Distribution and Abundance of Red-eared Sliders in the South Okanagan

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1 Distribution and Abundance of Red-eared Sliders in the South Okanagan Submitted to: British Columbia Ministry of Environment, Okanagan Region February, 2010 Authors: Natasha Lukey*, Karen Hodges, Melissa Tesche Dr. Karen E. Hodges, Associate Professor, Conservation Biology. Biology and physical geography, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC. V1V 1V7, Canada. Phone: (250) , fax: (250)

2 Distribution and Abundance of Red-eared Sliders in the South Okanagan Natasha Lukey*, Karen Hodges, Melissa Tesche Introduction Scientists are becoming more aware of the impacts invasive species can have on ecosystems and economies. Too many situations have been documented where an exotic species has proliferated far beyond the point of control, causing irreparable damage to indigenous species in the area (Crossland et al. 2008, Kenis et al. 2009). Invasive organisms may exhibit a lag period such that initial introduction and rapid population expansion may be decades apart from each other (Ficetola et al. 2009). The best form of managing invasive populations may be the identification and eradication of exotics before they establish reproductively stable populations (Ficetola et al. 2009, Simberloff, 2009). Moreover, if the exotic species in question exhibit long lifespans, the invasive individuals do not necessarily have to be reproducing to cause damage in their new range. This study focussed on red-eared slider turtles, Trachymes scripta elegans. This turtle species is a popular pet, and was transported around the world until the 1970 s, when it was recognized that they transmit disease to young children and were being released into local ecosystems. Despite the bans, they are still imported and exported in high volumes today (Laidlaw 2006). The ban on red-eared sliders has resulted in the black-market trade of this species, so exact trade quantification is difficult. The most recent estimation of Canadian import of red-eared sliders was just under in 1990 (Warwick 1991). Further, laws prohibit only the sale of red-eared sliders but still allow possession of red-eared sliders as pets (Laidlaw 2006). Red-eared sliders are now recognized as one of the top 100 most invasive species globally (Invasive Species Specialist Group, IUCN 2008). In areas of introduction, abundances of native freshwater turtle species have decreased (Cadi and Joly 2004, Polo-Cavia et al. 2008). Recent evidence shows red-eared sliders outcompete native turtle species in Europe (Cadi and Joly 2003, Cadi et al. 2004, Polo-Cavia et al. 2008). Red-eared sliders can also act as a vector for foreign disease for native freshwater turtles and therefore do not need to be actively reproducing to cause harm (Bunnell 2005). Finally, red-eared sliders can affect local waterfowl populations; turtles bask on nests found close to water. The bird s nest becomes submerged in water, and eggs contained in the nest are destroyed (IUCN 2008). Red-eared sliders have also preyed on young waterfowl (IUCN 2008). Red-eared sliders are the most widespread exotic turtle in Canada (Bunnell 2005). They occur in the South Okanagan of British Columbia, however abundance and ecological impacts in the area are unknown. There is particular concern with respect to their impact on the native western painted turtle (Chrysemes picta bellii), a species of special concern in British Columbia (COSEWIC 2006). In areas of the lower Fraser River Valley, near the coast, painted turtles have been seen to occur in lower abundances where sliders have been introduced (Bunnell 2005). The goal of this study was to determine the distribution and abundance of red-eared sliders in the South Okanagan-Similkameen region. Turtle populations were estimated using mark-recapture (CMR) at 13 ponds. At an additional 17 ponds, visual observations were used as 2

