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Removal of non-native fish populations can be crucial to the conservation of native species, but often presents a complex challenge for managers. The goal of Trojan Y chromosome (TYC) programs is to skew the non-native sex ratio until only males remain, leading to eradication. We present results from a simulation model used to explore effects of alternative management approaches on an in-progress mechanical removal and TYC program to eradicate non-native brook trout (Salvelinus fontinalis). Simulation results indicated that stocking fingerling YY males (~137 mm) was more effective than stocking catchable- sized YY males (~230 mm), although questions about intercohort competition warrant further investigation. Increasing the proportion of mature fingerling YY males reduced treatment time by increasing the number of YY male spawners and increasing density- dependent mortality on young, mature wild brook trout. Maximizing the spatial distribution of YY male releases may be crucial to program success but is also dependent upon immediate dispersal movements. Principles derived from our results can be broadly applied to the management of other aquatic invaded systems using TYC programs to eradicate non-native species. Si le retrait de populations de poissons non indigenes peut s'averer crucial pour la conservation d'especes indigenes, il constitue souvent un defi complexe pour les gestionnaires. L'objectif des programmes bases sur un chromosome Y << cheval de Troie >> (CYCT) est de modifier le rapport de masculinite d'especes non indigenes jusqu'a ce que seuls des males demeurent, menant a leur eradication. Nous presentons les resultats d'un modele de simulation utilise pour explorer les effets de differentes approches de gestion sur un programme en cours de retrait mecanique et base sur les CYCT visant l'eradication d'ombles de fontaine (Salvelinus fontinalis) non indigenes. Les resultats de simulations indiquent que l'ensemencement d'alevins males YY d'un an (~137 mm) est plus efficace que l'ensemencement de males YY de taille exploitable (~230 mm), bien que des questions concernant la concurrence entre cohortes necessitent un examen plus pousse. Une plus grande proportion d'alevins males YY matures reduit la duree du traitement en rehaussant le nombre de geniteurs males YY et la mortalite dependante de la densite des jeunes ombles de fontaine sauvages matures. La maximisation de la repartition spatiale des lachers de males YY pourrait constituer un element cle du succes de tels programmes, mais depend aussi des deplacements de dispersion immediats. Les principes derives de nos resultats peuvent s'appliquer plus largement a la gestion d'autres systemes aquatiques envahis par le recours a des programmes bases sur les CYCT pour eradiquer des especes non indigenes. [Traduit par la Redaction], Introduction The establishment and spread of non-native fish species present substantial challenges for the conservation and management of natural resources (Havel et al. 2015). One approach to the removal of [...]

For longer-lived species, individuals hedge their bets by skipping breeding when conditions are poor to preserve the opportunity for future breeding attempts. Thus, understanding the ecological drivers behind the 'choice' to reproduce or not is a key step in identifying and diagnosing causes of population change. We investigated both marine and terrestrial factors that might influence whether Kittlitz's Murrelets Brachyramphus brevirostris--a long-lived seabird of conservation concern that is often associated with glacially-influenced habitats--choose to breed in a given year. We used a suite of proxies to explain variation in reproductive metrics of radio-tagged Kittlitz's Murrelets, exploring three hypotheses related to prey availability, nest depredation risk, and energetic costs of nesting in Icy Bay, Alaska, 2007-2012. In two of the years, we compared results with the locally co-occurring, closely-related Marbled Murrelet B. marmoraus. Across the six-year period of our study, the posterior mean breeding propensity of Kittlitz's Murrelets was 0.21 (95% credible interval [CrI] = 0.15-0.27), nesting success was 0.41 (CrI = 0.25-0.57), and fecundity was 0.04 (CrI = 0.02-0.06). Although none of our three hypotheses were strongly supported by the data, our results collectively suggest that successful nesters expended greater effort than failed nesters and non-nesters to acquire sufficient prey--they stayed longer in the study area, had larger marine core use areas, spent slightly less time diving, and had shorter commuting distances and longer incubation shifts. Also, in years when fecundity was highest, overlap of individual marine core use areas was greatest, suggesting predictable foraging hotspots for murrelets in those years. Importantly, when comparing Brachyramphus species, we found that Marbled Murrelets outperformed Kittlitz's Murrelets reproductively by three to four times in overlapping years, suggesting different drivers of reproduction. From our collective results, we posit that the limitation to reproduction of Kittlitz's Murrelets may not be prey abundance or quality, but instead efficient access to prey. While our associations with indices of prey availability, depredation risk, and energetic costs to nesting did not explain much of the variation in fitness metrics, our study demonstrates the value of using a comparative approach and multiple metrics to diagnose factors limiting a population, especially when data are sparse. For bet-hedging species with complex life histories, we recommend using a combination of integrated modeling and a monitoring framework designed to accumulate evidence across studies to estimate population dynamics and improve inferences about ecological drivers. [ABSTRACT FROM AUTHOR]

Camera‐based abundance estimators are an alternative methodology of growing interest in both research and management applications. The statistical formulations of camera‐based abundance estimators using time‐lapse data should theoretically produce precise and unbiased estimates; however, production of unbiased results also requires meeting several important assumptions, and real‐world case studies evaluating such results remain relatively few. We applied instantaneous sampling (IS) and space‐to‐event (STE) estimators to remote camera data collected in April 2021 via time‐lapse sampling of closed populations of bighorn sheep (Ovis canadensis) and mule deer (Odocoileus hemionus) on Wild Horse Island in western Montana, USA, and compared results for bighorn sheep to aerial and ground‐based counts. Point estimates from camera‐based approaches underestimated bighorn sheep populations by 32–44% (IS estimator) and 62–69% (STE estimator) relative to aerial and ground counts. Patchy spatial distribution and group‐living behavior of sheep resulted in a high degree of noise surrounding the IS estimate. In comparison, a low point estimate with relatively narrow confidence intervals suggested potential sensitivity of the STE estimator to violating assumptions of independence among individual animals and sampling occasions. Estimates of mule deer had improved precision over sheep estimates, as indicated by lower estimated coefficients of variation of the mean (CVmean) derived from the analytic SE estimator. Using 15‐m viewsheds and the IS estimators, mule deer density estimates came with a 26% CVmean compared to 43% CVmean for bighorn sheep. This discrepancy may be a result of differences in distribution, behavior, and relative abundance between the 2 species. Accounting for group size and increasing time between sampling may improve accuracy of density estimates and adhere better to model assumptions when estimating precision. In addition, factors influencing viewshed and resulting density extrapolations must be considered carefully. While camera‐based methods theoretically provide an alternative way to estimate density when traditional methods are impractical, our results suggest that more work is needed to ensure density estimates are accurate and precise enough to inform population management. [ABSTRACT FROM AUTHOR]