Actinemys Marmorata) in Lentic

POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS

OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC

HABITATS ALONG THE TRINITY RIVER, CALIFORNIA

HUMBOLDT STATE UNIVERSITY

Leah Marie Sloan

A Thesis

Presented to

The Faculty of Biological Sciences

In Partial Fulfillment

Of the Requirements for the Degree

Master of Science

In Biological Sciences

May 2012

POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS

OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC

HABITATS ALONG THE TRINITY RIVER, CALIFORNIA

HUMBOLDT STATE UNIVERSITY

Leah Marie Sloan

We certify that we have read this study and that it conforms to acceptable standards of scholarly presentation and is fully acceptable, in scope and quality, as a thesis for the degree of Master of Science:

______Dr. Sharyn Marks, Major Professor Date

______Dr. Hartwell Welsh, Committee Member Date

______Dr. Erik Jules, Committee Member Date

______Dr. Kristine Brenneman, Committee Member Date

______Dr. Michael Mesler, Graduate Coordinator Date

______Dr. Jená Burges, Vice Provost and Dean of Graduate Studies Date

ABSTRACT

POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC HABITATS ALONG THE TRINITY RIVER, CALIFORNIA

Leah Marie Sloan

As populations of a species decline, an understanding of habitat use and regional variation in population health can aid in focusing conservation efforts. Western Pond

Turtle (Actinemys marmorata) populations have declined throughout much of their range as a result of habitat loss, overexploitation, introduced species, and water course alterations. The Trinity River, in northwestern California, has been modified from its natural state by damming and flow regulations; these alterations have decreased river quality for turtles. I investigated the health of Western Pond Turtle populations in lentic sites adjacent to the Trinity River and its tributaries using four indicators of population health: 1) age structure, 2) size structure, 3) body size, and 4) growth rate of young turtles. Of six lentic sites sampled, four were biased towards large, old turtles. These sites had prolific Bullfrog populations, while the other two sites lacked Bullfrogs. Given that Bullfrogs will eat hatchling turtles, Bullfrogs likely are inhibiting turtle recruitment.

The four lentic sites with Bullfrogs also had turtles with faster growth rates and larger sizes, likely a result of warmer water temperatures. I also used radio telemetry to monitor the terrestrial movements of turtles within a complex of lentic habitats along the Trinity

iii

River. The majority of turtles used multiple aquatic resources within a year, indicating that their home range can include multiple water bodies separated by upland habitat.

Overall, conservation efforts should focus on creating or preserving aquatic habitats free of Bullfrogs, and terrestrial corridors for turtles to move between them.

ACKNOWLEDGEMENTS

First and foremost I would like to acknowledge the organizations and people that provided the funding and equipment that made this project possible. Most especially, I thank the U.S. Bureau of Reclamation's Trinity River Restoration Program (Interagency agreement number # R10AC20019) for incorporating my project into their restoration efforts and for providing me with funding and support throughout my study; B.

Gutermuth was particularly instrumental in ensuring that I had all the necessary resources to successfully complete my project. I also thank the US Fish and Wildlife Service, particularly C. Chamberlain and J. Bettaso, for providing the majority of the equipment for this project and for funding my summer field assistants. A. Baker and A. Desch of the HSU Biology and Wildlife stockrooms were extremely helpful in providing me with additional equipment. I am grateful to the Bureau of Land Management for providing a campsite near my study site. I also thank the HSU Department of Biological Sciences for awarding me a Master’s Student Grant.

Numerous people lent their assistance and expertise to this project; I am profoundly grateful to you all! I especially thank my major advisor, S. Marks, for her patience, kindness, and dedication throughout this study and the many preliminary drafts of this thesis. Her guidance and assistance have been invaluable. In addition, I thank the members of my graduate committee, K. Brenneman, H. Welsh, and E. Jules, for lending me their advice and expertise. I am very grateful to J. Bettaso, D. Ashton, and C. Bondi

for sharing with me their vast knowledge and experience with Western Pond Turtles and all the members of the HSU Herpetology Group for lending me their support, guidance, and friendship throughout my time at HSU. I also thank R. van Kirk for his statistical guidance and A. Scheiff for downloading my temperature data. I am particularly obliged to the private landowners who allowed me access to their property and ponds; it would have been impossible to complete this study without their assistance and generosity.

This project could not have been completed without the tireless work of many people in the field. I thank my summer field assistants, J. Brown (2010) and J. Carlson

(2011), for spending their summers chasing turtles and mucking around in anoxic, leech- infested ponds. I am also profoundly grateful to I. Zacher for volunteering countless hours to this project, from rescuing my car out of the snow to picking insects out of mud in the pouring rain. I also thank many others who came camping with me in Weaverville in order to volunteer with fieldwork: N. O’Brien, C. Brady, A. Pesqueda, J. Cresswell, J.

Ponte, J. Paget-Seekins, H. Kurkjian, S. Hedrick, H. Hedrick, C. Bube, G. Leech, T.

Richards, and K. Wright.

Lastly, I most sincerely thank my parents for being wonderful naturalists and teaching me to love, cherish, and protect the natural world. I have become the biologist I am today because of your support, encouragement, and inspiration. Thank you!

TABLE OF CONTENTS

Page

ABSTRACT...... iii

ACKNOWLEDGEMENTS ...... v

TABLE OF CONTENTS ...... vii

LIST OF TABLES...... x

LIST OF FIGURES ...... xii

LIST OF APPENDICES...... xv

CHAPTER 1………………….……………………………………………………….…..1

INTRODUCTION...... 1

METHODS ...... 6

Study Area …...... 6

Turtle Sampling...... 9

Marking and Morphometrics...... 9

Population Health……………...... 10

Pond Characteristics………...... 11

Data Analysis ...... 12

RESULTS ...... 15

Proportion of Young to Old Turtles...…………...... 15

Proportion of Small to Large Turtles …………...... ………………………..… 15

Body Size………………...... 16

vii

Growth of Young Turtles…...... 21

Environmental Variables ...... 23

Bullfrog and Fish Presence ………………...……………………………………26

DISCUSSION ...... 28

Age and Size Structure ………………………………...……………..………….29

Growth Rate and Body Size ………………………………………..……………34

REFERENCES ...... 37

CHAPTER 2 …………………………………………………………………………….44

INTRODUCTION…………………………………………………………………...44

METHODS ……………………………………………………………………….....48

Study Area………………………………………………………………….……48

Turtle Capture, Marking, and Morphometrics……………………………….…..51

Radio Telemetry ………………………………………………………………....51

Pond Characterizations ……………………………………………………….…52

Data Analysis ………………………………………………………………..…..54

RESULTS …………………………………………………………………………...56

Terrestrial Movements ……………………………………………………….….59

Terrestrial Movements among Aquatic Habitats …………………………….….62

Overwintering Behavior …………………………………………………………63

Terrestrial Movements Associated with Reproduction ………………………….64

Environmental Characteristics ………………………………………………..…65

DISCUSSION ……………………………………………………………………….73

Use of an Aquatic Habitat Complex by Turtles……………………………….…73

viii

Proportion of Active Turtles ………………………………………………….…75

Terrestrial Distances …………………………………………………………….76

Overwintering ………………………………………………………………..….77

Nesting Movements ………………………………………………………..……78

Conservation Implications …………………………………………………..…..78

Conclusions ………………………………………………………………..…….80

REFERENCES …………………………………………………………….………..82

APPENDICES ………………………………………………………………………87

LIST OF TABLES

CHAPTER 1

Table Page 1. Ponds where Actinemys marmorata were trapped in six sites along the upper Trinity River and its tributaries ...... 8

2. Candidate models for the comparison of the proportion of old (≥ 10 years) to young (< 10 years) Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data ...... 19

3. Candidate models for the comparison of the proportion of large (carapace length ≥ 125 mm) to small (< 125 mm) Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data ...... 19

4. Mean maximum carapace lengths (CL), standard error (SE), and sample size (n) for large (≥ 125 mm carapace length) Western Pond Turtles in two lotic sites and six lentic sites along the Trinity River. * indicates data from Ashton et al. 2011 .... 20

5. Mean weight (WT), standard error (SE), and sample size for large (≥ 125 mm carapace length) male and non-gravid female Western Pond Turtles in six lentic sites along the Trinity River ...... 20

6. Estimated carapace lengths (mm), based on growth curves (Fig. 4), for young Actinemys marmorata in lentic habitats along the Trinity River, CA ...... 22

7. Presence or absence of Lithobates catesbeianus (American Bullfrog), Micropterus salmoides (Largemouth Bass), and other fish in the ponds at six lentic sites in Trinity County, CA ...... 27

CHAPTER 2

Table Page 1. Weight, carapace length, age (10+ represent turtle ≥ 10 years), sex (M = male, F = female), number of relocations, and duration and dates tracked for radio-tagged Actinemys marmorata. * turtles that were retagged after their initial transmitters failed ...... 57

2. Presence (1) or absence (0) of amphibians and fish in minnow traps set on five different occasions in the five permanent ponds at Lowden Ranch throughout 2010 and 2011...... 72

3. Numbers of aquatic insects found in each of the permanent ponds at Lowden Ranch in the summer and fall of 2010. Numbers given for the five most prevalent insect orders. Samples from three 0.5 meter kick-net sweeps...... 72

LIST OF FIGURES

CHAPTER 1

Figure Page 1. The upper Trinity River, Trinity County, CA from Lewiston (just below the Lewiston Dam) to Junction City. The approximate locations of the six sites are shown in bold; each site has from one to ten ponds ...... 7

2. Percent of young (<10 years) and old (≥10 years) turtles in lentic sites along the Trinity River. Sample sizes indicated within each column ...... 17

3. Percent of small (carapace length < 125 mm) and large (≥ 125mm) turtles of both sexes in lentic sites along the Trinity River. Sample sizes indicated within each column ...... 18

4. Growth of young (<10 years old) Western Pond Turtles using a power function. White circles (dashed regression line: R2 = 0.887, ln(carapace length) = 0.4404*ln(age)+3.7602) represent Browns Creek and Little Browns Creek lentic sites, while the grey diamonds (solid regression line: R2 = 0.6476, ln(carapace length) = 0.413*ln(age)+4.0226) represent Lewiston and Poker Bar sites ...... 22

5. Minimum bottom temperature of ponds in six sites near the Trinity River, CA. Sites with more than one pond show mean minimum bottom temperature, error bars show the range in minimum bottom temperature across all ponds...... 24

6. Maximum depth of ponds in six sites near the Trinity River, CA. Sites with more than one pond show mean maximum depth, error bars show the range in maximum depth across all ponds...... 24

7. Vegetation cover using the Braun-Blanquet cover scale [1 = Solitary plant, 2 = Few (1-2% cover), 3 = Many, but < 5% cover, 4 = 5-25% cover, 5 = 26-50% cover, 6 = 51-75% cover, 7 = >75% cover] for six sites along the Trinity River ...... 25

xii

CHAPTER 2

Figure Page 1. Lowden Ranch and the surrounding properties along the Trinity River, in Trinity County, CA. Solid lines represent permanent ponds or permanent portions of ponds; dashed lines represent ephemeral ponds or ephemeral portions of ponds ...... 50

