Eagle Hill Masthead



Southeastern Naturalist
    SENA Home
    Range and Scope
    Board of Editors
    Staff
    Editorial Workflow
    Publication Charges
    Subscriptions

Other EH Journals
    Northeastern Naturalist
    Caribbean Naturalist
    Urban Naturalist
    Eastern Paleontologist
    Eastern Biologist
    Journal of the North Atlantic

EH Natural History Home

  Help

About Southeastern Naturalist

 

Ecology and Morphology of Chelydra serpentina in Northwestern Florida
Matthew J. Aresco and Margaret S. Gunzburger

Southeastern Naturalist, Volume 6, Number 3 (2007): 435–448

Full-text pdf (Accessible only to subscribers.To subscribe click here.)

 

Site by Bennett Web & Design Co.
2007 SOUTHEASTERN NATURALIST 6(3):435–448 Ecology and Morphology of Chelydra serpentina in Northwestern Florida Matthew J. Aresco1,2,* and Margaret S. Gunzburger1,2 Abstract - Chelydra serpentina (Common Snapping Turtle) is a wide-ranging and often abundant turtle species in the eastern United States, but relatively little is known of its basic ecology in the Southeast. The objective of our study was to examine the ecology and population biology of and describe the morphology of Common Snapping Turtles in northwestern Florida. We intensively sampled five localities in Leon County, Fl using traps and hand collection (n = 111), and we also opportunistically collected Common Snapping Turtles as we encountered them through the course of other studies (n = 11). Analysis of seven morphological characters from a subset of individuals indicated that the Common Snapping Turtle in this study is an intergrade between C. s. serpentina and C. s. osceola. Estimated early growth rates were 20 mm carapace length (CL)/year, and females matured at about 220 mm CL (156 mm PL, approximately 6–8 years). Male Common Snapping Turtles (CL mean = 299 ± 6 mm) were larger than females (CL mean = 270 ± 5 mm), and the overall adult sex ratio was 1:1. Diet consisted primarily of aquatic plants (n = 4). Nesting females were found from early April through mid-May, and clutch size ranged from 5 to 49 eggs (n = 3). Common Snapping Turtle abundance varied over the five sites, but was highest (an average density of 16 individuals/ha) in small suburban ponds with abundant aquatic vegetation, a thick layer of organic sediment, and no alligators. In northwestern Florida, predation by alligators and humans and primary productivity appear to be the factors that influence the distribution and abundance of Common Snapping Turtles. Introduction Chelydra serpentina (Linnaeus) (Common Snapping Turtle) is one of the largest and most widely distributed turtles in North America (Ernst et al. 1994). This species occurs in lakes, ponds, streams, and slow-flowing rivers throughout southern Canada and the entire eastern and central United States (Ernst et al. 1994). A disjunct population occurs from Mexico through Central America and northern South America (Ernst and Barbour 1992). Four subspecies are currently recognized, two of which occur in the United States, C. s. osceola Stejneger (peninsular Florida) and C. s. serpentina (Linnaeus) (remainder of the US/Canadian geographic range), which are distinguished by several morphological characteristics (Ernst et al. 1994, Feuer 1971, Stejneger 1918). Intergradation has been documented between these subspecies in the Okefenokee Swamp area of southern Georgia (Feuer 1971). Recent research suggests that there is no genetic distinction between C. s. serpentina 1Department of Biological Science, Florida State University, Tallahassee, Fl 32306- 1100. 2Current address - Nokuse Plantation, 13292 County Highway 3280, Bruce, FL 32455. *Corresponding author - aresco@nokuse.org. 436 Southeastern Naturalist Vol. 6, No. 3 and C. s. osceola (Walker et al. 1998), and use of morphological characteristics may not allow diagnosis to subspecies (Phillips et al. 1996). The Common Snapping Turtle is not currently considered endangered in any part of its range, but threats to the Common Snapping Turtle that may result in local population declines include habitat destruction and alteration, pollution, and harvest (Aresco et al. 2006, Ernst et al. 1994, Gibbons 2003). Life history and demography of the Common Snapping Turtle are relatively well-studied in some areas in the northern portion of its range, such as the E.S. George Reserve in Michigan (Congdon et al. 1987, 1994) and Algonquin Provincial Park in Ontario (Galbraith and Brooks 1987a, Loncke and Obbard 1977). Demographic research on Common Snapping Turtles in the northern portion of its range indicates that this species has a typical life history of a long-lived, ectothermic vertebrate: slow growth rates, low recruitment, and high adult survivorship (Galbraith and Brooks 1987a, Galbraith et al. 1989, Yntema 1976). This species can reach high abundances in