Simulated Transport and Retention of Pelagic Fish Eggs during an Irrigation Release in the Pecos River, New Mexico

ABSTRACT The Pecos River between Sumner Dam and Brantley Reservoir (320 km), New Mexico, contains populations of several pelagic-spawning cyprinid fish species, including the federally threatened Pecos bluntnose shiner (Notropis simus pecosensis). Females of this reproductive guild release semi-buoyant eggs that are fertilized and drift, incubate, and hatch on increased flows associated with spring runoff, summer rainstorms, or irrigation releases from Sumner Reservoir. We used artificial eggs (beads) to estimate transport and retention of natural eggs during an irrigation release in five reaches of the Pecos River occupied by bluntnose shiner. Bead retention was highest (1.7–4.5%/km) in the broad complex reaches of upper critical habitat and the quality section (upper 200 km), and bead retention was lowest (0.6%/km) in the narrow, deep, channelized reach of lower critical habitat (60 km). Only 10% of beads were transported more than 50 km from their release location in the reach with highest retention. M...