Story last updated at 7:06 PM on Wednesday, March 22, 2006

National Marine Mammal Laboratory studies seals

By Robert Montgomery,
Peter Boveng and Josh London

In 2003, the National Marine Mammal Laboratory, with support from Minerals Management Service and the Kachemak Bay Research Reserve, began investigating the behavior and population dynamics of Cook Inlet’s harbor seals (Phoca vitulina richardsi). The study has three main objectives:

* Conduct aerial surveys to understand seasonal changes in the abundance of harbor seals in the inlet.

* Establish remote camera systems at specific sites to determine how harbor seal haul-out behavior is influenced by weather and tide conditions.

* Capture harbor seals and attach satellite transmitters to understand how harbor seals use aquatic and terrestrial habitat throughout the inlet.

We performed aerial surveys from 2003-2005 during April, June, August and October. These surveys covered all areas of central and lower Cook Inlet from the Forelands in the north to the Barren Islands in the south. We divided this expansive region into two routes and chartered planes from Northwind Aviation, Suburban Air Freight and Commander Northwest. When harbor seals were observed at haul-out sites we recorded the location with a GPS unit and took photographs of the animals. The number of seals in each photo were later counted in the laboratory.

From this study we have learned that there are definite seasonal changes in the abundance of harbor seals in the inlet. Harbor seal abundance peaks during June and August when seals are giving birth and molting their fur. The abundance of harbor seals is lowest in October with only slightly higher numbers in April. Further work is under way to determine the overall population size of harbor seals in the central and lower inlet.

Remote camera systems were constructed from commercially available parts and installed at various locations in the inlet. Systems were placed near Aurora Lagoon, on the bluff overlooking Troublesome Creek and on the south end of Augustine Island. The camera systems were programmed to shoot one digital photograph every hour during daylight.

We are currently in the process of counting each image to determine how the number of harbor seals on shore is influenced by weather and tide conditions. With this analysis we will better understand how harbor seals react to rain, temperature, high winds and rising tides.

Between 2004 and 2006 we performed four capture trips in the inlet during October and May. In total, we have attached satellite transmitters to more than 60 seals. Each transmitter was glued to the fur on the back of the harbor seal using durable epoxy. The transmitters fall off when the harbor seal molts in the autumn and have no known effects on the animal.

These tags transmit signals to satellites which link up to our personal computers allowing us to analyze data on the location and dive depths of seals in real time. This aspect of the monitoring program has provided us with an invaluable look at the daily life of a harbor seal in the inlet. This data will help answer questions about the way harbor seals travel in the inlet and how much time they spend at sea and on land.

Robert Montgomery is a wildlife biologist who has worked on the Cook Inlet harbor seal project for the last three years. Peter Boveng is the principal investigator and Josh London is the project leader of the harbor seal studies. All three are based in the Alaska Fisheries Science Center in Seattle. To learn more about the National Marine Mammal Laboratory, please visit

If you have questions about Kachemak Bay, contact reserve staff at 235-4799 or visit the Web site at

Bay Science is a project of the Kachemak Bay Research Reserve.