Age‐Specific Estimates Indicate Potential Deleterious Capture Effects and Low Survival of Stocked Juvenile Colorado Pikeminnow

Abstract

Hatcheries and stocking programs have become necessary to repatriate or augment populations of imperiled fishes worldwide. Over nearly two decades, millions of endangered juvenile Colorado Pikeminnow Ptychocheilus lucius have been stocked into the San Juan River (Colorado, New Mexico, and Utah); however, recruitment of these individuals to adult life stages (age ≥6) remains low. Using a mark–recapture data set collected from annual riverwide electrofishing efforts between 2003 and 2016, we investigated apparent survival and capture probabilities of stocked Colorado Pikeminnow to identify age‐specific bottlenecks contributing to this lack of recruitment. With relatively high capture rates, which averaged between 0.34 and 0.39 for the first 2 years after an individual's first encounter, our results indicated that survival was consistently less than 0.25 for young age‐groups (i.e., ages 1–3), and no appreciable increase in survival occurred until fish had been in the river for at least 3 years (i.e., age ≥4+). Although age and capture effects were confounded for most age‐groups, capture appeared to reduce apparent survival for age‐2 fish by approximately 50%. The confounding effects of age, a completely hatchery‐origin population, and extensive environmental alterations to the San Juan River make it difficult to disentangle factors associated with this overall reduced juvenile survival.

Hatchery‐reared endangered Colorado pikeminnow (Ptychocheilus lucius) undergo a gradual transition to piscivory after introduction to the wild

“…As the age at maturation of the species is 6 years at the earliest (Vanicek & Kramer, 1969), very few reproductive individuals occur in the river, limiting the self-sustainability of the population (Farrington, Dudley, Kennedy, Platania, & White, 2016;Franssen, Durst, et al, 2016;Schleicher, 2017). At present, it is unclear which factors are associated with the limited recruitment of stocked individuals to adults, and whether the current stocking programme is a viable means for reestablishing a self-sustaining population of Colorado pikeminnow in the San Juan River (Clark, Conner, Durst, & Franssen, 2018).…”

Keeping it classy: classification of live fish and ghost PIT tags detected with a mobile PIT tag interrogation system using an innovative analytical approach

“…Successful management of sport fisheries, conservation of native fish, and endangered species recovery rely on the ability to accurately assess the effectiveness of focused management actions (Parma 1998;Pine et al 2009;Clark et al 2018). To assess the impact of management actions, managers often estimate demographic parameters such as survival and abundance (Gibbs et al 1998;Maxwell and Jennings 2005;Osmundson and White 2017).…”

“…Vital rates can be affected by sampling efforts, methods, gear, and data analysis (e.g., Walther and Moore 2005). Owing to a lack of accuracy and precision in some estimates, for many species there is still uncertainty regarding the processes limiting their viability, probability of persistence or recovery, and the effectiveness of management actions (Al-Chokhachy et al 2009;Osmundson and White 2017;Clark et al 2018).…”

Efficacy of fluorescent calcein mark retention and identification in endangered Colorado pikeminnow Ptychocheilus lucius

“…After this time interval, fish should have reached a size at which passive integrated transponder tags can be implanted. Distinction of hatchery and wild‐spawned Colorado pikeminnow would also provide the opportunity to evaluate factors that affect the relatively low survival of stocked Colorado pikeminnow (Clark, Conner, Durst, & Franssen, ).…”