Use of depletion electrofishing and a generalized random tessellation stratified design to estimate density and abundance of redband trout in the northern Great Basin. Meeuwig, M., H. & Clements, S., P. Technical Report 2014.
Use of depletion electrofishing and a generalized random tessellation stratified design to estimate density and abundance of redband trout in the northern Great Basin [pdf]Paper  Use of depletion electrofishing and a generalized random tessellation stratified design to estimate density and abundance of redband trout in the northern Great Basin [link]Website  abstract   bibtex   48 downloads  
Redband trout (Oncorhynchus mykiss newberrii) in the Great Basin occupy a landscape characterized by spatial and temporal variability in environmental conditions that likely influences their abundance. Developing long-term monitoring protocols and effective conservation plans will require an understanding of spatial and temporal variability in abundance of redband trout as well as an understanding of the balance between sampling intensity and precision of empirical data. The objectives of this study were to 1) quantify the abundance and distribution of redband trout at two putative demographic scales over a six- year period in the northern Great Basin and 2) quantify variability in the sampling data to help guide development of conservation and monitoring plans for redband trout in the northern Great Basin. We used a generalized random-tessellation stratified design to select spatially well-distributed sample sites at the population and species management unit (SMU) scales. We conducted depletion electrofishing at about 30 to 40 sample sites within each of six SMUs annually from 2007 through 2012 and at about 30 sample sites per population within each SMU twice during the six year study. Electrofishing data were used to calculate site level density and abundance estimates that were extrapolated to the population and SMU levels. The abundance of redband trout varied from 1,716 to 191,690 among populations and from 17,709 to 566,514 among SMUs during the six years. Abundance was generally stable within populations and SMUs over the six-year study; however, inter-annual variation was observed in some populations and SMUs. We predicted that about 16 and 71 sample sites would need to be sampled at the population and SMU levels, respectively, to achieve desired levels of precision of abundance estimates (i.e., ≤ 80% and ≤ 40% relative confidence index at the population and SMU levels, respectively). Sampling intensities of > 60 and 100 sample sites at the population and SMU levels, respectively, result in little benefit in our ability to detect change in redband trout density using the current approach. Additionally, variability in point estimates of redband trout density did not decrease substantially at sampling intensities greater than about 20 sample sites at the population and SMU levels.

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