2. Number of turtles with radio transmitters on each occasion that turtles were relocated from April 2010 through January 2012 ...... 58

3. Percent of radio-tagged turtles that moved each month in 2010 and 2011 at Lowden Ranch, near Lewiston, CA...... 60

4. Mean monthly terrestrial movement of radio-tagged turtles in 2010 and 2011 at Lowden Ranch, near Lewiston, CA...... 61

5. Monthly maximum depth for five permanent ponds at Lowden Ranch for April 2010 through November, 2011 ...... 66

6. Aquatic vegetation cover for spring (vertical lines), summer (grey), and fall (horizontal lines) 2010, as well as, spring (white), summer (black), and fall (checkered) 2011 on five ponds at Lowden Ranch, near Lewiston CA, using the Braun-Blanquet cover scale (BBCS). (EV = emergent vegetation, FLP = floating leaved plants with roots in substrate, FPA = floating plants/algae, and OV = overhanging vegetation)...... 67

7. Mean monthly surface temperature (oC) from April 2010 through January 2012 for five ponds at Lowden Ranch. Temperatures were continuously recorded once an hour (RW-5a, RW-5b and PD-2) or every four hours (RW-3 and FEW-3) ...... 69

8. Mean monthly bottom temperature (oC) from April 2010 through January 2012 for five ponds at Lowden Ranch. Temperatures were continuously recorded once an hour (RW-5a, RW-5b and PD-2) or every four hours (RW-3 and FEW-3). Temperature loggers were placed in the deepest location in each pond ...... 70

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9. Mean monthly air temperature (oC) in complete shade and full sun from April 2010 through January 2012 at Lowden Ranch. Temperatures were continuously recorded once every four hours...... 71

xiv

LIST OF APPENDICES

CHAPTER 2

A. Movements for turtle #204 ...... 87

B. Movements for turtles #201 (green), #208 (blue), and #206 (red) ...... 88

C. Movements for turtles #205 (blue), #202 (red), and #302 (green) ...... 89

D. Movements for turtles #203 (red), #209 (blue), and #248 (green) ...... 90

E. Movements for turtles #210 (red) and #304 (blue) ...... 91

F. Movements for turtles #225 and #212 ...... 92

G. Movements for turtles #214 (blue) and #220 (red) ...... 93

H. Movements for turtles #222 (blue) and #223 (red)...... 94

I. Movements for turtles #225 (red) and #212 (blue) ...... 95

J. Movements for turtles #226 (red) and #232 (blue) ...... 96

CHAPTER 1: POPULATION STRUCTURE AND LIFE HISTORY OF WESTERN

POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC HABITATS ALONG

THE TRINITY RIVER, CALIFORNIA

INTRODUCTION

Long-lived species offer particular challenges for evaluating population status and enacting recovery plans; estimates of abundance are not sufficient to determine population viability and recovery is usually a slow process because of slow population growth rates and low fecundity (Congdon et al. 1993; Congdon et al. 1994). Because population numbers can often be high and stable over many years with little or no recruitment, an investigation of population structure and life history is necessary to determine the actual health of populations of long-lived species. Such a study can also determine where in the life cycle increased mortality is occurring; this can aide in focusing conservation plans, because long-lived vertebrates tend to have life history traits that make it difficult for them to tolerate increased mortality at any age group (Congdon et al. 1993; Congdon et al. 1994). Turtles are a particularly threatened clade of long- lived vertebrates, primarily due to habitat loss/fragmentation and overexploitation

(Kiester et al. 2011), with population declines occurring on a global scale (Gibbon et al.

2000; Klemens 2000; Moll and Moll 2004).

The Western Pond Turtle (Actinemys marmorata) is the only extant native freshwater turtle in California; it ranges from Washington to northern Baja California,

2 primarily in Pacific slope drainages (Storer 1930; Jennings and Hayes 1994; Stebbins

2003). Western Pond Turtles are aquatic habitat generalists, utilizing a variety of lentic and lotic systems, but generally preferring areas with slow moving or slack water

(Holland 1994; Jennings and Hayes 1994). Most activity occurs in the water, but terrestrial environments are used for hibernation, aestivation, and nesting (Reese and

Welsh 1997; Rathbun et al. 2002). Populations have declined throughout much of their range over the past century (Brattstrom 1988; Hayes et al. 1999), due to introduced competitors and predators, hunting, habitat loss, and water course alterations (Jennings and Hayes 1994; Hayes et al. 1999). The Western Pond Turtle is listed as a Species of

Special Concern in California (CA DFG: Jennings and Hayes 1994), a State Endangered species in Washington (WDFW: under WAC 232-12-014), and a Sensitive-Critical

Species in Oregon (ODFW 2006). In light of these declines, sustainability of existing populations is critical.

Age structure is an important demographic attribute for assessing the survival of

Western Pond Turtle populations, for it can indicate whether or not recruitment has been occurring. Western Pond Turtles are a long-lived species, with a maximum lifespan of at least 47 years (Ashton et al. 2011); populations consisting entirely of adult turtles can persist for many years without sufficient recruitment to ultimately sustain themselves over long periods. It is typical for healthy populations of Western Pond Turtles to be dominated by reproductively mature individuals, but these populations also have high proportions of relatively young turtles (<12 years old) (Bury and Germano 2008). In

3 areas where Western Pond Turtle populations are declining, many of the factors responsible for declines principally affect hatchlings (Jennings and Hayes 1994), creating populations primarily composed of old turtles.

Growth rate and size at maturity are also key life history parameters that can play a role in population survival. A high growth rate, especially during the first few years, can limit the amount of time spent in the very vulnerable juvenile stage (Reese 1996) and therefore may increase survival. Fast growth can also decrease the time before reproductive maturity is reached (Germano and Rathbun 2008). A large adult body size can lead to decreased vulnerability to predators (Holland 1994) and increased egg and/or clutch size (Congdon and Gibbons 1985; Congdon and van Loben Sels 1991; Iverson

1992; Holland 1994).

In the core of the Western Pond Turtle’s range (northern CA and southern OR) drastic declines have not been observed (Bury and Germano 2008); however, there is still concern about the persistence of these populations, especially in human-altered habitats like the mainstem Trinity River in northwestern California (Reese and Welsh 1998a;

Ashton et al. 2011). The Trinity River has been modified from its natural state by a combination of logging, dredge mining, and flow alterations. It was dammed in the early

1960s (Master EIR 2009), drastically altering the downstream hydrologic regime, especially near the dams. Flow was held at a constant rate year-round; this constant flow, without flood events, allowed for encroachment of the riparian vegetation, creating a simplified and channelized river that was disconnected from its floodplain (Master EIR

2009). In addition, summer water temperatures were (and still are) decreased and deep pools were filled with sediment (Hampton 1995). The dam-induced alterations of the

Trinity River appear to have decreased habitat quality for Western Pond Turtles (Reese and Welsh 1998b; Ashton et al. 2011). Therefore, alternative habitats, such as ponds and wetlands adjacent to the river, may be extremely important in providing resources not supplied by the river. However, the use of such alternative habitats by turtles has only been briefly studied along the Trinity River (Reese 1996).

The primary objective of this study was to evaluate if Western Pond Turtle population health parameters vary across lentic habitats on a watershed scale. Previous work has shown high variation in population structure and growth rates over a large spatial scale (southern OR and northern CA; Bury et al. 2010, Germano and Bury 2009).

I wanted to determine if these parameters still vary on a smaller, watershed scale, where differences in genetics and large-scale geographic parameters (e.g., rainfall, temperature, elevation) are minimal. Preliminary work revealed a highly adult-biased population of

Western Pond Turtles in ponds at a single site along the Trinity River (personal observation). To determine if this situation was typical for lentic habitats in this watershed, or simply a localized phenomenon, I examined the following four population health parameters for Western Ponds in lentic habitats along the upper Trinity River and its tributaries: 1) age structure, 2) size structure, 3) body size, and 4) growth rate of young turtles.

To help elucidate potential variation in population health parameters among lentic sites, I examined several habitat variables (depth, temperature, and aquatic vegetation cover) at each site; I also determined whether or not fish and American Bullfrogs

(Lithobates catesbeianus) were present. Bullfrogs and Largemouth Bass are voracious introduced predators that will eat small turtles (Moyle 1973; Holland 1994). Ponds with warm, shallow water and abundant aquatic vegetation for cover, characteristics that favor survival of hatching turtles, were expected to have a greater percentage of the population composed of young turtles than deep ponds with cold water and little vegetation. In addition, fewer young turtles were expected in lentic sites with Bullfrogs and Largemouth

Bass.

METHODS

Study Area

This study focused on lentic habitats associated with the upper Trinity River and two of its tributaries, located in Trinity County, California (Fig. 1). Sampling was conducted at six sites; four sites were adjacent to a 41 kilometer stretch of the Trinity

River between Lewiston (just below the Lewiston Dam) and Junction City, while the other two were beside tributaries of the Trinity River (Browns Creek and Little Browns

Creek). All sites were separated from each other by a minimum of 2.5 km (straight line distance; 3.5 km river distance). Some sites (Union Hill, Little Browns Creek, and Poker

Bar) consisted of only a single pond, while others (Lewiston, Junction City, and Browns

Creek) were composed of several ponds (Table 1). In sites with several ponds, the maximum distance between ponds was 0.65 km. All ponds were a maximum of 300 m from the Trinity River or its tributaries. Many of the ponds were hydrologically influenced by the river they were adjacent to, through a ground water connection or, in rare cases, from surface water inflow.

Fig. 1. The upper Trinity River, Trinity County, CA from Lewiston (just below the Lewiston Dam) to Junction City.

The approximate locations of the six sites are shown in bold; each site has between one to ten ponds. 7

Table 1. Ponds where Actinemys marmorata were trapped in sites along the upper

Trinity River and its tributaries.

Site Pond Northings Eastings Elevation (m) Lewiston RW-5a 4504707 512005 518 RW-5b 4504687 512094 555 RW-3 4504767 512209 537 FEW-3 4504954 512352 532 PD-2 4505134 512484 531 Hamilton 4504444 511939 530 Pvt 1a 4505357 512859 539 Pvt 1b 4505375 512897 543 Pvt 2a 4505623 512866 539 Pvt 2b 4505480 512812 535 Bucktail 4506238 513228 530 Union Hill UH 4500737 505381 536 Little Browns Creek Pvt 3 4509484 508997 709 Junction City Pvt 4a 4507296 496589 446 Pvt 4b 4507337 496536 465 Pvt 4c 4507241 496457 444 Pvt 4d 4507421 496628 451 Pvt 5a 4506834 496273 457 Pvt 5b 4506662 496198 453 Pvt 5c 4506542 496190 458 Pvt 5d 4506277 496127 461 JC BLM 4508068 496030 440 Browns Creek Pvt 6a 4498550 501565 503 Pvt 6b 4498578 501594 494 Pvt 6c 4498685 501608 489 Poker Bar Pvt 7 4503274 509431 508

Turtle Sampling

Turtles were trapped using collapsible crab traps with openings at both ends.

