From: Tim Stephens, University of California – Santa Cruz
Published February 28, 2014 03:26 PM

And the spotted seal said, "Say whaaaat?"

Two spotted seals orphaned as pups in the Arctic are now thriving at UC Santa Cruz's Long Marine Laboratory, giving scientists a rare opportunity to learn about how these seals perceive their environment. In a comprehensive study of the hearing abilities of spotted seals, UCSC researchers found that the seals have remarkably sensitive hearing in both air and water.

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The findings, published February 26 in the Journal of Experimental Biology, are important for understanding how spotted seals might be affected by noise from human activities in the rapidly changing Arctic environment. Reductions in sea ice due to climate change have led to increased shipping and industrial activity in the Arctic, including oil and gas exploration. Coauthor Colleen Reichmuth, director of the Pinniped Cognition and Sensory Systems Laboratory at UCSC, said few studies have been done on Arctic seals, which include the spotted seal, ringed seal, bearded seal, and several other species.

"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 said.

Using a specialized acoustic chamber to test the spotted seals' hearing, the researchers measured the lowest hearing thresholds ever recorded for a marine mammal in air. "In their range of most sensitive hearing, they can detect airborne sounds as well as terrestrial carnivores, like cats and dogs," said Jillian Sills, a graduate student in ocean sciences at UC Santa Cruz and first author of the paper. This makes sense, because the seals have to be vigilant for predators such as polar bears when they haul out on the ice, which they do to rest, molt, give birth, and nurse their pups.

In water, the range over which the spotted seals' hearing is most sensitive covers a remarkable seven octaves. In fact, they hear almost as well in water as fully aquatic species such as dolphins and porpoises. While the cetaceans have better sensitivity to higher-frequency sounds, the seals hear better at lower frequencies. "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," Sills said. 

The researchers also looked at how noise in the environment can interfere with seals' hearing. This "masking data" can be used to estimate, for example, the size of the zone around a noise source within which a seal would be unable to hear another seal some distance away. "Quantitative estimates of zones of masking around particular noise sources are relevant for management decisions about the potential effects of noise on hearing," Sills said.

Read more at University of California - Santa Cruz.

Spotted seal image via Shutterstock.

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