Chelonian Conservation and Biology, 2018, 17(1): 54–62 doi:10.2744/CCB-1290.1 Ó 2018 Chelonian Research Foundation Origin and Structure of a Large Aggregation of Suwannee Cooters ( concinna suwanniensis) in a Florida Spring

1, 2 3 GERALD R. JOHNSTON *,JOSEPH C. MITCHELL ,GEORGIA A. SHEMITZ , 3 4 PETER L. BUTT , AND JENNIFER M. ADLER

1Department of Natural Sciences, Santa Fe College, Gainesville, Florida 32606 USA [[email protected]]; 2Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611 USA [[email protected]]; 3Karst Environmental Services, High Springs, Florida 32643 USA [[email protected]]; 4School of Natural Resources and Environment, University of Florida, Gainesville, Florida 32611 USA [jennifermadler@ufl.edu] *Corresponding author

ABSTRACT. – aggregate to reduce predation risk, facilitate mating, and access resources with patchy distributions. During a long-term study of populations in the Santa Fe River (SFR) ecosystem in northern Florida, we observed a large aggregation of at Gilchrist Blue Springs Park (GBSP) in August–October 2013 and again in March–May 2014. On 8 September 2013, we hand-captured 496 turtles of 5 species in GBSP. The Suwannee cooter (Pseudemys concinna suwanniensis) was the most abundant species in the sample, with 477 individuals representing all demographic groups. Density of this species was 530 turtles/ha and biomass was 2242 kg/ha. We hypothesize that hydrological changes in the SFR basin contributed to the temporary turtle aggregations at GBSP. The 113-km SFR originates as a tannin-stained blackwater stream, but receives input of clear water from  45 artesian springs in its lower 37 km. Heavy rainfall in the upper SFR basin from Tropical Storm Debby in June 2012 resulted in a large influx of tannic water that overwhelmed the capacity of the springs to dilute the river water. This storm in combination with additional episodes of heavy rainfall and declining spring flows led to an unusually long (34-mo) tannic period in the typically clear lower 37 km of the SFR. The resulting loss of most submerged aquatic macrophytes in the river due to insufficient sunlight may have been the stimulus that led the herbivorous P. c. suwanniensis to seek food in one of the few locations that had abundant submerged aquatic vegetation in 2013 and 2014. Turtles previously marked upriver (to 16 km) and downriver (to 4.6 km) from GBSP were in the aggregation, suggesting the individuals gathered at GBSP represented a large portion of the SFR P. c. suwanniensis population.

KEY WORDS. – artesian springs; ecology; foraging behavior; population; river; turtle

Animals gather in aggregations to reduce predation risk, aggregation of turtles dominated by Suwannee cooters facilitate mating, and access resources with patchy distribu- (Pseudemys concinna suwanniensis) at Gilchrist Blue tions (Krebs and Davies 1993; Alcock 2013). Turtles are Springs Park (GBSP) in August–October 2013 and again known to aggregate at basking sites (Carr 1952; Lindeman in March–May 2014 (Figs. 1 and 2; Adler et al., in press). 2013), in hibernacula (Brown and Brooks 1994; Litzgus and The highly conspicuous aggregations exceeded anything Mousseau 2004; Newton and Herman 2009), at nesting we had previously seen and were apparently unprecedent- beaches (Alho and Padua´ 1982; Doody et al. 2003; Bernardo ed in the SFR ecosystem according to residents whose and Plotkin 2007; Vogt 2008), at drinking sites (Doody et al. families have lived along the SFR for multiple generations 2011), and at feeding sites (Dolbeer 1969; Bjorndal et al. (K. Davis, owner of GBSP, pers. comm., September 2013; 2000; Vogt 2008; Wood et al. 2013). These resources are not M. Wray, owner of Ginnie Springs Outdoors, pers. comm., always stable and may shift geographically and over time. September 2013). In this article, we describe the Our long-term study of a riverine ecosystem in northern aggregations, use data gathered while studying turtles in Florida provided an opportunity to study how a geographic GBSP and throughout the SFR ecosystem during 2006– shift in food resources affected one wide-ranging herbivo- 2016 to place the aggregations in context, and suggest a rous freshwater turtle. hypothesis that may explain why they occurred. In 2006, we initiated long-term capture–mark–recap- ture studies of the 11 native freshwater turtle species that STUDY AREA inhabit the Santa Fe River (SFR) and its associated springs in northern Florida (Johnston et al. 2012, 2015, 2016). The SFR is a 113-km tributary of the Suwannee River During the eighth year of our study, we observed a large that originates in swamps near Lake Santa Fe in northern JOHNSTON ET AL. — Suwannee Cooters in a Florida Spring 55

