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Land management and flood effects on the distribution and abundance of cutthroat trout in the Coeur d'Alene River Basin, Idaho Item Info

In January 1996, the largest flood since 1974 occurred in the Coeur d'Alene River basin, Idaho. In some areas the flood peaks were the second highest ever recorded and exceeded flows that have a 1% chance of occurring during any given year. The focus of this study was to expand the understanding of the influence of biological and physical processes and landscape patterns at the scale of watersheds and subbasins on the distribution, abundance and persistence of westslope cutthroat trout Oncorhynchus clarki lewisi. During the summer of 1996, I sampled 62 second and third order tributaries within the Coeur d'Alene River basin using a stratified random sampling design. Streams were divided into three reaches of equal length, and three sites within each reach were randomly chosen for single pass electrofishing. One of the nine sites in each stream was randomly selected for an estimate of absolute abundance using multiple pass electrofishing. Capture efficiency was estimated from the multiple pass sites using a maximum likelihood estimator. Mean capture efficiency was 68% and ranged from 23 to 100%. Single pass catches were adjusted using the average capture efficiency for the basin, and the adjusted catches were used to compute density estimates for all streams. All streams sampled contained westslope cutthroat trout, suggesting that local extinctions did not occur following the January 1996 flood. The mean stream density in 1996 for the entire basin was 0.057 fishlm2 and ranged from 0.001 to 0.219 fish. Estimated densities were highest in tributaries to the Main Coeur d'Alene River ( x = 0.083 ), followed by tributaries to the Upper Coeur d'Alene River ( x = 0.048 ), tributaries to Shoshone Creek ( x = 0.067) and tributaries to the North Fork Coeur d'Alene river ( x = 0.039 ). Mean densities for the Main Coeur d'Alene and North Fork Coeur d'Alene subbasins were not significantly different in 1996 than 1995 (p = 0.868 and p = 0.271 ). Mean densities in both the Upper Coeur d'Alene and Shoshone Creek subbasins were significantly lower in 1996 than 1995 (p = 0.063 and p = 0.008), but these differences can be accounted for by three streams in the Upper Coeur d'Alene drainage and one stream in the Shoshone Creek drainage. Densities in the North Fork Coeur d'Alene were nearly significantly different from densities in the Main Coeur d'Alene (p = 0.090) and Shoshone Creek (p = 0.1 08) in 1996, however, no other drainages showed significant differences in densities in 1996. Age-0 cutthroat trout were not found in any streams with wetted widths wider than 8 m. Logistic regression was used to model the probability of encountering cutthroat trout fry, and the best model used gradient to predict the probability of encountering age-0 cutthroat trout (p = 0.0005). Estimated density of westslope cutthroat trout was significantly related to large woody debris counts per 1000 m of channel, and cumulative equivalent clearcut acreage (R2 = 0.505, p = 0.004). Densities decreased with increased wetted width, increased with increased large woody debris count, and decreased with increased cumulative equivalent clearcut acreage. My results showed that cutthroat trout densities are better predicted by variables measured at the stream or watershed level than at the site or habitat type level. Cutthroat trout in the Coeur d'Alene River basin were able to persist following significant disturbance including disturbance due to land management activities, disturbance due to severe flooding, and the cumulative effects of both.

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Title:
Land management and flood effects on the distribution and abundance of cutthroat trout in the Coeur d'Alene River Basin, Idaho
Authors:
Abbott, Ann M.
Date Created (ISO Standard):
2000-12
Description:
In January 1996, the largest flood since 1974 occurred in the Coeur d'Alene River basin, Idaho. In some areas the flood peaks were the second highest ever recorded and exceeded flows that have a 1% chance of occurring during any given year. The focus of this study was to expand the understanding of the influence of biological and physical processes and landscape patterns at the scale of watersheds and subbasins on the distribution, abundance and persistence of westslope cutthroat trout Oncorhynchus clarki lewisi. During the summer of 1996, I sampled 62 second and third order tributaries within the Coeur d'Alene River basin using a stratified random sampling design. Streams were divided into three reaches of equal length, and three sites within each reach were randomly chosen for single pass electrofishing. One of the nine sites in each stream was randomly selected for an estimate of absolute abundance using multiple pass electrofishing. Capture efficiency was estimated from the multiple pass sites using a maximum likelihood estimator. Mean capture efficiency was 68% and ranged from 23 to 100%. Single pass catches were adjusted using the average capture efficiency for the basin, and the adjusted catches were used to compute density estimates for all streams. All streams sampled contained westslope cutthroat trout, suggesting that local extinctions did not occur following the January 1996 flood. The mean stream density in 1996 for the entire basin was 0.057 fishlm2 and ranged from 0.001 to 0.219 fish. Estimated densities were highest in tributaries to the Main Coeur d'Alene River ( x = 0.083 ), followed by tributaries to the Upper Coeur d'Alene River ( x = 0.048 ), tributaries to Shoshone Creek ( x = 0.067) and tributaries to the North Fork Coeur d'Alene river ( x = 0.039 ). Mean densities for the Main Coeur d'Alene and North Fork Coeur d'Alene subbasins were not significantly different in 1996 than 1995 (p = 0.868 and p = 0.271 ). Mean densities in both the Upper Coeur d'Alene and Shoshone Creek subbasins were significantly lower in 1996 than 1995 (p = 0.063 and p = 0.008), but these differences can be accounted for by three streams in the Upper Coeur d'Alene drainage and one stream in the Shoshone Creek drainage. Densities in the North Fork Coeur d'Alene were nearly significantly different from densities in the Main Coeur d'Alene (p = 0.090) and Shoshone Creek (p = 0.1 08) in 1996, however, no other drainages showed significant differences in densities in 1996. Age-0 cutthroat trout were not found in any streams with wetted widths wider than 8 m. Logistic regression was used to model the probability of encountering cutthroat trout fry, and the best model used gradient to predict the probability of encountering age-0 cutthroat trout (p = 0.0005). Estimated density of westslope cutthroat trout was significantly related to large woody debris counts per 1000 m of channel, and cumulative equivalent clearcut acreage (R2 = 0.505, p = 0.004). Densities decreased with increased wetted width, increased with increased large woody debris count, and decreased with increased cumulative equivalent clearcut acreage. My results showed that cutthroat trout densities are better predicted by variables measured at the stream or watershed level than at the site or habitat type level. Cutthroat trout in the Coeur d'Alene River basin were able to persist following significant disturbance including disturbance due to land management activities, disturbance due to severe flooding, and the cumulative effects of both.
Subjects:
trout flood damage
Location:
Coeur d'Alene Basin
Latitude:
47.52
Longitude:
-116.56
Collection:
Coeur d'Alene Basin
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
Publisher:
University of Idaho
Contributing Institution:
University of Idaho
Type:
Text
Format:
application/pdf
Cataloger:
wbv
Date Digitized:
2012

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Source
Preferred Citation:
"Land management and flood effects on the distribution and abundance of cutthroat trout in the Coeur d'Alene River Basin, Idaho", Idaho Waters Digital Library, University of Idaho Library Digital Collections, https://www.lib.uidaho.edu/digital/iwdl/items/iwdl-cda_abbott_2000.html
Rights
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
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