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