3 an index of abundance. This study was conducted from May-September, 2009 at various locations extending from Kelowna to Oliver, B.C. Methods The study was carried out between May 1 and September 7, The sites extended from Kelowna, B.C. in the north to Oliver, B.C. in the south. A total of 30 sites were visited, 13 of which were trapped, and 17 of which were surveyed visually. 1) Mark-recapture (CMR) estimation Turtles were trapped for 4-9 consecutive days per site. Basking and hoop-net traps were set up at each site, with 3 of each kind per pond. Manual dip-net searches were also conducted from a canoe. The hoop-net traps used were 2 ½ ft. diameter, 1 ½ in. square mesh traps from Memphis Net and Twine; the basking traps were Sun Deck Turtle traps with bait tower, from Heinsohn s Country Store (Texas). The bait used was canned, wet cat food, various brands. Trapping sessions were defined as the preceding 24 hours for set traps, and 1.5 hours per site for manual dip-net search. Individuals were marked with unique notch patterns on the marginal scutes of their carapace (top shell). Upon capture, the weight, size and sex of the turtles were recorded. The sex of the turtles was determined based on size and secondary sex characteristics as outlined by Cagle (1950). Males mature when they reach a minimum of 9 cm plastron length, and have long foreclaws and a cloaca set far from the base of their tails. Females are mature at 15 cm plastron length and have short foreclaws and cloaca set close to the base of their tails. Individuals under 9 cm length who do not display distinctive sex characteristics are juveniles. 2) Visual Surveys Each pond was visited at least twice on random days for 1 hour during 11:00 am and 4:00 pm to maximize the chance of seeing basking turtles. Red-eared sliders were differentiated visually by the red stripe on either side of the head, or, if absent in melanistic individuals, the yellow of their plastron. The date, time, and activity of the turtles were recorded, and a visual size estimate was taken as an approximation of age class and sex identification. The difference in size of mature adults, visibility of foreclaws while basking, and red-eared sliders size relative to surrounding objects and western painted turtles allowed for a reasonable estimation of sex in these circumstances. Results Red-eared sliders were trapped at 3 of 13 locations throughout the Okanagan. The sites include Redlich pond in Kelowna, and the north pond at the Skaha Marina and Nature Trust ponds, both on South Main street, Penticton (Figures 1 and 2, Table 1, Appendices 1 and 2). Redlich Pond, Kelowna, was trapped for a single day, and traps were pulled due to suspected vandalism. As a result, we captured and marked only 3 mature females. The minimum known number alive (MNA) reported for this pond was 3, however residents of the area have reported seeing a higher number of red-eared sliders at this location. The north pond at the Skaha Marina, Penticton, contained 1 mature male, 2 mature females, and 1 juvenile. The Nature Trust site contained 2 mature males, 5 mature females, and 1 juvenile. It is unknown whether the juveniles are the result of breeding within the ponds, or if they are present from separate human-facilitated release events. 3

All but one red-eared slider were trapped using the baited hoopnets. Manual dip-net searches caught the other single red-eared slider, while basking traps caught no red-eared sliders.

4 All but one red-eared slider were trapped using the baited hoopnets. Manual dip-net searches caught the other single red-eared slider, while basking traps caught no red-eared sliders. We observed that red-eared sliders have better predator avoidance skills than the western painted turtles. Upon spotting us, the red-eared sliders would stay submerged underwater or within their shells for much longer periods than the western painted turtles. They were also more aggressive than western painted turtles when handled. 5 Km Figure 1. All Kelowna sites visited during the study. Red tacks denote sites where red-eared sliders were found through both visual observation and trapping; green denotes sites that were extensively trapped and no red-eared sliders were found; yellow denotes sites that were visually observed and no red-eared sliders were found. All red-eared sliders found near Kelowna were in close proximity to human populations. 4

denotes sites that were visually observed and no red-eared sliders were found. a) All Penticton sites visited during the study. b) Close-up of the Penticton city sites.

5 5 Km 2 Km a) b) Figure 2. Penticton and area sites. Red tacks denote sites where red-eared sliders were found through both visual observation and trapping; green denotes sites that were extensively trapped and no red-eared sliders were found; yellow denotes sites that were visually observed and no red-eared sliders were found. a) All Penticton sites visited during the study. b) Close-up of the Penticton city sites. All red-eared sliders found in or near Penticton were in close proximity to human populations. Table 1. Mark-recapture and visual survey data for all sites with red-eared sliders. Sites containing markrecapture data have confirmed identification of individuals, and sites with visual observation contain estimations for sex of individuals only. When possible, Lincoln-Peterson population estimates are given; when unavailable, minimum number of alive individuals is reported. location (map label) method Lincoln- Peterson** 5 estimate minimum number alive males females juveniles Redlich Pond (D)* Mark-recapture Skaha Marina north (R) Mark-recapture Nature Trust (T) Mark-recapture Fascieux Creek (J) Visual Okanagan Lake Marina M) Visual Skaha Marina south (S) Visual *traps were pulled after one day due to suspected vandalism **95% Confidence Interval reported We saw 4 red-eared sliders at 3 other sites, Fascieux Creek Wetlands, Kelowna (1 individual), the Okanagan Lake Marina (2 individuals), and the south pond at the Skaha Marina (1 individual). All four of these turtles are suspected to be female, as they were estimated to be over 20 cm in plastron length. These observations are subjective however, and confirmation of sex/maturity can be determined only through trapping and handling of these individuals. Extensive observations were made at 14 sites throughout the South Okanagan that did not yield any sightings (Appendix 3). A lack of sightings does not mean that the red-eared sliders are not present. Red-eared sliders were found to be extremely diligent in observing their