Large (37˝x 25˝x 24˝) and small (28˝’x 20˝x 13˝) traps were set each trapping period and baited with fresh fish carcasses or chicken. In May through August 2011, traps were set in each site on one to three different occasions; each trapping period lasted two to three days and traps were checked at least once every 24 hours. In addition, in April through

September 2010, turtles were trapped approximately every other week in the ponds at the

Lewiston Site.

Marking and Morphometrics

Upon capture all turtles were marked, measured, and sexed. Each turtle was uniquely marked by filing triangular notches in one or more marginal shields (Holland

1994). I weighed each turtle with a Pesola® scale (measured to the nearest 0.5 grams for turtles ≤ 60 grams and to the nearest 5 grams for those > 60 grams) and measured the maximum carapace length, to the nearest millimeter, using a vernier caliper. Turtles were sexed using morphological characteristics. Specifically, males have shorter and thicker tails, a concave plastron, white throats (older males), and a cloacal opening on the tail beyond the posterior edge of the carapace. Females have longer and thinner tails, a flat plastron, a yellow and black flecked throat, and a vent that is at the posterior edge of the carapace (Storer 1930; Holland 1994).

Population Health

I compared the population health of Western Pond Turtles at my sites using four different techniques: age structure, size structure, body size, and the growth rate of young turtles. To determine age structure, turtles were classified as either “young” (< 10 years) or “old” (≥ 10 years), then the percentage of young and old turtles was compared among sites. Age was estimated by counting the number of annuli (rings) on the plastron. When turtles are young, annuli are deposited annually (Germano and Bury 1998; Bury and

Germano 1998); however, growth rate of Western Pond Turtles slows around ten years of age, and the annuli deposited after this time are less reliable and difficult to count, because they are so close together. In addition, annuli tend to wear off over time as turtles rub their plastrons against the substrate (Germano and Bury 1998; Bury and

Germano 1998). Therefore, I estimated the ages only for young turtles (< 10 years), counting all visible annuli (Ashton et al. 2011). To determine size structure, turtles were classified as either “small” (< 125 mm maximum carapace length) or “large” (≥ 125 mm), then the percentage of small and large turtles was compared among sites. In previous studies of Western Pond Turtles in the Trinity River, 125 mm has been used as a cutoff between juveniles and adults (Reese 1996; Reese and Welsh 1998a; Ashton et al.

2011). Because it is doubtful that all Western Pond Turtles mature at the same length, I will not be using the categories “juvenile” and “adult”; nonetheless, 125 mm is a convenient cutoff for size classes, for it allows comparison with previous research on the

Trinity River. I determined mean body size at each site only using large turtles (≥ 125

11 mm). To represent overall body size, I used maximum carapace and weight. Mean sizes were determined separately for males and females. The growth rate for young turtles

(<10 years) at each site was determined using cross-sectional data (i.e. only one measurement was taken for each individual and an overall population growth rate was determined).

Pond Characteristics

All pond characteristics were measured in September 2011 for all ponds at the six sites (with the exception of Pvt 6b, Pvt 6c, Pvt 2a, Pvt 2b, and Pvt 5a, which were already dry at this point).

Depth: A weighted measuring tape was lowered into each pond to measure depth (±0.5 cm). Each pond was divided into three approximately equal segments and a depth measurement was measured in the approximate center of each of these segments.

Temperature: Bottom temperatures (±0.05oC) were measured at the same locations that depths were taken.

Vegetation: The Braun-Blanquet cover scale was used to estimate vegetation cover [1 =

Solitary plant, 2 = Few (1-2% cover), 3 = Many, but < 5% cover, 4 = 5-25% cover, 5 =

26-50% cover, 6 = 51-75% cover, 7 = >75% cover]. Cover was estimated for the following four vegetation classes: 1) plants/algae floating on the surface of ponds, 2) plants rooted in the bottom of the ponds with leaves floating on the surface, 3) emergent vegetation (cattail, bulrushes), and 4) overhanging riparian vegetation (primarily Salix sp.).

Bullfrog and Fish Presence: While trapping turtles at each pond, I looked for evidence of the presence of Bullfrogs (Lithobates catesbeianus), using turtle traps, visual encounters, alarm calls, and male breeding calls. Bullfrogs were recorded as being present if adults or larvae were detected at least once in a pond. When possible, I also asked land owners if they had observed Bullfrogs on their property. Fish were recorded as being present when they were trapped in turtle traps or visually encountered.

Data Analyses

Data were analyzed using Excel (Microsoft Corporation) and R (R Development

Core Team, 2011). I used Pearson's chi-squared test to test the evenness of the sex ratio across the entire data set.

To determine how the proportion of young turtles to old turtles differed among sites I developed a posteriori candidate logistic regression models (using binary data). In the candidate models, age (0 = young turtle; 1 = old turtle) was always the response variable. I developed models using the categorical predictor “location”; my six sites made up the levels of the categorical predictor. Models differed in their definition of the categorical predictor and in their number of levels. The following four models were created: 1) null model: “location” was not included as a predictor (i.e., there was no difference across sites in the proportion of old to young turtles), 2) two-level model: level

1 = Browns Creek and Little Browns Creek, level 2 = Poker Bar, Union Hill, Lewiston, and Junction City, 3) three-level model: level 1 = Browns Creek and Little Browns

Creek, level 2 = Lewiston and Poker Bar, level 3 = Union Hill, and Junction City, 4) six-

13 level model: each site was included as its own level in “location” (i.e., level 1 = Browns

Creek, level 2 = Poker Bar, level 3 = Union Hill, etc.). I selected the above models as the most probable models based on plots of the proportion of young to old turtles. I then used Akaike’s Information Criterion (AIC) values to determine the best model. If none of the sites had similar proportions of young to old turtles, then the six-level model would have the lowest AIC value. If all of the sites had the same proportion of young to old turtles, then the null model would have the lowest AIC value. An intermediate model

(e.g., two-level model) would have the lowest AIC value if, for example, Browns Creek and Little Browns Creek had the same proportion of young to old turtles, while the other four sites shared a different proportion of young to old turtles.

I followed the process described above to determine how the proportion of small to large turtles differed among sites, with one exception. In this case the three-level model was defined as follows: level 1 = Browns Creek and Little Browns Creek, level 2

= Lewiston, level 3 = Union Hill, Poker Bar, and Junction City.

To compare mean size of large turtles (maximum carapace length) among sites, I used a 2-way analysis of variance (ANOVA), which tested the null hypothesis that site, sex, and their interaction had no effect on carapace length. If a significant difference existed between sites, I performed Tukey HSD pairwise comparisons to determine which sites differed. I performed an identical analysis comparing weight among sites, but gravid females were first removed from the data set.

I created growth curves for young (< 10 years old) Western Pond Turtles that were based on the power function: carapace length = α(Age)β. Not enough data were available to create a curve for every site, so a posteriori I created two groups out of the six sites. These two groups contained the sites that appeared to have similar growth in plots of age versus carapace length; sites with fewer than ten young turtles were excluded. Because growth curves were based on the power function, I ran a linear model on the natural logarithm of age and carapace length. The linear model contained (in the following order) age, group, and their interaction as predictor variables for carapace length. To illustrate the growth curves, I plotted ln(carapace length) versus ln(age).

To determine if pond depths and temperatures varied among sites, I used a

Kruskal-Wallis analysis of ranks test. If there was a significant difference among the sites, I used a multiple comparisons test to determine which sites differed.

RESULTS

Across all six sites on the upper Trinity River I caught a total of 365 Actinemys marmorata: 277 old turtles (≥ 10 years) and 88 young turtles (< 10 years). There was an

2 even sex ratio, with 1.07 males to 1.00 female (X 1,292 = 0.3425, p = 0.5584). Twenty percent of the turtles were small (<125 mm), while 24.4% were young turtles (<10 years).

Approximately 7.4% of turtles were less than five years old, including two turtles in their first year of growth and five turtles in their second year of growth.

Proportion of Young to Old Turtles

2 The ratio of young to old turtles differed among the six sites (X 5, 265 = 61.15; P <

0.001; logistic regression on binary data). A model combining the sites into three groups with similar ratios of young to old turtles was most highly supported (Table 2). Little

Browns Creek and Browns Creek had the greatest percentage of young turtles (44.4 and

47.8%, respectively), Lewiston and Poker Bar had a moderate number of young turtles

(19.0 and 23.2%, respectively) and Junction City and Union Hill had few young turtles

(8.5 and 9.1 %, respectively) (Fig. 2).

Proportion of Small to Large Turtles

2 The ratio of small turtles to large turtles differed among the six sites (X 5, 265 =

33.87; p < 0.001; logistic regression on binary data). A model combining the sites into three groups with similar small to large turtle ratios was most highly supported (Table 3).

Little Browns Creek and Browns Creek had the greatest percentage of small turtles

(47.6% and 56.5%, respectively), Lewiston had a moderate number of small turtles

(15.2%) and the other three sites had very few small turtles (6.3-9.1%) (Fig. 3).

Body Size

Maximum carapace length for large (≥125 mm carapace length) turtles differed significantly among sites (F5, 292 = 26.56, p < 0.001) (Table 4) and between the sexes (F1,

292 = 9.00, p = 0.003), but the interaction term was not significant (F5, 292 = 0.54, p =

0.745). Turtles from Browns Creek and Little Browns Creek had significantly smaller carapace lengths than those from the other four sites (p < 0.001 for all pairwise comparisons between these two sites and the other four).

When data from gravid females were removed, there was a significant difference in weight of large turtles among sites (F5, 266 = 22.07, p < 0.001) (Table 5), but no difference in weight between the sexes (F1,266 = 1.14, p =0.29) or within the interaction term (F5, 266 = 0.51, p = 0.804). Browns Creek and Little Browns Creek turtles weighed significantly less than turtles in the other four sites (p < 0.001 for all pairwise comparisons between these two sites and the other four).

100% 4 4 90% 29 12

80% 11 28 70%

60%

50%

43 40 Frequency 40% 96 51

30% 12 35 20%

10%

0% Browns Crk. Junction City Lewiston Little Browns Poker Bar Union Hill Crk. ≥10 years <10 years

Fig. 2. Percent of young (<10 years) and old (≥10 years) turtles in lentic sites along the

Trinity River. Sample sizes indicated within each column.

100% 3 4 4 90% 19

80% 30 26 16 70% 13 21 50

60%

50%

Frequency 40% 20 30% 24 8 23 33 20% 56

10% 13 2 0% Browns Junction Lewiston Little Poker Bar Union Hill Crk. City Browns Crk. Large Males Large Females Small Turtles

Fig. 3. Percent of small (carapace length < 125 mm) and large (≥ 125mm) turtles of both sexes in lentic sites along the Trinity River. Sample sizes indicated within each column.

Table 2. Candidate models for the comparison of the proportion of old (≥ 10 years) to young (< 10 years) Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data.

