Introduction Turtle Observer Program Report 216: Biological survey results and citizen science strategies Marin Municipal Water District Daniel Hossfeld, Watershed Stewards Program Member Eric Ettlinger, Aquatic Ecologist August 216 Years of habitat degradation and invasive competition have reduced western pond turtle (Actinemys marmorata) populations to a critical level. The International Union for the Conservation of Nature (IUCN) lists the western pond turtle as Vulnerable (IUCN, 216) - populations in the San Francisco Bay Area have struggled but effective management strategies can allow this species to persist in tandem with human use of its habitat. The western pond turtle species was recently split into northwestern and southwestern designations, with the northwestern species occurring north of the entrance to the San Francisco Bay. Persistent western pond turtle (WPT) populations exist in Marin Municipal Water District s (MMWD) reservoirs on Mount Tamalpais in Marin County, California. Due to the proximity to suburban areas, pet releases are common; non-native turtle species are in the majority throughout the watershed (MMWD, 21). The Water District s Aquatic Ecologist and Watershed Volunteer Coordinator have developed an observational survey designed to provide the District with an annual snapshot of the population dynamics in four reservoirs. The survey is designed with citizen science in mind- dedicated volunteers provide hours of surveys that would not be possible otherwise. Tracking of native pond turtles and removal of non-natives is carried out by MMWD staff and Watershed Stewards Program Members. 216 marks the eighth year of observational surveys. Data provided by the citizen scientists is summarized in this report to highlight population dynamics at each site, compare temperature data to observational success, identify a seasonal window for the observational peak, and review MMWD s citizen science methods. A western pond turtle at Lake Lagunitas (C. Samuelson) 1
Methods Citizen scientists attended a three hour classroom lesson covering the observational survey, identification techniques, and methods for public engagement. The identification portion included observing a captive western pond turtle, red-eared slider, and river cooter that had been trapped ahead of the training. Rainy weather prevented the training group from practicing observing turtles in the field. Participants were invited to visit any survey site between March th and May 31 st. MMWD provided all equipment necessary for the survey. A Watershed Stewards Program (WSP) Member curated and logged the data forms submitted by volunteers, and performed quality assurance by altering species identifications where necessary. Surveys occurred at one or more of four locations on MMWD s reservoirs- Alpine Lake (ALP), Bullfrog Trail (BFT), Phoenix Lake (PHX), and Lake Lagunitas (LAG). Each site was chosen due to previous success in observational surveys. Participants observed each location until all turtles were recordedsurveys lasted between. and 3. hours. Observations recorded at the same location on the same date were reduced to only the high count of each species for the day. Populations were estimated using the high count for each site. Daily observations were compared with water temperatures from a HOBO device, and air temperatures downloaded from NOAA. Observations were recorded on a paper data sheet which included the volunteer name, age, date, time interval, and weather. To minimize unknowns, volunteers were asked to record a series of qualitative observations. These observations are as follows: the observing location, whether the turtle was basking or swimming, if 1) the head was visible, 2) the turtle had a red stripe behind the eye, 3) the turtle had yellow facial stripes, 4) the throat was noticeably lighter than the face, and ) there were yellow markings on the shell. Based upon these observations, volunteers could then classify the turtle as a western pond turtle (), red-eared slider (TS), unidentified non-native (), or an unknown species (U). WSP Members were also able use this information to identify species classification errors. This was the second consecutive year of turtle trapping at the Bullfrog Creek Trail survey site. Two basking traps and three box traps were checked three or more times weekly, usually by WSP members or dedicated volunteers. Traps were operational between February 11 th and May 8 th. Nonnative turtles were removed to an enclosure at the Sky Oaks Headquarters (the Turtle Jail). Captured western pond turtles were weighed, measured, aged, and marked by notching scutes to assign a unique number, following Fidenci (1999) and GANDA (23). A GPS tag was fastened to female WPTs large enough to support the weight. At the end of trapping season, all non-natives were brought to Sonoma County Reptile Rescue. 2