Figure 1. Aggregation of Suwannee cooters (Pseudemys concinna suwanniensis) foraging on hydrilla (Hydrilla verticillata) in main spring run in Gilchrist Blue Springs Park. Photo by J.M. Adler. (Color version is available online.)

Figure 2. Santa Fe River basin in northern Florida, showing the location of Gilchrist Blue Springs Park and the large number of springs in the lower Santa Fe River. 56 CHELONIAN CONSERVATION AND BIOLOGY, Volume 17, Number 1 – 2018

Florida. It begins as a tannin-stained blackwater stream in and into the SFR. An elevated boardwalk follows the full its upper reaches but receives substantial input of clear length of the main run on its eastern edge (Fig. 3). The water from  45 artesian springs in its lower 37 km (Fig. total area of aquatic habitat created by the springs and their 2). Johnston et al. (2016) provided a detailed description of network of runs is 0.9 ha. During 2006–2013, aquatic the SFR and examined how the mosaic of habitats created vegetation was abundant and dominated by H. verticillata, by springs affects native freshwater turtles. In the upper with native species such as spring-run spider lily reaches of the SFR, tannin-stained water inhibits growth of (Hymenocallis rotata), red ludwigia (Ludwigia repens), submerged aquatic macrophytes. Aquatic vegetation is pickerel weed (Pontederia cordata), S. kurziana, and V. limited to floating plants such as spatterdock (Nuphar americana restricted to the margin or downstream section advena), duckweed (Lemna sp.), water spangles (Salvinia of the main run. During August–October 2013, a large minima), and introduced water hyacinth (Eichhornia aggregation of P. c. suwanniensis selectively consumed crassipes). Spring water dilutes the tannins in the lower almost all H. verticillata (Adler et al. in press). During the 37 km of the SFR and increases clarity of the river, 2013–2014 winter, H. verticillata regrew rapidly and especially during periods of little to no rainfall. Greater returned to its original abundance by March 2014. A water visibility allows growth of patches of submerged second aggregation of P. c. suwanniensis occurred in aquatic macrophytes such as muskgrass (Chara sp.), GBSP (March–May 2014), and the turtles again selective- carpet moss (Fontinalis sp.), introduced hydrilla (Hydrilla ly consumed almost all H. verticillata. The aquatic plant verticillata), introduced Indian swampweed (Hygrophila community was dominated by native species from June polysperma), water milfoil (Myriophyllum sp.), strap-leaf 2014 through 2016. sagittaria (Sagittaria kurziana), and tapegrass (Vallisneria americana). Epiphytic cyanobacteria (Lyngbya wollei) and METHODS algae (Vaucheria sp.) are abundant during drought periods. During periods of high rainfall, the entire 37-km We conducted visual surveys of P. c. suwanniensis in spring-influenced section of the SFR temporarily becomes GBSP by counting all turtles we observed in the clear dark due to large volumes of tannin-stained water flowing water while walking down the boardwalk that parallels the downstream from the upper SFR. During 2006–2016, we main GBSP Run (Fig. 3). We surveyed the run in this conducted mark–recapture studies of turtles by snorkeling manner approximately once per month during 2006–2016. in the spring-influenced section of the SFR during periods We made our observations between 0800 and 0930 hrs on of clear water. Our ability to conduct fieldwork was days when recreational activity in the park was relatively directly affected by the concentration of tannins in the low. Employees at GBSP made daily observations of water. Four periods (2–9 mo in duration) with water too turtles in the park and notified us if they observed any dark to permit snorkeling occurred during 2006–2012. obvious changes in turtle abundance or unusual turtle During 24–26 June 2012, Tropical Storm Debby brought activity. 28.8–35.3 cm of rain to the upper SFR basin (Suwannee We gathered most of our data on P. c. suwanniensis River Water Management District 2017a). This storm and throughout the SFR ecosystem by snorkeling and several subsequent episodes of heavy rainfall resulted in capturing turtles by hand (Johnston et al. 2011, 2016). tannic conditions lasting 34 mo (June 2012–May 2015) in During each snorkel survey, a group of 4–8 experienced the spring-influenced section of the SFR. Rainfall was snorkelers captured all turtles observed from midmorning higher than long-term (1932–2012) monthly averages to midafternoon (~ 0900–1500 hrs), placed the turtles in throughout the SFR basin during 11 mo between February canoes, and then returned to shore to measure and mark 2013 and September 2014 (Suwannee River Water them prior to release. In 2006–2016, we conducted 34 Management District 2017b). The spring-influenced sec- surveys of a 20.6-km section of the SFR, extending 16 km tion of the SFR was flooded during June–August 2012, upriver and 4.6 km downriver from GBSP. We also March–May 2014, and September 2014 (Suwannee River conducted 8 surveys in the Ichetucknee River, a major 9.7- Water Management District 2017c). When water visibility km spring-run tributary, and 8 surveys in GBSP. When we returned to normal in May 2015, we observed that nearly sampled in GBSP, 2–3 people and a multifilament gill net all submerged aquatic macrophytes had disappeared and (45.7 3 3.6 m; 0.1-m bar mesh) were positioned at the end were replaced by a community of macroalgae dominated of the spring run to temporarily prevent turtles from by Vaucheria sp. swimming out of the sampling area. Twenty snorkelers GBSP is a 120-ha privately owned park located on the captured turtles during the survey in GBSP on 8 southern shore of the SFR approximately 30 km upriver September 2013. from the confluence with the Suwannee River (lat We measured straight midline carapace length (CL) 29849047.6400 N, long 82840058.4400 W, WGS84; Fig. 2; and straight midline plastron length (PL) of each P. c. Johnston et al. 2016). Three large spring groups in the park suwanniensis to the nearest 1 mm using aluminum tree (Blue Spring, Naked Spring, and Little Blue Spring) calipers (Haglof¨ t,Langsele,˚ Sweden). We weighed turtles converge into a main run (approximately 1 m deep, 6–27 , 5 kg to the nearest 1 g using a portable digital scale m wide) that flows 350 m north through floodplain forest (Ohaust, Pine Brook, NJ) and those . 5 kg to the nearest JOHNSTON ET AL. — Suwannee Cooters in a Florida Spring 57