# parameters AIC Model estimated AIC Δ AIC weight

Three Groups([Browns Crk./ Little Browns Crk.] and [Lewiston/Poker Bar] and [Union Hill/ Junction City]) 3 375.86 0 1.000 Six Groups (each site grouped separately) 6 381.34 5.48 0.065 Two Groups ([Browns Crk./ Little Browns Crk.] and [Lewiston/ Union Hill/ Junction City/ Poker Bar]) 2 381.78 5.92 0.052 Null (no grouping by sites) 1 405.21 29.35 0.000

Table 3. Candidate models for the comparison of the proportion of large (carapace length ≥ 125 mm) to small (< 125 mm)

Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data.

# parameters AIC Model estimated AIC Δ AIC weight

Three Groups([Browns Crk./ Little Browns Crk.] and [Lewiston] and [Union Hill/ Junction City/ Poker Bar]) 3 311.02 0 1.000 Two Groups ([Browns Crk./ Little Browns Crk.] and [Lewiston/ Union Hill/ Junction City/ Poker Bar]) 2 313.67 2.65 0.266 Six Groups (each site grouped separately) 6 316.14 5.12 0.077 Null (no grouping by sites) 1 367.29 56.27 0.000

Table 4. Mean maximum carapace lengths (CL), standard error (SE), and sample size

(n) for large (≥ 125 mm carapace length) Western Pond Turtles in two lotic sites and six lentic sites along the Trinity River. * indicates data from Ashton et al. 2011.

Males Females Location CL SE n CL SE n Browns Creek 130.50 4.00 2 134.75 1.92 8 Junction City 154.48 2.35 24 149.21 1.24 21 Lewiston 153.73 1.30 55 149.75 1.47 50 Little Browns Creek 137.65 1.72 13 135.65 0.96 20 Poker Bar 158.42 1.94 33 154.96 1.80 26 Union Hill 151.71 2.30 24 150.59 2.18 16 *Mainstem Trinity R. 148.47 2.52 27 143.34 2.39 30 *South Fork Trinity R. 166.36 1.53 73 164.87 1.21 118

Table 5. Mean weight (WT), standard error (SE), and sample size for large (≥ 125 mm carapace length) male and non-gravid female Western Pond Turtles in six lentic sites along the Trinity River.

Males Females Location WT SE n WT SE n Browns Creek 297.50 37.50 2 380.63 23.29 8 Junction City 520.83 20.68 24 521.90 14.71 21 Lewiston 496.82 11.79 55 526.78 17.28 50 Little Browns Creek 366.92 16.00 13 381.50 9.57 20 Poker Bar 550.45 14.99 33 571.69 1.80 26 Union Hill 500.83 21.31 24 545.63 0.23 16

Growth of Young Turtles

Young turtles (<10 years) in Browns Creek and Little Browns Creek had similar growth rates and were grouped together; based on this logic I also combined the young turtles in Lewiston and Poker Bar into a single group (Fig. 4). There were only 4 young turtles for both Union Hill and Junction City, thus their growth rates could not be determined. Not surprisingly, age influenced carapace length (t8,88 = 9.89; P < 0.001); after accounting for age in the linear model there was a significant difference in carapace length, and therefore growth rate, between the two groups (t1,88 = -2.53; p =

0.013) (Fig. 4; Table 6), but not in the interaction between age and group (t8,88 = 0.40; P

= 0.69).

5.1

4.9

4.7

4.5

4.3

4.1 ln(Carapace Length[mm]) ln(Carapace 3.9

3.7 0 0.5 1 1.5 2 2.5 ln(Age[years])

Fig. 4. Growth of young (<10 years old) Western Pond Turtles using a power function. White circles (dashed regression line: R2 = 0.887, ln(carapace length) = 0.4404*ln(age)+3.7602) represent Browns Creek and Little Browns Creek lentic sites, while the grey diamonds (solid regression line: R2 = 0.6476, ln(carapace length) = 0.413*ln(age)+4.0226) represent Lewiston and Poker Bar sites.

Table 6. Estimated carapace lengths (mm), based on growth curves (Fig. 4), for young Actinemys marmorata in lentic habitats along the Trinity River, CA

Lewiston and Browns Creek and Age Poker Bar Little Browns Creek 1 − 43.0 2 74.4 58.3 3 87.9 69.7 4 99.0 79.1 5 108.6 87.3 6 117.0 94.6 7 124.7 101.2 8 131.8 107.3 9 138.4 113.1

Environmental Variables

There was some variation among the six sites in temperature, depth, and vegetation cover of the ponds. Minimum bottom temperatures ranged from 12.8 ºC

(Browns Creek) to 20.2 ºC (Union Hill) (Fig. 5). There was a significant difference in

2 bottom temperature (χ 5,60 = 12.41, P = 0.030) among sites, caused solely by a difference between Union Hill and Browns Creek. Maximum depth ranged from 80 cm (Browns

Creek) to 320 cm (Union Hill) (Fig. 6). There was a significant difference in depth

2 (χ 5,60 = 19.22, P = 0.002) among sites, caused by a difference between Union Hill and both Browns Creek and Junction City. Most sites did not have greater than 25% coverage by any of the vegetation types, with the exception of Poker Bar, which had 50-

75% coverage by floating plants and floating leaved plants, and Browns Creek, which had 25-50% coverage by emergent vegetation and overhanging riparian vegetation (Fig.

7).

° 15

5 Temperature ( Temperature 0 Browns Ck. Junction Lewiston Little Poker Bar Union Hill City Browns Ck.

Fig. 5. Minimum bottom temperature of ponds in six sites near the Trinity River, CA.

Sites with more than one pond show mean minimum bottom temperature, error bars show the range in minimum bottom temperature across all ponds.

350 300

250 200 150

Depth (cm) Depth 100 50 0 Browns Crk. Junction Lewiston Little Poker Bar Union Hill City Browns Crk.

Fig. 6. Maximum depth of ponds in six sites near the Trinity River, CA. Sites with more than one pond show mean maximum depth, error bars show the range in maximum depth across all ponds.

4 Blanquet cover scale cover Blanquet - 3

Braun 2

0 Browns Crk. Junction City Lewiston Little Browns Poker Bar Union Hill Crk.

Emergent Floating Leaved Plants Floating Plants/ Algae Overhanging Riparian

Fig. 7. Vegetation cover using the Braun-Blanquet cover scale [1 = Solitary plant, 2 =

Few (1-2% cover), 3 = Many, but < 5% cover, 4 = 5-25% cover, 5 = 26-50% cover, 6 =

51-75% cover, 7 = >75% cover] for six sites along the Trinity River.

Bullfrog and Fish Presence

Bullfrogs (adults and larvae) were seen and heard at all sites except Browns

Creek and Little Browns Creek (Table 7). In addition, at these two sites landowners reported never having encountered Bullfrogs. Where present, Bullfrogs were commonly encountered and appeared to abundant. One exception was Pvt 2a, where only a single adult Bullfrog was observed. This pond was ephemeral, thus this Bullfrog must have moved here as an adult.

Fish were observed at all sites except Browns Creek (Table 7). Three of the sites had Largemouth Bass (Junction City, Poker Bar, and Union Hill) and one site only had Rainbow Trout (Little Browns Creek).

Table 7. Presence or absence of Lithobates catesbeianus (American Bullfrog),

Micropterus salmoides (Largemouth Bass), and other fish in the ponds at six lentic sites in Trinity County, CA.

Lithobates Micropterus catesbeianus salmoides Other Fish Browns Creek Absent Absent Absent Junction City Present Present Present Lewiston Present Absent Present* Little Browns Creek Absent Absent Present** Poker Bar Present Present Present Union Hill Present Present Present * Lepomis cyanellus (Green Sunfish), Notemigonus crysoleucas(Golden Shiner), and others ** Oncorhynchus mykiss (Rainbow Trout)

DISCUSSION

My six lentic sites fell into three different categories with regard to their population health parameters: (1) Browns Creek and Little Browns Creek had a large percentage of their populations composed of young turtles (47.8% and 43.8%, respectively) and small turtles (56.5% and 47.6%, respectively). Growth rate of young turtles was lowest at these sites and average size for large turtles was the smallest

(length and weight); (2) Junction City and Union Hill had a very small percentage of their population composed of young turtles (8.5% and 9.1%, respectively) and small turtles (6.4% and 6.8%, respectively). Average size of large turtles was comparatively large at these sites and the growth rate of young turtles could not be determined because there were essentially no young turtles (n = 4 young turtles for both sites); (3) Poker Bar and Lewiston had a moderate percentage of their populations composed of young turtles

(19% to 23.4%, respectively) and few small turtles (6.3% to 15.2%, respectively).

Growth rate of young turtles was highest at these sites and average size of large turtles was comparatively large.

The population health parameters are interrelated, for changes in one parameter can cause changes in another. The relationship between population size structure and age structure at each site can be explained by growth rate. Turtles at Poker Bar and

Lewiston had high growth rates; there were fewer small turtles than young turtles because some young turtles (< 10 years) had grown fast enough that they were no longer considered small turtles. The reverse occurred at Browns Creek and Little

Brown Creek, where the percentage of small turtles was slightly higher than the

29 percentage of young turtles. Growth rate was so slow that old turtles (≥ 10 years) were still small turtles.

Age and Size Structure

The six sites varied in their percentage of young turtles from almost 50% to less than 10% young turtles. Four sites were moderately (Poker Bar and Lewiston) to highly

(Junction City and Union Hill) biased towards old Western Pond Turtles; these four sites had a smaller percentage of young turtles than reported for other populations of turtles in the Coast Range of northern California. For example, 2-8 year old turtles comprised 34.5% of turtles on the mainstem Trinity River and 42.6% of those on the

South Fork Trinity River (Ashton et al. 2001). By contrast, my four sites that were biased towards old turtles all had much smaller percentages (4.5–17.7%) of turtles in this same age class. These four lentic sites were all located directly adjacent to the mainstem Trinity River. This indicates that along the upper Trinity River there is a distinct difference in age structure for turtles dwelling in lentic versus lotic environments, although a limited amount of movement between these two environments does occur (Reese 1996; see also this study, Chapter 2). The two lentic sites in my study that had higher percentages of young turtles (Little Browns Creek and Browns

Creek) were located adjacent to tributaries of the Trinity River; these sites were similar to population in the mainstem Trinity River in terms of percentage of 2-8 year old turtles (30.4% and 34.4%, respectively), but had a smaller percentage of 2-8 year old turtles than did the South Fork Trinity River population. Bury et al. (2010) measured age structure in a reservoir, pond, and creek in the Coast Range of California; at all of

30 these sites they found a high proportion (42.6% to 47.1%) of young turtles (<10 years), further indicating that my four sites with 8.5%–23.4% young turtles are biased towards old turtles compared to what is typical in northwestern California.

In addition, these four lentic sites had a smaller percentage of young turtles than most populations outside the Coast Range of northwestern California. At six lentic and four lotic sites in southern Oregon, the percentage of young turtles ranged from 21.9% to 68.0%, with eight of the ten sites having greater than 30% young turtles (Germano and Bury 2009). In the Klamath Basin, 31.4% of the population was composed of young turtles (Bury et al. 2010). The percentage of young turtles ranged from 33.0% to

93.5% at four sites in the Central Valley of California (Germano and Bury 2001) and it was 69.0% on the California central coast in Santa Barbara County (Germano and

Rathbun 2008).