some habitats, but significant variation in density (0–66 adults/ha) and biomass (9–340 kg/ha) of Common Snapping Turtles has been documented in the northern and central portions of its range (Congdon and Gibbons 1989, Froese and Burghardt 1975, Galbraith et al. 1988, Iverson 1982, Iverson et al. 2000, Major 1975). However, no detailed ecological research has been published for Common Snapping Turtles in the southern portion of its North American range. A study at Lake Conway in central Florida found that snapping turtles (n = 21) were most commonly captured in shallow water areas with abundant aquatic vegetation and mud substrates (Bancroft et al. 1983), similar to the preferred habitat reported in other portions of its range (Ernst et al. 1994). As an ectothermic organism, demographic characteristics such as growth rate and age at maturity of Common Snapping Turtles are likely to be strongly influenced by the warmer climate and longer growing season in northern Florida compared to north temperate populations. The objective of this study was to collect a range of ecological and population data for Common Snapping Turtles in northwestern Florida. To accomplish this goal, we intensively sampled Common Snapping Turtles at five sites in Leon County, FL, and also collected data on other Common Snapping Turtles we opportunistically collected dead on roads and during the course of other research. Our results provide baseline ecological and population data for this species in the southern portion of its range and allow for comparisons to data from northern populations. We also examined several morphological characters of Common Snapping Turtles that have been used to discriminate subspecies in order to determine whether individuals in northwestern Florida are either intergrades or can be clearly assigned to one subspecies. Methods We sampled Common Snapping Turtle populations at five sites in Leon County, FL: McCord Pond, Harriman Pond, Chapman Pond, San Luis 2007 M.J. Aresco and M.S. Gunzburger 437 Pond, and Lake Jackson. Our sampling techniques and effort varied across these sites (Table 1) and included trapping, hand-collection, and drift fences. McCord Pond, Harriman Pond, Chapman Pond, and San Luis Pond are small ponds (< 3 ha) located within suburban parks in Tallahassee, FL, and we collected Common Snapping Turtles before and during drawdown and sediment-removal operations at these sites (Aresco and Gunzburger 2004). Prior to sediment removal, the substrate of these ponds was a thick layer of organic sediment that supported an abundance of aquatic macrophytes. Lake Jackson is a large (1620 ha), shallow lake with sand and organic substrate and abundant aquatic macrophytes. Water level is controlled naturally by variation in rainfall and by two sinkholes. During drought conditions, a lowering of the water table causes leakage into the groundwater through the sinkholes and most of the lake bottom dries, an event that has occurred 9 times during the last 100 years, drying on average every 12 years (Wagner 1984). We collected Common Snapping Turtles using several sampling techniques. At McCord Pond and Chapman Pond, we first used two doublethroated 1-m diameter hoop traps baited with sardines that we checked daily. Second, at these sites and at San Luis Pond and Harriman Pond, we surveyed each site daily during the drawdown and sediment removal operations and collected any Common Snapping Turtles we encountered. Turtles were detected and captured in each drying pool by walking transects and moving both hands up and down and from side to side in the shallow water and mud until the entire area was covered several times. Buried turtles of all sizes were easily detected in soft mud by following tracks and, in most cases, observing disturbed mud and/or a small snout-opening at the surface. We collected turtles in this manner from muddy areas surrounding drying pools of water, sediment piles, and from the sediment being actively excavated by machinery (Aresco and Gunzburger 2004). We feel confident that we collected every Common Snapping Turtle present at McCord Pond and Harriman Pond because the entire pond area was subjected to sediment removal, and we were present throughout the entire operation at these sites (Aresco and Gunzburger 2004). Our sampling effort at these sites was correlated with the length of time required for the drydown and sedimentremoval process. Our sampling methods at Lake Jackson differed significantly from the other sites. A large migration of turtles occurred during this study in response to the natural drydown of Lake Jackson in 2000 and the subsequent refilling of the lake in 2001. As Lake Jackson dried, turtles and other herpetofauna emigrated to the west towards Little Lake Jackson, which held water throughout the drought. We collected Common Snapping Turtles