The U.S. Geological Survey (USGS) was recently asked by the U.S. Fish & Wildlife Service (USFWS) to evaluate the status of Marbled Murrelets in Alaska and British Columbia. The Marbled Murrelet is a small diving seabird that resides in coastal waters of the North Pacific from central California to the western Aleutian Islands and Bering Sea. The species nests primarily on moss-covered branches of old-growth conifers, such as hemlock, firs and spruce.
Losses of nesting habitat to logging led the USFWS to list the Marbled Murrelet in the Lower 48 states as threatened under the Endangered Species Act in 1992. The status of murrelets in Alaska and British Columbia was of interest to ongoing deliberations on the status of the Marbled Murrelet in the lower 48.
The principal finding of the report is that Marbled Murrelet populations in Alaska and British Columbia appear to have declined within the past 2 decades. Compiling available information on abundance of Marbled Murrelets in Alaska, USGS estimated that in the recent past, Marbled Murrelets in Alaska numbered about 1 million birds. USGS examined trend information from at-sea surveys at sites spanning a wide geographic range in Alaska. USGS found that murrelet populations declined at 5 of 8 sites.
For British Columbia, the historic population size of Marbled Murrelets is unknown. Trend information from sites in the Haida Gwaii (Queen Charlotte Islands) and Vancouver Island showed that population declines of similar magnitude had also occurred.
The USGS concluded that the declines were likely the result of the combined and cumulative effects of human activities, such as logging, gillnet bycatch and oil pollution, and natural factors, such as climate-driven changes in oceanographic patterns and predation.
USGS estimated the amount of potential murrelet nesting habitat that has been lost due to timber harvest. In southeast Alaska, for example, USGS estimated that about 15% of potential nesting habitat has been lost. For British Columbia, they estimated that 33 to 49% of potential murrelet nesting habitat has been lost. Habitat loss in some areas has been accompanied by increases in avian predators of murrelets, such as eagles, jays and ravens.
The USGS report also updated information on the genetic structure of Marbled Murrelet populations and reviewed studies on the species' nesting and feeding biology. The report is now available on the web at http://pubs.water.usgs.gov/ofr20061387.
The lead author of the report is Dr. John Piatt, seabird ecologist with the Alaska Science Center. His 9 co-authors included Dr. Kathy Kuletz (U.S. Fish and Wildlife Service), Dr. Alan Burger (University of British Columbia), Drs. Tim Birt and Vicki Friesen (Queens University), Dr. Scott Hatch (USGS Alaska Science Center), Dr. Gary Drew (USGS Alaska Science Center), Ann Harding (Alaska Pacific University), and Mayumi Arimitsu and Kirsten Bixler (USGS Alaska Science Center).
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