In this study, all four sites with population compositions skewed towards old turtles had prodigious Bullfrog populations (Poker Bar, Junction City, Union Hill, and

Lewiston). Bullfrogs are generalist, opportunistic predators that often eat large vertebrate prey (Casper and Hendricks 2005), including hatchling Western Pond Turtles

(Moyle 1973). They thrive in human-altered environments and are especially abundant along the upper Trinity River, near the dams, in the same relict mine tailing ponds used by Western Pond Turtles (Fuller et al. 2010). It is highly probable that Bullfrogs are responsible for the small percentage of young turtles in these ponds. In general the probability of survival is low for hatchling turtles (Heppell and Crowder 1996); however, survival rates must drastically decrease with the addition of a highly abundant

31 predator that is always present in the system. Most native predators (e.g., herons, otters) are not residents, but pass through ponds and are therefore not a constant threat to hatchings.

Of the four sites with Bullfrogs, the Lewiston site had the highest percentage of young turtles, likely caused by the paucity of Bullfrogs at a single pond in this site, Pvt

2a. Turtles were trapped in ten different ponds at the Lewiston site; nine of these ponds had permanent water and numerous Bullfrogs, but Pvt 2a was an exception. It was ephemeral and only a single adult Bullfrog was observed here. The nearest permanent pond was approximately 260 meters away; it appears that this distance may be enough that very few Bullfrogs migrate to this pond each year, thus allowing for turtle recruitment. Willis et al. (1956) found that in a year only 7.6% of marked Bullfrogs ≥

50 mm moved at least 260 meters between ponds. I never observed hatching turtles at

Pvt 2a, but the private landowner reported having seen hatchlings. It appears, that Pvt

2a may be acting as a source for the other ponds at the Lewiston site because hatchlings seem to have a higher probability of survival there. In addition, I observed (via radio telemetry, see Chapter 2) two gravid female turtles moving from PD-2 to Pvt 2a (615 m straight line distance) during nesting season; these turtles then returned to PD-2 in late summer when Pvt 2a began to go dry. This suggests that at least some gravid females may be choosing to lay their eggs near Pvt 2a.

The two lentic sites with high percentages of young turtles (Browns Creek and

Little Browns Creek) completely lacked Bullfrogs, based on my observations and those of the land owners. These sites were adjacent to tributaries of the Trinity River, thus

Bullfrog populations have likely not had time to become established in these more isolated areas. In addition, these are free-flowing tributaries with minimal anthropogenic modifications, whereas Bullfrogs generally thrive in human-modified habitats with slack or slow moving water where reproduction can occur (Fuller et al.

2010).

The combined evidence of abundant Bullfrog populations at sites where there is a low percentage of young turtles, and no Bullfrogs in areas where there is a high percentage of young turtles, suggests that Bullfrogs may be altering the age structure of

Western Pond Turtle populations. Holland (1991) observed that percent abundance of juvenile Western Pond Turtles was smaller where Bullfrogs were present; however, because this study compared size structure between areas with and without Bullfrogs, rather than age structure, the differences observed may have been caused by different growth rates rather than Bullfrog predation. It has been proposed that Bullfrogs can affect the population dynamics of other turtle species where they have been documented eating hatching turtles (e.g., Sonoran Mud Turtle; Akins and Jones 2010). To our knowledge this is the first study to provide evidence that Bullfrogs may be altering the age structure of Western Pond Turtle populations.

An additional factor that may affect age structure is the presence of introduced fish. Largemouth Bass (Micropterus salmoides) likely prey on hatchling turtles

(Holland 1994), although there is some debate about whether they can actually eat live hatchlings (Semlitsch 1989). Largemouth Bass were present in the Junction City,

Union Hill, and Poker Bar sites. However, I never observed any in the Lewiston ponds;

33 there were other introduced fish species (Green Sunfish: Lepomis cyanellus and Golden

Shiner: Notemigonus crysoleucas), but no large fish likely to eat hatchling turtles. The

Little Browns Creek site was stocked with Rainbow Trout (Oncorhynchus mykiss), but lacked other fish species, and to my knowledge there were no fish in the ponds at the

Browns Creek site. Given that Largemouth Bass were present at most of the sites with low percentages of young turtles, the bass may be contributing to the skewed age structure at these sites; however, because the Lewiston site lacked Largemouth Bass and yet it still had a small percentage of young turtles, it appears likely that Bullfrogs are the primary cause of low turtle recruitment.

Lentic habitats along rivers can theoretically provide alternative habitats for turtles when rivers become unsuitable (e.g., from damming impacts); however, the nonnative Bullfrogs and possibly nonnative fishes may prevent lentic habitats from supporting viable populations of turtles. Conservation efforts should focus on eliminating Bullfrogs, if possible, and creating ephemeral ponds that dry in late summer or early fall; turtles and native anurans do not require permanent water, but Bullfrogs have aquatic larvae that usually take two years to metamorphose (Jones et al. 2005).

When ephemeral habitats dry turtles either move onto land to aestivate (Rathbun et al.

2002; Bondi 2009) or move to alternate aquatic resources (Reese 1996; see also this study Chapter 2). When turtles aestivate, foraging time is lessoned and therefore growth rate may decrease (Bondi 2009). However, turtles inhabiting ephemeral ponds adjacent to lotic environments have the option of moving to the lotic habitats as ponds

34 begin to dry, as has been observed for turtles inhabiting a vernal pool on the South Fork

Trinity River (Reese 1996).

Growth Rate and Body Size

There was a significant difference in the growth rate of young turtles at

Lewiston and Poker Bar versus those at Browns Creek and Little Browns Creek; the former grew faster, reaching 125 mm carapace length in approximately seven years, while the latter grew more slowly and were not yet this size at nine years. Average carapace length of nine year old turtles at Browns Creek and Little Browns Creek was approximately 113 mm (based on the growth curve), thus it would take several more years before these turtles reached 125 mm.

At Poker Bar and Lewiston growth rates fell within the typical range known for

Western Pond Turtles (Germano and Rathbun 2008; Germano and Bury 2009; Bury et al. 2010; Ashton et al. 2011), while at Browns Creek and Little Browns Creek the growth rates were slower than most other populations. Turtles reached 125 mm within five to ten years (Germano and Bury 2009) at ten southern Oregon sites and within six to nine years at three sites in the Coast Range of northern California (Bury et al. 2010).

On the California central coast and in the Klamath Basin, turtles reached 125 mm within approximately 4 years (Germano and Rathbun 2008; Bury et al. 2010), and on the South Fork Trinity River they reached this size within approximately 7 years

(Ashton et al. 2011). Growth rate was much slower for the Browns Creek and Little

Browns Creek sites than appears typical for most systems. However, the turtles in the mainstem Trinity River grew even slower (Ashton et al. 2011); eight year old turtles

35 were typically not yet 100 mm in length, thus they had many more years before reaching 125 mm.

Poker Bar, Lewiston, Junction City, and Union Hill all had larger turtles than

Browns Creek and Little Browns Creek. The former four sites, which were all directly adjacent to the mainstem Trinity River, had mean carapace lengths greater than that of the turtles in the river (Ashton et al. 2011). The ponds adjacent to the Trinity River are warmer (14.7-20.5oC in September) than the flowing river (average 11oC in September

2008, derived from http://odp.trrp.net/TSA/TSA.aspx); the higher temperatures likely allowed turtles that are living in the ponds to attain greater sizes than those in the

Trinity River, because size of turtles often increases with increasing temperature

(Gibbons 1970; Christy et al. 1974). However, turtles in the South Fork Trinity River

(average 19.8oC in September 2008, derived from http://odp.trrp.net/TSA/TSA.aspx) were much larger than those in either the mainstem Trinity River or in ponds along it.

Although the ponds along the mainstem Trinity River can get warmer than the river, many of them still receive cold river water through the ground water, preventing them from achieving very high temperatures.

The slow growth and small size of mainstem Trinity River turtles was attributed to the cold temperature of the water that is released into the Trinity River out of

Lewiston Dam (Ashton et al. 2011); it is possible that cold water was also retarding turtle growth at Browns Creek and Little Browns Creek (13.1-13.7oC in September).

Although the only significant difference in water temperatures was between Union Hill and Browns Creek, Browns Creek and Little Browns Creek had the lowest

36 temperatures, indicating that temperature may play a role in growth. In addition, these ponds were at least partially spring fed; spring water tends to be colder than other water sources, so Browns Creek and Little Browns Creek could have colder water than the other sites at certain times of year (e.g., summer when water temperature is maximized at other sites).

Although the Browns Creek and Little Browns Creek populations appear to be maintaining themselves, it is unlikely that reproduction is maximized. Previous research has shown carapace length to be correlated with clutch size and egg size

(Congdon and Gibbons 1985; Iverson 1992; Holland 1994). In addition, a slower growth rate means that it will take longer to reach reproductive maturity (Germano and

Rathbun 2008). Although these sites have a high proportion of young turtles, it is likely that their slow growth rate and small size (i.e., increased time before reproductive maturity and decreased clutch size) make them highly vulnerable; it is unlikely that these populations would be able to withstand the introduction of an invasive predator like the Bullfrog.

REFERENCES

Akins, C.M. and T.R. Jones. 2010. Kinosternon sonoriense (Sonoran Mud Turtle)

Predation. Herpetological Review 41: 486.

Ashton, D. T., J.B. Bettaso, and H.H. Welsh. 2011. Comparative ecology of western

pond turtle (Actinemys marmorata) populations on the free-flowing south fork

and regulated main fork Trinity River: demography, size and body condition

comparisons, thermal ecology, and spatial dynamics - Final report to the Trinity

River Restoration Program. USDA, Forest Service, Pacific Southwest Research

Station.

Bondi, C.A. 2009. A comparison of Western Pond Turtle (Actinemys marmorata)

movements in perennial and intermittent portions of a northwestern California

river system. Thesis, Humboldt State University, California, USA.

Brattstrom, B.H. 1988. Habitat destruction in California with special reference to

Clemmys marmorata: A perspective. In: Delisle, H.F., Brown, P.R., Kaufman,

B., McGurty, B.M. (Eds.). Proceedings of the Conference on California

Herpetology. Southwest Herpetological Society, Van Nuys, pp. 13–24.

Bury, R.B., and D.J. Germano. 1998. Annual deposition of scute rings in the Western

Pond Turtle, Clemmys marmorata. Chelonian Conservation and Biology 3: 108-

109.

Bury, R.B. and D.J. Germano. 2008. Actinemys marmorata (Baird and Girard 1952) -

Western Pond Turtle, Pacific Pond Turtle. In: A.G.J. Rhodin, P.C.H. Pritchard,

P.P. van Dijk, R.A. Saumure, K.A. Buhlman, and J.B. Iverson (eds.). The

Conservation Biology of Freshwater Turtles and Tortoises. A Compilation

Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group.

Chelonian Research Monographs 5: 1-9.

Bury, R.B., D.J. Germano, and G.W. Bury. 2010. Population structure and growth of

the turtle Actinemys marmorata from the Klamath-Siskiyou Ecoregion: age, not

size, matters. Copeia 3: 443-451.

