Download Mt. Tamalpais Watershed Western Pond Turtle Study

Mt. Tamalpais Watershed Western Pond Turtle Study
Prepared For:
Marin Municipal Water District
220 Nellen Avenue
Corte Madera, CA 94925
Prepared By:
Pierre Fidenci
Garcia and Associates
1 Saunders Avenue
San Anselmo, CA 94960
Job 374
November 2003
TABLE OF CONTENTS
1.0 EXECUTIVE SUMMARY .................................................................................................... 1
2.0 INTRODUCTION................................................................................................................... 1
2.1 PROJECT LOCATION AND ENVIRONMENTAL SETTING ............................................................ 1
2.2 STATUS AND NATURAL HISTORY OF THE WESTERN POND TURTLE ....................................... 2
3.0 METHODS .............................................................................................................................. 3
3.1 HABITAT CHARACTERIZATION ............................................................................................... 3
3.2 KNOWN WESTERN POND TURTLE POPULATION SIZE AND DISTRIBUTION WITHIN THE
REGION ........................................................................................................................................ 4
3.3 TURTLE POPULATION STUDY ................................................................................................. 4
4.0 RESULTS AND DISCUSSION ............................................................................................. 5
4.1 HABITAT CHARACTERIZATION ............................................................................................... 5
4.1.1 Alpine Lake - Bon Tempe Creek ................................................................................... 5
4.1.2 Bon Tempe Reservoir .................................................................................................... 6
4.1.3 Lake Lagunitas............................................................................................................... 6
4.1.4 Phoenix Lake ................................................................................................................. 7
4.2 KNOWN WESTERN POND TURTLE POPULATION SIZE AND DISTRIBUTION WITHIN THE REGION
..................................................................................................................................................... 7
4.3 WESTERN POND TURTLE POPULATION STUDY ...................................................................... 8
4.3.1 Alpine Lake – Bon Tempe Creek .................................................................................. 8
4.3.2 Bon Tempe Reservoir .................................................................................................... 9
4.3.3 Lake Lagunitas............................................................................................................... 9
4.3.4 Phoenix Lake ............................................................................................................... 10
4.4 NON-NATIVE TURTLE POPULATION STUDY.......................................................................... 10
4.4.1 Account of Non-Native Turtles Encountered .............................................................. 10
4.4.2 Alpine Lake – Bon Tempe Creek ................................................................................ 11
4.4.3 Bon Tempe Reservoir .................................................................................................. 12
4.4.4 Lake Lagunitas............................................................................................................. 12
4.4.5 Phoenix Lake ............................................................................................................... 12
4.5 NATURAL AND HUMAN THREATS ........................................................................................ 12
5.0 CONCLUSIONS AND RECOMMENDATIONS.............................................................. 15
6.0 LITERATURE CITED ........................................................................................................ 17
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Tables:
Table 1…………………………………………………………………………………………..11
Appendices:
Appendix A: Maps (Figures 1a, 1b, 2, 3, 4, and 5)
Appendix B: Population Structure and Dorsal Length Figures (Figures 6a, 6b, 7a, 7b, 8a, 8b,
9a, 9b, 10a, and 10b)
Appendix C: Representative Photographs of Turtle Species Encountered within the MMWD
Watershed and Western Pond Turtle Sexually Dimorphic Characters
Appendix D: Representative Site Photographs
Appendix E: Marking System (Figures 11 and 12)
Appendix F: Western Pond Turtle and Exotic Turtle Data Forms
Appendix G: Non-native Turtle Removal and Adoption Program
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1.0 Executive Summary
Garcia and Associates (GANDA) conducted a western pond turtle (Clemmys marmorata) study
from late April to mid-August 2003 at the Mount Tamalpais watershed within the Marin
Municipal Water District (MMWD) land, Marin County, California. The study characterized
western pond turtle habitat and assessed population size, structure, and density at four sites: Bon
Tempe Creek plus an arm of Alpine Lake (hereafter referred to as Alpine Lake-Bon Tempe
Creek), Bon Tempe Reservoir, Lake Lagunitas, and Phoenix Lake. Western pond turtles were
found at three of the four sites studied: Alpine Lake-Bon Tempe Creek, Lake Lagunitas, and
Phoenix Lake. No western pond turtles were encountered at Bon Tempe Reservoir.
Due to significant temporal and spatial change of water level at Alpine Lake-Bon Tempe Creek,
additional surveys should be conducted earlier in the year (March to mid-May) to properly assess
western pond turtle population characteristics at this site. Western pond turtle population size at
Lake Lagunitas is the largest observed within the watershed with very few juveniles encountered.
Due to the small number of individuals, skewed age structure, and no recruitment, western pond
turtle population at Phoenix Lake is believed likely to become extirpated in a few years.
Natural and artificial barriers preclude natural recruitment of western pond turtles within the Mt.
Tamalpais watershed, creating an isolation of the current metapopulation. Although the western
pond turtle is the only native turtle species of California, it is not the most common species in the
Mt. Tamalpais watershed. The red-eared slider (Trachemys sripta elegans), a well-known
successful invasive species around the world, was found in large number (67 individuals) at one
site (Phoenix Lake) and breeding at two sites (Phoenix Lake and Alpine Lake - Bon Tempe
Creek). Threats to western pond turtles within the watershed include predation by native and
exotic species, competition with red-eared slider, introduction of parasites and disease through
contact with other turtle species, fishing, illegal harvest of turtles, and watering the road along
Phoenix Lake, which could favor red-eared slider hatchling success.
Recommendations include improved techniques for surveying western pond turtles at the Mt.
Tamalpais watershed, a protocol survey for long-term population monitoring, management
recommendations supporting conservation of viable populations of western pond turtles, and
guidelines for removal of non-native turtles.
2.0 Introduction
2.1 Project Location and Environmental Setting
The western pond turtle study was conducted at the Mount Tamalpais watershed, Marin
Municipal Water District land, in Marin County, California. The Marin Municipal Water District
has operated reservoirs within the Mt.Tamalpais watershed since 1872. Currently, the MMWD
operates five reservoirs within the watershed at Lagunitas Lake, Phoenix Lake, Alpine Lake, Bon
Tempe Lake and Kent Lake. Study sites were located at all of the reservoirs except Kent Lake
and part of Alpine Lake. Alpine Lake is the largest of the four reservoirs, with an area of 90
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hectares, followed by Bon Tempe Lake (57 hectares), Phoenix Lake (9.3 hectares) and Lagunitas
Lake (9 hectares). The four reservoirs are located on the northeast side of Mt. Tamalpais and east
of Bolinas Ridge at various elevations. Lagunitas Creek is the primary inlet to Alpine Lake, Bon
Tempe Lake and Lagunitas Lake, and Ross Creek is the primary tributary to Phoenix Lake.
