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Great Basin Redband Trout

2011 Results

The summer 2011 field season was the fifth of six sampling efforts to assess the distribution and abundance of redband trout in the six interior basins of Oregon’s high desert.  Abundance was evaluated at the Species Management Unit (SMU) level for the Chewaucan, Fort Rock, Malheur Lakes, and Catlow Valley SMUs and at the population level in Goose Lake and Warner Valley SMUs.

Sites were randomly selected using EPA's Generalized Random Tessellation Stratified design protocol. We selected 30 sites for the Chewaucan, Fort Rock and Catlow Valley SMU’s and 40 sites in the Malheur Lakes basin.  We also selected 30 sites for each population assessed in the Goose Lake and Warner Valley, except the Thomas-Bauers Complex and Dry populations in Goose Lake had 40 and 20 sites, respectively.  Actual number of sites sampled approached but did not completely meet these targets. However, we were able to sample nearly 73% of selected sites across the range of each SMU. Extensive efforts (public meetings, letters, personal phone calls and visits) were made to obtain permission to access sites located on private property.  Field methods used to sample each site were the same as those used in 2007.

Length frequency analysis was used to categorize redband trout as either age 0 or age 1+ fish.  Separate age-class designations were made in each of six SMUs. Population estimates for age 1+ redband trout in each SMU were extrapolated from estimates of fish density at sample sites.  A calibration factor, calculated from the mean ratio between the depletion and mark-recapture density estimates at all sites where both methods were employed, was applied to estimates for all SMUs.

Depletion estimates were completed at 289 sites across the 2,340 km sample frame (potential summer distribution) of Great Basin redband trout. The final calibrated population estimates ranged from 15,000-402,000 at the SMU scale and from 20,000-86,500 at the population-scale. The precision of these estimates ranged from 17% to 50% and varied relative to the between-site variability (CV) and sample size for each sample stratum.  Densities estimated at individual sites were highly variable (density histograms).

 

 

RESULTS

SMU Population n Estimate Lower
95%
Confidence Limit
Upper
95%
Confidence Limit
Relative
95%
Confidence Interval
CV
Catlow Valley   19 34,486 19,106 49,865 45 % 0.97
Fort Rock   29 15,302 9,913 20,691 35 % 0.97
Chewaucan   28 176,623 97,126 256,120 45 % 1.33
Goose Lake   29 54,162 35,540 72,784 35 % 0.88
Warner Lakes   29 188,930 96,984 280,876 49 % 1.36
Malheur Lakes   158 401,835 334,265 469,406 17 % 1.15
  Blitzen 26 54,223 39,372 69,074 27 % 0.79
  East Burns 25 47,131 23,672 70,591 50 % 1.49
  McCoy 26 86,412 53,037 119,787 39 % 1.31
  Riddle 25 45,894 36,089 55,699 21 % 1.07
  Silver 30 19,852 11,811 27,892 41 % 1.67
  Silvies 26 148,323 98,122 198,524 34 % 1.05

 

MAPS & CHARTS

SMU

Length Frequency

Site Status

Site Density

Other Species

Catlow Valley 1+ > 61mm Catlow Status Catlow Density Catlow Species
Chewaucan 1+ > 65mm Chewaucan Status Chewaucan Density Chewaucan Species
Fort Rock 1+ > 73mm Fort Rock Status Fort Rock Density Fort Rock Species
Malheur Lakes 1+ > 75mm Malheur Lakes Status Malheur Lakes Density Malheur Lakes Species
Goose Lake 1+ > 55mm Goose Lake Status Goose Lake Density Goose Lake Species
Warner Lakes 1+ > 56mm Warner Lakes Status Warner Lakes Density Warner Lakes Species
All SMUs CDF and Density Histograms

 

Contact Shaun Clements with questions or comments.

 

Send comments or questions regarding this webpage to  Shaun.Clements@oregonstate.edu