Figure 3. Main spring run and boardwalk in Gilchrist Blue Springs Park. The view is looking upstream from the Santa Fe River. Photo by J.M. Adler. (Color version is available online.)

10 g using a spring scale (Pesolat, Baar, Switzerland). We adult females ( 296 mm PL), and adult males ( 180 marked small (, 120 mm PL) turtles individually by filing mm PL). We used Google Earth Pro to estimate distances or cutting notches in the marginal scutes and peripheral marked turtles travelled via river between GBSP and bones using a standard numbering system (Cagle 1939). capture sites before and after 8 September 2013. Visual We marked larger (. 120 mm PL) individuals with drill boardwalk survey data gathered before, during, and after holes following the same system. We marked turtles each aggregation are presented as mean 6 standard captured in the Ichetucknee River by inserting passive deviation (minimum–maximum) number of P. c. suwan- integrated transponder (PIT) tags into the muscle and niensis per survey. Turtle and common names connective tissue between the plastron and pelvis lateral to follow the Turtle Taxonomy Working Group (2017). the midline (Runyan and Meylan 2005). Turtles captured in the large sample at GBSP on 8 September 2013 were RESULTS also temporarily marked on the carapace with a small (1– GBSP Visual Boardwalk Surveys. — During 86 2-cm-diameter) dot of white, nontoxic, oil-based paint surveys of the main GBSP Run (June 2006–July 2013), (563 Speedry, Diagraph, Marion, IL; Kornilev et al. 2012) we observed an average of 15.1 6 3.7 (8–25) P. c. to ensure that individuals previously measured and suwanniensis. On 10 August 2013, we observed approx- released were recognized by snorkelers and not repeatedly imately 300 P. c. suwanniensis. We continued to observe captured during the same sampling session. Females were at least 250 turtles per survey (maximum 351 on 3 palpated to determine the presence of eggs. We released all September 2013) until 22 October 2013 (24 turtles). turtles at the capture site on the same day of capture. During November 2013–February 2014, counts returned We used the total number of individuals captured to baseline (16 6 4.1 per survey, 11–21, n = 4 surveys). during each survey in GBSP to estimate minimum density On 14 March 2014, we counted approximately 200 turtles of P. c. suwanniensis in the 0.9-ha study area. The sum of in the run. Our counts were at least 250 turtles per survey body masses of all P. c. suwanniensis captured during each (maximum 362 on 4 May 2014) during April and May survey in GBSP provided a minimum estimate of biomass. 2014. Turtle counts in all surveys during June 2014– To evaluate demographic composition of P. c. suwannien- December 2016 averaged 16.1 6 4.3 (6–24; n =31 sis in each survey at GBSP, we categorized each surveys). During the 2013 and 2014 aggregation events, individual into one of the following demographic groups we observed a daily routine in which turtles from the SFR following Johnston et al. (2016): unsexed juveniles entered GBSP at dawn, consumed primarily H. verticillata (, 180 mm PL), juvenile females (180À295 mm PL), for several hours, and then returned to the river. 58 CHELONIAN CONSERVATION AND BIOLOGY, Volume 17, Number 1 – 2018

