Eavesdropping on spotted seals

I still remember the first time I saw a spotted seal in the wild. I had traveled from sunny Santa Cruz, California to Kotzebue Sound, Alaska to do field work and, that first evening, walked to the edge of town at sunset. I noticed movement in the water and, moving closer, saw dozens of spotted seals swimming and splashing around, likely hunting for their dinner by crowding schooling fish against the seawall. I watched these seals until the light faded and my California-adapted fingers and toes went completely numb. The image has never left me, and neither have the questions it inspired: How do these seals survive in Arctic waters? How do they navigate, forage, and communicate with one another as they migrate with the pack ice between the Bering and Chukchi seas?

Spotted seals live in harsh, remote habitats that are difficult for researchers to access, and little is known about their biology or behavior. Luckily, at the Alaska SeaLife Center we have the unique opportunity to work with two spotted seals—Amak and Tunu—who stranded as pups in 2010 and were then rescued and rehabilitated. Amak and Tunu are no strangers to science. Most recently, this playful duo has been helping us learn about the physiology and energetic requirements of spotted seals in the wild. Prior to that, during a research sabbatical at the University of California Santa Cruz, these two little guys taught us that spotted seals have incredibly sensitive hearing both above and below the water’s surface. In fact, amazingly, they hear nearly as well in air as fully terrestrial mammals like cats, and nearly as well in water as fully aquatic mammals like dolphins. But what are these seals listening for?

spotted_seal_vocalization
Spotted seal vocalization

In the marine environment, sound travels much farther than visual cues. As a result, many marine mammals rely on sound to gain information about their environment, search for prey, avoid predators, and communicate with others of their species. For seals, underwater vocalizations may play an important role in communication, especially during the breeding season. Male seals like Amak and Tunu (pictured above) may vocalize to attract mates or to establish dominance. Up until now, little has been known about the vocal behavior of this species…but these two seals are helping us—yet again—to learn more.

Along with our team in Santa Cruz, I have been monitoring their vocal behavior since Amak and Tunu were just 5 months old, giving us the rare opportunity to track vocal development from its early beginnings. We have already learned a lot about what sorts of sounds spotted seals make, when they are most likely to vocalize, and how the patterns of their vocalizations change as they grow older. Amak and Tunu will be 7 this April, and their next breeding season is approaching. We expect them to have plenty to say! Last week, research manager Brandon Russell and the dive team at the SeaLife Center placed an underwater acoustic recorder in the large seal exhibit where Amak and Tunu currently live, so that we don’t miss a thing. This autonomous recorder provides us with details about the seasonal timing of their sound production and high quality recordings of their vocalizations — information that cannot readily be obtained in the open sea.

diver_deploying_acoustic_recorder
Diver deploying an underwater acoustic recorder in the large seal exhibit

When I think back to my first encounter with spotted seals, I realize how much we have learned since then about their sensory biology, their physiology, and their behavior. Although we still have so much to discover, we are learning more each day thanks to our research partners, Amak and Tunu, and the rare glimpses they give us into the underwater world of spotted seals.

(This research is being conducted under NMFS Permit No. 18902)

Written by: Dr. Jillian Sills

 

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