Sampling Bias of Hook‐and‐Line Gear Used to Capture Rainbow Trout in Gertrude Creek, Alaska

Abstract

Hook‐and‐line gear is commonly used for monitoring the size and abundance of resident fish populations in southwest Alaska. The selectivity of the gear, however, may contribute to bias in the catch, making it difficult to detect changes in population structure over time. This study assessed the potential bias in sampling a population of rainbow trout Oncorhynchus mykiss with angling gear. A bidirectional weir was operated on Gertrude Creek from 1997 to 1999 to intercept the annual upstream spring migration of rainbow trout into the stream. Captured fish were measured and tagged to establish a population of marked individuals with a known length distribution above the weir. The marked population was then sampled with angling gear on three occasions during each of three summers. A variety of terminal tackle was used, and types were selected to maximize the catch of rainbow trout. Size selectivity was evaluated by use of an exact Kolmogorov–Smirnov (KS) test of the hypothesis that the length distribution of all marked fish was equivalent to that of the subset of marked fish recaptured by anglers during a single recapture event. Test results were not significant for any of the recapture events, providing strong evidence that length selectivity did not exist for fish within the size range of the marked population. An exact KS test was also used to test length distribution equality between the marked population and all fish captured during an angling event. All of these KS tests were significant, suggesting that the marked group was a size‐biased subset of the rainbow trout population in the drainage. The results of this study support the use of angling gear as a potentially viable sampling method for monitoring the size composition of rainbow trout in small southwest Alaskan streams.

Similarities between Line Fishing and Baited Stereo-Video Estimations of Length-Frequency: Novel Application of Kernel Density Estimates

“…Understanding the true length-frequency of a population may be impossible as all methods, including rotenone stations, suffer from a tendency to under sample small individuals [15], although in fisheries monitoring studies it is more important to employ a standardised methodology, with standardised biases, than attempt to define the true length-frequency [31]. For example, it has been shown that a bias towards larger individuals can occur with line fishing, which may be due to dominance behaviours between fish of different size [32] and experimental studies have demonstrated that larger hook sizes tend to catch larger individuals [33]. Comparison of diver-based underwater visual census sampling (UVC) and long-lining has suggested that UVC can underestimate the mean length of some fished populations [34], [35].…”

“…Comparisons of mean length often require powerful transformations to account for heterogeneity of variance that may, in fact, be due to differences in the shape of the distributions. In contrast, the widely used Kolmogorov–Smirnov (KS) test provides a non-parametric approach for comparing length structures via the single greatest point-difference between cumulative length-frequency distributions and is sensitive to both differences in shape and location [32], [45].…”

“…Given that line fishing has a likely selectivity towards larger individuals [32] and forward-facing stereo-BRUVS has a suspected bias for a higher abundance of smaller fishes (Pers. Obs.…”

U.S. Fish and Wildlife Service

“…Variability in the sampler's angling experience and gear selection and a fish's previous experience with the gear may all affect the number of fish captured as well as the length composition of the sample. However, Hetrick and Bromaghin (2006) found that hook and line sampling for rainbow trout could provide an unbiased sample. In that study, a rainbow trout population with a known length frequency distribution was sampled using the same fishing gear described in this report.…”

Associations between Watershed Characteristics and Angling Success for Sport Fishes in Mississippi Wadeable Streams

“…Catch per unit of effort (CPUE [fish/angler-hour]) was used as an index of relative abundance and angling success because angler CPUE tends to be strongly correlated with other indices of abundance (Isaak et al 1992;Arterburn and Berry 2002;Hetrick and Bromaghin 2006) as well as the actual abundances of fish populations (Tsuboi and Endou 2008;Martin and Fisher 2009). Fishing intensity (e.g., casting frequency, reeling speed, and wading speed) was similar among anglers, sites, and sample dates, and no fish were removed from the streams.…”