Investigating the Effects of Reservoir Water Releases on Spawning Activities of Fishes in the Pecos River

Published Date:
August 2022

Jesse E. Filbrun, Richard M. Raymondi, Sara A. Ricklefs

Extreme drying and water management practices threaten the persistence of native fishes across the American Southwest. We designed this study to monitor the effects of reservoir block releases on the reproductive success of fishes in the middle Pecos River near Fort Sumner, New Mexico. We intensively surveyed fish adults, drifting eggs, and drifting larvae from April through August 2020. We found species responded differently to the single reservoir block release during June 2020. The block release interrupted the production of eggs and larvae by native River Carpsucker and Sand Shiner. However, nonnative Common Carp juveniles were present in the river immediately after the release. Nonnative Plains Minnow, which were the most abundant pelagic-spawning minnows at our site, decreased in abundance and body condition after the block release. Surprisingly, we collected only 34 native adult pelagic-spawning minnows, 19 eggs, and no larvae. These patterns confirm that the broader regional observation of ecological reshuffling in favor of nonnative species is also well underway in fish communities of the middle Pecos River. To mitigate further collapse of native species, we recommend water managers consider releasing pulsed blocks of water downstream that more closely mimic the historical hydrology of the river in which native species evolved.

Technical Report 401

Reservoir releases, streamflow, fish eggs, fish larvae, drift survey, spawning condition, pelagic-spawning minnows