MMWD s trap site at Bullfrog Trail Non-natives still outnumber WPTs Results High Count ofturtles 2 18 16 14 12 1 8 6 Figure 1. Actinemys Marmorata () and Non-Native () Turtle High Counts Phoenix Lake Lake Lagunitas Alpine Lake Bon Tempe Creek 4 2 23 29 21 211 212 213 214 21 216 Survey Year Figure 1 shows high counts of turtles at each site, combined to show total numbers across the watershed. The drastic increase in 214 can be explained by the increase in survey hours and use of spotting scopes. The decrease between 21 and 216 is sizeable, with western pond turtle numbers declining from 29 to 24 and non-natives decreasing from 176 to 92. 3
Bullfrog Trail Volunteers conducted 28 observational surveys at the Bullfrog Trail site through the 216 season. Volunteers observed six western pond () turtles and 49 non-native () turtles at the highest count, a dramatic decrease in both and from the 21 season. The single day high count was 63, on March 18 th. 7 Figure 2. Bullfrog Creek Trail Turtles Observations 216 Number of turtles observed 6 4 3 2 1 U TS Dates of observation (not temporally scaled) Figure 3. BFT High Count by Species 1 9 8 7 6 4 3 2 1 9 73 49 17 19 14 18 14 12 11 6 2 211 212 213 214 21 216 4
Alpine Lake Volunteers conducted 12 observational surveys at the Alpine Lake site beneath Bon Tempe Dam through the 216 season. Volunteers observed three western pond () turtles and 27 non-native () turtles at the highest count. The single day high count was 27, on March 24 th. 3 Figure 4. Alpine Lake Turtle Observation 216 Number of Turtle Observations 2 2 1 1 U TS 27-Jan 23-Mar 24-Mar 26-Mar 27-Mar 1-Apr 2-Apr 3-Apr 1-Apr 1-May 8-May 28-May Dates of Observations (not scaled temporally) Figure. ALP Turtle High Count By Species 6 4 3 2 1 27 19 14 12 6 4 3 4 3 3 211 212 213 214 21 216
Lake Lagunitas Volunteers conducted 12 observational surveys at the Lake Lagunitas site through the 216 season. Volunteers observed eight western pond () turtles and seven non-native () turtles at the highest count, a drastic decrease in observations from the 21 season. The high count was 14, on both February 24 th and 27 th. 16 Figure 6. Lake Lagunitas Turtle Observations 216 Number of Turtles Observed 14 12 1 8 6 4 2 U TS Dates of Observations (not scaled temporally) 3 3 2 Figure 7. LAG Single Day High Count By Species 3 2 2 1 1 18 1 9 9 9 8 7 4 3 3 211 212 213 214 21 216 6
Phoenix Lake Volunteers conducted 27 observational surveys at the Phoenix Lake through the 216 season. Volunteers observed seven western pond () turtles and 2 non-native () turtles at the highest count, a noticeable decrease in observations from the 21 season. The single day high count was 23, on February 7 th. 2 Figure 8. Phoenix Lake Turtle Observations 216 Number of Turtles Observed 2 1 1 U TS Dates (not scaled Temporally) 4 3 Figure 9. Phoenix Lake Single Day High Count By Species 37 3 2 2 2 21 2 1 1 3 9 3 7 212 213 214 21 216 7
Other Sites Bon Tempe Lake was not an official survey site, but volunteers were encouraged to survey for any turtles on the trek between Lake Lagunitas and Alpine Lake. Volunteers observed 11 on March 14 th. Volunteers have also noted seeing turtles in the Bon Tempe Dam spillway pool- WSP members also incidentally spotted turtles basking there. Unknowns Unknown observations increased by % from the 21 season, with 141 of the 11 observations input or corrected to Unknown. After the high percentage of Unknowns in 212, MMWD protocols were altered and unknowns have stayed low for the past four years (Figure 13). Number of Observations 18 16 14 12 1 8 6 4 2 Trapping Figure 1. Unknown Observations 211-216 23% 68% 21% 9% 9% 14% 211 212 213 214 21 216 Survey Year Positive ID Unknowns In 216 trapping was successful for both non-natives and western pond turtles at the Bullfrog Trail site. Basking and box traps