The Mt. Tamalpais watershed has a Mediterranean climate and the reservoirs receive an average
annual rainfall of 1,320 mm. The dominant plant community of the watershed is primarily mixed
evergreen forest, interspersed with shrubland, chaparral and grassland. The mixed evergreen
forest surrounding the four reservoirs includes coast redwood (Sequoia sempervirens), Douglas
fir (Pseudotsuga menziesii), tan oak (Lithocarpus densiflorus), Pacific madrone (Arbutus
menziesii), coast live oak (Quercus agrifolia), canyon live oak (Quercus chrysolepus), black oak
(Quercus kelloggii), California bay (Umbellularia californica), and California buckeye (Aesculus
californica). The reservoirs and their tributaries also support riparian and aquatic vegetation,
including alders (Alnus sp.), willows (Salix spp.), maples (Acer sp.), cattails (Typha sp.), and
sedges (Carex spp.).
2.2 Status and Natural History of the Western Pond Turtle
The western pond turtle is designated as a federal special concern species, and a California
Species of Special Concern. In Oregon, this species is listed as threatened and, in Washington, as
endangered.
Recent taxonomic revision based on phylogenetic analyses (Holman and Fritz 2001; Feldman
and Parham 2001) has resulted in a recommendation to change the classification of the western
pond turtle to a different genus. Holman and Fritz (2001) recommend placing Clemmys
marmorata in a monotypic genus Actinemys; whereas Feldman and Parham (2001) suggest the
use of the existing genus Emys for the monophyletic group that contains other related species.
Western pond turtles occur from sea level to 1,829 m from British Columbia south to
northwestern Baja California, principally west of the Sierra-Cascade Crest. Pond turtle habitat
includes slow-moving or stagnant waters that contain pools at least 1 m deep and 1 m in
diameter. Pond turtles are uncommon in high gradient streams (Holland 1994). An important
habitat feature for turtles is suitable protected basking sites, such as mats of emergent or aquatic
vegetation, exposed logs, rocks, or mud banks. Hatchlings and juveniles require shallow water
habitat with relatively dense submergent or short emergent vegetation in which to forage.
Population persistence in suitable aquatic habitat also requires adjacent suitable upland habitat
for overwintering and nesting. Suitable oviposition (egg-laying) sites appear to share the
following features: exposed, south-facing slopes, open scrub or open grassland vegetation, and
dense soils, which apparently provide the high temperature and low water potential required for
successful egg development (Holland 1994, Rathbun et al. 1992). Slopes up to 60 degrees have
been used for nesting, but most nests have been found on slopes of 25 degrees or less. Mating
typically occurs in April or May. Females migrate from the aquatic site to an upland location as
far as 500 m from the aquatic site; however most nesting occurs within 200 m of the aquatic site
(Holland 1994, Rathbun et al. 1992). Movements away from water can be common (Holland
1994). Furthermore, movements within a stream course are highly variable and can exceed 2.5
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km (Holland 1994). Females may lay more than one clutch in a year (Rathbun et al. 1992), and
most egg-laying occurs during May and June. Incubation lasts about 100 days and hatchlings
usually overwinter in the nest. Most hatchlings move to aquatic habitats in the spring, where
they feed on zooplankton. Growth in hatchling and juvenile turtles can be rapid; however
reproductive maturity normally does not occur until turtles are between 7 and 11 years old
(Holland 1994). This species is long-lived, with a large proportion of adults in a healthy
population 20 or more years old.
Major causes of decline of this species are associated with habitat loss or modification. Other
threats include recreation, urban growth, introduction of non-native predators, and diseases.
3.0 Methods
3.1 Habitat Characterization
A habitat characterization was conducted by GANDA herpetologist Pierre Fidenci in April and
August 2003. Habitat characterization involved documenting and mapping key habitat
characteristics of the western pond turtle habitat at the Alpine Lake - Bon Tempe Creek, Bon
Tempe Reservoir, Lake Lagunitas, and Phoenix Lake study sites. Key habitat features include
water depth, aquatic vegetation and debris cover, basking sites, sun exposure, soil texture, slope
degree, and terrestrial cover of upland habitat. Key habitat characteristics of western pond turtle
habitat are detailed below. Habitat characteristics were visually inventoried at each site and
mapped on topographic maps. At each site, a final map was created showing essential habitat
areas for hatchlings, juveniles, and adults (e.g., aquatic habitat, basking areas, and potential
nesting areas). Representative photographs of sites assessed are included in Appendix D.
Shallow waters (<0.5 m). These areas are used by hatchlings and juveniles where they find
refuges against larger predators (e.g., fish), warmer waters for faster growth, and foraging areas
with small abundant food items (e.g., zooplankton). Shallow waters occasionally can be used by
adults.
Deep waters (0.5 m<depth<3 m). These areas are used by sub-adults and adults. Western pond
turtles use deep water for refuge and foraging.
Aquatic vegetation and debris cover. Vegetative cover is an essential component of the hatchling
and juvenile western pond turtle habitat. It provides protection and camouflage against predators,
thermoregulation areas, and foraging areas (e.g., zooplankton, small prey size). Adults also will
take refuge under root and vegetation and will forage on plant matter.
Aerial basking sites. These are key features of western pond turtle habitat. Suitable basking sites
include logs, rocks, high gradient banks, and vegetation.
Sun exposure. Sun exposure is an essential component for aerial and surface basking,
thermoregulation, and egg incubation. For example, nests are located on sunny slopes (at least
partially south-facing).
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Soil texture, slope degree, and terrestrial cover of upland habitat. These are essential parameters
for nesting. Western pond turtles usually nest within 200 m of the aquatic site but may lay eggs
as far as 500 m. They nest on open scrub or open grassland vegetation in a substrate with high
clay and silt content. Slopes up to 60 degrees have been used for nesting, but most nests have
been found on slopes of less than 25 degrees.
3.2 Known Western Pond Turtle Population Size and Distribution Within the Region
To identify the known western pond turtle populations within the region, several current
information sources on western pond turtle were reviewed, including the California Natural
Diversity Database (CDFG 2003), A Field Guide to Western Reptiles and Amphibians (Stebbins
2003), and other pertinent literature such as Jennings and Hayes (1994). Additionally, major
museum collection databases (California Academy of Sciences, Santa Barbara Natural History
Museum, and Stanford University) were consulted. Potential habitats for western pond turtles
within a 50 km buffer zone were inventoried using USGS topographic maps. Potential corridors
(e.g., creeks) and barriers (e.g., ridges, urbanization) were identified within the 50 km buffer
zone using GIS and USGS 7.5 minute topographic maps (Bolinas, Novato, San Geronimo, and
San Rafael quadrangles) to assess potential dispersal between the Mt. Tamalpais metapopulation
and other potential metapopulations.
3.3 Turtle Population Study
GANDA biologists Pierre Fidenci, Chloe Scott, and Jeff Mitchell conducted a population study
of western pond turtles and other non-native turtle species in the Alpine Lake - Bon Tempe
Creek, Bon Tempe Reservoir, Lake Lagunitas, and Phoenix Lake. The population study was
conducted from April 30 to August 22, 2003 between 0830 and 1800 hrs, during clear days with
wind conditions less than 7 m/s. The study included geographic distribution and demography.