migrating between these two lakes at a 700-m drift fence along the road separating these lakes (Aresco 2005). During the drydown in 2000, we also performed regular surveys of the drying lakebed and collected any turtles found in the soft mud of drying pools (Aresco 2005). Since virtually all 438 Southeastern Naturalist Vol. 6, No. 3 Table 2. Variation in morphological features associated with subspecies distinction (Ernst et al. 1994, Feuer 1971, Stejneger 1918) of Chelydra serpentina serpentina and Chelydra serpentina osceola from a population at McCord Pond, Tallahassee, Leon County, Fl (n = 35). Subspecies description McCord Pond, northwest Florida Character C. s. osceola C. s. serpentina Mean ± SD (range) % with C. s. osceola trait Width 3rd vertebral/total length of vertebrals > 0.33 < 0.33 0.32 ± 0.02 (0.30–0.37) 12% Plastral forelobe length/carapace length > 0.4 < 0.4 0.40 ± 0.02 (0.36–0.47) 66% Width 3rd vertebral/ height 2nd pleural > 0.9 < 0.9 0.88 ± 0.06 (0.78–1.07) 31% Number of pairs of chin barbels Two One 9% Prominence of lateral caudal tubercules Moderate Well-developed 11% Dorsal keel knobs Center of scute Rear of scute 0% Neck tubercles Long, pointed Round, wart-like * *100% of individuals had moderately pointed (intermediate) neck tubercules. Table 1. Variation in density, biomass, and percent composition in the Chelydra serpentina (Common Snapping Turtle) community among five sites in Leon County, FL. Sampling effort includes trap hours and visual-encounter surveys (see methods for description of sampling methods at each site). Percent composition is the percent of Common Snapping Turtles in the overall turtle community at each site. Sampling Number collected Density Biomass Percent Locality Area (ha) Sampling dates effort (hr) Juv M F total (#/ha) (kg/ha) composition McCord Pond 2.0 1 Aug 1999–Mar 2000 1182 9 25 30 64 32 128 18.0% Harriman Pond 0.5 1 Oct 2000–30 Oct 2000 154 2 5 4 11 22 69.5 10.0% San Luis Pond 2.2 13 Mar 2004–24 Apr 2004 102 1 10 5 16 7.3 32.0 na Chapman Pond 1.0 1 Jul 2003–30 Jul 2003, 1476 1 1 1 3 3.0 11.0 3.5% 16 Sept 2003–27 Sept 2003 Lake Jackson 405.0 22 Feb 2000–1 Nov 2005 6204 9 4 4 17 0.04 0.07 0.2% 2007 M.J. Aresco and M.S. Gunzburger 439 individuals of all turtle species were migrating overland west from the north part of the drying Lake Jackson in 2000, we were able to estimate absolute abundance and population structure of each species, including Common Snapping Turtles. In addition to the five sites in which we intensively sampled Common Snapping Turtle populations, we also opportunistically collected Common Snapping Turtles at other localities in Leon County, Fl as we encountered them dead on roads (DOR) or during other research projects (Aresco and James 2005). For each Common Snapping Turtle collected, we recorded maximum carapace length (CL) and plastron length (PL) in mm, weight (g), and sex. We used secondary sex characteristics including tail size and location of cloacal opening (Ernst et al. 1994) to determine sex of individuals larger than the minimum size at maturity for females, which we confirmed through dissection of a gravid DOR female that measured 225 mm CL, 162 mm PL. We did not confirm size at maturity of male Common Snapping Turtles through dissection, so we classified individuals less than 220 mm CL as juveniles. It is possible that males mature at a larger size than females, and individuals greater than 220-mm CL with male secondary sex characteristics are subadult males. We counted lines of arrested growth (LAGs) for those Common Snapping Turtles with clearly visible LAGs on the 2nd pleural scute (n = 21). We did not verify that LAGs are deposited annually using markrecapture of known-age animals, thus the age estimates based on counts of LAGs may be inaccurate (Galbraith and Brooks 1987b). We measured seven morphological characters from a subsample of 35 Common Snapping Turtles from McCord Pond to identify subspecies (Table 2). We collected clutch-size data from three Common Snapping Turtles: we dissected one female found DOR and we radiographed two females hand-collected on land. We obtained diet data by collecting fecal samples from two Common Snapping Turtles and dissecting the stomach of two others (one that became entangled and drowned in a trap at McCord Pond and one found DOR). In some cases, we were unable to measure or sex turtles due to time constraints or degradation of specimens collected DOR; thus, not all data were collected from each individual. We also counted individuals of all other species of turtles captured during our sampling at all five sites except San Luis Pond. We attempted to return Common Snapping Turtles collected during this research to their original collection location when possible. For San Luis Pond, we held all Common Snapping Turtles (n = 16) in large cattle tanks at the