Casper, G.S. and R. Hendricks. 2005. Rana catesbeiana (Shaw 1802) American

Bullfrog. In: Lannoo, M. (ed.). Amphibian Declines: The Conservation Status of

United States Species, University of California Press, Berkeley, pp. 540-546.

Congdon, J.D., A.E. Dunham, and R.C. van Loben Sels. 1993. Delayed sexual maturity

and demographics of Blanding's turtles (Emydoidea biandingii): implications for

conservation and management of long-lived organisms. Conservation Biology 7:

826-833.

Congdon, J.D., A.E. Dunham, R.C. Van Loben Sels. 1994. Demographics of common

snapping turtles (Chelydra serpentina): implications for conservation and

management of long-lived organisms. American Zoologist 34: 39-408.

Congdon, J.D. and R.C. van Loben Sels. 1991. Growth and body size in Blanding's

turtles (Emydoidea blandingi): relationships to reproduction. Canadian Journal

of Zoology 69: 239-245.

Congdon, J.D. and J.W. Gibbons. 1985. Egg components and reproductive

characteristics of turtles: relationships to body size. Herpetologica 41: 194-205.

Fuller T.E., K.L. Pope, D.T. Ashton, and H.H. Welsh Jr. 2010. Linking the distribution

of an invasive amphibian (Rana catesbeiana) to habitat conditions in a managed

river system in Northern California. Restoration Ecology. DOI 10.1111/j.1526-

100X.2010.00708.x.

Germano, D.J., and R.B. Bury. 1998. Age determination in turtles: evidence of annual

deposition of scute rings. Chelonian Conservation and Biology 3: 123-132.

Germano, D.J. and R.B. Bury. 2009. Variation in body size, growth, and population

structure of Actinemys marmorata from lentic and lotic habitats in southern

Oregon. Journal of Herpetology 43: 510-520.

Germano, D.J. and Bury, R.B. 2001. Western pond turtles (Clemmys marmorata) in the

Central Valley of California: status and population structure. Transactions of the

Western Section of The Wildlife Society 38: 22-36.

Germano, D.J. and G.B. Rathbun. 2008. Growth, population structure, and

reproduction of Western Pond Turtles (Actinemys marmorata) on the central

coast of California. Chelonian Conservation and Biology 7:188-194.

Gibbons, J.W. 1970. Reproductive dynamics of a turtle (Pseudemys scripta) population

in a reservoir receiving heated effluent from a nuclear reactor. Canadian Journal

of Zoology 48:881-885.

Gibbons, J. W. 1967. Variation in growth rates in three populations of the painted turtle

Chrysemys picta. Herpetologica 23: 296-303.

Gibbons, J. W., D.E. Scott, T.J. Ryan, K.A. Buhlmann, T.D. Tuberville, B.S. Metts, J.L.

Greene, T. Mills, Y. Leiden, S. Poppy, and C.T. Winne. 2000. The global

decline of reptiles, déjà vu amphibians. BioScience 50: 653–666.

Hampton, M.A. 1995. Current status of fish habitat. In: R. L. Ridenhour (ed.).

Proceedings from the Trinity River Restoration Program colloquium. American

Fisheries Society, Weaverville, California, USA, pp. 4-6.

Hayes, D. W., K. R. McAllister, S. A. Richardson, and D. W. Stinson. 1999.

Washington State Recovery Plan for the Western Pond Turtle. Wash. Dept. Fish

and Wildlife, Olympia.

Heppell, S.S. and L.B. Crowder. 1996. Models to evaluate headstarting as a

management tool for long-lived turtles. Ecological Applications 6: 556-565.

Holland, D.C. 1991. A synopsis of the ecology and current status of the western pond

turtle (Clemmys marmorata) in 1991. Unpublished Report U.S. Fish and

Wildlife Service, National Ecology Resource Center, Fort Collins, Colorado.

Holland, D.C. 1994. The Western Pond Turtle: habitat and history. Prepared for the

Oregon Department of Fish and Wildlife and DOE/BP. Report #62137-1,

Bonneville Power Administration, Portland, Oregon.

Iverson, J.B. 1992. Correlates of reproductive output in turtles (Order Testudines).

Herpetological Monographs 6: 25-42.

Jennings, M.R. and M.P. Hayes. 1994. Amphibian and Reptile Species of Special

Concern in California. California Department of Fish and Game technical report,

Inland Fisheries Division, Rancho Cordova, California, USA.

Jones, L.L.C., W.P. Leonard, and D.H. Olson (eds). 2005. Amphibians of the Pacific

Northwest. Seattle Audubon Society.

Kiester, A.R., and D.H. Olson. 2011. Prime time for turtle conservation.

Herpetological Review 42: 198-204.

Klemens, M.W., ed. 2000. Turtle Conservation. Smithsonian Institution Press,

Washington D.C., USA.

Moll, D. and E.O. Moll. 2004. The Ecology, Exploitation, and Conservation of River

Turtles. Oxford University Press, New York.

Moyle, P. B. 1973. Effects of introduced bullfrogs, Rana catesbeiana, on the native

frogs of the San Joaquin Valley, California. Copeia 1973:18-22.

North Coast Regional Water Quality Control Board and U.S. Bureau of Reclamation.

2009. Channel rehabilitation and sediment management for remaining Phase 1

and Phase 2 sites. Master Environmental Impact Report, Environmental

Assessment/Environmental Impact Report. Trinity River Restoration Program.

August 2009. SCH#2008032110.

Oregon Department of Fish and Wildlife. 2006. Oregon conservation strategy. Oregon

Department of Fish and Wildlife, Salem.

Rathbun, G. B., N.J. Scott, and T.G. Murphey. 2002. Terrestrial habitat use by Pacific

Pond Turtles in a Mediterranean climate. The Southwestern Naturalist 47: 225-

235.

R Development Core Team (2011). R: A language and environment for statistical

computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-

900051-07-0, URL http://www.R-project.org/

Reese, D. A., and H. H. Welsh. 1997. Use of terrestrial habitat by Western Pond

Turtles, Clemmys marmorata: implications for management. In: Van Abbema,

J., Ed. Proceedings: Conservation, Restoration, and Management of Tortoises

and Turtles - An International Conference. New York Turtle and Tortoise

Society, pp. 352-357.

Reese, D. A. 1996. Comparative demography and habitat use of Western Pond Turtles

in northern California: the effects of damming and related alterations.

Dissertation, University of California at Berkeley, Berkeley, California, USA.

Reese, D.A. and H.H. Welsh, Jr. 1998a. Comparative demography of Clemmys

marmorata populations in the Trinity River of California in the context of dam-

induced alterations. Journal of Herpetology 32: 505-515.

Reese, D.A. and H.H. Welsh, Jr. 1998b. Habitat use by Western Pond Turtles in the

Trinity River, California. Journal of Wildlife Management 62: 842-853.

Semlitsch, R.D. 1989. Lack of largemouth bass predation on hatchling turtles

(Trachemys scripta). Copeia 4: 1050-1051.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians 3rd ed.

Houghton Mifflin Company, Boston.

Storer, T.I. 1930. Notes on the range and life history of the Pacific Freshwater Turtle,

Clemmys marmorata, University of California Publications in Zoology 32: 429-

433.

United States Department Interior. 2000. Record of Decision for the Trinity River

Mainstem Fishery Restoration Final Environmental Impact

Statement/Environmental Impact Report. United States Department of the

Interior, Weaverville, California, December.

Willis, Y.L., D.L. Moyle, T.S. Baskett. 1956. Emergence, breeding, hibernation,

movements and transformation of the Bullfrog, Rana catesbeiana, in Missouri.

Copeia 1956: 30-41.

CHAPTER 2: TERRESTRIAL MOVEMENTS OF WESTERN POND TURTLES IN

A COMPLEX OF LENTIC HABITATS IN THE TRINITY BASIN, NORTHWEST

CALIFORNIA

INTRODUCTION

It has been estimated that over 50% of the wetlands have been destroyed in the contiguous United States, causing dramatic population declines, especially in aquatic and semi-aquatic species (Mitsch and Gosselink 2007). Current federal (USA) wetland practices support a “no net loss” policy; however, there is concern that not all types of wetlands are preserved equally, especially when natural wetlands are replaced with

“created” wetlands as part of mitigation procedures (Whigham 1999). In addition, only large wetlands tend to be regulated, and they are often viewed as individual entities rather than parts of a landscape system consisting of full-terrestrial, riparian, and aquatic components (Amezaga et al. 2002). This view can be detrimental to semi-aquatic species that utilize both aquatic and terrestrial habitats (Burke and Gibbons 1995; Joyal et al. 2001; Semlitsch and Jensen 2001; Semlitsch and Bodie 2003; Roe and Georges

2007). These two different habitat types often contain different resources and semi- aquatic organisms may need to travel among them to attain all required resources.

Furthermore, semi-aquatic species often require multiple types of aquatic and terrestrial habitats. If passage between habitat types containing essential resources for some part of the life cycle is prevented, then an organism cannot reproduce and recruitment will not occur (Dunning et al. 1992). From a conservation standpoint, it is critical to know

45 what habitat types are indispensable for a species and how movement occurs among these habitat types.

Western Pond Turtles (Actinemys marmorata) are the only semi-aquatic turtles native to California. They utilize a variety of aquatic systems, including rivers, streams, ponds, lakes, and wetlands, where they forage, mate, and bask (Holland 1994; Jones and

Stokes, 2004). Populations vary in their use of terrestrial habitat, but at a minimum, females must nest in upland habitats; the terrestrial environment is also used in some populations to hibernate, aestivate, or travel between aquatic habitats (Reese and Welsh

1997; Rathbun et al. 2002). Over the past century, Western Pond Turtle populations have declined throughout most of their range (Washington to Baja California) due to introduced species, hunting, habitat alterations from agriculture and livestock, urbanization, and water course alterations (Jennings and Hayes 1994; Hayes et al.

1999). As a result, Western Pond Turtles are listed as a Species of Special Concern in

California (CA DFG: Jennings and Hayes 1994), a State Endangered species in

Washington (WDFW: under WAC 232-12-014), and a Sensitive-Critical Species in

Oregon (ODFW 2006).

In northern California, one of the primary concerns for Western Pond Turtles is habitat alterations that result from damming. The mainstem of the Trinity River was dammed in the early 1960s (Master EIR 2009); this caused numerous habitat alterations that decreased habitat quality for turtles (Reese and Welsh 1998; Ashton et al. 2011), including channelization of the flow (via encroachment of a riparian berm), loss of access to the floodplain, decreased water temperature, and the filling of deep pools with

46 fine sediment (Master EIR 2009; Hampton 1995). In addition, the river valley was heavily modified by large-scale dredge mining, which left huge tailing piles and ponds that are still present along the river. The Trinity River Restoration Program (TRRP) was formed to implement physical channel rehabilitation (USDI Record of Decision,

2000); this is a multi-year project, which includes restoring different sections of the upper Trinity River each year.

