambient noise that masks whale communication. Near ship ports and shipping lanes there is an especially elevated pattern of noise peaks in addition to elevated ambient noise. In order to assess the chronic effects of communication masking on Baleen whales, the noise level must be quantified in order to distinguish between natural and human-induced contributions to noise.
Hatch and colleagues placed 9 marine autonomous recording units (MARUs) in the Stellwagen Bank National Marine Sanctuary off the coast of Massachusetts in April of 2008. This time of data collection was optimal because it maximized the number of foraging whales and the overall traffic in the area. A total of 22,423 whale contact calls were recorded from 89 right whale animals. Communication masking resulted in a loss of 60% of communication space relative to the hypothesized historical ambient levels, and for more than half of the month of sampling, masking resulted in a loss of 63% or greater of communication space. This amounts to a loss of 63% of communication opportunities that were once available in the mid-20th century, which increased to 67% when commercial vessels were passing at the time of data collection. This extremely high level of acoustic masking by commercial ships could greatly affect the survival of Baleen whales, which rely on communication mechanisms for critical survival skills (navigation, predator detection).
The masking of acoustic habitat of Baleen whales could have detrimental effects for the already endangered species. Any impairment or distortion of pod cues necessary for survival could decrease the fecundity of whales, as well as decrease the efficacy of foraging, migration timing, and reproduction. Future studies should further develop methods for translating the effects of communication masking on ecosystem services in order to completely integrate the effects of masking on marine animals. Continued research should evaluate both individual and population-level costs of habitat acoustic loss by human-induced communication masking. If a clear understanding of the long-term effects of low-frequency ambient noise on whale behavior and survival is developed, then a model can be designed to assess the trade-offs in ecosystem services. Today, advocates of marine reserves are assessing the trade off between the cost of limiting fishing in these areas and positive economic incentives in tourism for preserving marine wildlife. Similarly, preserving marine habitats could potentially enhance ecotourism through whale watching and marine education.
Citation: Hatch L. (2012). Quantifying Loss of Acoustic Communication Space for Right Whales in and around a U.S. National Marine Sanctuary. Conservation Biology 26(6) 983-994.