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Studying At-Risk Harbor Seals in Western Aleutians - Post 2

September 20, 2016

Navigating the tide and current to perfectly time a successful first day of sampling.

Grass in foreground, lagoon in middle ground and hills in the distance.

There’s a collective excitement through the entire science team as all four of our inflatable boats rest on a beach outside of Clam Lagoon on Adak Island, Alaska. It’s Sept. 12 and the first day of our research cruise capturing, sampling and releasing a severely reduced population of harbor seals. But patience and precise planning are key. We will only have one chance to catch seals here today; the tides and current mean there’s a narrow window of time when the seals are present and our boats can operate safely.

The science team counted more than 100 seals resting on the sand bar. Photo by Shawn Dahle

The science team counted more than 100 seals resting on the sand bar.

Our program leader, Peter Boveng returns from scouting the haul-out location, where the seals rest on a sand bar. Binoculars in hand and a smile on his face, he says, "there are a lot of seals today.”

Yesterday, Shawn Dahle, the chief scientist for the project, counted more than 100 seals resting on the sand bar. The numbers are similar today. Everyone recognizes with this many seals, we will need to work quickly to get the net ashore and transfer seals out of the net. We’ve decided to catch just 10 seals because that is the maximum we can safely get back to the ship and process in a timely manner.

We’ll use a net cannon, a 24-inch wide and 10-foot long plastic drainage pipe we’ve engineered to help encircle seals in Clam Lagoon. Using the net cannon at the sand bar requires coordination. Peter will drive the boat and another scientist, Heather Ziel, will throw a buoy and anchor. That triggers the net to stream out of the tube, containing seals in a semi-circle just off the haul-out site. The timing has to be just right because the seals see us coming once we enter the lagoon. We need to be fast.

Researchers measure a harbor seal's girth. Photo by Shawn Dahle

Researchers measure a harbor seal's girth

Back outside the lagoon, the lead boat is carrying the net canon and it is carefully navigating under an old wooden bridge but then accelerates into the lagoon. The drivers of the three other inflatable boats follow. Many seals see us coming and move into the water before we get there but the net is being deployed perfectly. About 30 seals are surrounded.

Now, every member of the research team must work to quickly to get the net and seals ashore and, then, sort which seals to sample and which to release immediately. Stacy DiRocco and Jennifer Rego, two veterinary professionals from SeaWorld, have joined us for the cruise. They’re constantly monitoring the seals and are helping us provide the best care. Ten of the seals are transported back to the Norseman, the research vessel we’ve contracted for this study.

The seals are craned on board, weighed and assigned a unique identifier.

The main components of our sampling efforts are: morphometrics, blood and tissue sampling, and attachment of satellite tags. Morphometrics are measurements we take from each animal such as length, girth, and mass. We also use a portable ultrasound machine to measure blubber depth. These values provide information on the overall condition of seals in the area.

After we measure the animals, we collect blood and tissue samples. The blood samples provide information into the health status of the animal and provide insights about contaminant exposure and what the animals are eating. We also swab the nose, collect hair, and take a small amount of tissue for genetic analysis.

Two satellite tags are typically attached to the seals. One is attached to the webbing of the rear flipper and is designed to provide basic location and haul-out behavior for more than a year. The other tag provides higher resolution location data and information on dive behavior. This tag is attached to the hair on the head with super glue. We hope the tag will remain on the animal until next summer when seals shed and grow a new coat.

Throughout this time, the seals are closely monitored by one of our veterinary professionals. To help ease stress on the animals and for the safety of our researchers (seals have sharp teeth and they can bite), each animal is given a sedative similar to valium. The procedures can take anywhere from 45 minutes to an hour. Once completed the seal is carefully moved to an opening on the side rail of the ship where they can leave on their own accord. Most seals take a while to look around and get their bearings. Then, they're back in the water and heading for home.

Meet the Bloggers


Shawn Dahle

Shawn Dahle is a biologist at the Alaska Fisheries Science Center’s Marine Mammal Laboratory. Shawn joined the Lab's Polar Ecosystems Program in 2002 after completing his M.S. in Fisheries Conservation at the University of Minnesota. His research focuses on population monitoring and status assessments of seals in Alaska.






Josh London

Josh London is a wildlife biologist at the Alaska Fisheries Science Center’s Marine Mammal Laboratory. He focuses on population assessment and ecology of harbor seals and ice seals. Josh received a B.S. and Ph.D. from the University of Washington.







Peter Boveng

Peter Boveng is the leader of the Polar Ecosystems Program for research on harbor seals and ice-associated (ringed, bearded, spotted, and ribbon) seals in Alaska. His primary research interests are in the estimation of fundamental quantities for population assessment, such as abundance, trends, and vital rates, and in satellite telemetry studies of movements, distribution, and foraging behavior. Peter received Ph.D. and M.S. degrees in biology from Montana State University and a B.A. from Cornell University.



Heather Ziel


Heather Ziel is a research biologist at the Alaska Fisheries Science Center's Marine Mammal Laboratory. She works in the Lab's Polar Ecosystems Program.