Partial migration and spawning movements of humpback chub in the Little Colorado River are better understood using data from autonomous PIT tag antennas

Choosing whether or not to migrate is an important life history decision for many fishes. Here we combine data from physical captures and detections on autonomous passive integrated transponder (PIT) tag antennas to study migration in an endangered fish, the humpback chub (Gila cypha). We develop hidden Markov mark-recapture models with and without antenna detections and find that the model fit without antenna detections misses a large proportion of fish and underestimates migration and survival probabilities. We then assess survival and growth differences associated with life history strategy and migration for different demographic groups (small male, small female, large male, large female). We find large differences in survival according to life history strategy, where residents had much lower over-winter survival than migrants. However, within the migratory life history strategy, survival and growth were similar for active migrants and skipped migrants for all demographic groups. We discuss some common challenges to incorporating detections from autonomous antennas into population models and demonstrate how these data can provide insight about fish movement and life history strategies.

An Evaluation of Sedatives for Use in Transport of Juvenile Endangered Fishes in Plastic Bags

Trucks and aircraft typically transport rare or endangered fishes in large unsealed tanks containing large volumes of water (typically hundreds of liters) during conservation efforts. However, to reduce weight and overall shipping costs, fish breeders commonly send ornamental fishes by mail in small sealed plastic bags filled with oxygen, minimal water, and a small amount of sedative. Our goal was to evaluate if we could also use these “minimal-water” methods used for shipping ornamental fishes to safely transport endangered Humpback Chub Gila cypha into remote locations within Grand Canyon on foot to eliminate helicopter transportation costs associated with conservation actions. In the laboratory, we placed 20 (mean = 193.9 g of fish/L, SD = 37.8) juvenile Bonytail Gila elegans or Humpback Chub in plastic bags containing 1 L of water and pure oxygen for 4, 8, and 12 h. Treatments contained either no sedative or one of three sedatives—AquaCalm (metomidate hydrochloride), Tricaine-S (tricaine methanesulfonate or MS-222), or Aqui-S 20E (eugenol)—to evaluate the effectiveness of minimal-water methods for use in fish transport. Aqui-S 20E and the control without sedatives exhibited the highest survival (logistic regression, Aqui-S 20E, p = 0.994, 95% CI [0.978, 0.998]; control, p = 0.995, 95% CI [0.981, 0.998]), followed by Tricaine-S (p = 0.933, 95% CI [0.902, 0.955]) and AquaCalm (p = 0.355, 95% CI [0.307, 0.406]). We also conducted a field trial in which we placed 240 juvenile Humpback Chub in shipping bags (n = 20 fish/bag/L of water; mean = 143.2 g of fish/L, SD = 9.72) with no sedative or 10.0 mg/L of Aqui-S 20E and transported them by vehicle and on foot. No fish perished during transport, indicating fisheries personnel can use these minimal-water methods to safely, and at little expense, transport endangered Humpback Chub into remote locations.

Body Condition of Endangered Humpback Chub in Relation to Temperature and Discharge in the Lower Colorado River

Determining the population status of endangered Humpback Chub Gila cypha is a major component of the adaptive management program designed to inform operation of Glen Canyon Dam upstream from Grand Canyon, Arizona. In recent decades, resource managers have identified a portfolio of management actions (with intermittent implementation) to promote population recovery of Humpback Chub, including nonnative fish removal, changes in water release volumes and discharge ramping schedules, and reductions in hydropower peaking operations. The Humpback Chub population in Grand Canyon has increased over this same period, causal factors for which are unclear. We took advantage of unusual hydrology in the Colorado River basin in 2011 to assess trends in juvenile Humpback Chub length–weight relationships and condition in the Colorado River below Glen Canyon Dam as well as in the unregulated Little Colorado River. Within each river, we observed higher length–weight b-parameter estimates (exponent of the standard power equation) at higher water temperatures. We also found higher slope estimates for the length–weight relationship at higher temperatures in the Little Colorado River. Slope estimates were more variable in the Colorado River, where mean water temperatures were more uniform. The next step is to examine whether Humpback Chub length–weight relationships influence population metrics such as abundance or survival. If these relationships exist, then monitoring condition in juvenile Humpback Chub would provide a quick and low-cost technique for assessing population response to planned management experiments or changing environmental conditions.