To estimate turtle population distribution, size, structure and density at the Mt. Tamalpais
watershed, GANDA collected mark-recapture data through repeated trapping and release of
marked turtles. GANDA captured turtles using turtle traps (funnel and basking traps). A total of
30 funnel traps and 9 basking traps were used for the study. Funnel traps varied in size, with the
smallest measuring 0.6 m in length and 0.5 m in width and height, and the largest 1 m in length
and 0.7 m in width and height. The rectangular structure was shaped using 2 cm mesh, nonstretch, metallic netting. The mouth of the trap was an elliptical funnel decreasing in diameter
towards the bait. The mouth of the trap was large enough to allow adult turtles to enter (carapace
width of the largest individuals is about 130 mm). Traps were baited with raw beef. Baits were
attached around a fine metal wire hung in the center of the trap. A small colorful ribbon attached
to the metal wire was placed to emerge from the water. Traps were anchored to the shore with a
line tied to a stable portion of the shoreline. They were placed close to the banks of water bodies
where turtles are believed to forage. Traps were checked every 20-30 minutes using an inflatable
boat without removing the trap from the water. Checking from a distance with binoculars
reduced disturbance. When a turtle was trapped inside the trap, the plastic ribbon would jiggle.
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Basking traps were held afloat at their perimeter with PVC pipe (0.75 m in length and 0.5 m in
width). Two opposite ramps allowed turtles to climb on the main log for basking. When their
basking session was interrupted, turtles immediately dove into the water where they became
captured in the net. Basking traps were placed at locations where turtles are believed to bask or
where basking areas are usually absent. Basking traps were checked twice a day without
removing the trap from the water. Traps were not removed at the end of each day.
Hatchlings and juveniles use specific microhabitats that can be missed during population
surveys. To maximize the observation and capture of small turtles, special attention was given in
placement of traps in shallow areas, and among root masses, emergent vegetation, and other finescale aquatic cover.
Captured turtles were measured using calipers (dorsal and plastron lengths to the nearest 1 mm),
sexed, marked for permanent identification, and immediately released. Sex was determined using
characteristics described by Holland and Bury (1988) which include plastron concavity, carapace
shape, head shape and coloration, and tail shape. Turtles above 120 mm of carapace length were
classified as adults (Bury and Germano 1998). Through the use of a triangular file, each trapped
individual received a notch or notches in the marginal(s) of the carapace. The sum of the notches
represented the turtle’s identification number (Appendix E, Figure 11). The marking system on
the carapace is the same for each study site, whereas the marking system for the plastron differs
for each study site depending where the turtle was captured (Appendix E, Figure 12). At Phoenix
Lake, turtles did not receive any notches on the plastron. Turtles found at Alpine Lake - Bon
Tempe Creek received one notch on the right gunal of the plastron. Turtles captured at Bon
Tempe Reservoir received one notch on the right humeral of the plastron. Finally, turtles
captured at Lake Lagunitas received a notch on the left gunal of the plastron. This system allows
for long-term data collection for population dynamic studies and for future monitoring programs.
Turtles were trapped and marked under a California Fish and Game Permit for trapping western
pond turtles (Pierre Fidenci # 801154-05).
4.0 Results and Discussion
4.1 Habitat Characterization
4.1.1 Alpine Lake - Bon Tempe Creek
In general, Alpine Lake –Bon Tempe Creek site provides potential habitat for western pond
turtle during winter and spring. Due to sharp decreases in water levels (several meters) during the
summer and fall, the previously abundant suitable habitat then becomes rapidly unsuitable. This
change forces turtles to adapt to new environmental conditions by changing their activities (i.e.,
most of the turtles become inactive or move to other aquatic habitats). Bon Tempe Creek is a
small creek that becomes wider and deeper by the time it reaches Alpine Lake. The creek
provides potential habitat for western pond turtles during the winter and spring when the water
level is high (Appendix D, Photos 31 and 32). At this time of the year, different sized logs offer
potential basking sites for juveniles and adults. The basking sites are located at the western side
of the creek where the morning sun hits the area (Appendix A, Figure 1a). Logs and a few steep,
sunny rocky banks located at the end of the arm provide most of the basking sites. During high
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water periods, Bon Tempe Creek has more key habitat features essential to western pond turtle
than during lower water periods. Shallow and deep waters are present with abundant aquatic
vegetation and debris where turtles can find refuge. During lower water levels (summer and
fall), potential habitat is located at the end of the arm where Alpine Lake and Bon Tempe Creek
join (Appendix A, Figure 1b). At this time of the year, a few basking sites are located on the
west side that receive morning sun, and where steep banks and deep water occur. As the water
level drops, less aquatic habitat is available for turtles. In general, the remainder of Alpine Lake
provides little-to-no potential for western pond turtle (Appendix D, Photos 29 and 30). It lacks
basking sites and its shorelines do not contain aquatic or emergent vegetation. Furthermore,
Alpine Lake is mostly surrounded by forest, which does not provide nesting sites for turtles. The
only potential nesting area within Alpine Lake is located at the arm where Bon Tempe Creek
meets Alpine Lake (Appendix A, Figure 1a). Due to the deep water and lack of aquatic
vegetation, no potential habitat for hatchlings and juveniles is found at the arm of Alpine Lake
(Appendix A, Figure 1a). Potential nesting sites within 200 m of upland habitat are mainly
located at the west side of the Alpine Lake - Bon Tempe Creek (Appendix A, Figures 1a and 1b;
Appendix D, Photos 33 and 34). Soil texture (silt content), slope (low degree), and upland
habitat (grassland) meet the western pond turtle nesting area criteria.
4.1.2 Bon Tempe Reservoir
Bon Tempe Reservoir is a large reservoir that provides little-to-no potential habitat for western
pond turtles (Appendix A, Figure 2). Bon Tempe Reservoir lacks aquatic vegetation including
emergent vegetation. A few potential basking sites (logs) are available at the southern part of the
lake but, otherwise, the reservoir is devoid of aquatic habitat characteristics suitable for
hatchlings and juveniles. Suitable nesting site characteristics are present along the north and
southeast side of the reservoir (Appendix A, Figure 2). These sites are characterized by low
canopy, grassland ground cover, and moderate to no slope. Due to the lack of suitable aquatic
characteristics, Bon Tempe Reservoir is not expected to support a resident population of western
pond turtles but could temporarily be used by western pond turtles during movement between
suitable lakes within the watershed.
4.1.3 Lake Lagunitas
Lake Lagunitas provides suitable habitat for the western pond turtle (Appendix A, Figure 3).
Aquatic habitats for adults are mostly located within the lake’s coves. Coves offer shallow and
deep areas where adults can forage, find refuge, thermoregulate, and overwinter. Aquatic habitat
for smaller turtles is localized a few meters from the shoreline where shallow areas with dense
aquatic vegetation are present. At Lake Lagunitas most of the coves with dense cattail vegetation
offer habitat characteristics for hatchlings and juveniles (Appendix C, Figure 3). Suitable
basking sites for adults are mostly found where large logs are present (Appendix D, Photos 2326). These sites are located on the west side of the lake where trees have fallen and where logs
were intentionally placed near Lagunitas Dam. Other basking sites for adults are found along dry
vegetation and emerged roots at the east side of the lake. Basking sites for smaller turtles are
mostly present where dense emergent vegetation and smaller logs occur (Appendix D, Photos 27
and 28). Open basking areas are usually not suitable for juveniles, which use deeper emergent
vegetation as refuge and camouflage while basking. Potential nesting sites are mainly located at
the east side of Lake Lagunitas (Appendix A, Figure 3) where upland habitat is characterized by
open grassland, good sun exposure, low slope degree, and suitable soil texture. The rest of the
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terrestrial habitat surrounding Lake Lagunitas is mostly covered by dense canopy, which does
not meet nesting site suitability criteria.
