Native Fish Investigations Project

The summer 2007 field season was the first 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. Extensive efforts (public meetings, letters, and personal phone calls and visits) were made to obtain permission to access sites located on private property. Unfortunately in the Catlow Valley access was obtained only for sites in Rock Creek, therefore the results do not include streams on the east side of the basin.

Field crews block-netted each sample site and implemented a 2-pass depletion protocol using electroshockers to estimate trout abundance. To calibrate the depletion estimates, mark-recapture methods were also employed at about 10% of the sample sites.

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.

NOTE: These results were updated in 2009 to incorporate the 2006 - 2009 calibration sites into the estimate.

RESULTS

SMU Population n Estimate Lower
95%
Confidence Limit Upper
95%
Confidence Limit Relative
95%
Confidence Interval CV

Catlow Valley Rock Creek 7 29,952 12,409 47,495 59 % 0.81

Chewaucan 31 147,175 86,678 207,670 41 % 1.33

Fort Rock 27 85,825 66,028 105,622 23 % 0.68

Malheur Lakes 39 546,783 368,497 725,070 33 % 1.00

Goose Lake 90 125,543 84,796 166,290 33 % 1.44

Drews 20 17,196 8,853 25,540 49 % 1.54

Dry 12 2,869 0 6,765 136 % 2.76

Eastside 17 22,556 17,489 27,623 23 % 0.57

Thomas 21 39,981 18,871 61,090 53 % 1.33

West Goose 20 42,941 9,711 76,171 77 % 1.87

Warner Lakes 53 82,586 47,683 117,488 42 % 1.44

Deep 18 52,030 18,780 85,281 40 % 1.22

Honey 17 5,168 2,377 7,959 64 % 1.57

20mile 18 25,387 15,152 35,622 54 % 1.21