Annual calf indices for Beluga whales (Delphinapterus leucas) in Cook Inlet, Alaska 2006-2010
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Annual calf indices for Beluga whales (Delphinapterus leucas) in Cook Inlet, Alaska 2006-2010
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    "Beluga whales (Delphinapterus leucas) in Cook Inlet, Alaska, form an isolated, depleted population that is now listed as endangered. One monitor of population health is through documenting calving rates. This study provides an index of the number of calves seen in Cook Inlet in August. Although the August survey is the focus for the calf index, given most births are thought to occur by late July, data collected during the annual June abundance survey are used for comparison. Analyses cover the period from 2006 to 2010 (a feasibility and techniques study occurred in August 2005). Systematic aerial surveys covered primary habitat for belugas in Cook Inlet, and paired video cameras provided images used in laboratory analysis. A total of 44 groups of whales from the August surveys were examined, of which most contained images of calves that were identified by color (darker than adults), small size, and proximity to adults. Among these whale groups, 688 usable images were found and examined. By rating inter-whale proximity in five categories, and estimating the ages represented, we developed criteria for recognizing young calves, an index that represents primarily young-of-the-year calves, and a second index that represents young-of-the-year, yearling calves, and some young juveniles. It appears that more calves were born in 2006 (12%) than in subsequent years (2007-2010 ranged from 0.5% to 3%). However, these calving rates have several potential biases and should be used for trend analysis only, not for absolute estimates of calf production. Overall, the 5-year average (2006-2010) birth rate was 3.6%. With mortality rates per year of roughly 3% or more (based on counts of beach-cast carcasses), this would suggest that the birth rate estimated here is probably at or below the replacement level necessary for recovery of this population"--Abstract.
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