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We quantified tag retention, survival, and growth in juvenile, captive‐reared Humpback Chub Gila cypha marked with three different tag types: (1) Biomark 12.5‐mm, 134.2‐kHz, full duplex PIT tags injected into the body cavity with a 12‐gauge needle; (2) Biomark 8.4‐mm, 134.2‐kHz, full duplex PIT tags injected with a 16‐gauge needle; and (3) Northwest Marine Technology visible implant elastomer (VIE) tags injected under the skin with a 29‐gauge needle. Estimates of tag loss, tagging‐induced mortality, and growth were evaluated for 60 d with each tag type for four different size‐groups of fish: 40–49 mm, 50–59 mm, 60–69 mm, and 70–79 mm TL. Total length was a significant predictor of the probability of PIT tag retention and mortality for both 8‐mm and 12‐mm PIT tags, and the smallest fish had the highest rates of tag loss (12.5–30.0%) and mortality (7.5–20.0%). Humpback Chub of sizes 40–49 mm TL and tagged with VIE tags had no mortality but did have a 17.5% tag loss. Growth rates of all tagged fish were similar to controls. Our data indicate Humpback Chub can be effectively tagged using either 8‐mm or 12‐mm PIT tags with little tag loss or mortality at sizes as low as 65 mm TL. Received July 24, 2014; accepted October 31, 2014

Over the period 2014-2016, the number of nonnative brown trout (Salmo trutta) captured during routine monitoring in the Lees Ferry reach of the Colorado River, downstream of Glen Canyon Dam, began increasing. Management agencies and stakeholders have questioned whether the increase in brown trout in the Lees Ferry reach represents a threat to the endangered humpback chub (Gila cypha), to the rainbow trout (Oncorhynchus mykiss) sport fishery, or to other resources of concern. In this report, we evaluate the evidence for the expansion of brown trout in the Lees Ferry reach, consider a range of causal hypotheses for this expansion, examine the likely efficacy of several potential management interventions to reduce brown trout, and analyze the effects of those interventions on other resources of concern. The brown trout population at Lees Ferry historically consisted of a small number of large fish supported by low levels of immigration from downstream reaches. This population is now showing signs of sustained successful reproduction and is on the cusp of recruiting locally hatched fish into the spawning class, based on analysis with a new integrated population model. The proximate causes of this change in status are a large pulse of immigration in the fall of 2014 and higher reproductive rates in 2015-2017. The ultimate causes of this change are not clear. The pulse of immigrants from downstream reaches in fall 2014 may have been induced by three sequential high-flow releases from the dam in November of 2012-2014, but may also have been the result of a unique set of circumstances unrelated to dam operations. The increase in reproduction may have been the result of any number of changes, including an Allee effect, warmer water temperatures, a decrease in competition from rainbow trout, or fall high-flow releases. Correlations over space and time among predictor variables do not allow us to make a clear inference about the cause of the changes. Under a null causal model, and without any changes to management, we predict there is a 36-percent chance the brown trout population at Lees Ferry will not show sustained growth, and will remain around a mean size of 5,800 adults, near its current size; in contrast, we predict there is a 64-percent chance that the population has a positive intrinsic growth rate and will increase 3-10 fold over the next 20 years. A humpback chub population the ecosystem, potentially undermining goals associated with sandbar building, recreation, and riparian vegetation, but would increase hydropower revenue. Trout management flows would reduce hydropower revenue. From the standpoint of humpback chub, the alternative strategies largely follow the effect on brown trout; when brown trout abundance is reduced, predation pressure decreases, and humpback chub viability is predicted to increase, but the variation in predicted chub viability is not large across strategies or causal hypotheses. To design a response to brown trout, management agencies will need to navigate both the tradeoffs among resourc...

1. Managers often move, or translocate, organisms into habitats that are assumed to be suitable; however, the consequences of these translocations are usually not rigorously assessed. Robust assessment of these management experiments should consider impacts to both donor and recipient populations and compare the costeffectiveness of translocations to other actions.2. Here we evaluate the translocations of a federally listed fish species, humpback chub within a tributary to the Colorado River in its Grand Canyon reach (Arizona, USA). We analyse mark-recapture data with multistate models to estimate vital rates (growth, survival and movement) for the donor and recipient populations while accounting for substantial temporal variation in vital rates. We then use stochastic matrix projections to quantify the impact of translocations on adult population size. Lastly, we compare the costs of translocations to another, legally required management action, non-native fish removal, by modifying an existing bioeconomic model.3. We estimate that six of eight translocations during the study period positively impacted adult abundance and that the overall population impact was positive.Population projections suggest that each chub translocated per year increases the equilibrium adult population size by 1.2 (95% CI: 0.4-2.2) adults, lessening the need for non-native fish removal.4. The continuation of translocations at the current rate is expected to save managers ~$50,000 per year by decreasing the annual probability of removals from 0.26 to 0.15. Further savings and decreases in removals could be attained by avoiding translocations in years when there has been no winter/spring runoff and modifying the number of translocated individuals based on the estimates of juvenile production in the lower Little Colorado River. Synthesis and applications.Translocations that increase the abundance of a rare species can sometimes be viewed as a hedge against future declines that might necessitate more costly interventions. Quantifying population benefits and economic costs of management actions like translocations and comparing alternative actions can lead to cost-effective conservation that is more easily sustained.

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