Understanding the relative strengths of intrinsic and extrinsic factors regulating populations is a long-standing focus of ecology and critical to advancing conservation programs for imperiled species. Conservation could benefit from an increased understanding of factors influencing vital rates (somatic growth, recruitment, survival) in small, translocated populations, which is lacking owing to difficulties in long-term monitoring of rare species. Translocations, here defined as the transfer of wild-captured individuals from source populations to new habitats, are widely used for species conservation, but outcomes are often minimally monitored, and translocations that are monitored often fail. To improve our understanding of how translocated populations respond to environmental variation, we developed and tested hypotheses related to intrinsic (density dependent) and extrinsic (introduced rainbow trout Oncorhynchus mykiss, stream flow and temperature regime) causes of vital rate variation in endangered humpback chub (Gila cypha) populations translocated to Colorado River tributaries in the Grand Canyon (GC), USA. Using biannual recapture data from translocated populations over 10 years, we tested hypotheses related to seasonal somatic growth, and recruitment and population growth rates with linear mixed-effects models and temporal symmetry mark-recapture models. We combined data from recaptures and resights of dispersed fish (both physical captures and continuously recorded antenna detections) from throughout GC to test survival hypotheses, while accounting for site fidelity, using joint live-recapture/live-resight models. While recruitment only occurred in one site, which also drove population growth (relative to survival), evidence supported hypotheses related to density dependence in growth, survival, and recruitment, and somatic growth and recruitment were further limited by introduced trout. Mixed-effects models explained between 67% and 86% of the variation in somatic growth, which showed increased growth rates with greater flood-pulse frequency during monsoon season. Monthly survival was 0.56-0.99 and 0.80-0.99 in the two populations, with lower survival during periods of higher intraspecific

Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown and rainbow trout suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression, and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial-thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized-linear mixed-effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (~480%) once trout suppression surpassed ~60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression, and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery.

The Humpback Chub Gila cypha, a large-bodied, endangered cyprinid endemic to the Colorado River basin, is in decline throughout most of its range due largely to anthropogenic factors. Translocation of Humpback Chub into tributaries of the Colorado River is one conservation activity that may contribute to the expansion of the species' current range and eventually provide population redundancy. We evaluated growth, survival, and dispersal following translocation of approximately 900 Humpback Chub over a period of 3 years (2009, 2010, and 2011) into Shinumo Creek, a tributary stream of the Colorado River within Grand Canyon National Park. Growth and condition of Humpback Chub in Shinumo Creek were consistent among year-classes and equaled or surpassed growth estimates from both the main-stem Colorado River and the Little Colorado River, where the largest (and most stable) Humpback Chub aggregation remains. Based on passive integrated tag recoveries, 53% (D 483/902) of translocated Humpback Chub dispersed from Shinumo Creek into the main-stem Colorado River as of January 2013, 35% leaving within 25 d following translocation. Annual apparent survival estimates within Shinumo Creek ranged from 0.22 to 0.41, but were strongly influenced by emigration. Results indicate that Shinumo Creek provides favorable conditions for growth and survival of translocated Humpback Chub and could support a new population if reproduction and recruitment occur in the future. Adaptation of translocation strategies of Humpback Chub into tributary streams ultimately may refine the role translocation plays in recovery of the species.