Date of Award:

12-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Phaedra Budy

Committee

Phaedra Budy

Committee

Robert K. Dudley

Committee

Mary Conner

Abstract

Fishes are unified in their need to move within the systems they occupy, and their movement patterns can be fundamental to their ecology and survival. Many large rivers in North America are fragmented by dams that modify natural flow regimes, compromise connectivity, and imperil freshwater fishes dependent on unrestricted movement in order to complete their life history. Coincident with widespread river fragmentation, are the declines of numerous endemic desert fishes in the American southwest. The Rio Grande Silvery Minnow (Hybognathus amarus, RGSM), has experienced a 95% reduction in its historical range and is now restricted to a highly fragmented stretch of river. Despite the important role of movement in riverine fishes, there are few studies describing the movement patterns of RGSM. The overall goal of this study is to document and better understand the movement ecology and patterns of RGSM. We used Passive Integrated Transponder (PIT) tags in hatchery-reared RGSM with stationary and mobile PIT-tag antenna systems to detect and track movement patterns across time and space. We released a total of 37,215 PIT-tagged RGSM between 2018 and 2022. Of those released, we detected 13,706 RGSM making at least one movement (e.g., detected at two different locations). We found RGSM to be highly mobile and documented individuals moving farther distances than ever previously recorded. Individuals moved a mean total distance of 12.2 river kilometers (rkm) over the course of one year, with a maximum total distance of 103.0 rkm. Overall, total distances moved by individuals was larger than linear home range sizes within one year of release, suggesting RGSM were moving at finer scales within the extent of the river they occupied. Although individuals moved large distances, movement patterns were leptokurtic, with a larger portion of RGSM remaining near their initial release location. We documented a total 198 unique upstream passages through a diversion dam. The documentation of these passages is particularly meaningful as passage through this diversion by RGSM has not been previously documented and the diversion is not equipped with a formal fish passage. As indicated by the high number of repeated detections over the study period, as well as our high redetection rate (36.8%), the efficacy of our study design to detect an imperiled small-bodied fish species has crucial conservation applications. Our study elucidates the movement patterns of RGSM and can be an important model for other fish species in fragmented desert systems.

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