Table 1. Numbers of turtles hand-captured during sampling Table 2. Numbers of unsexed juvenile, juvenile female, adult sessions in Gilchrist Blue Springs Park. Combined data from 7 female, and adult male Suwannee cooters (Pseudemys concinna sessions in 2006–2012 presented as mean (minimum–maximum) suwanniensis) hand-captured during sampling sessions in Gil- per session. christ Blue Springs Park. Combined data from 7 sessions in 2006–2012 presented as mean (minimum–maximum) per 8 Sep session. Definitions of demographic groups follow Johnston et Species 2006–2012 2013 al. (2016). Chelydra serpentina 0.14 (0–1) 0 Species 2006–2012 8 Sep 2013 Kinosternon baurii 2.71 (0–8) 0 Pseudemys concinna suwanniensis 14.86 (7–26) 477 Unsexed juveniles 7.71 (2–13) 15 Pseudemys nelsoni 2.43 (1–7) 6 Juvenile females 0.43 (0–1) 49 Pseudemys peninsularis 0.14 (0–1) 0 Adult females 3.43 (0–11) 240 Sternotherus minor 7.14 (0–14) 3 Adult males 3.29 (0–13) 173 Sternotherus odoratus 0.57 (0–2) 1 Total 14.86 (7–26) 477 scripta 4.29 (0–9) 9 Total 32.28 (24–48) 496 suwanniensis in the 8 September 2013 sample (n = 477) was 18.4 times greater than the maximum captured during Snorkel Surveys. — During 7 snorkel surveys in any previous snorkel survey. GBSP between May 2006 and August 2012, we hand- Pseudemys c. suwanniensis was the most abundant captured 8 species, with an average of 5.4 species/survey species in all GBSP surveys (Table 1). Density (530 and 32.3 individuals/survey (Table 1). The largest total turtles/ha) and biomass (2242 kg/ha) of this species on 8 sample was 48 turtles representing 5 species on 21 September 2013 were vastly higher than the previous February 2010. On 8 September 2013, we hand-captured maximum values at GBSP (17.8 turtles/ha, 47.3 kg/ha). 496 turtles in GBSP representing 5 of the 8 previously All demographic groups and all size classes between 52 documented species (Table 1). The numbers of Florida and 363 mm PL were represented in the 8 September 2013 red-bellied cooters (Pseudemys nelsoni), loggerhead musk sample (Fig. 4). We captured all demographic groups in turtles (Sternotherus minor), common musk turtles greater numbers on 8 September 2013 than the maximum (Sternotherus odoratus), and yellow-bellied sliders (Tra- in any previous survey (Table 2). We found no gravid chemys scripta) in the 8 September 2013 sample were females on 8 September 2013; however, we captured 21 within the range of the number of individuals captured in gravid females in GBSP during April–July in previous previous surveys at GBSP. However, the number of P. c. years.