4.1.4 Phoenix Lake
Phoenix Lake provides suitable habitat for western pond turtles (Appendix A, Figure 4). In
general, potential aquatic sites for adults are located along the shoreline at the west and southeast
sides of the lake where aquatic vegetation is present and extends a few meters until deep areas
are reached. Smaller turtles use areas where shallow waters and dense vegetation are
encountered. Basking sites are located on the north side of the lake (Appendix A, Figure 4). A
few large logs, emergent roots, and dry cattails provide basking sites for turtles (Appendix D,
Photos 37 and 38). In general, upland habitat is characterized by forest with dense canopy and
therefore does not provide suitable nesting habitat. Potential nesting sites are mostly located at
the north side of Phoenix Lake where open and flat terrestrial habitat exists (Appendix A, Figure
4; Appendix D, Photos 35 and 36).
4.2 Known Western Pond Turtle Population Size and Distribution within the Region
The CNDDB (CDFG 2003) documents 11 occurrences of western pond turtles within a 50 km
buffer zone of the project location (Appendix A, Figure 5). Most of the CNDDB occurrences are
located at least 20 km east of the study area and are isolated from natural barriers (San Francisco
Bay and urban development). Other western pond turtle occurrences (31 sightings) occur within
the 50 km buffer zone (Fidenci, unpublished data). Most of these sightings are located on the
west and northwest portion of the buffer zone within the Point Reyes National Seashore and
Golden Gate National Recreation Area (Appendix A, Figure 5). The closest occurrence to the
study area is located about 6 km away. This occurrence is isolated from the MMWD area by
extensive urban development. The other sightings are at least 14 km from the project area.
Natural barriers (ridges, steep terrain) and urban development (mainly roads) hinder turtle
dispersal to the Mt. Tamalpais watershed. The museum databases document two historical
occurrences of western pond turtles within the 50 km buffer zone of the survey area in Marin
County. These two occurrences originate from two voucher specimens collected in April 1898,
but which were later reported missing in 1993 (CAS database). Information on sex and the exact
location where they were collected was also lost.
Disjunct distribution of western turtle occurs over a local scale (50 km radius). Western pond
turtle populations at Bon Tempe Creek, Alpine Lake, Lake Lagunitas, and Phoenix Lake should
be considered as a metapopulation. This metapopulation is likely isolated from other
metapopulations within Marin County. Other metapopulations appear to be located within Point
Reyes National Seashore, Golden Gate National Recreation Area, and the east side of the San
Francisco Bay (Appendix A, Figure 5).
Two major factors control western pond turtle dynamics: (1) the number or density of individuals
dispersing among suitable habitats (e.g., ponds, lakes, reservoirs), and (2) the density of aquatic
sites and suitable upland areas that determine dispersal distances and the probability of
successfully reaching aquatic sites. The population size or density of western pond turtle
individuals within the Mt. Tamalpais watershed is too small (see section 4.3) to act as a source
metapopulation. The dynamic of other potential metapopulations found in the regions is
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unknown. However, due to increased urbanization in the region, their population size is
probably too low to allow colonization dispersal. The low density of suitable aquatic sites and
the presence of significant barriers between the Mt. Tamalpais watershed metapopulation and
other potential metapopulations hinder turtle dispersal processes.
Ecological connectivity is critical to allow or maintain western pond turtle dispersal. In general,
very steep ridges and terrain, urban development, and the lack of suitable aquatic sites and
upland areas isolate the turtle metapopulation of the Mt. Tamalpais watershed from other
metapopulations. On the west side of the Mt. Tamalpais watershed, suitable habitat for western
pond turtle is located west of the Bolinas Ridge within the Golden Gate National Recreation
Area and Point Reyes National Seashore. The Bolinas Ridge creates a natural barrier against
turtle dispersal. Therefore, turtle movement from east of the Bolinas Ridge to west of the ridge
(to Mt. Tamalpais watershed) is unlikely. On the east side of the Mt. Tamalpais watershed,
urbanization precludes turtle dispersal. The south part of the Mt. Tamalpais watershed is isolated
by steep natural barriers (e.g., Mt. Tamalpais) and urbanization. Creeks on the south part have
very deep gradients with small pools which do not provide suitable dispersal aquatic habitat.
The north side of the study area is isolated by steep terrain and light urbanization (roads).
4.3 Western Pond Turtle Population Study
4.3.1 Alpine Lake – Bon Tempe Creek
At Alpine Lake-Bon Tempe Creek, 42.9% of the turtles (n=5) captured were western pond turtles
and the rest were introduced species. The structure of western pond turtles captured was
dominated by adults (66.7% adult males, 16.7% adult females, 16.7% sub-adults; Appendix B,
Figure 6a). No hatchlings or juveniles were encountered during our study. The absence of
observation and capture of hatchlings and juveniles could be attributed to low fecundity (only
one female captured while gravid), high predation rate (bullfrog, bass and various predatory
birds), and drastic water change associated with aquatic habitat modification. Additionally,
hatchlings and juveniles are more difficult to observe than adults in the field (Reese 1996;
Fidenci 1999). Due to their small size and feeding habit, our survey method could have failed to
account for smaller individuals. However, GANDA biologists caught one red-eared slider
hatchling at Bon Tempe Creek and spent significant time looking for hatchlings at locations
where suitable habitat was encountered. Surveys at Bon Tempe Creek overlapped with peak
periods for hatchlings (emergence from nest between March and June) and juveniles should have
seen by biologists juveniles if recruitment was occurring.
Our capture rate decreased sharply around mid-May when turtles changed their activity pattern.
Most of the turtles bask in March, April, and early May when water temperature is low and water
level is still high. As soon as the water temperature increased and water level dropped due to
water consumption and no rainfall (mid May), turtles showed unusual activity changes leading to
a very low capture rate. During this time, turtles may have been aestivating and/or moved to
other aquatic sites. Since GANDA started the surveys at the Alpine Lake - Bon Tempe Creek by
late April 2003, most of the peak period for capturing adults and sub-adults was missed.
Therefore, the trapping results do not allow for an accurate population estimate. It is
recommended in future survey effort that trapping for western pond turtles at Alpine Lake –Bon
Tempe Creek should start as early as March and continue until mid-May when most of the turtles
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can still be found in the lake. At that time, basking traps should be placed at locations with poor
basking opportunities. Funnel traps should be located where adult and juveniles western pond
turtle aquatic habitats were identified during the habitat characterization (Appendix A, Figure
1a).