Florida State University greenhouse facility for two months during the sediment-removal project. These turtles were released back to San Luis Pond after the project was completed. At Lake Jackson, we returned all Common Snapping Turtles captured back to Little Lake Jackson, which retained water throughout the course of this study. At our three remaining study sites, we were unable to return the turtles we collected to their original pond for several reasons. At all three sites, the sediment removal operations 440 Southeastern Naturalist Vol. 6, No. 3 resulted in poor habitat quality immediately after completion, with little organic sediment or aquatic vegetation remaining (Aresco and Gunzburger 2004). At McCord Pond, the extended duration of the sediment removal operation (nine months) and the large number of Common Snapping Turtles collected (n = 64) made holding turtles in cattle tanks an unviable option. Thus, from McCord Pond, we moved all Common Snapping Turtles collected to Lake Iamonia, Lake Overstreet, and Lake Hall, three large nearby lakes with similar habitat characteristics to McCord Pond prior to sediment removal. At Harriman Pond and Chapman Pond, we moved all Common Snapping Turtles collected to McCord Pond in an effort to reestablish this population, as the habitat quality had improved over time through growth of macrophytes and sediment deposition. Results Morphological characters and subspecies classification A sample of 35 Common Snapping Turtles from McCord Pond shared characteristics of both C. s. serpentina and C. s. osceola, suggesting that the population consisted of intergrades of characters used to separate these subspecies (Table 2). The proportion of Common Snapping Turtles with osceola-like traits varied across traits from 0 to 66% (Table 2). Most traits could be classified into one of the two subspecies, but for neck tubercles, all individuals had an intermediate morphology with moderately pointed tubercles. An examination of variation in plastral forelobe length/carapace length to third vertebral width/second pleural height showed considerable overlap in these characters between C. s. serpentina and this population from northwestern Florida, but little overlap with C. s. osceola (Aresco et al. 2006). Population and community structure Abundance and density of Common Snapping Turtles varied over the five sites in Leon County, Fl from a low of 0.04/ha at Lake Jackson to a high of 32/ha at McCord Pond (Table 1). Biomass of Common Snapping Turtles ranged from 128 kg/ha at McCord Pond to 0.07 kg/ha at Lake Jackson (Table 1). Common Snapping Turtles were very abundant at ponds in suburban parks; at these four sites, average density was 16/ha and average biomass was 60 kg/ha (Table 1). Sex ratio of adult males:adult females was not significantly different from 1:1 at McCord Pond, our highest density site (28 males:25 females; 􀁲2 = 0.08, df = 1, p = 0.78), and from all five sites pooled (41 males:45 females; 􀁲2 = 0.1, df = 1, p = 0.75). The abundance of Common Snapping Turtles relative to other turtle species varied strongly across the five sites. Common Snapping Turtles represented only 0.2% of the turtle community at Lake Jackson, whereas it represented 18% of the turtle community at the much smaller McCord Pond (Table 1). Other turtle species found syntopically with Common Snapping Turtles included Trachemys scripta (Schoepff) (Yellow-bellied 2007 M.J. Aresco and M.S. Gunzburger 441 Slider), Pseudemys floridana (LeConte) (Florida Cooter), Sternotherus odoratus (Latreille) (Stinkpot), S. minor (Agassiz) (Loggerhead Musk Turtle), Kinosternon subrubrum (Lacepède) (Mud Turtle), and Apalone ferox (Schneider) (Florida Softshell). Growth rates and size relationships The size distribution of Common Snapping Turtles at these sites was dominated by large adults, with a few juveniles to indicate low levels of recruitment (Table 1, Fig. 1). Adults outnumbered juveniles at all sites except Lake Jackson (Table 1). Estimated early growth (1–6 years) of Common Snapping Turtles in Leon County, Fl was variable among individuals and ranged from 20–30 mm CL/year (Fig. 2). Based on estimated age using LAGs and the minimum size at maturity for females (based on one dissected DOR individual), we estimate that females matured at about 6–8 years (Fig. 1, Fig. 2). Male Common Snapping Turtles (CL mean = 299 ± 6 mm, PL mean = 216 ± 5 mm, n = 38) were larger than females (CL mean = 270 ± 5 mm, PL mean = 200 ± 4 mm, n = 43) in this study (t-test for CL: t = -3.81, df = 80, P < 0.001; Fig. 1). Reproductive ecology We recorded clutch size for three female Common Snapping Turtles collected while nesting from 4 April through 16 May (Table 3). Clutch size ranged from 5–49 eggs. In addition, a Common Snapping Turtle was observed nesting on 28 Mar 1996 at Wakulla Springs State Park, Wakulla