Figure 4. Comparison of size distributions of Suwannee cooters (Pseudemys concinna suwanniensis) hand-captured at Gilchrist Blue Springs Park during 2006–2012 and during a large aggregation event on 8 September 2013. JOHNSTON ET AL. — Suwannee Cooters in a Florida Spring 59

The 8 September 2013 sample included 134 P. c. all H. verticillata was consumed, clearly illustrating that suwanniensis that had previously been marked. Seventy- the aggregations were associated with the presence of food seven marked individuals had previously been captured in in GBSP. Although abundant aquatic vegetation dominat- GBSP and/or in the SFR within 2 km of GBSP. Forty had ed by H. verticillata occurred in GBSP every year since previously been captured in the SFR 2–16 km upriver the beginning of our study, we never observed an from GBSP, and 10 had previously been captured 2–5 km aggregation prior to 2013. The proximate cause of the downriver from GBSP. aggregation events likely involves other factors in addition During 2014–2016, we recaptured 122 marked P. c. to the presence of food in GBSP. suwanniensis that had been captured in the 8 September We hypothesize that hydrological changes in the SFR 2013 GBSP aggregation. Seven individuals were recap- basin contributed to the turtle aggregations at GBSP. tured in GBSP, 49 in the SFR within 2 km of GBSP, 36 in Water levels in the Floridan Aquifer have declined since the SFR 2–16 km upriver from GBSP, and 18 in the SFR the 1950s, which has led to reduced spring flow at several 2–5 km downriver from GBSP. We also recaptured 19 springs in the SFR basin (Knight 2015; Johnston et al. individuals in the Ichetucknee River 25–30 km downriver 2016). The most severe declines in flow occurred in from GBSP. springs at relatively high elevations. These springs are located upstream from GBSP and contribute clear water DISCUSSION that helps to dilute tannic water originating from the upper SFR. With reduced spring flow, there is less water to The present study provides another example of the achieve the dilution effect in the lower reaches of the SFR, benefits of long-term ecological research. The data we especially during periods of heavy rainfall. An extreme collected during the 7 yrs prior to and 3 yrs after the 2013 drought in May 2012 caused several springs to stop and 2014 aggregation events allowed us to examine this flowing. When Tropical Storm Debby arrived in late June aggregation phenomenon in context and evaluate its 2012, heavy rainfall in the upper SFR basin resulted in a causes. Large groups of P. c. suwanniensis have been substantial increase in tannic water flowing down from the reported previously from Florida. Knight (1871) noted that upper reaches. It overwhelmed the capacity of springs to groups occurred in bayous near the mouths of streams near dilute the river water and contributed to the unusually long Tallahassee, and Carr (1952) reported seeing hundreds of tannic period (34 mo) in the lower 37 km of the SFR. The P. c. suwanniensis in the grassy flats at the mouth of the consequent loss of most submerged aquatic macrophytes Suwannee River. Both of these reports are anecdotal and in the SFR due to insufficient sunlight penetration was neither provided insights into the functional significance of probably the stimulus that led the herbivorous P. c. the aggregations. Data provided by Jackson (1970) suggest suwanniensis to seek food in GBSP. It was the only habitat a density of 741 P. c. suwanniensis/ha in Fanning Spring in the lower SFR we observed with abundant submerged in the Suwannee River basin. The aggregation was aquatic vegetation in 2013 and 2014. Anecdotal observa- dominated by juveniles, suggesting Fanning Spring tions of P. c. suwanniensis feeding on terrestrial grasses functioned as a nursery. along the shore of the SFR near GBSP during August 2013 Johnston et al. (2016) suggested that GBSP also (M. Wray, owner of Ginnie Springs Outdoors, pers. functioned as developmental habitat for P. c. suwannien- comm., September 2013) further suggest that turtles were sis. During 2006–2012, GBSP was dominated by unsexed experiencing and responding to a period of low food juveniles, and females were frequently observed nesting in availability. the surrounding uplands. However, our data and observa- Our observations suggest the turtles did not gather at tions during 2013 and 2014 suggest the aggregation events GBSP in response to flooding. Although the SFR was were unrelated to nesting or an influx of unsexed juveniles. flooded during the March–May 2014 aggregation, it was The 8 September 2013 sample included all demographic below flood stage during the August–October 2013 groups and only 3.1% were unsexed juveniles (Table 2; aggregation. We witnessed 6 flood events in 2006–2016 Fig. 4). No female in the 8 September 2013 sample was during which no aggregations occurred. gravid. The last nesting of which we are aware in 2013 Our recapture data provide further evidence that the occurred during July. Suwannee cooters are known to nest aggregation phenomenon was not a localized event. from late March through early August (Jackson and Turtles in the 2013 aggregation originated from a section Walker 1997). We did not capture and examine turtles in of the SFR that is at least 20 km long. Some marked turtles the March–May 2014 aggregation, but the demographic swam 16 km downstream to reach GBSP; others swam at composition appeared to be similar to the first aggregation. least 4 km upstream. The 19 turtles recaptured in the Only 1 female was observed nesting at GBSP during Ichetucknee River 25–30 km from GBSP during 2014– March–May 2014 (L. Matthews, pers. comm.). 2016 further suggest that the concentration of individuals We suggest that the herbivorous P. c. suwanniensis at GBSP represented a large portion of the P. c. gathered at GBSP to forage based on our observations of suwanniensis population in the SFR basin. The long- their feeding behavior during the aggregations (Fig. 1). distance movements we observed in this study build on a Furthermore, both aggregation events ended after almost recent report by Johnston et al. (2017) of a P. c . 