Targeting Aggregations of Telemetered Lake Trout to Increase Gillnetting Suppression Efficacy

Abstract

Conserving Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri by suppressing invasive Lake Trout Salvelinus namaycush in Yellowstone Lake is a high priority for Yellowstone National Park resource managers. Here, we tested whether targeting telemetered Lake Trout could increase the efficacy of Lake Trout suppression by gill netting. Mobile acoustic tracking surveys were performed to identify aggregations of tagged Lake Trout in summer (June–August) 2017. Lake Trout aggregations were relayed daily to suppression crews by phone, radio, or text and a printed map. Suppression crews set 30 large‐mesh gill nets targeting telemetered Lake Trout aggregations (target treatment) and 124 large‐mesh gill nets not targeting telemetered aggregations (nontarget treatment). Mean loge(CPUE) was higher for the target treatment (0.37; 95% credible interval [CRI] = 0.08–0.65) than for the nontarget treatment (−0.37; 95% CRI = −0.51 to −0.21). Mean of the target treatment was higher than the mean of the nontarget treatment for over 99% of the 1,000 draws from the joint posterior distribution. Because of telemetry costs, mean CPUE per US$10,000 spent was similar between the target treatment (0.20; 95% CRI = 0.15–0.26) and the nontarget treatment (0.15; 95% CRI = 0.13–0.17). Telemetry is an effective strategy for improving Lake Trout CPUE, which corresponds to an increased efficiency in the Lake Trout suppression program.

Movement and Space Use of Grass Carp in the Sandusky River, Ohio: Implications for Lake Erie Eradication Efforts

“…Using detection information from a few tagged individuals to identify locations of untagged fish for removal efforts is referred to as the “Judas technique” and has been identified as a beneficial tool for efforts to reduce abundances of invasive species (Lennox et al 2016; Crossin et al 2017). Aquatic species for which the Judas technique has proven successful in helping to inform response efforts include the Common Carp Cyprinus carpio (Bajer et al 2011; Taylor et al 2012), Northern Snakehead Channa argus (Lapointe et al 2010), Silver Carp (Coulter et al 2016), and Lake Trout Salvelinus namaycush (Dux et al 2011; Williams et al 2020). The premise of the Judas technique is that tagging and releasing fish back into the system will provide the information needed to increase capture rates in the future so as to justify the inherent risk of releasing the individuals into the wild rather than simply killing them.…”

Invasive Lake Trout Reproduction in Yellowstone Lake under an Active Suppression Program

“…2020; Williams et al. 2020). Based on assessment modeling results, annual exploitation levels of Lake Trout fully selected to suppression gill nets (≥4 years of age) has exceeded 50% since the mid‐2010s (Syslo et al.…”

“…In Yellowstone Lake, Lake Trout suppression has been conducted throughout the lake during the ice-free season but fall gillnetting effort has been heavily concentrated on known spawning locations, using larger mesh sizes to target spawning capable (>500 mm) females (Syslo et al 2011). Passive and active tracking of acoustically telemetered Lake Trout have also been used to identify movement corridors to spawning locations and to target aggregations that are proximal or moving towards these grounds through a "Judas fish" technique (Gutowsky et al 2020;Williams et al 2020). Based on assessment modeling results, annual exploitation levels of Lake Trout fully selected to suppression gill nets (≥4 years of age) has exceeded 50% since the mid-2010s (Syslo et al 2020).…”

“…Through a combination of direct observation and telemetry studies, some aspects of Lake Trout spawning in Yellowstone Lake have been well-documented. For example, littoral habitat in Yellowstone Lake is abundant (Bigelow 2009), and numerous Lake Trout spawning locations have been identified (Ruzycki et al 2003;Gutowsky et al 2020;Williams et al 2020). Lake Trout spawning in Yellowstone Lake occurs from September to early October, with the greatest proportion of spawning-capable (a fish capable of spawning within the current reproductive cycle, Brown-Peterson et al 2011) females generally captured in the last week of September.…”

“…2020; Williams et al. 2020). Lake Trout spawning in Yellowstone Lake occurs from September to early October, with the greatest proportion of spawning‐capable (a fish capable of spawning within the current reproductive cycle, Brown‐Peterson et al.…”