Figure 1. Size distribution of Chelydra serpentina (Common Snapping Turtles) collected from five sites (McCord Pond Harriman Pond, San Luis Pond, Chapman Pond, and Lake Jackson) in Leon County, FL. 442 Southeastern Naturalist Vol. 6, No. 3 County, FL, just south of Leon County (Scott Savery, Wakulla Springs State Park, Crawfordville, FL, pers. comm.). Thus, we infer that the nesting season of Common Snapping Turtles in Leon County begins in late March/ early April and probably continues at least through late May. Diet The diet of four Common Snapping Turtles collected in Leon County consisted of predominantly aquatic plants, with one aquatic insect (Table 4). We found no evidence of consumption of fish or other vertebrates by Common Snapping Turtles. Terrestrial movement Subadult and adult males and females (independent of nesting movements) were observed moving overland in pine flatwoods in the Apalachicola National Forest, Liberty County, FL, between permanent water in swamps and ephemeral cypress dome ponds (M.J. Aresco and J.G. Palis, unpubl. data). At Lake Jackson, two juveniles (40 mm CL) were found Table 3. Clutch size for three Chelydra serpentina (Common Snapping Turtles) collected in Leon County, FL. Lines of arrested growth (LAG) were not visible on the two larger females. Female Date Locality CL (mm) Weight (g) LAG Clutch size Method 4 Apr 2002 San Luis Pond 225 1920 6 5 Di s sect ion (DOR) 28 Apr 2003 Lake Jackson 285 4850 - 34 X-ray 16 May 2003 Goose Pond 387 9750 - 49 X-ray Figure 2. Relationship of estimated age and size (CL) of Chelydra serpenti-na (Common Snapping Turtles) (n = 21) in Leon County, FL. Age was estimated using counts of lines of arrested growth (LAG) on the 2nd pleural scute and included only those turtles with complete sets of clearly visible LAGs. 2007 M.J. Aresco and M.S. Gunzburger 443 at the drift fence moving directly towards Little Lake Jackson after apparently migrating at least 0.5 km from the nearest remaining pool on the lake bottom during the final days of drying. A large male (346 mm CL) migrated from a drying pool at Lake Jackson on 20 April 2000 to Little Lake Jackson and was captured migrating back to Lake Jackson on 15 March 2001 as the lake refilled. During the dry-down of Lake Jackson, under severe drought conditions, two Common Snapping Turtles, a 140 mm CL juvenile and 268 mm CL adult, were found dead on the dry lake bottom, both probably killed by raccoons. Discussion Common Snapping Turtles in this study in Leon County, Fl were classified as intergrades because for the first 3 characteristics in Table 2, the individuals in this population are almost exactly equal to the dividing value for the two subspecies. In addition, the fact that there is significant variation in the proportion of individuals with traits characteristic of C. s. osceola (0– 11%, Table 2) suggests that there are not two different morphotypes present in the population, but rather a mix of morphology consistent with hybridization. Further research, including analysis of additional portions of the genome, is needed to clarify the subspecific relationships. Abundance of Common Snapping Turtles varied considerably over the five sites sampled in this study in Leon County, FL. Abundance was highest in small (< 3 ha) suburban ponds and much lower in the one large lake (1620 ha) (Table 1). It is unlikely that this is due to variation in sampling effort, as the site with the highest sampling effort had the lowest density. This result is supported by a separate study of turtle communities in northwestern Florida that included a survey of 14 additional lakes (4–2330 ha) in Leon County (Aresco and James 2005). In that study, Common Snapping Turtles were caught in hoop traps at only 2 sites (McCord Pond and Chapman Pond) and Table 4. Diet of four C. serpentina collected in Leon County, FL. CL Weight Sample Date Locality (mm) (g) Sex type Diet item Percent 5 Jul 2003 Chapman Pond 310 5700 M Fecal Spirodela polyrhiza (L.) 95% (duckweed) Nelumbo lutea (Willd.) 5% (American lotus) 28 Jul 2003 Bradford Road 282 4450 F Stomach Utricularia sp. (L.) 100% Pond (bladderwort) 8 Aug 1999 McCord Pond 369 9000 M Stomach Colocasia esculenta (L.) 100% (wild taro) 9 Oct 2003 Waverly Pond 249 2800 M Fecal Lethocerus americanus (Leidy) < 1% (giant water bug) Panicum sp. (L.) 1% (maidencane grass) Nitella sp. (Agardh) 99% (stonewort) 444 Southeastern Naturalist Vol. 6, No. 3 were not trapped at any large lakes (> 4 ha) (Aresco and James 2005). Other studies have also demonstrated that Common Snapping Turtles can be very abundant in small ponds and wetlands, ranging from 61 individuals/ha in a 0.4-ha pond (Major 1975) to 59 individuals/ha at a 0.8-ha pond (Froese and Burghardt 1975). Population density of Common Snapping Turtles was correlated with primary productivity across two populations