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