Effectiveness of single-pass backpack electrofishing to estimate juvenile coho salmon abundance in Alaskan headwater streams

摘要

The use of techniques with low or inconsistent sampling efficiency may lead to erroneous estimates of abundance. Although an increase in sampling intensity can improve sampling efficiency and precision, its cost can limit a study’s spatial extent. A low-effort approach may be preferred for landscape-scale studies of fish distribution and abundance; however, this requires information on whether the low-effort sampling is vulnerable to habitat-mediated bias and imprecision of the estimator. To determine how habitat features affected sampling efficiency of juvenile coho salmon Oncorhynchus kisutch in headwater streams of the Little Susitna drainage, Alaska, we validated single-pass backpack electrofishing methods with closed population mark–recapture sampling. We found that habitat features, such as stream size and density of wood debris, had no measurable or consistent effect on sampling efficiency within the range of conditions present in these headwater systems, and single-pass catch explained 94.8?% of the observed variation in log-transformed mark–recapture estimates. This suggests that low-effort methods in headwater streams of the Little Susitna River can approximate actual fish numbers without accounting for habitat covariates that may influence sampling efficiency, and the advantage of sampling a greater spatial extent may sufficiently offset any concerns over low estimator precision.