in Ontario (Galbraith et al. 1988). In Leon County, FL, Aresco and James (2005) found that overall turtle abundance was highest in lakes with high periphyton productivity, a mud/organic substrate, and no alligators; however, their sample size of Common Snapping Turtles was too low to allow for analysis of specific habitat correlates to abundance of this species. Size at maturity of Common Snapping Turtles was similar between our study in northwestern Florida and that in north temperate populations (Christiansen and Burken 1979, Mosiman and Bider 1960, White and Murphy 1973). Growth rates are typically greater in turtles at lower latitudes with a corresponding reduction in age at maturity. We estimated that female Common Snapping Turtles in our study matured at six to eight years, which was similar to a population in Iowa (six or more years; Christiansen and Burken 1979), whereas they require twice that in Michigan (17–20 years; Congdon et al. 1987) and Ontario (11–16 years; Galbraith et al. 1989). Clearly, both the length of the growing season and productivity as it relates to quantity and quality of food resources influences variation in growth rates and age-at-maturity of Common Snapping Turtles. In northwestern Florida, Common Snapping Turtles apparently reaches its highest abundance in small ponds without alligators and with abundant aquatic vegetation and deep organic sediment (Aresco and Gunzburger 2004, Aresco and James 2005). Similarly, in the St. Croix River in Minnesota and Wisconsin, abundances of Common Snapping Turtles, Chrysemys picta (Schneider) (Painted Turtle), and Graptemys geographica (LeSueur) (Northern Map Turtle) were associated with muck substrates (Wright et al. 1999). In southeastern lakes, survival of Common Snapping Turtle juveniles may be increased by a muck substrate, which provides a refuge from alligator predation. During extremes in temperature in shallow ponds, turtles may also benefit from a soft, deep, mud/muck bottom into which they can bury into during aestivation or winter dormancy. A muck substrate also provides optimal microhabitat for diet items of Common Snapping Turtles such as macroinvertebrates, macrophytes, and macroalgae. Although our analysis of gut contents suggested that Common Snapping Turtles is primarily herbivorous, this analysis was limited to four individuals, and the diet of Common Snapping Turtles is known to be highly variable across individuals within and among populations (Alexander 1943, Lagler 1943). Trophic position of Common Snapping Turtles at Lake Jackson based on stable isotope analysis was 3.5, which reflects a more carnivorous diet at that site (Aresco and James 2005). This result may also indicate inefficient digestion and assimilation of plant material. 2007 M.J. Aresco and M.S. Gunzburger 445 This study demonstrates the importance of small wetlands to Common Snapping Turtle populations. The four small ponds in our study (McCord Pond, Harriman Pond, San Luis Pond, and Chapman Pond) were once natural ponds that have been modified over the last two decades to serve as stormwater retention ponds in city parks (Aresco and Gunzburger 2004). Populations of Common Snapping Turtles in suburban ponds in such parks have been protected from human harvest for several decades. This may be why large individuals, which were presumably old adults, dominated the size distribution in the ponds in this study compared to a large lake that is subjected to intense fishing, including trotlines, and also potential harvest of turtles (Michael Hill, Florida Fish and Wildlife Conservation Commission, Tallahassee, FL, pers. comm.). Intensive muck-removal operations, where entire wetlands are drained and dredged to deepen ponds for stormwater, can extirpate Common Snapping Turtle populations (Aresco and Gunzburger 2004). Demographic and life-history traits of Common Snapping Turtles, including long generation times and naturally high rates of egg and juvenile mortality, limit their annual recruitment (Congdon et al. 1994). They may not be able to compensate for sudden or chronic losses of large numbers of breeding adults, and even small increases in annual mortality rates of mature females (< 10% increase) can lead to long-term declines with little or no population recovery possible (Brooks et al. 1991, Congdon et al. 1994). Although the Common Snapping Turtle is an excellent overland disperser, habitat fragmentation such as roads and development may limit the ability of Common Snapping Turtles to recolonize ponds, especially with increasing distance to the nearest unaltered wetland (Gibbs and Shriver 2002). In addition, habitat alteration resulting from sediment-removal operations probably reduces the likelihood of population recovery even if some individuals recolonize the pond. Large-scale sediment-removal operations leave ponds with