were used to capture 11 non-native turtles - ten red-eared sliders and one river cooter. MMWD staff and watershed visitors found five red-eared sliders on fire roads. One captured red-eared slider was a hatchling, evidence of successful reproduction. Out of the 16 captured non-natives, only the river cooter was identified as male. All red-eared sliders were identified as female. Of the 16 western pond turtles that were captured, six had been captured previously (had notched scutes). Three WPTs were captured 2+ times in the 216 season. Four WPTs were recaptured at the BFT site with markings from Lake Lagunitas or Phoenix Lake. The sex ratio of captured WPT was 12 males and four females. Three of the females were the three smallest WPTs collected- the fourth was tagged in hopes of locating a nest. The largest western pond turtle ever recorded (Turtle 18 from Lake Lagunitas) was recaptured at Bullfrog Trail- he has since grown to 23mm in carapace length. 8
Turtle Ages We estimated turtle ages based on the number of annuli (annual rings) we could see on marginal scutes, although those annuli wear off on older turtles. Germano and Rathbun (28) determined growth rates for western pond turtles along the central California coast, which can be used to estimate turtle ages based on size. We used that age-at-size relationship to estimate the ages of all 7 individual western pond turtles captured since 23, including the 16 captured in 216. Western Pond Turtles 16 14 12 1 8 6 4 2 Figure 11. Western pond turtle age distribution 2 4 6 8 1 12 14 16 18 2 22 24 26 28 3 32 34 36 38 4 42 44 46 Age (Years) at Time of Capture (age-at-size based on Germano and Rathbun (28)) GPS Tracking One female western pond turtle of adequate size was captured, tagged, and released. Location data was lost when the first tag flooded, and the second tag is currently in use. As of this report, no nests have been successfully located. Optimal Basking Temperature Daily water and air temperatures were compared with basking observations in an effort to find the optimal temperature range for basking behavior. No substantial correlations were found between the number of basking turtles and factors including maximum daily water temperature, average daily water temperature, maximum daily air temperature, and average daily air temperature. Peak Basking Dates Over the course of all turtle observer seasons, basking peaks at the four sites have ranged between February 7 th and May 29 th. All sites show trends of earlier peak basking dates throughout the years. 9
Figure 12. Peak basking dates across years and survey sites. Peak dates have been trending earlier in recent years. 31-May 11-May 21-Apr 1-Apr 12-Mar 21-Feb 1-Feb Bullfrog Trail 21 211 212 213 214 21 216 31-May 11-May 21-Apr 1-Apr 12-Mar 21-Feb 1-Feb Lake Lagunitas 21 211 212 213 214 21 216 31-May 11-May 21-Apr 1-Apr 12-Mar 21-Feb 1-Feb Alpine Lake 21 211 212 213 214 21 216 31-May 11-May 21-Apr 1-Apr 12-Mar 21-Feb 1-Feb Phoenix Lake 212 213 214 21 216 Volunteer Statistics MMWD s Turtle Observer Program volunteers contributed a total of 84 survey hours over 66 surveys. The March th training was attended by 29 individuals, 19 of whom provided survey data during the season. Five returning volunteers contributed as well. Volunteers made 11 individual turtle observations, up from 21. Volunteer observation hours fell from 91 to 84, although observations and surveys increased. 4 3 3 2 2 1 1 Figure 13. Total number of volunteers participating 3 37 22 24 19 9 11 1 12 1 7 2 Figure 14. Total number of observation visits 131 4 37 7 42 63 66 28 24 2 16 12 8 4 Figure 1. Total volunteer 21 observation hours 13 16 76 63 91 84 1
Discussion The 216 Turtle Observer season was successful in providing a snapshot of the population dynamics between native and non-native residents on the Mount Tamalpais Watershed. One quarter of the western pond turtles captured were originally marked in other lakes. This finding shows high mobility of turtles, indicating that the turtles of the Mount Tamalpais Watershed should be considered as a single population. This year the fewest western pond turtles were seen since 212, and observations of non-native turtles also declined sharply from 21. These declines may reflect changes in the turtle populations, although it seems unlikely that the non-native turtle population declined