POPULATION STRUCTURE OF THE HELLBENDER (CRYPTOBRANCHUS ALLEGANIENSIS) IN A GREAT SMOKY MOUNTAINS STREAM Kirsten A. Hecht-Kardasz1, Max A. Nickerson2, Michael Freake3, and Phil Colclough4 ABSTRACT The hellbender (Cryptobranchus alleganiensis) is an imperiled salamander that has experienced population declines in many parts of its range. Young hellbenders, particularly larvae, have rarely been found in the wild. In 2000, a short study in Little River in Great Smoky Mountains National Park, Tennessee, discovered a population of C. alleganiensis where larvae were regularly encountered and few adults were observed. However, the 2000 study was limited in scope, and additional research was needed to accurately describe the overall hellbender population structure. Three additional studies of C. alleganiensis in the same section of Little River occurred from 2004–2010. This paper analyzes the results of all four studies conducted between 2000–2010 to examine trends in the hellbender population structure within Little River, and to provide reference data for future monitoring efforts in the park. From 2000–2010, a total of 533 captures, including 33 recaptures, occurred with larvae representing a quarter of overall captures. Adults were more abundant than suggested by the 2000 study, but individuals representing larger size classes were still relatively rare. Although the structure of the sampled population varied among years, larvae were relatively abundant except following years of extreme stream flow events, suggesting that turbulent current may be an important influence on the population structure of Little River’s hellbender population. Key Words: hellbender, Cryptobranchus alleganiensis, Great Smoky Mountains, amphibian population, salamanders, population structure, size structure. 1School of Natural Resources and Environment, University of Florida, Gainesville, FL 32611-6455 USA <[email protected]> 2Florida Museum of Natural History, University of Florida, Gainesville, FL 32611-7800 USA <[email protected]> 3Department of Natural Sciences and Mathematics, Lee University, Cleveland, TN 37320-3450 USA <[email protected]> 4Knoxville Zoological Gardens, 3500 Knoxville Zoo Drive, Knoxville, TN 37914-4416 USA <[email protected]> Hecht-Kardasz, K. A., M. A. Nickerson, M. Freake, & P. Colclough. 2012. Population structure of the hellbender (Cryptobranchus alleganiensis) in a Great Smoky Mountains stream. Bulletin of the Florida Museum of Natural History 51(4):227–241. 228 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 51(4) INTRODUCTION (Duellman & Trueb 1986; Alford & Richards 1999; Swanack et al. 2009; Gillespie 2010). As Size, age, or life stage structures are integral obtaining amphibian population and life history components to understanding population dynamics data that accurately considers all life stage classes and can give more insight into population status can be problematic due to complex life cycles and than population size estimates alone (Alexander ontogentic shifts, data are often lacking for specific 1958; Downing 1980; Gillespie 2010). In size or life stage classes (Swanack et al. 2009; species of conservation concern, demographic Gillespie 2010). Larval and juvenile classes can be composition can indicate overall population difficult to study because they are generally cryptic, stability and lead to more accurate predictions small, and sometimes use different habitats than regarding future population trends (Crowder et al. 1994). A population composed primarily of older other life stages (Gillespie 2010). The resulting individuals may be at risk of decline or extirpation gaps in population structure data have hindered due to low recruitment (Alexander 1958; Downing researchers from fully comprehending the scope 1980). A population with few older individuals, but of amphibian declines (Lips 2011). The failure to many young individuals could indicate population elucidate potential mechanisms affecting individual growth, high adult mortality, or a failure to recruit amphibian populations has limited mitigation young life stage classes into adults (Alexander efforts (Alford & Richards 1999; Gillespie 2010). 