60 CHELONIAN CONSERVATION AND BIOLOGY, Volume 17, Number 1 – 2018 suwanniensis that moved 260 km to and from a site in the verticillata and the variety of native macrophytes in the SFR near GBSP and the mouth of the Suwannee River. SFR and its springs. Our study provides a context that may explain why P. c. We are unaware of any published report of a suwanniensis move such long distances. freshwater turtle feeding aggregation similar to those we We do not know which environmental cues the turtles observed in GBSP. Our observations more closely may have used to locate the concentrated food source at resemble the high-density aggregations of green sea GBSP. Turtles downriver from GBSP may have used turtles (Chelonia mydas), which gather to forage on olfaction to detect chemical cues emitted by H. verticilla- turtle grass (Thalassia testudinum) pastures and then ta, but the olfaction hypothesis cannot explain how turtles disperse when this food resource is depleted (Bjorndal upriver would have detected this food source. We et al. 2000). Unfortunately, the extraordinary aggrega- hypothesize that turtles upriver may have moved out of tion of P. c. suwanniensis at GBSP may be an early their normal home ranges in search of food and symptom of major ecological changes occurring in the opportunistically encountered GBSP. Alternatively, some SFR basin, particularly the effect of declining aquifer type of communication among turtles may have enabled levels and associated reduction in spring flows. Loss of the upriver turtles to locate the food source at GBSP. spring habitats and submerged aquatic macrophytes Ferrara et al. (2014) demonstrated that acoustically could severely impact the SFR P. c. suwanniensis mediated social behavior occurs in giant South American population. river turtles (Podocnemis expansa), and we cannot rule out the possibility that P. c. suwanniensis and other wide- ACKNOWLEDGMENTS ranging riverine turtles also communicate this way. If we observe another large aggregation of P. c. suwanniensis in We thank Sam Cole, Kim Davis, Elias Esquivel, our study area in the future, we hope to apply some of the Dale Kendrick, Vernest Legree, Rose Meadows, Ginger techniques used by Ferrara et al. (2014) to examine the Morgan, Morgan Tyrone, Mark Wray, Phil Younts, and possible role of acoustic communication. the entire staffs at Camp Kulaqua, Gilchrist Blue Springs The aggregation of P. c. suwanniensis individuals at Park, Ginnie Springs Outdoors, Ichetucknee Springs GBSP was dominated by adult females. In the 8 State Park, Poe Springs Park, and River Rise Preserve September 2013 sample, 50.3% of all individuals were State Park for facilitating our study. The majority of this adult females and the adult sex ratio was 0.72 male:1 project was self-funded, but additional support was female (Table 2). These data differ substantially from provided by The Three Rivers Trust, Turtle Survival those of the general SFR population (Johnston et al. 2016). Alliance, Santa Fe College, and a grant from the National Of 1226 P. c. suwanniensis hand-captured in the SFR and Science Foundation (award 1700818). The following its springs, 23.4% were adult females and the adult sex people contributed substantially to fieldwork: Garret ratio was 1.39 males:1 female (Johnston et al. 2016). We Alvar, Ashley Ballou, Mackenzie Bell, Jennifer Blaire, hypothesize that the disproportionate relative abundance of Saska Boswell, Brenda Campbell, Matthew Carrigan, adult females in the GBSP aggregation reflects the greater Adam Casavant, Brett Caudill, Austin Cave, Rebecca nutritional requirements of that demographic group Cox, Jill Cunningham, Patricia Eaton, Mariposa Ehlers, relative to all others. Because of their larger body sizes, Odell Encinosa, Darcy Garrenton, Jeremy Geiger, Hailey adult females may also have a greater ability to travel long Getzlaf, Bethan Gillett, Cody Godwin, Stacie Greco, Don distances in a riverine ecosystem to access localized food Heesen, Celine Hickey, Scott Holznagel, Tabitha Hoot- resources. man, Matt Hubner, Matthew Kail, Yurii Kornilev, Hydrilla verticillata is an invasive, introduced species Anthony Lau, Jennifer Lauture, Travis Lowke, Calvin that grows rapidly (up to 2 cm/d), smothers native aquatic Martin, Ginger Martin, Phoebe Martin, Shelby Massucci, macrophytes, and clogs waterways (Langeland 1996). Lance Matthews, Collin McAvinchey, Jessica McGuin- However, our observations show that it provided ecolog- ness, Eric Munscher, Leroy Nunez, Elena Oehmig, ical benefits to P. c. suwanniensis during a period of food Wayne Osborne, Adrienne and Ben Owen, Amanda scarcity. We do not know where the turtles would have Powell, Michael Randall, Jordi Sallent, Nicole Salvatico, foraged or if survivorship would have been affected if H. Essa Samarah, Terri Skiles, Cody Statler, Eric Suarez, verticillata had not been abundant in GBSP during the 34- Ken Sulak, Katie Szewczyk, Travis Thomas, Dylan mo tannic period in the lower SFR. We suggest future Vega, Ande Williams, Ben Williams, and William research to examine how H. verticillata dynamics affect P. Wollman. We especially thank Odell Encinosa and c. suwanniensis and other native turtles. Species known to William Wollman for working 20 consecutive hours to consume H. verticillata include the North American help us measure, weigh, and mark all of the turtles snapping turtle (Chelydra serpentina) (Johnston and captured on 8 September 2013. This study was conducted Suarez 2012), P. nelso ni (Bjorndal et al. 1997), P. under permit LSSC-10-00039 (originally WX04230) peninsularis (Bjorndal et al. 1997), and T. scripta from the State of Florida Fish and Wildlife Conservation (Bjorndal and Bolten 1993). Future studies should also Commission, and permit 06040412 from the Florida examine the comparative nutritional content of H. Department of Environmental Protection. Because Santa JOHNSTON ET AL. — Suwannee Cooters in a Florida Spring 61

