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

Abstract

Recent studies evaluating the size selectivity of standard, horizontal, benthic gill nets for some common sport fish have demonstrated congruence across regions and gear configurations. Studies evaluating retention in gill nets designed to sample pelagic‐oriented fish (e.g., vertical and curtain nets) are rare, which has limited corresponding assessments of generality. This study estimated the retention of kokanee Oncorhynchus nerka (lacustrine Sockeye Salmon) in multimesh vertical gill nets using catch data compiled over three decades from a large montane reservoir in Colorado. The corresponding best‐fit retention model was compared with that developed for kokanee in Idaho using multimesh curtain nets. There was strong congruence (Pearson's r = 0.98) between the total retention values (integrated over all mesh sizes) estimated by the two models for kokanee 50–430 mm total length, and the values followed a 1:1 relationship. This result indicated that the retention of fish in pelagic gill nets may also be largely conserved across regions and gear configurations. Thus, the retention models for kokanee compared in this study should be flexible and broadly applicable. These properties enable practitioners to easily adjust length‐frequency distributions for bias arising from size‐dependent retention when minimally biased estimates of size structure are needed for addressing management or research questions.

Evaluation of the influence of correcting for gillnet selectivity on the estimation of population parameters

“…Various authors have suggested that accounting for selectivity will lead to more accurate estimates of population parameters [7,14,15,33]. Smith et al [7] suggested that data collected…”

Influence of Population Density and Length Structure on Angler Catch Rate in Kokanee Fisheries

“…Therefore, managers may want to consider using larger mesh sizes or alternative size selectivity adjustments when monitoring kokanee populations that contain individuals larger than 440 mm. For instance, Hansen () extended size selectivity adjustments of kokanee up to 500 mm by incorporating a “tangling” parameter to account for fish whose girth exceeded that of the available mesh. Conversely, managers may wish to consider the applicability of fisheries‐dependent data for characterizing kokanee populations.…”

Rapid proliferation of the parasitic copepod, Salmincola californiensis (Dana), on kokanee salmon, Oncorhynchus nerka (Walbaum), in a large Colorado reservoir

“…In fall 2020, a floating trap net called a Merwin trap (Hubert et al., 2012) was deployed nearshore and retrieved on 19 October and 26 October to collect mature kokanee salmon ( n = 146) in addition to those collected during the salmon run to Roaring Judy Hatchery. Finally, from 2018 to 2020, vertical gill nets, a standard suite of six multi‐mesh nets described in Hansen (2019), were deployed overnight in offshore regions of Blue Mesa Reservoir in the spring (May/June), summer (July/August) and fall (November) to collect both mature and immature kokanee salmon ( n = 580).…”