Use of Ultrasonic Imaging to Evaluate Egg Maturation of Humpback Chub Gila cypha in Grand Canyon
Humpback Chub Gila cypha are endangered cyprinids endemic to the Colorado River drainage and are adapted to live in fast currents of warm, turbid water. Although nine known aggregations of Humpback Chub currently exist in the main-stem Colorado River in the Grand Canyon, little is known about their reproduction. We hypothesized that recruitment of juvenile Humpback Chub in Grand Canyon was limited because hypolimnetic water releases from Glen Canyon Dam create water temperature conditions that are too cold for female Humpback Chub to develop mature eggs for spawning. Our goal was to use ultrasonic imaging, a non-lethal method, to evaluate reproductive condition of female Humpback Chub in Grand Canyon to determine if water temperature limits egg development in female Humpback Chub. We documented egg development in female fish from the main-stem Colorado River, Little Colorado River, Havasu Creek, and Shinumo Creek. Egg development in Humpback Chub varies by location and time of year. Potentially ripe female fish were found at all sample locations and dates except at Shinumo Creek in 2013 and 2014. Potentially ripe females were also detected in every main-stem aggregation except for Pumpkin Springs and in two locations outside of established aggregations. Our findings indicate that female Humpback Chub are able to produce eggs throughout the main-stem Colorado River and that internal egg development and egg production likely do not limit Humpback Chub recruitment in Grand Canyon. However, if female fish experience the environmental triggers, they need to spawn remains unknown. Furthermore, if these fish do spawn, the degree that their spawned eggs survive and develop in the cold-water temperatures currently present within much of the Colorado River in Grand Canyon remains unknown. A thesis on this work was completed in May 2016, and results are being prepared for publication.