6 surroundings and avoiding possible perceived predators. The red-eared slider predator avoidance abilities were best demonstrated through the capture of only 1 red-eared slider by manual dip-net, compared to a much higher frequency of western painted turtles captured by manual dip-net. Further, visits to ponds where we knew there to be sliders yielded no sightings on multiple occasions, regardless of the measures we took to be undetected or the length of time spent at the pond. At the ponds known to have sliders, we tried approaching the water from different angles and under varying amounts of brush cover, however the red-eared sliders detected us at high rates and would quickly submerse themselves under water. One site that had reports of sliders and no sightings during this study include the Oxbows at the intersection of Green Mountain Road and Highway 97, Penticton. Recommendations We have found individuals of both sexes and varying age classes at various ponds around the Okanagan. The presence of juveniles indicates the possibility of reproductive capabilities in the Okanagan. It is highly recommended that all of the populations discovered here be monitored. Many other areas in the world have been subject to unchecked slider populations and are now dealing with serious consequences including the decline of their native freshwater turtle species in areas where the native turtles and red-eared sliders coexist (Cadi and Joly 2003, Cadi and Joly 2004, Outerbridge 2008). The need for future monitoring of the populations is highlighted through the high levels of uncertainty in the population abundance estimates. Areas of highest priority for monitoring include the sites in Penticton, particularly where juveniles were detected. The Penticton sites are all linked to one water system via channels, or are in very close proximity to each other, making the movement of the red-eared sliders into new areas more likely there than in isolated ponds surrounded by inhospitable matrix, such as roads and developed land. Management of these populations would be most successful and most easily carried out in the early portion of population establishment (Ficetola et al. 2009, Simberloff, 2009). The method found to best detect red-eared sliders in this study was the hoop-net traps. The allocation of resources to hoop-net trapping is better for the future monitoring than on-shore observation or manual dip-net searches. We observed red-eared sliders to be far more diligent and able to avoid predators than the western painted turtles. Many visual observation visits yielded no red-eared slider sightings where we knew there to be red-eared sliders. It is extremely important that sites where red-eared sliders were visually observed be further investigated as well. Trapping of the areas we were not able to trap will reveal the abundance and population structure, as data provided here is based on visual estimation only. The investigation of ponds wherein red-eared sliders were reported but not found during this study is also recommended. In addition to direct red-eared slider population management, public education programs regarding invasive pets are highly recommended. Research has shown that for the prevention of red-eared slider establishment and spread, simply removing existing individuals from ponds is not sufficient (Teillac-Deschamps et al. 2009). In France, where red-eared sliders have become a large problem, Cadi and Joly (2004) demonstrated that without public education, release events continue, and the public s attitude regarding releasing pets goes unchanged (Teillac-Deschamps et al. 2009). The release of red-eared sliders by civilians is the primary problem. Without solving the primary problem management efforts are wasted. 6

7 Acknowledgments This study was funded by the IK Barber Endowment Fund through the University of British Columbia s Undergraduate Research Awards program. The Ministry of Environment, particularly Orville Dyer, and the City of Kelowna were extremely cooperative and played a large role in site selection and access. We would also like to thank Alexis Friesen for her support in the field. 7

8 Literature Cited Bunnell, C. G Field survey of red-eared sliders (Trachemys scripta elegans) in the Lower Fraser River Valley, British Columbia, in Wildlife Afield 2: Cadi, A. and P. Joly Competition for basking places between the endangered European pond turtle (Emys orbicularis) and the introduced red-eared slider (Trachemys scripta elegans). Canadian Journal of Zoology 81: Cadi, A. and Joly, P Impact of the introduction of the red-eared slider (Trachymes scripta elegans) on survival rates of the European pond turtle (Emys orbicularis). Biodiversity and Conservation 13: Cadi, A., V. Delmas, A. Prevot-Julliard, P. Joly, C. Pieau, and M. Girondot Successful reproduction of the introduced slider turtle (Trachemys scripta elegans) in the South of France. Aquatic Conservation: Marine and Freshwater Ecosystems 14: Cagle, F.R The life history of the slider turtle, Pseudemys scripta troostii (Holbrook). Ecological Monographs 20: Crossland, M.A., G.P. Brown, M. Anstis, C.M. Shilton, and R. Shine Mass mortality of native anuran tadpoles in tropical Australia due to the invasive cane toad. Biological Conservation 141: Ficetola, G.F., W. Thuiller, and E. Padoa-Schioppa From introduction to the establishment of alien species: bioclimatic differences between presence and reproduction location in the slider turtle. Diversity and Distributions 15: Invasive Species Specialist Group, IUCN Species Survival Commission of the world s worst invasive species. (1/23/2009). Kenis, M., M. Auger-Rozenberg, A. Roques, L. Timms, C. Pere, M.J.W. Cock, J. Settele, S. Augustin, and C. Lopez-Vaamonde Ecological effects of invasive alien insects. Biological Invasions 11: Laidlaw, R Scales and Tails, the Welfare and Trade of Reptiles Kept As Pets In Canada. Report to the World Society for the Protection of Animals. Obtained 11/11/09 from Outerbridge, M Ecological notes on feral populations of Trachemys scripta elegans in Bermuda. Chelonian Conservation and Biology 7: Polo-Cavia, N., P. Lopez, and J. Martin Interspecific differences in responses to predation risk may confer competitive advantages to invasive freshwater turtle species. Ethology. 114:

