The National Oceanic and Atmospheric Administration said continuing current fishing practices will likely jeopardize the existence of Stellers in the western Aleutians.
The agency has ordered reduced catches of Atka mackerel and Pacific cod -- the main source of food for Steller sea lions -- as of Jan. 1. Fishing also will be closed in some important feeding areas for Stellers.
Another measure imposes a 3-mile buffer zone around a newly established rookery.
The measures apply only to the western population of Stellers, listed as endangered under the Endangered Species Act.
According to National Marine Fisheries Service scientists, the western population of Steller sea lions is either declining or failing to recover in the western and central Aleutian Islands. The most serious decline is in the most westernmost area, where numbers fell 45 percent between 2000 and 2008.
About 45,000 sea lions lived on the western Aleutian Islands in 2008, compared with perhaps 250,000 in the late 1960s and early 1970s. They were listed as endangered in 1997 under the Endangered Species Act.
Fishermen harvest more than 4 billion pounds of fish from the Bering Sea, Aleutian Islands and Gulf of Alaska each year. Most of the world's sea lions live along Alaska's vast coastline.
NOAA said the eastern population of Steller sea lions is doing better and may have recovered enough to come off the endangered species list. Alaska, Washington and Oregon petitioned for the delisting.
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