STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN by JESSICA L. DAVIS (Under the Direction of Mary C. Freeman and Stephen W. Golladay) ABSTRACT Streamflow alteration from the combined effects of water extraction and climate change is recognized as a major threat to aquatic ecosystems. The Ichawaynochaway Creek Basin is a Gulf Coastal Plain stream system in southwestern Georgia, where streamflows are strongly influenced by agricultural water withdrawals and recent droughts. This study explores effects of stream intermittency and drying on the composition of biologically diverse fish communities, and life history traits that may influence persistence of four closely related cyprinid species. Intermittent stream communities were found to be a subset of perennial stream communities, with the highest persistence rates among adults and juveniles of species that commonly occur in intermittent streams. My results identify life history traits that may be useful for understanding differences in how closely related species respond to changing environments, with smaller body size at maturity along with appropriate reproductive timing promoting greater persistence given more frequent and intense disturbances. INDEX WORDS: Warmwater Streams, Fish Community Structure, Drought, Persistence, Colonization, Life History Traits STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN by JESSICA DAVIS B.S., University of North Carolina, Asheville, 2015 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTERS OF SCIENCE ATHENS, GEORGIA 2017 © 2017 Jessica L. Davis All Rights Reserved STREAM FISH RESPONSE TO INTERMITTENCY AND DRYING IN THE ICHAWAYNOCHAWAY CREEK BASIN by JESSICA L. DAVIS Major Professor: Mary C. Freeman Stephen W. Golladay Committee: Seth J. Wenger Robert B. Bringolf Electronic Version Approved: Suzanne Barbour Dean of the Graduate School The University of Georgia December 2017 DEDICATION For pop, the best dad a kiddo could ever have asked for. iv ACKNOWLEDGEMENTS I couldn't have made it through this project without the support from my colleagues, family, and friends. My project would have been little compared to what it is without the help of Mary Freeman at every turn. From helping write code, to always making herself available for questions big and small, I couldn't have found a more caring and supportive advisor. Special thanks to Steve Golladay, my co-advisor, for his support of both me and my husband, d.w., during our time at the Jones Center. To my committee members, Seth Wenger and Robert Bringolf, thank you for helping develop my understanding of statistics and fishes. I would also like to thank the Odum School of Ecology and the Joseph W. Jones Ecological Research Center for funding me through this endeavor. The opportunity to live and work in such a magical part of the world is something I will always look back on fondly. I would also like to thank those at the Jones Center who helped make this project possible. Especially, Denzell Cross, Meg Hederman, and Robert Ritger we made it through the heat, the gnats, the mosquitoes, and the snakes, all while singing songs and dancing the electrofish dance! Denzell, you were with me from day one, and words can’t describe how happy I am to see you at Odum in pursuit of your PhD. Chelsea Smith, you are my live version of stackexchange, thank you for always being there to bounce ideas off and help me with statistics. Camille Herteux and Cara McElroy, thank you for all of the laughs and little distractions that helped keep me sane. v A final thanks to d.w. giddens, my husband and partner in all else, without whom I would rarely have taken a step back to appreciate all that is wonderful in the Universe. I give my deepest love and appreciation for the encouragement and sacrifices you gave and made throughout this project. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS .................................................................................................v LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES .......................................................................................................... xii CHAPTER 1 LITERATURE REVIEW AND SUMMARY OF OBJECTIVES ...................1 2 STREAM DRYING AND FISH OCCUPANCY DYNAMICS IN THE ICHAWAYNOCHAWAY CREEK BASIN ..................................................10 3 IDENTIFYING LIFE HISTORY TRAITS THAT PROMOTE FISH SPECIES PERSISTENCE IN INTERMITTENT STREAMS ......................73 4 CONCLUSIONS AND SUMMARY ...........................................................140 APPENDICES A SPECIES OCCURRENCE OF TAXA FOUND FOR CHAPTER 2 ..........146 B DETAILED DESCRIPTION OF OCCUPANCY MODEL ........................157 C SPECIES AND AGE CLASS OCCURRENCES OF TAXA FOUND AT INTERMITTENT STREAMS FOR CHAPTER 2 .....................................163 D R CODE USED FOR DYNAMIC OCCUPANCY MODEL ......................165 E INDICATOR ANALYSIS AND CLASSIFICATION FOR SPECIES STRATEGISTS ENDPOINTS .....................................................................169 vii LIST OF TABLES Page Table 2.1: Summary statistics of water quality data obtained in 90 isolated pools monitored in 12 stream sites in the Ichawaynochaway Creek basin, June through September 2015 and 2016, followed by their values centered and scaled around zero by subtracting the mean and dividing by the standard deviation. Scaled values were used as covariate effects on observed fish occurrence in isolated pools. Numbers of isolated pools (n), and mean covariate value are shown along with standard deviation (SD), standard error (SE), minimum (Min) and Maximum. ..............................................................................................................43 Table 2.2: Effects of covariates on regression coefficients for persistence, colonization, and detection from multi-taxa, dynamic occupancy models using a time-series (2015-2017) of detection for adults of 21 species and juveniles of 25 species in the Ichawaynochway Creek basin. Stream state, sampling method and cool season use binary coding. Distance is the distance of the study site from the nearest downstream perennial stream, standardized by subtracting the mean and dividing by the standard deviation. Effects of indicator-species covariates (Intermittent Nonindicative species and Perennial species, with Intermittent species as the baseline) on regression coefficients are shown for persistence during the number of weeks a site was isolated (Weeks Slack) and for colonization after resumption of flow (Weeks Flowing). Variance terms are for random effects of site and date viii (“surveys”) on intercepts for persistence, colonization, and detection, and on species-slopes for relations between persistence and Weeks Slack, and between colonization and Weeks Flowing. All values are on the logit scale, and show the posterior means and 95% credible intervals (in parentheses) ................................44 Table 2.3: Modeled effects of environmental covariates on probability of observed occurrence of adult fishes in 90 isolated stream pools in the Ichawaynochway Creek basin, 2015-2016. Values are the estimated effects on the log-odds of occurrence (95% confidence intervals) for predictor variables (values were centered and scaled around zero by subtracting the mean and dividing by the standard deviation) and the estimated random variance in intercepts attributable to species, surveys, and pools (nested within repeated survey of a pool), and in slopes attributable to species ..................................................................................45 Table 2.4: Modeled effects of environmental covariates on probability of observed occurrence of juvenile fishes in 90 isolated stream pools in the Ichawaynochway Creek basin, 2015-2017. Values are the estimated effects on the log-odds of occurrence (95% confidence intervals) for predictor variables (values were centered and scaled around zero by subtracting the mean and dividing by the standard deviation) and the estimated random variance in intercepts attributable to species, surveys, and pools (nested within repeated survey of a pool), and in slopes attributable to species ..................................................................................46 Table 3.1: Ovary and oocyte stages and descriptions of development based on oocyte size, coloration, yolk condition, and physical location within the ovum modified from Heins and Rabito (1986) and Heins and Baker (1987) ...............................106 ix Table 3.2: Standard lengths of males and females of four species assessed for reproductive development (>25mm) from seven study sites in the Ichawaynochaway Creek Basin from May 2016- April 2017. Numbers of individuals (n), and mean lengths are shown along with standard deviation (SD), standard error (SE), minimum (Min) and maximum (Max) ................................107 Table 3.3: Results from Chi-square tests of significance, which were performed separately on sexually mature individuals and non-reproductive individuals. Significant differences are marked with an * (p>.05) between the expected sex ratio of 1:1 and the observed sex ratio for males and females of a given species ..................................................................................................................108 Table 3.4: Standard