No abstract

In the western United States, the ability of non‐native lake trout (Salvelinus namaycush) to attain large sizes, > 18 kg under favorable conditions, fueled the popularity of lake trout fisheries. In the past, restrictive regulations were adopted to increase lake trout abundance and produce trophy specimens. More recently, lake trout have become increasingly problematic because they prey upon and potentially compete with native and sport fishes. We review the experiences of agencies in seven western states which are considering or implementing strategies to address lake trout impacts despite management difficulties due to mixed public perception about lake trout's complex interactions with native or introduced fauna. Special regulations protecting lake trout have often been liberalized or rescinded to encourage their harvest and reduce their negative effects. More intensive methods to control or reduce lake trout abundance include promoting or requiring lake trout harvest, commercial‐scale netting, disrupting spawning, and stocking sterile lake trout.

Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem.

Introduced lake trout (Salvelinus namaycush) threaten to extirpate native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) in the 34 000 ha Yellowstone Lake in Yellowstone National Park, USA. Suppression (and eventual eradication) of the lake trout population is deemed necessary for the conservation of Yellowstone cutthroat trout. A US National Park Service gill-netting program removed nearly 450 000 lake trout from Yellowstone Lake from 1995 through 2009. We examined temporal variation in individual growth, body condition, length and age at maturity, fecundity, mortality, and population models to assess the efficacy of the lake trout suppression program. Population metrics did not indicate overharvest despite more than a decade of fish removal. The current rate of population growth is positive; however, it is lower than it would be in the absence of lake trout suppression. Fishing effort needs to increase above observed levels to reduce population growth rate below replacement. Additionally, high sensitivity of population growth rate to reproductive vital rates indicates that increasing fishing mortality for sexually mature lake trout may increase the effectiveness of suppression. Lake trout suppression in Yellowstone Lake illustrates the complexities of trying to remove an apex predator to restore a relatively large remote lentic ecosystem with a simple fish assemblage.Résumé : Les touladis (Salvelinus namaycush) introduits dans le lac Yellowstone de 34 000 ha dans le parc national de Yellowstone, É.-U., menacent d'en extirper la truite fardée de Yellowstone (Oncorhynchus clarkii bouvieri) indigène. On croit que la réduction (et éventuellement l'éradication) de la population de touladis est nécessaire à la conservation des truites fardées de Yellowstone. Un programme de pêche au filet maillant mené par le service des parcs nationaux des É.-U. a retiré presque 450 000 touladis du lac Yellowstone de 1995 jusqu'à la fin de 2009. Nous examinons la variation temporelle de la croissance individuelle, de la condition corporelle, de la longueur et de l'âge à la maturité, de la fécondité, de la mortalité et des modèles démographiques afin d'évaluer l'efficacité du programme d'élimination des touladis. Les métriques de la population n'indiquent pas de récolte excessive malgré le retrait de poissons pendant plus d'une décennie. Le taux actuel de croissance de la population est positif; cependant, il est plus bas qu'il ne le serait en absence du programme d'élimina-tion des touladis. L'effort de pêche devra être accru au-delà des niveaux observés afin de réduire le taux de croissance de la population sous le seuil de remplacement. De plus, la forte sensibilité du taux de croissance de la population aux taux vitaux reproductifs indique que l'augmentation de la mortalité due à la pêche chez les touladis à maturité sexuelle pourrait améliorer l'efficacité de l'élimination. L'élimination des touladis dans le lac de Yellowstone illustre les difficultés reliées aux efforts pour retirer un prédateur de sommet de réseau...

Yellowstone Lake in Yellowstone National Park, USA, has the longest ongoing suppression program for non-native lake trout (Salvelinus namaycush) in the western USA. Harvest data from the suppression program, along with data from an assessment program initiated in 2011, was used to estimate lake trout abundance and mortality rates. Abundance and biomass estimates were used to estimate stock–recruitment dynamics, which were inputs to a simulation model forecasting responses to continued suppression. Abundance increased during 1998–2012 when total annual mortality exceeded 0.59 and declined thereafter. The fishing mortality rate required to reduce abundance was 67% greater than predicted by models that used prerecruit survival estimates from the lake trout’s native range. Prerecruit survival in Yellowstone Lake was estimated at four to six times greater than native range survival rates. Simulated abundance continued to decline if recent suppression efforts were maintained. High prerecruit survival in Yellowstone Lake likely illustrates ecological release for an invasive species in an ecosystem containing few predators or competitors and demonstrates the potential pitfalls of assuming equal demographic rates for native and non-native populations.