a hard, graded sand substrate devoid of any organic material. Therefore, the conservation of small, vegetated wetlands in suburban and natural areas should be a priority for the conservation of Common Snapping Turtles in Florida. The level of harvest of Common Snapping Turtles in Florida is unknown because the Florida Fish and Wildlife Conservation Commission (FFWCC) does not require permits or reporting for turtles harvested for personal consumption. In addition, most commercial turtle harvest (65– 85%) goes unreported (Enge 1993). Collection for the pet trade apparently focuses on hatchlings raised from eggs from wild-caught females (Kevin Enge, FFWCC, Quincy, FL, pers. comm.). Local turtle trappers in north Florida often capture Common Snapping Turtles on trotlines, set lines, and bush hooks, both intentionally and as bycatch while trapping fish and Florida Softshell Turtles. According to trappers, snapping turtle meat is kept for personal consumption or sold locally. In the 1980s–1990s, baited trotlines set to catch Florida softshells were prevalent on Lake Jackson, Leon County, Fl (Michael Hill, FFWCC, Tallahassee, FL, pers. comm.). 446 Southeastern Naturalist Vol. 6, No. 3 Although Common Snapping Turtles may naturally be less abundant in large lakes, long-term exploitation of Common Snapping Turtles as bycatch to Florida softshell harvest may at least partially explain the very low density of this species at Lake Jackson compared to nearby ponds, which have relatively high densities of Common Snapping Turtles but no harvest pressure. Therefore, although levels of unreported harvest for personal consumption or local sales may be relatively low, some Common Snapping Turtles populations may be adversely affected if population densities are naturally low and the same populations are exploited over time. Even low levels of harvest of adult Common Snapping Turtles may result in dramatic population declines (Congdon et al. 1994). Recent concerns that increases in harvest of turtles for Asian markets may lead to population declines have prompted some states to regulate or ban harvest of Common Snapping Turtles. Harvest bans in some states may lead to an increase in harvest pressure in states without regulations. Further research on Common Snapping Turtles should be conducted throughout the southern portion of its range in order to establish baseline demographic rates and evaluate population trends in order to better predict the effects of harvest. Acknowledgments We thank the sediment-removal crews, Mike Brezin, Bob Walker, and especially Dean Hansen for assistance collecting turtles. We thank Michael Hill, Jesse Sasser, Joseph Daltry, Ray Einarson, and Curtis Watkins for providing access to sedimentremoval sites. This research was conducted under FSU ACUC Protocol # 0015 and Florida Fish and Wildlife Conservation Commission Scientific Collecting Permit WX01666. Our research at San Luis Pond was partially supported by the City of Tallahassee, Department of Public Works. We thank Joseph Travis for supporting us during this study under National Science Foundation grant DEB 99-03925. M.S. Gunzburger was supported by the Amphibian Research and Monitoring Initiative of the United States Geological Survey during preparation of this manuscript. Literature Cited Alexander, M.M. 1943. Food habits of the Snapping Turtle in Connecticut. Journal of Wildlife Management 7:278–282. Aresco, M.J. 2005. Mitigation measures to reduce highway mortality of turtles and other herpetofauna at a north Florida lake. Journal of Wildlife Management 69:540–551. Aresco, M.J., and M.S. Gunzburger. 2004. Effects of large-scale sediment removal on herpetofauna in Florida wetlands. Journal of Herpetology 38:115–119. Aresco, M.J., and F.C. James. 2005. Ecological relationships and abundance of turtles in north Florida lakes: A study of omnivory and an analysis of the trophic structure of a whole lake food web. Final Report. Contract NG01-011, Florida Fish and Wildlife Conservation Commission, Tallahassee, FL. Aresco, M.J., M.A. Ewert, M.S. Gunzburger, G.W. Heinrich, and P.A. Meylan. 2006. Chelydra serpentina - Snapping Turtle. Pp. 44–57, In P.A. Meylan. (Ed.). Biology and Conservation of Florida Turtles. Chelonian Research Monographs 3. 2007 M.J. Aresco and M.S. Gunzburger 447 Bancroft, G.T., J.S. Godley, D.T Gross, N.N Rojas, D.A. Sutphen, and R.W McDiarmid. 1983. Large-scale operations management test of use of the white amur for control of problem aquatic plants. The herpetofauna of Lake Conway: Species accounts. Miscellaneous Paper A-83-5. US Army Engineer Waterways Experiment Station, CE, Vicksburg, MS. Brooks, R.J., G.P. Brown, and D.A. Galbraith. 1991. Effects of a sudden increase in the natural mortality of adults in a population of the Common Snapping Turtle (Chelydra serpentina). Canadian Journal of Zoology 69:1314–1320. Christiansen, J.L., and R.R. Burken. 