Evaluating Two Observational Sampling Techniques for Determining the Distribution and Detection Probability of Age‐0 Smallmouth Bass in Clear, Warmwater Streams

Abstract

AbstractAccurate determination of the distribution and abundance of age‐0 sport fish, such as smallmouth bass Micropterus dolomieu, is an important aspect of successful species management (e.g., characterizing nursery habitats for protection or enhancement; identifying reproductive dynamics and influences of environmental variables). Two observational techniques—snorkeling and above‐water (AW) observation—were evaluated in several Missouri Ozark streams to determine (1) accuracy of identifying age‐0 smallmouth bass with each technique, (2) detection probabilities under a variety of channel unit (CU) conditions (i.e., discrete morphological features such as riffles or pools) and the relations between detection probability and hydraulic variables, and (3) behavioral responses (fright response, return response, or no response) of fish to the observers using each technique. Identification of age‐0 smallmouth bass was over 90% accurate when using AW observation in shallow water and when snorkeling in deep water. In both streams, detection probabilities differed depending on the CU sampled and the method used. In deep pools, detection probabilities when snorkeling were two to three times those obtained from AW observation; however, AW observation was more efficient for sampling most shallow‐water (<0.5‐m) CUs. Velocity had no significant relation to detection probability, whereas depth was significantly related to detection probability for both sampling methods (the relationship was positive for snorkeling and negative for AW observation). The percentage of age‐0 smallmouth bass that exhibited a fright response was greatest for fish observed by snorkeling in shallow‐water CUs. On average, approximately 20% of fish showed a fright response, but a large proportion of these fish exhibited a return response. Our results indicate that multiple sampling methods may be necessary to achieve high accuracy when sampling small fish in a variety of CUs, and snorkeling and AW observation may be viable methods for selecting CUs in many warmwater streams. Additional work is recommended to address knowledge gaps, especially those related to the influence of biotic and abiotic variables that were not measured in this study.Received November 9, 2010; accepted May 12, 2011