4.3.2 Bon Tempe Reservoir
No western pond turtles were observed or captured at Bon Tempe Reservoir. As previously
discussed in the habitat characterization, Bon Tempe Reservoir provides very little-to-no
potential habitat for western pond turtle. Native turtles could temporarily use Bon Tempe
Reservoir while moving between Lake Lagunitas and Alpine Lake - Bon Tempe Creek or during
dispersal.
4.3.3 Lake Lagunitas
The western pond turtle population at Lake Lagunitas appears to be the healthiest of all the sites
studied. Lake Lagunitas harbors the largest number of native turtles within the Mt. Tamalpais
watershed (n=18). Ninety five percent of the turtles captured at Lake Lagunitas were western
pond turtles (Appendix C, Photos 2, 13 and 14). Among the western pond turtles captured, there
were 13 adult males, four adults females, and one juvenile (Appendix B, Figure 7a). Adults
dominate the western pond turtle population with only one juvenile captured (Appendix B,
Figure 7b) and another one observed basking. No hatchlings were encountered at Phoenix Lake.
The world’s biggest western pond turtle ever recorded (dorsal length of 223 mm) was captured
and marked at Lagunitas Lake (Jennings and Hayes 1994, Photos 23 and 24). The predominance
of males, especially large and old ones, and a small number of juveniles, suggests an unstable
population structure. The sex ratio (3.25:1; male/female) is higher than those reported in
previous studies. For example, Fidenci (1999) found a 1.23:1 ratio at one site in Marin County
with similar aquatic conditions as Lake Lagunitas. At another site in Alameda County, Fidenci
(unpublished data 2002) found a 1.9:1 sex ratio, with a large percentage of hatchlings and
juveniles (36 percent). Bury (1972) noted a 1.17:1 ratio in Hayfork Creek. Both even and
unbalanced sex ratios may occur naturally in some populations of turtles (Bury 1972). The high
percentage of male versus female could be attributed to several factors. The observed sex ratio
could be the result of biased sampling, or could reflect the actual sex ratio. Since GANDA
biologists conducted most their surveys at Lake Lagunitas between June and August, females
could have been less active in the water during those months due to nesting activities, and
therefore more males could have been found active in the lake. The sex of some species of
turtles is influenced by the temperature at which the eggs are incubated (Pieau 1974). Usually,
turtles lay eggs that develop as females at higher temperatures and males at lower temperatures.
Pivotal temperatures vary between 26°C and 29°C. The correspondence between hatchling sex
ratios and adult sex ratios has never been studied for the western pond turtle but it is likely to
occur.
The observation of western pond turtle juveniles at Lake Lagunitas (Appendix C, Photos 9 and
10) reveals that some recruitment is occurring at an unknown rate. The recruitment for western
pond turtle could be attributed to the lack of bass and the extremely low density of exotic species
precluding potential competition between western pond turtles and non-native species.
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4.3.4 Phoenix Lake
At Phoenix Lake, only 8.2% of the turtles captured were western pond turtles (n=7), and the rest
were introduced species. Among the western pond turtle population found at Phoenix Lake, four
were adult males and three were adult females (Appendix B, Figure 8a; Appendix C, Photos 1
and 17); however, no hatchlings, juveniles or sub-adults were found. Based on the number of
turtles captured, the western pond turtle population size at Phoenix Lake appears very small (less
than 10 individuals). The sex ratio (1.3:1; male/female) is similar to other western pond turtle
populations (Bury 1972; Fidenci 1999). If recruitment is occurring for the western pond turtle at
Phoenix Lake, one would expect to observe and/or capture juveniles and sub-adults. GANDA
biologist found hatchling and sub-adult red-eared sliders, suggesting that small turtles were
encountered when present. Successful recruitment is dependent on both gravid females and
neonate survival. Due to the low number of females (n=3) and expected high predation rate, the
western pond turtle population at Phoenix Lake is probably suffering from severely limited
recruitment or no recruitment. A disease outbreak or illegal harvesting of the few remaining
females could totally decimate the western pond turtle population at Phoenix Lake. Similarly,
without recruitment, the remaining females could reach their normal life span in a few years and
the mature turtles could become extirpated from Phoenix Lake.
4.4 Non-native Turtle Population Study
4.4.1 Account of Non-Native Turtles Encountered
Although the western pond turtle is the only native turtle species of California, it is not the most
common species in the Mt. Tamalpais watershed (Table 1). The red-eared slider (Trachemys
sripta elegans), a well-known successful invasive species around the world, was found abundant
at one site (Phoenix Lake) and breeding at two sites (Phoenix Lake and Alpine Lake - Bon
Tempe Creek). A total of four non-native species, including three sub-subspecies of Trachemys
scripta native to the North America, were encountered in the watershed. These species include
the red-eared slider (Trachemys scripta elegans), the Rio Grande slider (Trachemys scripta
gaigeae), the yellowbelly slider (Trachemys scripta scripta), the midland painted turtle
(Chrysemys picta marginata), the cooter (Pseudemys sp.), and the common musk turtle
(Sternoterus odoratus). The non-native species encountered within the Mt. Tamalpais watershed
are common within the pet trade.
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Table 1. Family, genus and species of turtles encountered in the Mt. Tamalpais watershed during
the 2003 surveys.
Family
Species
Total number captured
Clemmys marmorata
30
Trachemys scripta elegans and T. s. gaigeae *
74
Trachemys scripta scripta
1 (observed not captured)
Pseudemys ssp.
2 (observed not captured)
Chrysemys picta marginata
2
Sternoterus odoratus
1
Emydidae
Kinosternidae
* Subspecies difficult to differentiate
The red-eared slider (Appendix C, Photos 4, 19, 20, 21, and 22) occupies the Mississippi Valley
from Illinois to the Gulf of Mexico (Gibbons 1990). It is a well-known successful invasive
species around the world. This species was found at all the sites studied. The Rio Grande slider
(Appendix C, Photos 3, 11, and 12) is found in the Rio Grande and Rio Conchos drainages of
Texas and New Mexico of the United States, Chihuahua and Coahuila States of Mexico
(Gibbons 1990). The Rio Grande slider was encountered at Phoenix Lake. Interbreeding
between the red-eared slider and the Rio Grande Slider is possible. The midland painted turtle
(Appendix C, Photo 5) ranges from the Great Lakes region of Canada and the United States
south to southern Illinois, Tennessee, and extreme northern Alabama. This species was captured
at Lake Lagunitas (one male) and Alpine Lake (one male). The yellowbelly turtle is a common
turtle of the southeastern United States (Conant and Collins 1991). This species inhabits a wide
variety of habitats including rivers, ditches, sloughs, lakes, and ponds. The yellowbelly turtle
was observed basking on emergent roots at Lake Lagunitas. The common musk turtle
(Appendix C, Photos 7 and 8) is encountered from the coast of Maine, west through southern
Ontario to extreme southern Wisconsin, south to the tip of Florida, and west to east central Texas
(Conant and Collins 1991). This small species is highly aquatic and frequents deep water bodies.
An adult female was captured at Alpine Lake - Bon Tempe Creek.
