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Great Basin Redband Trout

2010 Results

The summer 2010 field season was the fourth 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 83% 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 272 sites across the 2,340 km sample frame (potential summer distribution) of Great Basin redband trout. The final calibrated population estimates ranged from 18,000-277,000 at the SMU scale and from 300-37,000 at the population-scale. The precision of these estimates ranged from 22% to 167% 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   13 17,982 10,011 25,953 44 % 1.35
Chewaucan   30 131,995 82,906 181,085 37 % 1.29
Fort Rock   27 33,548 25,474 41,623 24 % 0.68
Malheur Lakes   36 277,354 150,006 404,701 46 % 1.04
Goose Lake   87 48,862 37,717 60,007 23 % 1.27
  Drews 20 10,630 5,507 15,753 48 % 1.47
  Dry 4 287 5 765 167 % 1.73
  Eastside 21 14,599 11,450 17,747 22 % 0.60
  Thomas 22 18,191 10,293 26,088 43 % 1.34
  West Goose 20 5,156 111 10,200 98 % 2.47
Warner Lakes   79 63,905 44,222 83,587 31 % 1.49
  Deep 30 37,227 19,498 54,955 48 % 1.58
  Honey 20 11,657 6,884 16,431 41 % 1.19
  20mile 29 15,021 7,927 22,114 47 % 1.51

 

MAPS & CHARTS

SMU

Length Frequency

Site Status

Site Density

Other Species

Catlow Valley 1+ > 75mm Catlow Status Catlow Density Catlow Species
Chewaucan 1+ > 63mm Chewaucan Status Chewaucan Density Chewaucan Species
Fort Rock 1+ > 61mm Fort Rock Status Fort Rock Density Fort Rock Species
Malheur Lakes 1+ > 65mm Malheur Lakes Status Malheur Lakes Density Malheur Lakes Species
Goose Lake 1+ > 68mm Goose Lake Status Goose Lake Density Goose Lake Species
Warner Lakes 1+ > 66mm Warner Lakes Status Warner Lakes Density Warner Lakes Species
All SMUs CDF and Density Histograms

 

Contact Stephanie Miller or Steve Jacobs with questions or comments.

 

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