spotted seal
February 28, 2014

Increased Human Activity Could Impact Arctic Spotted Seals

Brett Smith for - Your Universe Online

A new study from researchers at the University of California at Santa Cruz has provided additional details on the hearing capabilities of spotted seals, which are being exposed more and more to shipping noise as global warming has opened up lanes through the Arctic.

"These spotted seals actually hear much better in both air and water than was previously thought based on earlier data for harp seals and ringed seals," said study author Jillian Sills, a graduate student in ocean sciences at UC Santa Cruz.

The shrinking of Arctic sea ice due to climate change has led to greater human activity in the Arctic, the research team noted. Study author Colleen Reichmuth, director of the Pinniped Cognition and Sensory Systems Laboratory at UCSC, said her team was trying to determine just how sensitive Arctic seals might be to noise created by human activity.

"We wanted to develop a better understanding of how Arctic seals use sound in their environment and how human intrusions and other changes in that environment may influence them," Reichmuth UCSC's Tim Stephens.

In the study, which was published in the Journal of Experimental Biology, researchers used an acoustic chamber to measure the spotted seals' hearing both in and out of water. The team found that seals were able to hear a four-octave range in the air and a seven octave range underwater.

"In their range of most sensitive hearing, they can detect airborne sounds as well as terrestrial carnivores, like cats and dogs," Sills said.

In the water, the spotted seals’ hearing compares favorably to cetaceans such as dolphins and porpoises. While these marine mammals have excellent hearing for higher register sounds, the seals’ hearing is more calibrated for lower sounds.

The researchers also looked at how ‘masking’ noise in the surrounding environment can disrupt seals' hearing. They found that spotted seals react to masking noise in much the same way as harbor seals, a more-researched temperate species.

"Our findings suggest that we can probably apply much of what we know about harbor seals to spotted seals,” Sills said. “For harbor seals, we know a lot more about how different types of sounds interfere with hearing, and how their hearing sensitivity can be reduced after exposure to very loud sounds.”

"We don't know as much about behavioral effects as we would like to because it's so difficult to do research in the Arctic,” she added. “At least now we are starting to learn about the hearing sensitivity of these seals, which is a first step toward understanding how they perceive sound in air and water, and how they might be influenced by increasing noise levels.”

"Because they're hunting under water and living in dark conditions for parts of the year, we assumed that hearing would be an important sensory modality," Reichmuth said.

Sills added that potential impacts of noise on ice seals must be assessed along with other threats.

"It's difficult to separate out impacts from multiple sources,” she said. “These animals will have to deal with the combination of multiple changes in their environment happening at the same time.”