Research calculates survival rates of sea lions

Posted: Monday, July 07, 2008

Researchers aboard the Norseman departed Dutch Harbor on June 24 on a voyage to monitor Steller's sea lion populations.

The team, headed by Lowell Fritz, will be stopping during a three week voyager to Seward to gather data on sea lions tagged between 2000 and 2003.

"We're doing this so we can calculate survival rates of animals, at least up until 8 years old. We also look for adult females with pups so we can calculate reproductive rates," Fritz said.

Fritz has been working with Steller's sea lions since 1990. He has been monitoring the survival and reproductive rates since initially tagging pups in 2000. The data was gathered to look at trends in the population and survivorship.

An aerial survey is also being conducted. An aircraft will begin taking photographs of rookeries in Southeast Alaska and will travel up through the Aleutians.

"That's our index of change in the population. We use that as our thumb on the pulse of the population. How the adult and juvenile population change over time and the branding gives us the details of how the juvenile and adult survivorship is changing over time," Fritz said.

Fritz said a major change in population began in the 1980s with a steep drop in juvenile survival. He attributed the decline to various issues, including both legal and illegal shooting, incidental take in fisheries, changes in the environment and an increase of fishing. In recent years, the survivorship has stabilized.

"We're seeing a decline in reproduction, and that's probably contributing to the stability we're seeing now. Good survivorship, but not a lot of reproduction. They're kind of just hanging on and not increasing like we think they should," Fritz said.

The study is run by the National Marine Fisheries Service and makes biannual runs through the Aleutians to gather information about the tagged sea lions.

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