Assessing Size‐Dependent Population‐Level Effects of Largemouth Bass Tournament Mortality

Abstract

As black bass Micropterus spp. tournaments continue to grow in popularity, so too must evaluations on the population‐level effects of live‐release angling events. Although factors influencing the tournament mortality of individuals are well studied, assessments at the population level are lacking. We evaluated differences in tournament capture probability and survival of two size‐classes of Largemouth Bass M. salmoides (medium: 381–457 mm; large: >457 mm) using a multistate mark–recapture model. Changes in estimated capture and survival rates of medium and large bass were then simulated to assess potential effects on population size structure. Tournament capture probabilities for medium bass were approximately three times higher than those for large bass, and tournament capture probabilities for both size‐classes increased with air temperature. Medium bass also experienced higher survival rates than large bass after tournaments, and survival rates of both groups declined with increasing water temperature. Our simulations indicated that both increases in tournament capture probability and reductions in posttournament survival of large bass resulted in some reductions in population size structure. However, increases in tournament capture probability or reductions in tournament survival of medium bass or medium and large bass alone had little to no effect. Our results suggest that under the observed tournament conditions, tournaments have little effect on bass population size structure, but size structure could be reduced with higher capture probabilities and lower posttournament survival; this information is useful for managing the fishery effects of tournament angling. Our modeling approach also provides a framework for understanding population‐level effects of tournaments on other populations under alternative conditions.

Effects of Length and Bag Limits on Largemouth Bass Tournament Capture and Mortality

“…Thus, our estimate of weigh‐in probability (referred to as “capture probability” in Sylvia et al. 2021a; Sylvia and Weber 2022) only included bass that were weighed in at tournaments and not individuals that were released prior to the weigh‐in (e.g., culled bass). As the vast majority of anglers did not weigh in their limit, instances of culling were likely very low throughout the study.…”

“…To reduce the number of parameters to estimate, we fixed known transition and survival rates when possible (for examples, see Sylvia et al 2020Sylvia et al , 2021aSylvia and Weber 2022). Parameters are difficult to estimate in multistate models with more than one unobservable state.…”

“…For some populations, 5% of legal-length bass are weighed in and tournament mortality contributes 1-16% of total annual mortality (Driscoll et al 2007), while in other instances, up to 43% of bass populations are weighed in annually, resulting in tournament mortality that represents a high proportion of fishing mortality (Hysmith et al 2014). In Brushy Creek Lake, 27-30% of 381-457-mm bass and 28-37% of bass larger than 457 mm were weighed in at tournaments annually, resulting in tournament mortality of 7-10% of bass from each size category (Sylvia and Weber 2022). When fishery managers are concerned about tournament mortality, daily bag limits would need to be reduced to one or two bass and/or length limits would need to be increased to over 381 mm to reduce the number of bass that are exposed to tournament stress and associated mortality.…”

“…A bass was considered to be in Brushy Creek Lake (B in Figure S1) until captured by a tournament angler and weighed in during a tournament, at which point it transitioned into the tournament state (T in Figure S1). Thus, our estimate of weigh-in probability (referred to as "capture probability" in Sylvia et al 2021a;Sylvia and Weber 2022) only included bass that were weighed in at tournaments and not individuals that were released prior to the weigh-in (e.g., culled bass). As the vast majority of anglers did not weigh in their limit, instances of culling were likely very low throughout the study.…”

“…Multistate model.-To evaluate the effect of length and bag limits on bass weigh-in probability during live-release tournaments, we analyzed daily individual bass encounter histories from capture-recapture data (electrofishing, tournaments, telemetry, or recreational angler reports) during the 2018 and 2019 tournament seasons using a livecapture multistate model in program MARK to obtain maximum likelihood estimates of survival (S), detection probability (P), and bass weigh-in probability (transition of bass from Brushy Creek Lake to a tournament [Ψ]; White et al 2006). Details of multistate model frameworks, their assumptions, and their use in fisheries research can be found in Sylvia et al (2021b) and Sylvia and Weber (2022). In our specific model, bass could reside in one of three states (Figure S1 available in the Supplementary Materials in the online version of this article).…”