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. I hypothesized that Colorado River water temperatures below Glen Canyon Dam are too low due to hypolimnetic water releases from Lake Powell for female Humpback Chub to develop mature eggs for spawning. Ultrasonic imaging, also called ultrasound, is an effective, non-lethal method used to determine sex and maturity of a variety of freshwater, anadromous, and marine fishes. However, many previous studies have been performed in laboratory environments. I developed a standardized method for ultrasonically scanning endangered Humpback Chub Gila cypha in remote locations within Grand Canyon, Arizona, USA. This method minimized stress to individual fish and took less than 1 min to perform. I was able to identify female fish with eggs based on two jpeg images and one 10 s video clip collected in the field. I also used ImageJ®, a National Institute of Health image processing program, to develop a brightness index to evaluate the maturity of eggs in female fish. I collected ultrasonic scans of captive, ripe Humpback Chub held at the Southwestern Native Aquatic Resources and Recovery Center (SNARRC) to determine that female fish were potentially ripe when a subsample of their eggs exhibited a brightness value within the 32-44 range. Although I was able to estimate egg maturity, I was not able to estimate egg mass of female fish. I used ultrasound to evaluate reproductive condition of 751 Humpback Chub in Grand Canyon. I 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 (stage 3) 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. Fisheries managers can use ultrasound to collect vital information about the reproductive status of fishes that cannot be killed and that are found in remote or rugged field locations. My 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 recruitment. However, female fish may never experience the environmental triggers they need to spawn or may not experience conditions that would allow eggs and larvae to survive.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/612435 |
| Date | January 2016 |
| Creators | Brizendine, Morgan E. |
| Contributors | Bonar, Scott A., Matter, William J., Ward, David L. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Electronic Thesis |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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