1979. Growth and maturity of the Snapping Turtle Chelydra serpentina in Iowa. Herpetologica 35:261–266. Congdon, J.D., and J.W. Gibbons. 1989. Biomass productivity of turtles in freshwater wetlands: A geographic comparison. Pp. 583–592, In R.R. Sharitz and J.W. Gibbons (Eds.). Freshwater Wetlands and Wildlife. Department of Energy, Charleston, SC. DOE Symposium Series No. 61. Congdon, J.D., G.L. Breitenbach, R.C. van Loben Sels, and D.W. Tinkle. 1987. Reproduction and nesting ecology of Snapping Turtles (Chelydra serpentina) in southeastern Michigan. Herpetologica 43:39–54. Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1994. Demographics of Common Snapping Turtles (Chelydra serpentina): Implications for conservation and management of long-lived organisms. American Zoologist 34:397–408. Enge, K.M. 1993. Herptile use and trade in Florida. Final Performance Report, Nongame Wildlife Program, Florida Game and Fresh Water Fish Commission, Tallahassee, FL. Ernst, C.H., and R.W. Barbour. 1992. Turtles of the World. Smithsonian Institution Press, Washington, DC. 290 pp. Ernst, C.H., J.E. Lovich, and R.W. Barbour. 1994. Turtles of the United States and Canada. Smithsonian Institution Press, Washington, DC. 578 pp. Feuer, R.C. 1971. Intergradation of the snapping turtles Chelydra serpentina serpentina serpentina (Linnaeus, 1758) and Chelydra serpentina osceola. Herpetologica 27:379–384. Froese, A.D., and G.M. Burghardt. 1975. A dense natural population of the Common Snapping Turtle (Chelydra s. serpentina). Herpetologica 31:204–208 Galbraith, D.A., and R.J. Brooks. 1987a. Survivorship of adult females in a northern population of Common Snapping Turtles, Chelydra serpentina. Canadian Journal of Zoology 65:1581–1586. Galbraith, D.A. and R.J. Brooks. 1987b. Addition of annual growth lines in adult Snapping Turtles Chelyda serpentina. Journal of Herpetology 21:359–363. Galbraith, D.A, C.A. Bishop, R.J. Brooks, W.L. Simser, and K.P. Lampman. 1988. Factors affecting the density of Common Snapping Turtles (Chelydra serpentina serpentina). Canadian Journal of Zoology 66:1233–1240. Galbraith, D.A., M.W. Chandler, and R.J. Brooks. 1989. The influence of growth rate on age and body size at maturity in female Snapping Turtles (Chelydra serpentina). Copeia 1989:896–904. Gibbs, J.P., and W.G. Shriver. 2002. Estimating the effects of road mortality on turtle populations. Conservation Biology 16:1647–1652. Gibbons, J.W. 2003. Terrestrial habitat: A vital component for herpetofauna of isolated wetlands. Wetlands 23:630–635. Iverson, J.B. 1982. Biomass in turtle populations: A neglected subject. Oecologia 55:69–76. 448 Southeastern Naturalist Vol. 6, No. 3 Iverson, J.B., D. Hearne, J. Watters, D. Croshaw, and J. Larson. 2000. Chelydra serpentina (Common Snapping Turtle). Density and biomass. Herpetological Review 31:238. Lagler, K.F. 1943. Food habits and economic relations of the turtles of Michigan with special reference to game management. American Midland Naturalist 29:257–312. Loncke, D.J. and M.E. Obbard. 1977. Tag success, dimensions, clutch size, and nesting-site fidelity for the Snapping Turtle, Chelydra serpentina, (Reptilia, Testudines, Chelydridae) in Algonquin Park, Ontario, Canada. Journal of Herpetology 11:243–244. Major, P.D. 1975. Density of Snapping Turtles, Chelydra serpentina, in western West Virginia. Herpetologica 31:332–335. Mosimann, J.E., and J.R. Bider. 1960. Variation, sexual dimorphism, and maturity in a Québec population of the Common Snapping Turtle, Chelydra serpentina. Canadian Journal of Zoology 38:19–38. Phillips, C.A., W.W. Dimmick, and J.L. Carr. 1996. Conservation genetics of the Common Snapping Turtle (Chelydra serpentina). Conservation Biology 10:397–405. Stejneger, L. 1918. Description of a new snapping turtle and a new lizard from Florida. Proceedings of the Biological Society of Washington 31:89–92. Wagner, J.R. 1984. Hydrogeological assessment of the October 1984 draining of Lake Jackson, Leon County, Florida. Northwest Florida Water Management District, Havanna, FL. Water Resources Special Report 84-1. Walker, D., P.E. Moler, K.A. Buhlmann, and J.C. Avise. 1998. Phylogenetic uniformity in mitochondrial DNA of the Snapping Turtle (Chelydra serpentina). Animal Conservation 1:55–60. White, J.B., and G.G. Murphy. 1973. The reproductive cycle and sexual dimorphism of the Common Snapping Turtle, Chelydra serpentina serpentina. Herpetologica 29:240–246. Wright, D.M.D., M.A. Bozek, J.R. Probst, and E.M. Anderson. 1999. Responses of turtle assemblage to environmental gradients in the St. Croix River in Minnesota and Wisconsin, USA. Canadian Journal of Zoology 77:989–1000. Yntema, C.L. 1976. Effects of incubation temperatures on sex differentiation in the turtle, Chelydra serpentina. Journal of Morphology 150:453–462.