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data. www.mysuwanneeriver.org/portal/rivers.htm (October VOGT, R.C. 2008. Amazon Turtles. Lima, Peru: Biblos, 104 pp. 2017). WOOD, L.D., HARDY, R., MEYLAN, P.A., AND MEYLAN, A.B. 2013. TURTLE TAXONOMY WORKING GROUP [RHODIN, A.G.J., IVERSON, Characterization of a hawksbill turtle (Eretmochelys imbrica- J.B., BOUR, R., FRITZ, U., GEORGES, A., SHAFFER, H.B., AND VAN ta) foraging aggregation in a high-latitude reef community in DIJK, P.P.]. 2017. Turtles of the world: annotated checklist and atlas of taxonomy, synonymy, distribution, and conservation southeastern Florida, USA. Herpetological Conservation and status. Eighth edition. In: Rhodin, A.G.J., Iverson, J.B., van Biology 8:258–275. Dijk, P.P., Saumure, R.A., Buhlmann, K.A., Pritchard, P.C.H., and Mittermeier, R.A. (Eds.). Conservation Biology of Received: 3 November 2017 Freshwater Turtles and Tortoises: A Compilation Project of Revised and Accepted: 20 December 2017 the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group. Chelonian Research Monographs 7:1–292. doi:10. Published Online: 21 May 2018 3854/crm.7.checklist. atlas.v8.2017. Handling Editor: Peter V. Lindeman