Population studies of desert redband trout


Schill, Daniel J.. (2009). Population studies of desert redband trout. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Population studies of desert redband trout
Schill, Daniel J.
Columbia River redband trout--Idaho--Snake River South Fork Watershed
Natural Resources
Redband trout residing in Snake River basins of southwest Idaho are the least studied of Idaho salmonids. In this study, I estimate the exploitation rate and various life history parameters for a range of Idaho high desert populations, investigate appropriate aging techniques, quantify reproductive demographics, compare growth between sexes, and build predictive models that relate habitat parameters to first year growth rate and length at maturity. The latter model is used along with density estimates from 595 randomly selected sites to estimate total population sizes and mature adult abundance. These data, and Ne/NAdult ratios derived via stochastic population simulations are used to approximate effective population size in roughly half the identified sub-populations. Desert redband trout in southern Idaho streams are virtually unexploited by anglers. Otoliths proved an accurate aging structure for redband trout while scales were both inaccurate and imprecise. Lack of multi-species study designs evaluating otolith growth patterns and zonation via formal research hypothesis testing has resulted in longstanding confusion about the timing and meaning of otolith zone formation in fishes. Several such hypotheses are advanced. Abiotic stream parameters such as stream order and conductivity can be used to predict maturity status of individual trout across the study area. Females grow slower than males and natural mortality rates are similar to that reported in montane rainbow trout stocks. Stream temperature and elevation explain the majority of observed variation in age 1 growth. Desert redband trout grow primarily in the fall and spring with growth cessation in mid-winter and in mid-summer due to unfavorable temperatures. Extrapolation resulted in conservative total abundance estimates of nearly a million trout (greater than or equal to) 100mm in total length across the study area and about a quarter million mature adults. Effective population size (Ne) for sub-populations ranged from 38 to 41,000 with all but three exceeding 1000. Although a final assessment regarding the prevalence of introgression is necessary, results suggest that existing desert redband trout populations are not at risk in the near term when evaluated by common rules of thumb. However, a sizable annual trend monitoring program should be developed for representative desert redband trout sub-populations.
Thesis (Ph. D., Natural Resources)--University of Idaho, 2009.
Major Professor:
George LaBar.
Defense Date:
Format Original:
xii, 180 leaves :ill., maps ;29 cm.

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