Little bugs, big data, and Grand Canyon: light trapping by river rafters yields insights into Colorado River aquatic insect dynamics

Authors: Theodore* Kennedy, Jeffrey Muehlbauer, Charles Yackulic, David Lytle, Eric Kortenhoeven, Anya Metcalfe

Year: 2015 (xlvii)

Abstract

Enter abstract text (English);Glen Canyon Dam has greatly altered the discharge and temperature regimes of the Colorado River in Grand Canyon, which may explain why only two aquatic insect taxaÁ¢â‚¬’ midges and blackfliesÁ¢â‚¬’ are common in this river segment. In 2012, we initiated a citizen science project in collaboration with river rafters to quantify insect emergence for the 386 km Grand Canyon segment of the Colorado River. Rafters conducted standardized light trapping each night in camp, yielding an unprecedented emergence dataset (750+ samples each year). This dataset has elucidated insect emergence patterns related to dam operations, including pronounced decreases in midge emergence (catch per hour) coincident with abrupt increases in regulated discharge. Longitudinal patterns of emergence for midges were sinusoidal and appear related to the time of day when low versus high water associated with hydropeaking waves occurs in different reaches. Specifically, we observed higher and lower rates of insect emergence in locations of the Canyon where afternoon flows represented the daily minima and maxima, respectively. Because mating and egg-laying by aquatic insects often occurs in late afternoon/evening, these sinusoidal patterns in emergence may reflect differences in the quality of the egg-laying environment for aquatic insects. These results indicate that frequent hydropeaking may represent a bottleneck that limits aquatic insects by causing high mortality at the egg stage. Our findings suggest that aquatic insect assemblages might be enhanced through changes in flow management alone, even without more natural temperature regimes.