COMPARATIVE GROWTH AND DEMOGRAPHICS OF TWO SYMPATRIC NATRICINE SNAKES Kent A. Bekker A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December 2007 Committee: Dr. Daniel M. Pavuk, Advisor Dr. Richard B. King Dr. Jeffery G. Miner ii ABSTRACT Dr. Daniel M. Pavuk, Advisor The northern water snake, Nerodia sipedon and the queen snake, Regina septemvittata, are two species of the subfamily Natricinae that occur sympatrically throughout much of their ranges in Ohio. Regina septemvittata does not appear to be as abundant as it once was in much of its range, and published natural history information is lacking. Nerodia sipedon, however, has exhibited no decrease in abundance, and there is a relative abundance of published natural history information on this species. This study compares growth and population size for both species utilizing mark-recapture techniques and skeletochronology at the Sandusky Bay Fishing Access Site in Ottawa County, Ohio. The Sandusky Bay fishing access site supports populations of the following snake species: the northern water snake, Nerodia sipedon, the queen snake, Regina septemvittata, the eastern garter snake, Thamnophis sirtalis, Butler’s garter snake, Thamnophis butlerii, the eastern fox snake, Elaphe gloydi, and Dekay’s snake, Storeria dekayi. Population estimates for Nerodia sipedon result in densities similar to published values for nearby populations. Population estimates for Regina septemvittata displayed a decline over the course of the study, which was mirrored in the relative abundance of queen snake within the total sample for each year. Growth has an impact on snake conservation through delayed maturation, longer time spend at a size class experiencing a higher rate of mortality, and reduced reproductive advantage. Nerodia sipedon is growing faster than most of the previously published rates, and growth rates are similar to those experienced in Lake Erie populations since the introduction of the round goby. Regina septemvittata females and juveniles are growing slower than the previously published values. iii Skeletochronology was used to age individuals via lines of arrested growth (LAG) in bones. Tail vertebrae were sampled in an attempt to age individuals of both Nerodia sipedon and Regina septemvittata. There was no correlation between snout-vent length and number of LAGs. There was very little agreement between multiple investigators with respect to the number of LAGs counted within a single sample. The results of this study suggest an overall decline in the queen snake, Regina septemvittata and a stable population of the northern water snake, Nerodia sipedon, at the Sandusky Bay location. The difference in growth rates between this study and previously published values for both species may be influenced by the introduction of round gobies. iv Sandusky Bay Fishing Access Site v ACKNOWLEDGMENTS Many thanks to my understanding wife Staci Bekker for her continual support and encouragement. Thanks to my many herp friends who also encouraged me to finish; Kristin Stanford, Bill Flanagan, Greg Lipps and Rich King. Thanks to all the people who assisted with catching snakes, especially: Tim Herman, Trevor Walsh, Joe Timar, Michael Dawson, and Dustin Chandler. Thanks to the Toledo Zoo for professional development funds, Department of Herpetology staff for schedule flexibility, and Andy Odum curator of herpetology for supporting my efforts. Thanks to the additional slide readers; John Chastain, Jeff Cypher, Tim Herman and Leisje Meates. Thanks to my committee members for there comments and assistance. vi TABLE OF CONTENTS Page INTRODUCTION ................................................................................................................. 1 METHODS………….. .......................................................................................................... 6 Study Site ............................................................................................................ 6 Mark-recapture........................................................................................................... 7 Skeletochronology ..................................................................................................... 13 RESULTS……………. ......................................................................................................... 15 Population Composition............................................................................................. 15 Population Size Estimation........................................................................................ 15 Growth………. .......................................................................................................... 18 Skeletochronology ..................................................................................................... 25 DISCUSSION………............................................................................................................ 28 Population Composition and Size.............................................................................. 28 Growth……... ............................................................................................................ 29 Skeletochronology ..................................................................................................... 34 REFERENCES ...................................................................................................................... 37 vii LIST OF FIGURES Figure Page 1 Map of Sandusky Bay showing study area ................................................................ 6 2 Aerial photograph of Sandusky Bay Fishing Access................................................. 7 3 Seasonal distribution of sampling effort in four years of the study ........................... 9 4 Size frequency distribution for Nerodia sipedon <50cm ........................................... 12 5 Size frequency distribution for Regina septemvittata <50cm ................................... 12 6 Size distribution of snakes sampled for skeletochronology....................................... 14 7 Schumacher-Eschmeyer population estimates for both species for all three years ... 17 8 Proportion of each capture of the four species of snake caught each year ................ 17 9 Relationship between SVL and estimated age in juvenile Nerodia sipedon ............ 19 10 Relationship between SVL and estimated age in juvenile Regina septemvittata ..... 19 11 Growth intervals used in adult growth analysis ......................................................... 20 12 Predicted von Bertalanffy growth curves for Nerodia sipedon ................................. 21 13 Growth rates derived from intervals for Nerodia sipedon ......................................... 22 14 Predicted von Bertalanffy growth curves for Regina septemvittata .......................... 23 15 Growth rate derived from intervals for Regina septemvittata ................................... 24 16 Results of skeletochronological analysis for Nerodia sipedon .................................. 25 17 Variation in number of LAGs counted by multiple investigators.............................. 26 18 Prepared Nerodia sipedon vertebrae .......................................................................... 27 19 Growth rates from other published studies for female Nerodia sipedon ................... 30 20 Growth rates from other published studies for male Nerodia sipedon ...................... 30 21 von Bertalanffy growth curves compared to other published values......................... 31 22 Hypothetical growth curves explaining areas of sampling ........................................ 32 viii LIST OF TABLES Table 1 Number of snakes captured of all species.................................................................. 15 2 Schumacher-Eschmeyer adult population estimates for both species ....................... 16 3 Jolly-Seber adult population estimates for both species ............................................ 16 4 ANCOVA of SVL for each species with sex as a factor and age as a covariate ....... 18 5 ANCOVA of SVL with species as a factor and age as a covariate ........................... 19 6 Parameters from von Bertalannfy curves for Nerodia sipedon ................................. 22 7 ANCOVA of daily growth rate for Nerodia sipedon................................................. 22 8 Parameters from von Bertalanfy curves for Regina septemvittata ............................ 24 9 ANCOVA of daily growth rate for Regina septemvittata ........................................ 24 10 Growth values for neonatal Regina septemvittata from other published studies....... 33 1 INTRODUCTION Reptiles appear to be declining at an increasing rate worldwide (Gibbons et al., 2000). These declines may or may not be attributable to anthropogenic causes. However, habitat loss and alteration, invasive species, and pollution may all be factors leading to the decline of local reptile species. Even for many of the common species, basic life history information is lacking. Basic information about a species natural history is paramount to understanding species ecology. Without a good understanding of species ecology goals of conservation biology cannot be achieved (Rivas, 1997). If ecological data are deficient, models are not valuable (Noss, 1996). Even with a single population study’s inherent geographic constraint, the information attained from such an endeavor