4.4.2 Alpine Lake – Bon Tempe Creek
At Alpine Lake – Bon Tempe Creek, 57.1% of the turtles captured were non-native turtles (four
males; three females, one hatchling; Appendix B, Figure 9a). Most of the exotic turtles captured
were red-eared slider with the exception of one male midland painted turtle and one female
common musk turtle. The capture of one red-eared slider hatchling (Appendix C, Photos 19 and
20) suggests that the red-eared slider is breeding successfully but the recruitment rate is
unknown. Since GANDA biologists did not start the surveys at Alpine Lake - Bon Tempe Creek
until late April 2003, most of the peak period for capturing sub-adults and adults was missed.
Trapping results preclude a population estimate of non-native turtles. Based on turtle basking
observations, GANDA expects the exotic population to be much larger than the current number
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of turtles captured. Exotic turtle appears to largely outnumber the western pond turtle at this
location.
4.4.3 Bon Tempe Reservoir
No non-native turtles were captured at Bon Tempe Reservoir. Only one red-eared slider was
observed basking on a log during spring. In general, habitat at Bon Tempe Reservoir provides
low suitability for exotic species. It is surmised that the number of non-native turtles at Bon
Tempe Reservoir is lower than those found for the other Alpine Lake – Bon Tempe Creek and
Phoenix Lake due to comparatively more difficult public access at this site (e.g., proximity to
large parking lots).
4.4.4 Lake Lagunitas
At Lake Lagunitas, 5% of the turtles captured were non-native. The only exotic species capture
was a male midland painted turtle (Appendix C, Photo 5). However, GANDA biologists
observed one yellowbelly slider basking on dry cattails and one sub-adult red-eared slider
foraging in shallow water. Lake Lagunitas contains very few non-native turtles in contrast to
Alpine Lake – Bon Tempe Creek and Phoenix, where these are illegally released. At the present
time, the non-native turtle population of Lake Lagunitas does not appear to pose a threat to
western pond turtles. However, over time, the non-native turtle population could become
problematic if illegal release is not stopped. In addition, migration from larger non-native
populations at Alpine - Bon Tempe Creek and Phoenix Lake could adversely affect the western
pond turtle population.
4.4.5 Phoenix Lake
At Phoenix Lake, 91.8% of the turtles captured were red-eared sliders (n=67). Another exotic
species, the cooter, was observed but not captured. The red-eared slider population appears
healthy, and with successful recruitment (e.g., presence of hatchlings). Most red-eared slider
individuals captured were large (dorsal length ≥120 mm) adults (38 females; 20 males; Appendix
B, Figures 10a and 10b) while smaller individuals were less common (4 sub-adults, 5 juveniles,
and 4 hatchlings). Hatchlings (Appendix C, Photos 21 and 22) and juveniles encountered are
offspring of adults released into Phoenix Lake, since juveniles under 10 cm in length are not
legally available within the pet trade in the United States. Due to the significant number of
reproductive females, the breeding success of the red-eared slider is much higher than that of the
western pond turtle. The red-eared slider population size at Phoenix Lake is the largest within the
Mt. Tamalpais watershed. Due to the proximity of the urban area, most non-native turtle species
are released at Phoenix Lake. Also, most of the species released (e.g., Trachemys sp.) find
adequate aquatic habitat at Phoenix Lake, similar to the habitat they occupy in their natural
range.
4.5 Natural and Human Threats
Threats to western pond turtles within the Mt. Tamalpais watershed include predation by native
and exotic species, competition with red-eared slider, introduction of parasites and disease
through contact with other turtle species, starvation or manultrition following ingestion of fish
hooks, illegal release of non-native turtles, and illegal harvest of turtles. In addition, it is possible
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that watering the road along Phoenix Lake could favor red-eared slider hatchling success since
higher substrate moisture conditions is required for the red-eared slider.
During the western pond turtle study, GANDA found one dead western pond turtle male at
Phoenix Lake (dead at least six months), two dead red-eared slider females at Phoenix Lake
(dead within a few days), and one live red-eared slider male with a fishhook embedded in its
stomach (Appendix C, Photo 6) at Bon Tempe Creek. At Lake Lagunitas, one western pond
turtle female with a tail injury (Appendix C, Photos 15 and 16) and one old western pond turtle
male that was blind on one eye were captured. Despite their physical injuries, both showed no
unusual behavior and appeared to be in good health.
Predation. Predators of western pond turtle include raccoon (Procyon lotor), domestic dog
(Canis familiaris), great blue heron (Ardea herodias), osprey (Pandion haliaetus), bullfrog
(Rana catesbiana), and large fish such as the largemouth bass (Mustela vision). These species
are known to prey on the western pond turtle, especially hatchlings and juveniles (Holland 1994).
Suspected predators found within the watershed encompass rainbow trout (Oncorhynchus
mykiss), squawfish (Ptycholeilus spp.), smallmouth bass (Micropterus dolimeiui), and common
garter snake (Thamnophis sirtalis). Potential nest predators include raven (Corvus corax),
common crow (Corvus brachyrhynchos), gopher snake (Pittuophis melanoleucus), common
kingsnake (Lampropeltis getulus), and possibly small rodents. All of these predators have been
observed at the study sites. Competition with non-native turtles could create a higher impact on
western pond turtle survival than natural predation (see illegal release of non-native turtle
below).
Parasites and disease. A few parasites such as trematodes, helminths, nematodes, lungworms,
and leeches use western pond turtle as a host (Holland 1994) but none are fatal to western pond
turtle. At Lake Lagunitas, Phoenix Lake and Alpine Lake, GANDA captured western pond
turtles with leaches attached on their carapace or skin. Also, six leeches were attached to one
single male red-eared slider. Exotic turtles such as the red-eared slider have the potential to
introduce disease that could decimate native turtles. For example, populations of western pond
turtle in Washington State were decimated by a respiratory infection in 1990 and Hays et al.
(1999) implicated the red-eared slider as a likely vector for the infection. With non-native turtles
being released in the Mt. Tamalpais watershed, there is a possibly that some disease will be
introduced at the same time. Due to the small western pond turtle population size found at
Phoenix Lake, a disease outbreak could be fatal for the few remaining C. marmorata individuals.
Fishing. Incidental catch by fisherman can have a significant impact on western pond turtle
populations when the populations are small and fishing is common. In Oregon, 3.6% of the
western pond turtle captured had ingested a fishhook (Holland 1994). At a site in southern Sierra
Nevada, 6% of the western pond turtle were affected by fishhooks (Holland 1994). Within the
Mt. Tamalpais watershed, no western pond turtles were found with ingested fishhooks but one
red-eared slider was captured with a fishhook in its stomach (Appendix C, Photo 6). Due to
significant fishing activities at Alpine Lake - Bon Tempe Creek, Lake Lagunitas and Phoenix
Lake, a significant number of western pond turtles could be injured and/or killed. At Phoenix
Lake, where the western population size is very small, a mortality fishing tackle in one adult
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turtle would cause the population to decrease by 14%. Turtles with ingested fishhooks die either
from associated trauma or starvation.
