Uniquely tagged animals provide an opportunity to study changes in population demographics and movement. Passive integrated transponder (PIT) tags are used to monitor growth, movement, and survival of fishes. Laboratory studies of tag retention and mortality in small‐bodied, warmwater cyprinids after insertion of PIT tags are rare. Mortality induced by two PIT tag implantation methods was compared, and tag retention after implantation was assessed. Relations between standard length and tag retention and between standard length and survival in Rio Grande silvery minnow Hybognathus amarus were examined. Fish were randomly selected and PIT‐tagged with 12.5‐mm tags via surgical incision or needle injection and were held in laboratory aquaria for 32 d. Mean (±SE) survival on day 32 was 99 ± 1% for control fish, 87 ± 6% for fish that received tags by incision, and 50 ± 5% for fish that received tags by injection. We also tagged 280 fish by incision and held them in aquaria for 49 d. On day 49, survival and tag retention were both 90%. Longer fish had higher survival, but tag retention was not related to fish length. Rio Grande silvery minnow can be reliably tagged with PIT tags if the fish are greater than 60 mm standard length. Treatment with antibiotics and holding of fish in captivity for a minimum of 6 d before release are recommended.

This is an open access article under the terms of the Creat ive Commo ns Attri bution-NonCo mmerc ial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Habitat fragmentation and changes in flow regime can structure fish assemblages, resulting in extirpations or invasions. A guild of freshwater stream fishes that spawn semi‐buoyant, nonadhesive eggs directly in the water column are particularly susceptible to extirpation in fragmented streams. The pelagic broadcast‐spawning Rio Grande Silvery Minnow Hybognathus amarus was listed as endangered in 1994 and has been intensely managed since. I used mean May flows and the number of times the channel dried within a year to predict numbers of Rio Grande Silvery Minnow captured in isolated pools in the Middle Rio Grande, New Mexico. Adult Rio Grande Silvery Minnow numbers increased as previous year's mean May discharge increased, and generally decreased with each subsequent drying event. Similarly, numbers of young‐of‐year Rio Grande Silvery Minnow increased with increasing mean May discharge in the current year. However, young‐of‐year minnow were either very abundant or nearly absent in isolated pools, depending on mean May discharge. Overall trends show a strong decrease in total yearly numbers of adult and young‐of‐year Rio Grande Silvery Minnow collected in isolated pools from 2009 to 2014, coupled with an increase in the proportion of hatchery‐reared adults. Overall numbers fell from >1,000/km in 2009 to <15/km in 2014. Hatchery‐reared fish increased from 0% in 2009 collections to 90% in 2014 collections. Managers should focus recovery efforts on providing spring flows that improve recruitment, and avoiding consecutive years of low spring flow because any population recovery will likely be negated by three consecutive years of recruitment failure. A self‐sustaining population of Rio Grande Silvery Minnow is unlikely without management options that mitigate the effects of multiyear droughts. Received August 3, 2015; accepted February 12, 2016 Published online June 21, 2016

As precipitation and temperature patterns change, the resulting alterations in hydrologic conditions may adversely affect some stream fishes. The unique guild of freshwater, pelagic broadcast-spawning minnows found in the western United States appears to be particularly sensitive to low-flow conditions. We examined reproductive and recruitment patterns of one of these species, Rio Grande silvery minnow (Hybognathus amarus), over a three-year period, which included one year of extreme drought. We followed gonadal development from March through September each year, from 2017 to 2019, to determine if Rio Grande silvery minnow were reproductively active during extreme drought. The population structure was also monitored to confirm successful recruitment over the same period. We found that in all years Rio Grande silvery minnow were reproductively active in April through early June, including during extreme drought in 2018. However, almost no recruitment occurred in 2018, and by early 2019 the population was dominated by older, wild age-2 fish and hatchery-reared fishes. Our work supports previous research on pelagic broadcast-spawning minnows and confirms that extreme low-flows results in near-complete recruitment failure of Rio Grande silvery minnow. This work will help inform management and conservation of Rio Grande silvery minnow and other pelagic broadcast-spawning minnows during drought or low flows years.

Managers charged with recovering endangered species in regulated river segments often have limited flexibility to alter flow regimes and want estimates of the expected population benefits associated with both flow and nonflow management actions. Disentangling impacts on different life stages from concurrently applied actions is essential for determining the effectiveness of each action, but difficult without models that integrate multiple information sources. Here, we develop and fit an integrated population model for endangered Rio Grande Silvery Minnow (Hybognathus amarus) in the Middle Rio Grande, New Mexico. We integrate catch per unit effort monitoring data collected during 2002-2018 with population estimates, data collected during rescue of minnow from drying pools, habitat availability estimates, laboratory results, releases of hatchery reared minnow, and expert opinion. We use expert elicitation to develop a larval carrying capacity index as an informed proxy for the complex interactions among flow, habitat, and life history in this species. We evaluate the model using out-of-sample forecasts of 2019 and 2020, develop an algorithm to identify supplemental water releases that maximize benefits to the minnow, and quantify the effectiveness of various actions. Experts generally agreed on the duration and

Streamflow intermittency can reshape fish assemblages and present challenges to recovery of imperiled species. During streamflow intermittency, fish can be subjected to a variety of stressors, including exposure to crowding, high water temperatures, and low dissolved oxygen, resulting in sublethal effects or mortality. Rescue of fishes is often used as a conservation tool to mitigate the negative impacts of streamflow intermittency. The effectiveness of such actions is rarely evaluated. Here, we use multi-year water quality data collected from isolated pools during rescue of Rio Grande silvery minnow Hybognathus amarus, an endangered minnow. We examined seasonal and diel water quality patterns to determine if fishes are exposed to sublethal and critical water temperatures or dissolved oxygen concentrations during streamflow intermittency. Further, we determined survival of rescued Rio Grande silvery minnow for 3–5 weeks post-rescue. We found that isolated pool temperatures were much warmer (>40 °C in some pools) compared to upstream perennial flows, and had larger diel fluctuations, >10 °C compared to ~5 °C, and many pools had critically low dissolved oxygen concentrations. Survival of fish rescued from isolated pools during warmer months was <10%. Reactive conservation actions such as fish rescue are often costly, and in the case of Rio Grande silvery minnow, likely ineffective. Effective conservation of fishes threatened by streamflow intermittency should focus on restoring natural flow regimes that restore the natural processes under which fishes evolved.

We designed a study to determine if Rio Grande silvery minnow Hybognathus amarus, an endangered species, would use an instream, rock channel fishway on the Rio Grande near Albuquerque, New Mexico. We implanted 6,657 Rio Grande silvery minnow with passive integrated transponders and used a passive scanning station with two antennas located within the fishway to document movements from seven release locations, up to 19.7 km upstream and 13.5 km downstream of the diversion dam. Between 11 March and 21 August 2011, 243 individuals were detected (3.7% of all fish released), with 74.1% fish being detected from upstream release sites and 25.9% from downstream release sites. We determined 14 Rio Grande silvery minnow successfully ascended the fishway, and an additional 20 fish from downstream release locations were detected on the upstream antenna only, inferring passage. We conclude Rio Grande silvery minnow can use appropriately constructed fishways. Received October 17, 2011; accepted March 21, 2012

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