Assessment of Trout Abundance and Distribution in the Waiparous Creek Drainage 2006


Kevin Fitzsimmons


The primary objective of this study was to provide estimates of abundance and distribution of bull trout, cutthroat trout, and brook trout in the Waiparous Creek drainage to assist with management of trout populations. In 2006, I backpack electrofished stream sites along Waiparous, Meadow, Johnson and Unnamed creeks to obtain monitoring data needed to estimate fish abundance, distribution and movement. I sampled 500‐m sites in two periods; early season (late spring to early summer; n = 59)
and late season (early fall; n = 32). During the early season, I marked 53 bull trout and 133 cutthroat trout (all > 150 mm in fork length, FL). I used capture‐mark‐recapture population estimation methods at a subset of sites to estimate electrofishing capture efficiency. Maximum likelihood estimates of capture efficiency varied among creeks, but were typically higher for cutthroat trout (0.36 to 0.65), followed by bull trout (0.20 to 0.54), and then brook trout (0.38 to 0.46). Of the three study species, bull trout capture efficiencies exhibited the least precision. Next, I used a non‐parametric generalized additive model to estimate fish (> 70 mm FL) abundance in 500‐m intervals along study streams. Estimates were replicated 10,000 times to develop 95% confidence intervals around abundance projections. 

Based on capture‐mark‐recapture methods and non‐parametric modeling, brook trout was the most abundant of the three species along 40 km of Waiparous Creek. Waiparous Creek supported the most bull trout and cutthroat trout compared to tributaries of Waiparous Creek. Surveys were only conducted along Meadow Creek in the early sampling period on 13.5 km of stream. In this stream, I estimated relatively few bull trout or cutthroat trout, whereas I estimated brook trout to be 33 times more abundant than bull trout. In Johnson Creek, early sampling indicated that cutthroat trout was approximately 2.2 times more abundant than bull trout, and that brook trout was the most abundant species in this creek at 14 times more abundant than bull trout. Fall sampling did not occur along the full length of Johnson Creek. I failed to capture brook trout in Unnamed Creek (3.5 km). Bull trout abundance in Unnamed Creek was relatively low; however, the majority of fish could be considered juveniles. I captured few cutthroat trout in Unnamed Creek in either the early or late season.

To identify fish movement patterns and life history strategies used by fish in the Waiparous Creek drainage, I marked 53 bull trout and 133 cutthroat trout. Of tagged fish, I recaptured five bull trout and 17 cutthroat trout at later dates. One bull trout moved a minimum of 23.3 km between captures, and all others were recaptured within 500 m of their initial capture location. Although there was an increase in bull trout abundance between early and late sampling periods, considerable variance exists around these estimates and no strong support for a fluvial or ad‐fluvial life history strategy was found. Further, the number of mature large bull trout in the drainage was relatively unchanged between sampling periods.

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