Illegal release of non-native turtles. Non-native turtles found in the Mt. Tamalpais watershed
are believed to be due to people releasing unwanted pets. The impact of introduced turtles on the
western pond turtle population is difficult to assess but almost certainly negative. Competition
may occur between the red-eared slider and the western pond turtle for basking sites. Lindeman
(1999) has shown that in competition for basking sites between the red-eared slider and other
emydid turtles, the largest turtle successfully displaces the smaller, regardless of the species. At
Phoenix Lake, the red-eared slider adults are about 11% larger than the western pond turtle
adults (Appendix C, Photos 17 and 18). Competition could also occur for food resources as well.
In addition, non-native turtles can be significant vectors for fatal diseases that could decimate
western pond turtle populations (see parasites and diseases above).
Illegal harvest of turtles. Until the 1930s, thousands of western pond turtles were sold in the
San Francisco market for human consumption. In California, commercial harvesting of western
pond turtles is now prohibited and illegal collection of western pond turtles for the pet trade
occurs at an unknown level. Turtles become vulnerable to illegal harvest when using upland
habitat. Females are mostly active on land during the nesting period (late spring and early
summer) and terrestrial movements appear most common in summer and winter for adults
(Reese and Welsh 1997). Also, Reese and Welsh (1997) demonstrated that females spent time
on land year-round, whereas males did not spend time on land in July and August. They noted
that western pond turtles can move as far as 500 m away from their original aquatic site.
The detrimental effect of human recreation on a freshwater turtle (Clemmys insculpta) has been
clearly documented in a 20-year study in Connecticut (Garber and Burger 1995). They observed
that the turtle population protected in a restricted-access watershed collapsed shortly after the
area was opened to recreational use. During another study near Davis, California, Spinks et al.
(2003) suggested that the skewed sex ratio western pond turtle population of that was consistent
with the loss of adult females due to higher risk of encounters with humans when they crossed
paved walkway to nest. Model predictions also suggest that even modest harvests (intentional or
incidental) of long lived, late-maturing turtle species are likely to result in a declining population
(Crouse et al 1987; Congdon et al. 1993). At Lake Lagunitas, a regular cyclist has reported
observing hikers collect a turtle as a pet (anonymous personal communication 2003). At
Phoenix Lake, where the population size is very small, a harvest of one western pond turtle each
year, would lead to a 100% decline in less than eight years, assuming total failure of recruitment
(extremely low-to-no recruitment is most likely the case at Phoenix Lake).
Watering road and upland habitat. By watering upland habitat, the hatchling success of
introduced turtles might be enhanced by providing high substrate moisture conditions favored by
species such as red-eared slider. The western pond turtles have evolved in a summer rain-free
environment; when under conditions of excess moisture, their hard eggshell cannot expand. At
that point, eggshell ruptures lead to embryo failure (Feldman 1982). Non-native turtles, such as
the red-eared turtle, require higher moist substrate conditions than the western pond turtle for the
eggs to hatch. By watering Phoenix Lake Road along Phoenix Lake during summer, the
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hatchling success of the red-eared slider could be enhanced, to the detriment of the western pond
turtle.
5.0 Conclusions and Recommendations
Although the western pond turtle is the only native turtle species of California, it is not the most
common species in the Mt. Tamalpais watershed. The red-eared slider, a well-known successful
invasive species around the world, was present at all sites studied (Alpine Lake - Bon Tempe
Creek, Bon Tempe Reservoir, Lake Lagunitas, and Phoenix Lake). The red-eared slider was
abundant at Phoenix Lake and breeding at Phoenix Lake and Alpine Lake - Bon Tempe Creek.
Western pond turtles have long life spans, delayed sexual maturity, iteroparity, and high adult
survival rates. Particular attention should be paid to evidence of skewed age structures or other
indications of population sinks suggesting long-term impacts to populations with limited
recovery capabilities. The western pond turtle metapopulation at the Mt Tamalpais watershed is
isolated from other metapopulations found in the region. This isolation makes any natural
recovery more problematic if the population is at risk. The population of western pond turtle at
Phoenix Lake showed no recruitment with a population size near extinction (sink population).
Since the western pond turtle appears to have no recovery capabilities at Phoenix Lake, low-tono recruitment at Alpine Lake - Bon Tempe Creek, and an adult-dominated age structure at Lake
Lagunitas, key measures should be implemented to promote a sustainable western pond turtle
population at the Mt. Tamalpais watershed.
Additional turtle surveys are needed at Alpine Lake - Bon Tempe Creek and Lake Lagunitas to
accurately assess the population size, structure, and health for the entire Mt. Tamalpais
watershed. Surveys should follow the 2003 survey methodology, with a few modifications, and
be conducted from March to mid-May 2004 when most turtles can be captured and marked.
Since most turtles bask during spring and appear to forage later during the day, GANDA
recommends the use of additional basking traps. An average of 10 basking traps per site should
be used. Funnel traps with an entrance that closes once turtles get into the traps should be used
when regular funnel traps cannot be checked every 20 minutes (i.e., the area covered is too
large). Ten funnel traps with automatic close entrances should be used at each site.
Basking activities represent an important part of western pond turtle biology. The habitat for
juveniles and adults should be enhanced by providing additional basking sites of different sizes
at key locations defined in the habitat characterization. Additional basking sites should be
included at Lake Lagunitas, Phoenix Lake, and Alpine Lake - Bon Tempe Creek. Logs of
different size work well as basking sites.
The removal and control of exotic species is another important component of sustainable
management strategies for western pond turtle. A recent study near Davis (Spinks et al. 2003)
has clearly shown that an aggressive trapping program can control populations of non-native
turtles. Exotic species at Alpine Lake - Bon Tempe Creek, Phoenix Lake, and Lake Lagunitas
should be removed. The removal program should occur during spring and early summer when
turtles are easier to trap. Non-native species captured should be adopted, if possible. Adoption
programs should be organized in conjunction with, but not limited to, turtle clubs and local
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environmental organizations (Appendix G for details). For example, the California Turtle and
Tortoise Club (CTTC) has a turtle adoption program. In 2002, 2,364 non-native turtles were
adopted through the CTTC program. Non-native turtles should be placed at safe artificial ponds
within urbanized areas (e.g., artificial parks and zoos). Past projects have euthanized red-eared
sliders that could not be adopted (Spinks personal communication 2003). In conjunction with
the removal of non-native turtles, interpretative signs and brochures should be located at key
entrance locations and near direct access to shoreline of Lake Lagunitas, Phoenix Lake, Bon
Tempe Reservoir, Alpine Lake, and Bon Tempe Creek. In the meantime, press coverage should
be released. Removal of non-native species may require California Department of Fish and
Game approval.
Since the western pond population appears to be extirpated at Phoenix Lake, an additional
management strategy is necessary to boost recruitment and significantly increase the number of
adults in the long run. Since the metapopulation of the Mt. Tamalpais watershed is isolated from
other potential metapopulations, natural movement of western pond turtles to Phoenix Lake
would have to come from the Mt. Tamalpais metapopulation (Lake Lagunitas or Alpine Lake Bon Tempe Creek). Population size and density at Lake Lagunitas and Bon Tempe Creek appear
too low to allow significant recruitment required to reverse the current decline of the native turtle
population at Phoenix Lake. In that situation, headstarting can be a viable management strategy,
although it does not eliminate the cause of low recruitment and mortality. Reasons for low
recruitment can be diverse, such as harvesting turtles during recreational activities, a high
predation rate, and competition with non-native turtles. Headstarting would increase recruitment
at Phoenix Lake and could increase the population size to a level allowing self-recruitment.