by nearly half. A more likely explanation is that fewer turtles were observed basking, either because they were basking in other locations or they spent less time basking. More years of monitoring data will hopefully elucidate the reasons for declining observations. In 217 we intend to investigate whether we can detect a decline in non-native observations as a result of this year s removal efforts. Fewer observations at the Bullfrog Trail site relative to observations at other lakes would support the success of trapping efforts. The age distribution of western pond turtles (Figure 11) indicates a low level of recruitment into the population. However, small turtles have been captured since 23, indicating some reproductive success. Given the longevity of this species, this low recruitment rate may be adequate to maintain a stable population. The peak basking dates for each survey site are trending earlier into the calendar year. This trend may be related to warmer temperatures earlier in the year, as expected due to climate change. According to surveys by returning volunteers, basking peaks occurred at both Lake Lagunitas and Phoenix Lake before the new volunteers were trained. Similar findings occurred in 21, and therefore it is recommended that trainings be scheduled earlier in the year. The peak basking day at Phoenix Lake in 21 was in mid-may, so for next year at least the observer season should continue through May. The skewed sex ratio of the trapped red-eared sliders indicates that we relied too heavily on the shape of the plastron when identifying turtle sex. We recommend that all of the following characteristics be considered when identifying turtles to sex in the future: Female Male Cloaca Location Close to plastron Close to tail tip Front Claws Short Long Plastron Shape Flat Concave Citizen Science Citizen Science Statistics & Strategies Volunteer citizen scientists have been crucial to the turtle observer program since its inception in 29. MMWD and WSP employees, as well as volunteers, have identified strategies to minimize error in the survey process, as well as streamline the wildlife ecology experience for curious citizen scientists. 11
The use of binoculars and spotting scopes was emphasized at training and contributed to the low percentage of unknown observations in the 216 season. Volunteers who turned in surveys with high unknown numbers were sought out and offered extra identification practice. Future Strategies While the Turtle Observer Training is regularly at capacity, there are certainly ways to increase the popularity of the program and engage the public more successfully. A Facebook group linked to MMWD s volunteer page has been suggested as a way for observers to connect, ask questions and build a following for the program. Regular updates could provide a method of reaching busy volunteers. Another strategy to increase the success of volunteers is active education. The use of live captured turtles at the training was clearly a successful lesson in species identification. It is recommended that future Turtle Program leaders also provide field trip lessons for volunteers who wish to practice before venturing out on their own. Finally, encouraging wildlife and hobbyist photographers to participate will likely reduce unknowns further- WSP Members were often able to retroactively alter unknown identifications when volunteers submitted labeled photos associated with their survey forms. References An example of a helpful photo- red-eared sliders are visible (R. Snipes) Fidenci, P. 1999. Relationship between cattle grazing and the western pond turtle Clemmys marmorata populations in Point Reyes National Seashore. Master s Thesis. University of San Francisco, San Francisco. Garcia and Associates (GANDA). 23. Mt. Tamalpais Watershed Western Pond Turtle Study. Prepared for Marin Municipal Water District. Germano, D.J. and G.B. Rathbun. 28. Growth, Population Structure, and Reproduction of Western Pond Turtles (Actinemys marmorata) on the Central Coast of California. Chelonian Conservation and Biology, 7(2): 188 194. Rogers, V. and E. Ettlinger. Turtle Observer Program Report. June 21. Marin Municipal Water District. Tortoise & Freshwater Turtle Specialist Group. 216. Actinemys marmorata. The IUCN Red List of Threatened Species 216: e.t4969a9729242. Downloaded on 7 July 216. 12