Sound review finds some marine mammals really feel the noise

A new review of the levels of human-generated noise and the marine mammals exposed to it shows that some animals may be more sensitive than scientists previously thought.

Porpoises, in general, show evidence of being more sensitive to noise, said Brandon Southall, a research affiliate at the University of California, Santa Cruz and a marine scientist and owner of the research organization Southall Environmental Associates, Inc. Southall is the lead author of a study published recently in Aquatic Mammals.

The authors originally conducted a major assessment of the way that noise can affect different species of marine mammals in 2007. The recent study revises these numbers to account for new discoveries, including research by co-author Colleen Reichmuth on how seals, sea lions (Otariidae) and sea otters (Enhydra lutris) hear.

They found that many species, such as bottlenose dolphins (Tursiops truncatus), ringed seals (Pusa hispida) and spotted seals (Phoca largha), were less sensitive to noise than previously believed.

Others may be more sensitive to a noisy environment.

They discovered that harbor porpoises (Phocoena phocoena) are more sensitive to a variety of sounds including air guns, which are used in seismic testing by oil and gas exploration companies to look for resources underneath the seabed. They are also sensitive to the types of sounds made by pile-driving equipment used for the construction of offshore wind farms.

These discoveries show that additional mitigation strategies might be necessary in these cases, Southall said, whether it means avoiding certain areas at key times for these species or the use of additional silencing technology.

Excessive underwater noise can cause deafness among sea animals just as it does in humans, Southall said.

Gaps in researchers’ knowledge still remain when it comes to some marine mammals. It’s not exactly easy to put a blue whale (Balaenoptera musculus) in a lab to test its hearing ability, for example, he said. So, for blue whales and other species, the researchers used estimates based on their mass and the biological properties of their hearing systems, or anatomical modeling.

Significant gaps in knowledge also remain for species such as sperm whales (Physeter macrocephalus), and orcas (Orcinus orca), but the researchers believe their level of hearing likely differs from that of other species.