Movement and Growth of Juvenile Colorado Pikeminnows in the San Juan River, Colorado, New Mexico, and Utah

Abstract

Understanding patterns of animal distribution and abundance based on their movements is important to identify the habitats and factors that maximize growth and reproductive success. Despite stocking age-0 hatchery-reared Colorado Pikeminnow Ptychocheilus lucius for over 10 years in the San Juan River of Colorado, New Mexico, and Utah, the population consists primarily of stocked juveniles; adults remain rare. We investigated seasonal movement and growth of juvenile Colorado Pikeminnows in the San Juan River from 2009 to 2012 to inform recovery efforts throughout the Colorado River basin. Our results indicated fish made long-distance upstream movements from spring to summer while moving back downstream over winter. Seasonal movements may be associated with maximizing growth along longitudinal and seasonal temperature regimes. Length-at-age relationships reveal Colorado Pikeminnows in the San Juan River were larger than individuals of the same age in other populations in the upper Colorado River basin. While warmer water temperatures may have played some role in the larger lengths at age we observed, the hatchery-reared fish that are stocked at age 0 are probably larger than their wild-spawned counterparts of the same age. Variation in growth rates among size-classes indicates small Colorado Pikeminnows (<200 mm TL) had slower growth rates than larger individuals in the San Juan River, suggesting a possible resource limitation for smaller juvenile fish. Understanding how seasonal movement and growth of all life stages of Colorado Pikeminnow interact with modified river systems will be important for population conservation and recovery efforts in the upper Colorado River basin.

A Tribute to Tributaries: Endangered Fish Distributions within Critical Habitat of the San Juan River, USA

“…Smaller Razorback Suckers tended to move farther away (e.g., upstream) from the mouth of McElmo Creek—maybe to search for better habitat, such as low‐velocity habitat that is less prevalent within that area—compared with more limited movements around Chaco Wash (Bliesner and Lamarra ). Movement distances of Colorado Pikeminnows were best explained by season (e.g., downstream in nonsummer) and to some extent size, similar to other findings that indicate greater movement in main‐stem and tributary habitats during nonsummer periods by subadult individuals (Durst and Franssen ; Cathcart et al. ).…”

“…Given the variable movements among populations of Colorado Pikeminnows in the Colorado River basin and different tributary use by them in the San Juan River, revived consideration of alternative life history tactics (i.e., movers versus stayers) is warranted. For example, testing “moving” versus “staying” tactics in the context of the San Juan River Colorado Pikeminnow could demonstrate that a staying strategy promotes retention of individuals in the system and a potentially smaller viable population compared with the movers (especially subadults) that may swim too far downstream and pass over the waterfall, never to return (sensu Durst and Franssen ).…”

“…Fish tagged with transmitting tags allow biologists to track them through various habitat types (Durst and Franssen ; Cathcart et al. ).…”

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

“…The evidence examined here, however, suggested that variation in annual flows or prey‐fish densities had little impact on the consumption of fish prey by age‐1 or age‐2 Colorado pikeminnow. Moreover, the San Juan River demonstrates strong longitudinal variation in prey‐fish availability, but juvenile Colorado pikeminnow tend to only occur in areas of the river with high prey densities seasonally (Durst & Franssen, ; Franssen & Durst, ). There were positive relationships between the size of Colorado pikeminnow and δ 15 N in both age classes, with no discernible nonlinear steps or sharp increases in δ 15 N, suggesting that characteristics associated with fish growth are affecting rates of fish‐prey consumption (e.g.…”

“…Stomach‐content analysis indicates, as for other piscivorous fishes, that wild Colorado pikeminnow are mostly insectivorous as juveniles (Muth & Snyder, ), but demonstrate almost complete piscivory once TL = 200 mm (Vanicek & Kramer, ). For stocked individuals in the San Juan River, this dietary transition to piscivory is predicted to occur between age 1 and age 2, based on their size‐at‐age (at age 1, mean TL = 177 mm; at age 2, mean TL = 235 mm; Durst & Franssen, ). However, given extirpations (i.e.…”