Using DNA Mark-recapture to Estimate Population Parameters of the Louisiana Black Bear in the Upper Atchafalaya River Basin

The Louisiana black bear (Ursus americanus luteolus) was listed under the U.S. Endangered Species Act as Threatened in 1992. The U.S. Fish and Wildlife Service cites loss of habitat as the primary cause of population decline, along with human-related mortality as a secondary cause. One of the delisting criteria in the Recovery Plan for the Louisiana black bear is that two of the three subpopulations must be viable, one in the Tensas River Basin and one of the two in the Atchafalaya River Basin. To determine population viability, accurate estimates of basic population parameters including abundance, growth rate, density, and apparent survival are necessary. My study will assess the status of the subpopulation located in the Upper Atchafalaya River Basin based on non-invasive DNA mark-recapture techniques. Hair samples were collected beginning in summer 2006, and I will continue to collect data annually through 2011 using barbed-wire sampling sites. Thus far, we have collected 6,414 samples from 115 sites. Of those, we have analyzed 586 samples representing 81 individuals (46 F : 35 M). Data from the first three summers of collecting suggested a sex ratio skewed toward females but trail cameras revealed that large bears (probably males) were able to step over the wire without leaving a hair sample. In an attempt to reduce this capture heterogeneity, we switched to a two-wire system in 2010. The ratio of identified females to males subsequently increased from 1:0.5 to 1:0.75. We will use a spatially explicit model to estimate density and a robust design Huggins full heterogeneity model in Program MARK to estimate population parameters for the viability analysis.

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