Beaver ecology in Bridge Creek, a tributary to the John Day River Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bk128f00z

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  • The American beaver (Castor canadensis) was nearly extirpated by the late 1800's due to the fur trade. Due to reintroduction efforts, it now occupies much of its former range. Beavers are a keystone species and ecosystem engineers, greatly influencing riparian and instream habitats through selective harvesting of plant materials and dam building. Beaver dams can accelerate the recovery of stream and riparian habitats. These habitats are beneficial to a variety of wildlife, including some fish species. Relocating nuisance beavers to areas where their damming activity will benefit fish habitat by helping restore degraded streams is gaining interest as a restoration and management tool in Oregon. However, little is known about the extant beaver populations in Oregon, including in the areas of restoration interest. We used genetic and radio telemetry approaches together to investigate the ecology of beavers in Bridge Creek; the site of a project partnering with beaver to aid in restoration efforts. Radio telemetry was used to estimate the home range size, habitat use, and survival rates for beavers in Bridge Creek and mitochondrial DNA was used to investigate the genetic diversity of beavers in Bridge Creek. In order to put the genetic diversity of this watershed in the historical context of beaver management in Oregon, we used samples from the John Day River upstream of the Bridge Creek confluence and samples from another study being conducted in western Oregon. These samples together would represent a broader context of the western and eastern parts of Oregon, on both sides of the Cascade Range. We tracked 24 radio tagged beavers in the summer of 2011 and 22 beavers in the spring of 2012 to estimate home ranges. The mean linear home range length was 1.56 ± 0.71 km. Home ranges did not differ by sex or age except for spring 2012; female home ranges were longer than males. Home ranges encompassed nearly the entire study area of Bridge Creek and in some cases overlapped. Habitat use showed that beavers used areas of grasses and herbaceous vegetation in greater proportion to its availability for spring 2012 but did not deviate from random in summer 2011. The survival rate was estimated to be 0.92 ± 0.05 for the entire 18 month study period. While radio tagging captured beavers, a tissue sample was taken for mitochondrial DNA genetic analysis. Genetic diversity was very low for the samples from Bridge Creek beavers, and therefore we were unable to discern any genetic structuring. Eastern Oregon samples overall (Bridge Creek and John Day samples) had a low nucleotide and haplotype diversity (0.001 ± 0.001, 0.441 ± 0.056 respectively) while western Oregon samples had a higher nucleotide and haplotype diversity (0.003 ± 0.002, 0.546 ± 0.098 respectively). The two subpopulations were significantly differentiated from each other (P < 0.001, pairwise F[subscript ST] = 0.499). The information gained on the survival, home range, habitat use, and genetic diversity of beavers in Bridge Creek is important in assisting managers; partnering with beaver to meet their stream restoration goals. Although beaver relocation is an attractive tool for alleviating nuisance beaver issues while potentially restoring fish habitat, our results indicate that Bridge Creek may not be able to support more beavers in its current condition. Additional research on the social structure, through the use of microsatellites, and continued year-round monitoring of beavers within Bridge Creek and the greater John Day basin will further inform managers on the feasibility of the use of beavers as a stream restoration tool.
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