1958; Downing 1980). Understanding population Once population declines occur, information is structure is also important because demographic even more difficult to obtain as individuals become rates can vary among different segments of the rare (Gillespie 2010). population (Crowder et al. 1994; Dobson & Oli One amphibian species with few studies 2001). regarding its basic demographics and population In aquatic environments, organisms often dynamics is the hellbender salamander, Crypto- adapt life strategies that can cause differences in branchus alleganiensis (Daudin 1803). A member demographic rates among age or life stage classes of the giant salamander family Cryptobranchidae, (Duellman & Trueb 1986; Pough et al. 2004). this long-lived (at least 29 years), large (740 Many species, including fish, aquatic insects, mm), aquatic species resides primarily in cool, and amphibians, develop complex life cycles or oxygen-rich streams in the eastern United States ontogenetic shifts in habitat use and diet, which are (Nickerson & Mays 1973a). There are currently believed to be adaptations for increasing survival two accepted subspecies: the eastern hellbender, in a stressful environment (Werner & Gilliam Cryptobranchus alleganiensis alleganiensis (Dau- 1984; Foster et al. 1988; Giller & Malmqvist din 1803) which ranges from Missouri to New 1998). These types of shifts can serve as a form York, and the Ozark hellbender, Cryptobranchus of refugia, limiting intra-specific competition alleganiensis bishopi (Grobman 1943) found only and predation (Werner & Gilliam 1984; Colley in Missouri and Arkansas (Nickerson & Mays et al. 1989; McGrath et al. 2007). While these 1973a). Currently listed as near threatened on the adaptations may help reduce individual mortality, International Union for Conservation of Nature they can also make studying population dynamics (IUCN) red list (Hammerson & Phillips 2004), more complicated. The difficulties associated with hellbender populations appear to be declining in studying organisms with complex life cycles or many parts of its range (Trauth et al. 1992; Wheeler ontogenetic shifts have caused knowledge gaps in et al. 2003; Briggler et al. 2007; Foster et al. 2009; the field of amphibian population ecology. Nickerson et al. 2009; Burgmeier et al. 2011). The Although many amphibian populations exact cause or causes of declines remain difficult to are declining worldwide (Alford & Richards elucidate, but siltation, disease, collection, species 1999; Vié et al. 2009), population dynamics and introductions, and habitat loss are just some of demographics of many species remain unstudied the cited problems facing this species (Trauth et HECHT-KARDASZ ET AL.: Hellbender population structure in a mountain stream 229 al. 1992; Hiler et al. 2005; Briggler et al. 2007; sized (< 130 mm) (Nickerson et al. 2002). This Nickerson & Briggler 2007; Nickerson et al. 2009). percentage was in stark contrast to those recorded Due to these declines, the hellbender is protected for other hellbender populations (e.g., Peterson et at the state-level throughout most of its range, and al. 1988; Wheeler et al. 2003; Foster et al. 2009). was recently added to CITES appendix III and the Furthermore, the proportion of adult hellbenders federal endangered species list (Anonymous 2011). to larvae within Little River was the lowest of Despite the conservation interest in Crypto- any studied river system (Nickerson et al. 2003). branchus alleganiensis, data regarding the However, the findings of Nickerson et al. (2002) population dynamics of this species remain sparse. were limited by small sample size and reduced Many hellbender localities lack data regarding search hours. Additional data were needed to population size, status, and demographics. Popu- confirm the differences in population structure in lation studies have primarily focused on snapshot Little River from those in well-studied streams. estimates of population size or adult population We compiled and analyzed data from surveys structure. Few studies have examined growth rates, conducted in Little River from 2004–2010 with fecundity, and survivorship in hellbenders and the results of Nickerson et al. (2002) in order to those that have were restricted to a few localities investigate the size structure of the hellbender in Missouri (Taber et al. 1975; Topping & Ingersol population in Little River, provide reference data 1981; Peterson et al. 1988). Existing examples may for this site, and to investigate long-term trends in not be representative for hellbenders across their population structure. range, particularly for the eastern subspecies. Limited historical data from a few studied MATERIALS AND METHODS drainages in New York and Missouri have given STUDY SITE better insight into long-term hellbender population To better elucidate the structure of Little trends and indicated that some populations were River’s hellbender population within Great Smoky declining and shifting in overall structure (Wheeler Mountains National Park, skin-diving surveys were et al. 2003; Foster et al. 2009). Comparisons of conducted within the 3 km section investigated historical and recent data in Missouri populations by Nickerson et al. (2002). Little River, located suggested that in declining hellbender populations, in the Blue Ridge Physiographic Province of size