Utility of Electrofishing Censusing Fish in Headwater Streams: Why Validation Is Essential

Estimation of fish abundance or fish presence/absence in streams using electrofishing and snorkeling methods is common practice, but, without a full understanding of how well these methods work under a range of conditions, these approaches could produce misleading results.  Further, the use of models such as the removal model to estimate fish abundance can result in erroneous conclusions when assumptions are violated.  Studies that validate sampling methods through temporal replication or index-to-index comparisons can also give an inaccurate impression of estimate precision.  We evaluate different methods for estimating fish abundance and developing models of sampling efficiency.  These models can be used to produce unbiased estimates of fish abundance and the amount of sampling effort needed to produce reliable presence/absence information.  Sampling efficiency of electrofishing and snorkeling is affected by habitat features such as instream structure, time of sampling, fish size, and fish species.  Ignoring the effects of these features on sampling efficiency could result in a variety of errors, including inadequate sampling to establish fish presence and erroneous conclusions regarding fish/habitat relationships.  Validating sampling methods requires effort beyond that associated with routine sampling, but this understanding can help fisheries biologists avoid use of biased data and facilitate standardization among studies.  Further, it can allow for more extensive, streamwide sampling with a known understanding of bias and limited sampling efficiency of low-effort approaches.