Also, by removing exotic species (reducing competition), improving habitat for juveniles, and
informing the public, the headstarting program would have a better chance of success.
Informing the public about the turtle management plan is also an important component of the
management strategy. Press releases should be issued during removal of non-native turtles. The
public information campaign on the western pond turtle population should focus on the
following issues: (1) western pond turtle is the only native freshwater turtle and is a special status
species in California; (2) western pond turtle populations are at risk in the Mt. Tamalpais
watershed and close to extinction at Phoenix Lake; (3) non-native turtles are successfully
breeding in the Mt. Tamalpais and have a negative impact on western pond turtle populations;
(4) several actions will be implemented to enhance viable populations of western pond turtle at
Mt. Tamalpais watershed, including removal of non-native turtles; an "adopt a turtle" program;
and developing signage and interpretative materials to alert the public to turtle biology and
threat, illegal practices and MMWD management strategies.
A long-term monitoring program will assess western pond turtle population recovery and
viability within the Mt. Tamalpais watershed. Monitoring programs cannot be based only on
abundance. Apparently healthy populations of turtles may, in fact, already be imperiled because
of chronic reproductive failure. Thus, in addition to abundance, reproductive rates and/or age
structure must be monitored. To implement a monitoring program that uses affordable and
reasonable resources, GANDA proposes one visit per site per week by one to two biologists from
early March to the end of June. Biologists should have experience with turtle biology and
identification. Western pond turtles are mostly seen during spring and early summer in the Mt.
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Tamalpais watershed. Neonates and juveniles are usually observed and/or captured from midMarch to early July; therefore, a monitoring program should occur until the end of June to assess
recruitment success. Monitoring should occur at the Alpine Lake - Bon Tempe Creek, Lake
Lagunitas, and Phoenix Lake using similar methodology as used during this study. An average
of eight basking traps and 10 funnel traps will allow significant capture during monitoring
process. Any new individuals should be marked following the marking system already initiated
during this study. Data should be entered into a database and the population dynamic assessed
yearly until signs of recovery are observed. Any non-native turtles captured during monitoring
program should be removed from the Mt. Tamalpais watershed and turtles found dead and/or
captured by fishermen should be immediately reported to the MMWD biologists.
In summary, GANDA recommends the following key management strategies:
1. Conduct additional western pond turtle surveys at Alpine Lake - Bon Tempe Creek and Lake
Lagunitas from March to mid-May 2004 when most turtles are active.
2. Remove exotic species from Alpine Lake - Bon Tempe Creek, Lake Lagunitas, and Phoenix
Lake during spring and early summer of 2004. If some turtles are still present, removal
should start again during September.
3. Enhance basking sites (down trees of different sizes) for western pond juveniles and adults at
Alpine Lake - Bon Tempe Creek, Lake Lagunitas and Phoenix Lake.
4. Conduct a headstarting program (rearing juveniles to a certain size before release to reduce
the impact of predation) in 2005 for increasing recruitment at Phoenix Lake where the
western pond turtle population has no recruitment and the population is nearly extirpated.
5. Interpretative signs and brochures prohibiting the release of turtles should be located at key
entrance locations and near direct access to shoreline of lakes. Additionally, a press release
should be issued. Information could also be added to the MMWD website.
6. Apply a long-term monitoring protocol for western pond turtle, starting into the spring of
2004 and evaluate exotic species removal success and western pond turtle recruitment
success within the Mt. Tamalpais watershed. Any turtles found dead and/or captured by
fishermen should be immediately reported to the MMWD biologists.
6.0 Literature Cited
Bury, B.R. 1972. Habits and home range of the Pacific pond turtle, Clemmys marmorata in a
stream community. Ph.D. Dissertation. University of California, Berkeley.
Bury, R. B., and D. J. Germano. 1998. Annual deposition of scute rings in the western pond
turtle, Clemmys marmorata, Chelonian Conservation 3:108-109.
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California Department of Fish and Game (CDFG). 2003. California Natural Diversity Data Base
(CNDDB). Electronic Database, Sacramento, California. February 2003.
Conant R., and J. Collins. 1991. Reptiles and Amphibians Eastern Central North America.
Peterson Field Guide. Third edition, 450 pp.
Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1993. Delayed sexual maturity and
demographics of Blanding’s turtles (Emydoidea blandingii): Implications for
conservation and management of long-lived organisms. Conservation Biology 7:826-833.
Crouse, D.T., L.B. Crowder, and H. Caswell. 1987. A stage-based population model for
loggerhead sea turtles and implication for conservation. Ecology 3:95-104.
Feldman, M., 1982. Notes on the reproduction in Clemmys marmorata. Herpetological Review
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Feldman. C.R., and J. F. Parham. 2001. Molecular phylogenetics of Emydine turtles: taxonomic
revision and the evolution of shell kinesis. Phylogenetics and Evolution. 10: 1-11
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.
Garber, S.D., and J. Burger. 1995. A 20-year study documenting the relationship between turtle
decline and human recreation. Ecological Applications 5:1151-1162.
Gibbons, J.W. 1990. Life history of the slider turtle. Smithsonian Institution Press. Washington
DC. 367 pp.
Hays, D.W., McAllister, K.R., Richardson, S.A., and Stinson, D.W. 1999. Washington State
Recovery Plan for the Western Pond Turtle. Washington Department of Fish and
Wildlife, Olympia.
Holland, D.C. 1994. A synopsis of the ecology and status of the western pond turtle (Clemmys
marmorata marmorata) in 1991. Report prepared for the U.S. Fish and Wildlife Service,
National Ecology Research Center, San Simeon Field Station, San Simeon, California.
Holland, D.C. and R. B. Bury. 1998. Clemmys marmorata (Baird and Girard 1852) Western
pond turtle. In P. C. Pritchard and A. G. Rhodin, (eds.) Conservation Biology of
Freshwater Turtles, Chelonian Res. Monogr. Vol II. In press.
Holman, A.J., and U. Fritz. 2001. A new emydine species from the middle Miocene
(Barstovian) of Nebraska, USA with a new generic arrangement for the species of
Clemmys sensus McDowell (1964) (Reptilia:Testudines: Emydidae). Zoologische
Abhandlungen Staatliches Museum für Tierkunde Dresden 51, 331-353.
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Jennings, M.R. and M. P. Hayes. 1994. Amphibian and reptile species of special concern in
California. California Department of Fish and Game, Sacramento.
Lindeman, P.V., 1999. Aggressive interactions during basking among four species of emydid
turtles. Journal of Herpetology 33, 214-219.
Pieau, C. 1974. Différenciation du sexe en fonction de la température chez les embryons d’Emys
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Western Pond turtle Study
MMWD Mt. Tamalpais Watershed
November 2003
Garcia and Associates
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