Length Selectivity and Size‐Bias Correction for the North American Standard Gill Net

Abstract

Gill nets are inherently size selective, but selectivity curves can correct this bias. We sampled eight reservoirs with the North American standard gill net to develop a large length‐specific data set for six species: Channel Catfish Ictalurus punctatus, hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), saugeye (Sauger Sander canadensis × Walleye S. vitreus), Walleye, White Bass, and White Crappie Pomoxis annularis. We then used the SELECT (share each lengthclass's catch total) method to find the best‐fit selectivity model to adjust the gill‐net catch for contact selectivity. To determine the magnitude of these selectivity corrections, we compared adjusted and unadjusted length frequencies and size indices for each species at each reservoir. The bimodal model was the best fit selectivity model for all species. When selectivity‐adjusted length‐frequency data were compared with the original data, one‐third of hybrid Striped Bass length frequencies and two‐thirds of White Bass length frequencies were significantly different (unadjusted distributions underestimated smaller length classes). Roughly one‐third of the proportional size distributions (PSDs) from all species analyzed showed meaningful changes (≥5 PSD units) after selectivity adjustments were made (unadjusted PSDs were too large). By correcting for contact selectivity the data are improved, and at times the adjustments can be large enough to alter management decisions. Therefore, we recommend that selectivity adjustments should become a part of routine data analysis for the design of the North American standardized gill net as this will improve data for fisheries management. Received September 1, 2015; accepted December 21, 2015 Published online May 16, 2016

Size‐Dependent Retention of Pelagic‐Oriented Kokanee in Multimesh Gill Nets

“…Bimodal models were developed to characterize the combined processes of wedging and tangling (Hamley ; Millar and Fryer ) and were used in some recent studies of gill‐net retention (Shoup and Ryswyk ; Klein et al. ).…”

“…Studies characterizing the retention of common warmwater fishes in North American standard gill nets showed congruence among models developed independently for the same species from lakes and reservoirs extending from Ontario to Oklahoma (Walker et al. ; Shoup and Ryswyk ; Smith et al. ).…”

“…Previous assessments of gill‐net retention combined catch data across multiple regional populations to incorporate variation in fish body form and to develop more general models (Walker et al. ; Shoup and Ryswyk ; Smith et al. ; Klein et al.…”

“…) has spurred increased effort into estimating retention curves for some common sport fish captured in standard, horizontal, benthic gill nets (Walker et al. ; Shoup and Ryswyk ; Smith et al. ).…”

Spatial and Temporal Variability in a Large‐Reservoir Fish Assessment and Application of a Stratified Random Sampling Approach

“…Bias of fish sampling gears is inherent, and several studies have been conducted to evaluate the catchability of select gears (Wilde ; Koupal et al. ; Shoup and Ryswyk ; Smith et al. ).…”