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Great Basin Redband Trout

2009 Results

The summer 2009 field season was the third 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 Catlow Valley, Goose Lake, Malheur Lakes, and Warner Valley SMUs, and at the population level in Chewaucan and Fort Rock SMUs.

Sites were randomly selected using EPA's Generalized Random Tessellation Stratified design protocol. We targeted 30 sites for the Goose and Warner Lakes SMU’s, 40 sites in the Malheur Lakes, and 20 sites in the Catlow Valley SMU.  We also targeted 30 sites for each population assessed in the Chewaucan and Fort Rock basins. Actual number of sites sampled approached but did not completely meet these targets. However, we were able to sample nearly 75% 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.  Because they are not completely vulnerable to our gear, age-0 fish were not included in our estimates. Separate age-class designations were made in each of the six SMUs. Population estimates for age-1+ redband trout in each SMU were extrapolated from depletion estimates of fish density at sample sites.  A calibration factor was applied to estimates to adjust for the bias associated with depletion estimates. The calibration factor was calculated as the mean ration between depletion and mark-recapture estimates at a subsample of sites where both methods were employed.

Depletion estimates were completed at 218 sites across the 2,340 km sample frame (potential summer distribution) of Great Basin redband trout. The final calibrated population estimates ranged from 16,000-400,000 at the SMU scale and from 1,000-150,000 at the population-scale. The precision of these estimates ranged from 15% to 45% 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 9 15,869 7,767 23,971 51 % 0.98
Goose   29 45,294 24,907 65,680 45 % 1.02
Malheur Lakes   31 398,478 273,487 523,468 31 % 0.80
Warner Lakes   30 129,569 82,004 177,134 37 % 1.16
Chewaucan   65 130,180 98,488 161,872 24 % 1.05
  Chewaucan 24 118,458 86,956 149,959 27 % 1.03
  Crooked 22 9,776 6,408 13,144 35 % 1.26
  Willow 19 1,946 1,111 2,782 43 % 1.24
Fort Rock   53 44,888 36,676 53,099 18 % 0.67
  Bridge 21 15,662 13,002 18,322 17 % 0.56
  Buck 19 12,629 10,800 14,457 15 % 0.53
  SilverFR 13 16,598 9,047 24,148 46 % 0.88

 

MAPS & CHARTS

SMU

Length Frequency

Site Status

Site Density

Other Species

Catlow Valley 1+ > 76mm Catlow Status Catlow Density Catlow Species
Chewaucan 1+ > 62mm Chewaucan Status Chewaucan Density Chewaucan Species
Fort Rock 1+ > 68mm Fort Rock Status Fort Rock Density Fort Rock Species
Malheur Lakes 1+ > 71mm Malheur Lakes Status Malheur Lakes Density Malheur Lakes Species
Goose Lake 1+ > 88mm Goose Lake Status Goose Lake Density Goose Lake Species
Warner Lakes 1+ > 71mm 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