Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
AK PENINSULA/ BECHAROF: Cooperative Project Identifies Critical Component of Caribou Decline
Alaska Region, November 30, 2007
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The Alaska Peninsula comprises a mosaic of state, private, Alaska Native Corporation, and federal lands where the Northern Alaska Peninsula caribou herd (NAPCH) ranges from the southern extent of their distribution near Port Moller to their wintering grounds over 200 miles north along the Naknek River.  The Alaska Peninsula and Becharof National Wildlife Refuges comprise over 4 million acres along the Alaska Peninsula providing important summer and winter habitats for this caribou herd.  The NAPCH is an extremely important subsistence resource to local residents as well as to recreational users from around the world.

The size of the NAPCH has historically fluctuated extensively reaching peaks of more than 20,000 animals in the early 1940s and late 1980s.  However, annual population counts of the NAPCH have declined significantly since the early 1990s.  Decreased range conditions, disease, predation, and parasitism have been identified as potential factors causing the current decline of the NAPCH.  Although the negative impact of these factors has likely been cumulative in nature, the discrete effects of specific factors have not yet been fully evaluated.

Calf survival is a fundamental factor affecting the growth and stability of all caribou herds.  In an effort to evaluate calf survival in the declining NAPCH, the Alaska Peninsula and Becharof Refuges initiated a cooperative study with the Alaska Department of Fish & Game (ADF&G) in 2005.  During this three-year study, ADF&G and Refuge biologists captured and monitored NAPCH calves through critical life stages.  Completed in 2007, this project is only one component of a large-scale cooperative effort between the two agencies to identify important factors limiting caribou numbers on the Alaska Peninsula. 

Caribou calf survival is typically low during the first two weeks of life, after which survival typically increases dramatically as calves grow and become able to outrun predators.  Calf survival during the first two weeks of life was low during all three years of the NAPCH study with only 42 percent (2005), 43 percent (2006), and 19 percent (2007) of calves reaching the critical two-week milestone.  As is consistently observed in Alaskan caribou herds, predation by wolves, brown bears, and other predators was the leading cause of calf mortality during the first two weeks of life.  However, extended monitoring beyond this critical period indicates that calf survival in the NAPCH does not increase after two weeks of age, as would typically be expected.  These findings highlight the importance of calf survival in the NAPCH after the two-week period and indicate that calves in the NAPCH might not develop as rapidly as in other caribou herds due to nutritional stress as a result of poor range conditions or the effects of parasitism.  The specific causes for the observed low calf survival after calves reach two weeks of age are currently being investigated. 

A summary of the three-year study was recently presented to the Bristol Bay Subsistence Regional Advisory Council at a public meeting held in Naknek, Alaska.   

Contact Info: Kristen Gilbert, 907-786-3391, Kristen_Gilbert@fws.gov
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