9 Simberloff, D We can eliminate invasions or live with them. Successful management projects. Biological Invasions 11: Teillac-Deschamps, P., R. Lorrilliere, V. Servais, V. Delmas, A. Cadi, and A. Prevot-Julliard Management strategies in urban green spaces: Models based on an introduced exotic pet turtle. Biological Conservation 142: Warwick, C Conservation of red-eared terrapins (Trachymes scripta elegans): threats from international pet and culinary markets. Lecture: British Chelonia Group Symposium, University of Bristol. Obtained 09/23/09 from TERRAPINS-(TRACHEMYS-SCRIPTA-ELEGANS) 9

10 Appendix 1. Attributes of captured turtles in All but one turtle were trapped with hoopnets; the single turtle captured by dip-net is denoted by *. site notch sex/stage plastron length (mm) plastron width (mm) carapace length (mm) carapace width (mm) Nature Trust (T) 8,10-11 F Nature Trust (T) 8,12-0 F Nature Trust (T) 8,11-9 F Nature Trust (T) 8,11-10 F Nature Trust (T) 8,11-11 F Nature Trust (T)* 8,12-9 M Nature Trust (T) 8,12-10 M Nature Trust (T) 8,12-12 J Redlich Pond (D) 1,2-8,12 F Redlich Pond (D) 1,2-10,11 F Redlich Pond (D) 1,2-11,12 F Skaha Marina (R) 8,9-23 F Skaha Marina (R) 8,10-1 F Skaha Marina (R) 8,10-9 J Skaha Marina (R) 8,11-12 M weight (g) 10

11 Appendix 2. Okanagan Valley sites trapped for turtles in All sites are within zone 11 of the UTM coordinate system. location (map label) Easting Northing trapping period sliders detected Redlich Pond (D) Aug 16- Aug 16 y Skaha Marina north (R ) July 9- July 17 y Nature Trust (T) July 10- July 17 y Chichester Wetlands (E) July 28- Aug 5 n Blair Pond (L) Aug 5- Aug 16 n White Lake (W) July 1- July 4 n Green lake (X) June 13- June 27 n Vaseaux lake (Y) Aug 23- Aug 30 n Ripley (Z) July 21- July 26 n Sawmill/Burnell Lake (AA) Sept 1- Sept 8 n Oliver restoration 1 (AB) May 23- May 30 n Oliver restoration 2 (AC) May 25- May 31 n Yellow Lake (AD) June 1- June 10 n 11

12 Appendix 3. Sites where we carried out visual surveys for turtles in The sites were visited at random times between 11:00 am and 4:00 pm for a total of 2 hours. All sites are in zone 11 of the UTM coordinate system. location name (map label) Easting Northing observation dates sliders detected Fascieux Creek Wetlands (J) May 18, June 13 y Okanagan Lake Marina (M) June 7, Aug 9 y Skaha Marina south (S) July 14, Aug 27 y Glenmore pond north (A) May 20, June 11 n Glenmore pond south (B) May 20, June 11 n Rotary Marsh (C ) June 12, July 5 n Mission Creek (F) May 15, July 5 n Molnar Pond (G) May 20, June 11 n Lewis Pond (H)* June 6, July 5 n Belgo Pond (I) June 6, July 5, n MichaelBrook Marsh (K) May 20, June 11 n Warren Ave/ Hwy 97 (N) July 12, Augt 23 n McIntyre Pl/ Hwy 97 (O) July 12, Aug 24 n Brandon Ave/ Hwy 97 (P) July 13, Aug 25 n Green Ave/ Hwy 97 (Q) July 13, Aug 26 n St. Andrews Golf Course (U) June 14, July 4 n White Lake Rd. side pond (V) June 14, July 4 n * Lewis pond was visited for a total period of 1.5 hours 12

RED-EARED SLIDER TURTLES AND THREATENED NATIVE RED-BELLIED TURTLES IN THE UPPER DELAWARE ESTUARY. Steven H. Pearson and Harold W.

RESOURCE OVERLAP AND POTENTIAL COMPETITION BETWEEN INVASIVE RED-EARED SLIDER TURTLES AND THREATENED NATIVE RED-BELLIED TURTLES IN THE UPPER DELAWARE ESTUARY Steven H. Pearson and Harold W. Avery Six Most