As part of their restoration efforts, TRRP creates new ponds along the Trinity

River for use by Western Pond Turtles and other wildlife. However, there is a paucity of knowledge on the spatial ecology of Western Pond Turtles in lentic habitats, which makes it difficult to predict how newly created ponds will be used. Very little is known about the seasonality, frequency, and distance of terrestrial movements among aquatic habitats (Holland 1994; Reese 1996; Davis 1998). Turtles that spend the spring and summer in rivers may overwinter in ponds (Reese 1996; Davis 1998), or visit ponds on the way to or from terrestrial nesting and overwintering sites (Reese 1996). Information on movement of Western Pond Turtles in a lentic complex (sets of closely spaced ponds and wetlands) is limited to a single study in a series of agricultural ponds (Reese 1996).

Better knowledge of how Western Pond Turtles utilize lentic habitat complexes could allow the TRRP and other restoration and conservation organizations to make more informed decisions when creating new habitat or improving existing habitats for

Western Pond Turtles. In addition, detailed information on the spatial ecology of

Western Pond Turtles in lentic complexes is needed to better understand the scale at

47 which conservation efforts need to focus to protect terrestrial and aquatic habitats and the corridors between them.

The primary objective of this study was to describe the terrestrial movements of

Western Pond Turtles in a lentic habitat complex. This was accomplished using radio- telemetry throughout most of 2010 and 2011. More specifically, my objectives were to:

1) quantify the percentage of turtles that make terrestrial journeys and the timing of these journeys, 2) quantify the terrestrial distances that turtles move, 3) describe movements associated with travel between aquatic resources, overwintering, and nesting, and 4) use pond characteristics (temperature, depth, vegetation, amphibians/minnows, and insects) to suggest reasons for the frequency with which turtles use different ponds. Preliminary observations revealed that this site had high numbers of Western Pond Turtles in many of the ponds. In addition, TRRP was performing a river restoration project at this site and creating additional lentic habitats.

This allowed me to examine movements within an already established lentic habitat complex and determine if turtles will quickly use newly created lentic habitats.

METHODS

Study Area

This study was conducted at a site along the Trinity River, near Lewiston,

California. The site is approximately 12 kilometers downstream (west) of Lewiston

Dam, and includes Lowden Ranch and the surrounding properties (Fig. 1). Lowden

Ranch lies along a one-kilometer section of the southern bank of the Trinity River, and stretches southward ~0.5 kilometers to Lewiston Road. The western edge of the site is defined by Grass Valley Creek, a tributary to the Trinity River. Grass Valley Creek flows into two large settlement ponds (the Hamilton Ponds) before emptying into the

Trinity River.

There are many permanent and ephemeral ponds throughout Lowden Ranch and the properties upstream. Lowden Ranch has five permanent ponds (RW-5a, RW-5b,

RW-3, FEW-3 and PD-2); these were created by dredge mining, thus they are fairly steep-sided with limited shallow areas. Their hydrology is controlled primarily by river level and secondarily by precipitation and runoff. RW-5a (west) and RW-5b (east) are connected at high water levels. Lowden Ranch also has several ephemeral wetlands

(PD-1, FEW-2, FEW-1 and FEW-3b), and many wet meadows and moist areas that do not have standing water for more than a few weeks after the rains stop. FEW-1 is connected to the permanent pond PD-2 at high water levels. Upstream of Lowden

Ranch there are four ponds on private property: Pvt 1a and Pvt 1b are permanent ponds,

49 and Pvt 2a and Pvt 2b are ephemeral. Also, there is a permanent pond at an earlier

TRRP restoration site (Bucktail).

In mid-July of 2010, TRRP began a restoration project at Lowden Ranch, which continued though the fall of that year. Some of the features of this project included lowering the river’s floodplain, creating a large slow-flowing inlet (R-2) and two side channels, and connecting one of the ponds (FEW-3) to the river. Although heavy equipment moved in close proximity to the ponds, no work was done in the ponds themselves; they were left primarily undisturbed, except their water level increased in late summer and early fall of 2010 as a result of construction-related activities. TRRP also created four new ponds (Liner 1, Liner 2, Settlement, and Scraper); the former two are small liner ponds that go dry in the middle of the summer, while the latter two are larger, deeper ponds. These larger ponds were intended to be ephemeral, and TRRP is still modifying them to insure that they dry once a year.

100 meters

Fig. 1. Lowden Ranch and the surrounding properties along the Trinity River, in

Trinity County, CA. Solid lines represent permanent ponds or permanent portions of ponds; dashed lines represent ephemeral ponds or ephemeral portions of ponds.

Turtle Capture, Marking, and Morphometrics

Turtles were caught in collapsible crab traps with openings on both ends. Large

(37˝x 25˝x 24˝) and small traps (28˝’x 20˝x 13˝) were set each trapping period and baited with fresh fish carcasses or chicken. Traps were set for two to three day periods and checked twice a day. All captured turtles were uniquely marked by filing triangular notches in one or more marginal shields, using the marking pattern described by

Holland (1994). White numbers were also painted on each side of the carapace so that basking turtles could be identified at a distance. Weight, maximum carapace length, and sex were recorded for each turtle. Males have shorter and thicker tails, a concave plastron, white throats (older males), and a vent that is located beyond the posterior edge of the carapace. By contrast, females have longer and thinner tails, a flat plastron, a yellow- and black-flecked throat, and a vent that is located at the posterior edge of the carapace (Storer 1930; Holland 1994). Captured females were palpated for eggs to determine whether they were gravid.

Radio Telemetry

At Lowden Ranch, twenty-four turtles (12 males, 12 females) were fitted with

Lotek NTC-6-2 radio tags (Lotek Wireless Inc., Ontario, Canada) in the spring of 2010.

Tags were attached to the third pleural scute with Devcon® 5-minute epoxy gel

(Rathbun et al. 2002; Bondi 2009), and the antenna was left free (Bondi 2009). Turtles were relocated with a Lotek SRX 400 receiver. An additional eight turtles were fitted with transmitters throughout 2011 to replace turtles whose transmitters failed or were lost. The total weight of the transmitter and epoxy was approximately 15 grams; no

52 turtles weighing 300 grams or less were tagged. This weight restriction ensured that the package weighed less than 5% of the body weight, in order to minimize behavioral alterations resulting from the tags (Aldridge and Brigham 1988).

I monitored the terrestrial movements of Western Pond Turtles throughout the course of this study. Detection of a terrestrial movement was direct (visual sighting of a turtle on land) or indirect (inferring that a turtle moved overland to get between two unconnected water bodies). When on land, a visual observation of each turtle was made or they were located to within a 1 m radius. On the few occasions that turtles traveled into the Trinity River or Grass Valley Creek, their approximate location was estimated by triangulation from shore. Relocation efforts were concentrated in the months when turtles are most active. From April through mid-May and September through mid-

November, turtles were relocated once a week. From mid-May through August turtles were relocated twice a week. Turtles were relocated once a month in January and

February, and twice a month in March, April, and late November.

Pond Characterizations

The following pond characteristics were measured for the five permanent ponds at

Lowden Ranch (RW-5a, RW-5b, RW-3, FEW-3, and PD-2):

Depth: In the Trinity River and its tributaries, turtles are more likely to be found in deeper pools (Bury 1972; Reese 1996; Reese and Welsh 1998). As ponds shallow in the summer, turtles may be induced to move to deeper aquatic habitats. Therefore, I measured maximum pond depth once a month with a weighted measuring line.

Temperature: Western Pond Turtles tend to be associated with warmer water temperatures (Reese 1996; Reese and Welsh 1998) and they will select patches of warmer water for aquatic basking (Bury 1972; Holland 1985). Consequently, pond temperatures were continuously recorded with one of two types of Onset® (Onset

Computer Corporation, Cape Cod, USA) temperature loggers, either the StowAway

Tidbit Temperature Logger or the HOBO Pro v2 Water Temperature Data Logger. Two loggers were placed in each pond, one floating on the surface and the other at the bottom of the deepest location in each pond. Two loggers were also placed on land, one in full shade and the other in full sun.

Vegetation cover: Different types of pond vegetation serve different functions for turtles, like providing substrate for basking (i.e., cattail mats) or habitat for prey. In the eastern United States, some turtle species show seasonal associations with specific vegetation types (Beaudry et al. 2009). To investigate this possibility for Western Pond

Turtles, the Braun-Blanquet cover scale was used to estimate vegetation cover: 1 =

Solitary plant, 2 = Few (1-2% cover), 3 = Many, but < 5% cover, 4 = 5-25% cover, 5 =

26-50% cover, 6 = 51-75% cover, 7 = >75% cover. Cover was estimated for the following four vegetation classes: 1) plants/algae floating on the surface of ponds, 2) plants rooted in the bottom of the ponds with leaves floating on the surface, 3) emergent vegetation (cattail, bulrushes), and 4) overhanging riparian vegetation (e.g., willows).

Vegetation type was measured once each spring, summer, and fall.

Amphibians/ small fish: Western Pond Turtles will eat anuran tadpoles and fish (Bury

1986; Holland 1994), thus the presence of these species in certain ponds could serve as

54 an attractant. Presence or absence of amphibians and small fish in each pond was determined by setting minnow traps in each pond on five different occasions. Minnow traps were set and left out overnight on each occasion. Traps were set once in the summer and fall of 2010, and once in the spring, summer, and fall of 2011.

Aquatic insects: A large portion of the diet of Western Pond Turtles consists of aquatic insects (Bury 1986); therefore, high abundance of aquatic insects could influence turtle movements among ponds. Three 0.5 meter kick net sweeps were performed in each pond in the summer and fall of 2010 to measure the relative abundance of macro- invertebrates. All insects were picked from the samples in the field, preserved in 70% ethanol and later identified to order.

Data Analysis

Terrestrial distances that turtles moved between locations were calculated as straight-line distances estimated from maps (±2.5 m); therefore, the reported distances are the minimum distance that turtles could have moved. If a turtle was found in the same pond on two consecutive relocations, I assumed that it had remained in the pond and had not made any terrestrial movements in the intervening time. If a turtle was found in a new pond, I assumed that it had arrived at that location on the day that it was relocated.

Because of transmitter failures I did not always have the same number of turtles tagged. Therefore, to calculate the percent of turtles that made terrestrial journeys each month, I divided the number of turtles that made movements in a particular month by the average number of turtles tagged that month. Similarly, I calculated the average

55 monthly distance moved as the total distance moved by all turtles in a given month divided by the average number of turtles tagged.

RESULTS

Over the course of this study 32 individual turtles were tracked (Table 1); 24 (12 males and 12 females) were tagged at the onset of the study (by June 15th, 2010), while

8 (6 males and 2 females) more were added as transmitters failed or were lost. Two transmitters fell off turtles and were subsequently recovered (turtle #211 and #231). A third transmitter likely fell off turtle #302; the signal kept coming from the same location in a pond for over a year, yet the transmitter could not be recovered and the turtle was never recaptured. It is possible that this turtle died in the pond with its transmitter still attached. For these three turtles, I removed all movement data after their last confirmed movement from subsequent analyses (see Table 1). Beginning in

March of 2011, some of the transmitters began to fail. As transmitters failed, I attempted to tag new turtles as soon as possible, but was unable to maintain the sample size and sex ratio (Fig. 2). Beginning in August of 2011 I began to remove the original transmitters, as the rate of transmitter failure had increased dramatically the previous month. Only six turtles were tracked continuously over the entire study (June 15th,

2010 to January 10th, 2012), but fifteen were continuously tracked through July, 2011.

Table 1 shows the age (based on scute annuli), sex, and morphological characters for all tagged turtles. Most tagged turtles were ten years or older, except for three 7-year-olds and one 9-year-old. The mean weight was 515 g (minimum = 344 g; maximum = 738 g) and the mean maximum carapace length was 152 mm (minimum =

135 mm; maximum = 167 mm).

Table 1. Weight, carapace length, age (10+ represent turtle ≥ 10 years), sex (M = male,

F = female), number of relocations, and duration and dates tracked for radio-tagged

Actinemys marmorata. * turtles that were retagged after their initial transmitters failed

Carapace Duration Turtle Weight Length Number Tracked Second Second End # (g) (mm) Age Sex Relocations (days) Start Date End Date Start Date* Date*

201 553 165 10+ M 87 522 5/1/2010 10/12/2011

202 478 152 10+ M 93 603 5/1/2010 1/10/2012

203 452 148 10+ M 79 457 5/8/2010 8/17/2011

204 485 149.5 10+ M 66 414 5/8/2010 7/5/2011

205 710 162.5 10+ F 78 455 5/18/2010 8/15/2011

206 427 146.5 9 M 70 508 5/19/2010 6/14/2011 9/18/2011 1/10/2012

208 380 143.5 7 M 45 314 5/19/2010 3/27/2011

209 584 151.5 10+ F 62 395 5/20/2010 6/23/2011

210 490 153 10+ M 91 596 5/20/2010 1/10/2012

211 344 134.5 7 F 32 136 5/26/2010 10/9/2010

212 543 152 10+ M 85 576 6/1/2010 1/10/2012

213 384 154.2 10+ M 73 440 6/2/2010 8/27/2011

214 514 157.5 10+ M 92 603 5/19/2010 1/10/2012

216 381 140.9 10+ F 68 416 6/2/2010 8/3/2011

220 610 151.5 10+ F 84 554 6/3/2010 8/15/2011 9/18/2011 1/10/2012

222 738 166.5 10+ F 70 423 6/4/2010 8/3/2011

223 580 152.5 10+ F 66 409 6/4/2010 7/20/2011

225 637 161 10+ F 86 221 6/8/2010 1/10/2012

226 420 142 10+ F 69 421 6/8/2010 8/3/2011

229 627 158 10+ F 85 576 6/10/2010 1/10/2012

230 563 156 10+ M 58 385 6/8/2010 6/28/2011

231 657 156 10+ F 43 326 6/15/2010 5/7/2011

232 472 146 10+ F 33 211 6/14/2011 1/10/2012

242 515 150 10+ M 8 12 10/2/2011 1/10/2012

244 408 145 10+ M 9 107 9/19/2011 1/10/2012

248 650 166.5 10+ M 11 122 9/11/2011 1/10/2012

265 435 150 10+ M 12 45 7/12/2011 8/27/2011

302 475 158 10+ M 24 103 4/17/2010 7/29/2010

304 378 138 7 F 88 587 6/5/2010 1/10/2012

307 590 166 10+ M 10 115 9/11/2011 1/10/2012

418 480 151 10+ M 32 181 5/17/2011 8/3/2011 10/1/2011 1/10/2012

5134 660 161 10+ F 9 29 7/13/2011 8/11/2011

25 Total

Males

Females

10 # Turtles with Transmitters with Turtles #

Jul-10 Jul-11

Jan-11

Jun-10 Jun-11

Oct-10 Oct-11

Apr-10 Apr-11

Sep-10 Feb-11 Sep-11

Dec-10 Dec-11

Aug-10 Aug-11

Nov-10 Nov-11

Mar-11

May-10 May-11

Fig. 2. Number of turtles with radio transmitters on each occasion that turtles were relocated from April 2010 through

January 2012

Terrestrial Movements

Most tagged turtles at Lowden Ranch made terrestrial movements in both 2010 and 2011 [69.6% (n = 23) and 80.0% (n = 10), respectively, for turtles tagged at least four of the five months between June and October]. The turtles were active and made terrestrial journeys approximately seven months out of the year, from April 8th through

November 5th (Fig. 3). During the turtles’ active season in 2010, an average of 24.4%

(28.0% males; 21.7% females) of tagged turtles made terrestrial journeys each month

(June through October); in 2011 an average of 37.9% (39.8% males; 32.1% females) moved each month (June through October). The percentage of turtles making terrestrial movements each month was fairly consistent for spring through early summer (April through July), with peaks in female movement in June of 2010 and July of 2011 (Fig. 3).

In August of 2010 and 2011, there was a decrease in the percentage of turtles making terrestrial movements, especially females. In 2010 the percentage of turtles moving remained low in September and October, but in 2011 there was an increase in movement for these months.

The average terrestrial distance turtles moved (Fig. 4) was higher in months where a greater percentage of turtles made terrestrial movements (Fig. 3). In 2010 the average terrestrial movement during the active season (June through October) was 26.9 meters/month (34.8 for males; 20.5 for females), while in 2011 turtle movement averaged

70.3 meters/ month (72.3 for males; 54.1 for females) (June through October) (Fig. 4).

80 Total Males 70 Females

40 % turtles%

Fig. 3. Percent of radio-tagged turtles that moved each month in 2010 and 2011 at Lowden Ranch, near Lewiston, CA.

180 Total 160 Males Females

140

120

100

60 mean monthly movement (m) movement monthly mean

Fig. 4. Mean monthly terrestrial movement of radio-tagged turtles in 2010 and 2011 at Lowden Ranch, near Lewiston, CA.

Terrestrial Movements among Aquatic Habitats

The vast majority of terrestrial movements (93%) and the longest terrestrial distances moved (615 m) were between aquatic habitats. Approximately 68% of tagged turtles used multiple aquatic habitats each year. Permanent ponds were used more frequently than any other aquatic habitat. For example, in June, when there was an equal number of permanent and ephemeral ponds with water in them (7 of each), on average

89.8% of tagged turtles used permanent ponds, while 6% used ephemeral ponds, and

4.2% used lotic habitats. Of the five permanent ponds at Lowden Ranch, RW-3 was used much less frequently than the other four ponds. Only three tagged turtles visited it over both years and no turtles overwintered in it (Appendices B and D). The other four permanent ponds were frequently used year round.

Of the 32 tagged turtles, seven visited a lotic habitat and six visited an ephemeral lentic habitat. Four turtles visited Grass Valley Creek (Appendices B, C, and F) and one these turtles (#202) spent both summers in Hamilton Pond, a settlement pond that Grass

Valley Creek flows through (Appendix C). Two turtles visited the Trinity River

(Appendices A and G); one of these turtles (#204) and another turtle (Appendices A and

J) also visited a large, slow flowing, inlet off the Trinity River, R-2, which had been created during the 2010 restoration project. The ephemeral ponds FEW-1 and FEW-2 were used by several turtles for short periods (less than 2 weeks) (Appendices E, H, I, and J), and the ephemeral pond FEW-3b was used by a single turtle for over a month

(Appendix E). Two turtles moved out of Lowden Ranch to the ephemeral pond Pvt 2a

(Appendix J). In 2011 one radio-tagged turtle (#210), and three other turtles (observed basking), visited the settlement pond, which had just been created by TRRP in 2010

(Appendix E).

Some turtles had very similar movement patterns in 2010 and 2011, while others had completely different movements between years. For example, Turtle #202 had practically identical movements in both years, starting in RW-5 in the spring, spending the majority of the summer in Hamilton Pond and moving back to RW-5 in the fall to overwinter (Appendix C). Turtle #205 also had similar movements between years; she overwintered on land (winter of 2010/2011), spent a short time in RW-5 in the spring, and moved to Grass Valley Creek for the summer (Appendix C). In contrast, in 2010 turtle #204 made its way from the RW-5 ponds to PD-2, where it overwintered; in 2011 it kept moving in the same direction, eastward, following the Trinity River and eventually taking the river upstream (Appendix A). In 2010, Turtle #226 remained in PD-2, while in

2011 it moved to Pvt 2a in the spring and back to PD-2 in the summer, a roundtrip distance of 1,285 meters (Appendix J).

Overwintering Behavior

The vast majority of tagged turtles overwintered within the ponds. In the winter of 2010/2011, 95.5% of tagged turtles (n=22) overwintered within the ponds. All turtles that were in ponds in the fall of 2010 overwintered within the ponds; however, turtle

#205 was living in a lotic habitat (Grass Valley Creek) and moved onto land to overwinter (55 meters from Grass Valley Creek). Unfortunately, I have no data on where

64 this turtle overwintered the following winter. For the winter of 2011/2012, 93% (n=15) of tagged turtles overwintered within the ponds. All turtles were in lentic habitats in the fall of 2011 and one turtle (#225) moved onto land to overwinter (Appendix I). The overwintering location was only 10 meters from the pond (PD-2) it had previously been detected in. Turtle #225 had overwintered in PD-2 the previous winter.

Despite the lack of terrestrial movements onto land to overwinter, turtles likely made terrestrial movements in the fall to preferred overwintering ponds. In both years, turtles appeared to select RW-5a over RW-5b as an overwintering location. Although turtles continuously moved back and forth between the two ponds throughout their active season (both when the ponds were connected in the spring and after the connection dried in mid-summer), almost all turtles in RW-5b moved over land to RW-5a to overwinter.

Almost 90% (n = 9) of the turtles in the RW-5 ponds overwintered in RW-5a in the winter of 2010/2011, while 100% (n = 7) overwintered in RW-5 the following winter.

Terrestrial Movements Associated with Reproduction

No turtles were detected in the act of nesting; however, several terrestrial movements were likely associated with nesting, including movements between ponds, and roundtrip journeys onto land and back to the same pond. Five of 15 (33.3%) females captured and palpated in June 2010, and 2 of 4 (50%) females in June 2011 had detectable eggs. In neither year were any of the turtles trapped in May or July gravid. In

June 2010, one of the five gravid turtles (#220) was found on land in a blackberry/willow thicket (Appendix G); it was presumably going on land to nest, for the next time this

65 turtle was relocated (via telemetry) it was back in its original pond, RW-5a. In June

2011, two gravid females (#232 and #226) moved to Pvt 2a from PD-2 (Appendix J); it appears that these females moved to this ephemeral pond in order to nest in the vicinity, for they returned to PD-2 in July.

Environmental Characteristics

Depth: Depth of the permanent ponds at Lowden Ranch was primarily controlled by the level of the Trinity River through a hyporheic connection. Flows are released from the

Lewiston Dam in a semi-natural pattern, with high spring releases (13,000 cfs in 2011) and a low base flow in the fall and winter (300 cfs). Figure 5 shows the depth of the five permanent ponds at Lowden Ranch. Water level was highest in the spring and then decreased into the summer. Sudden increases in late summer depth in 2010 were influenced by construction-related activities and do not represent natural water levels.

Vegetation cover: In RW-5a, RW-5b, FEW-3, and PD-2 had similar vegetation coverage, while RW-3 was unique (Fig. 6). In the former four ponds, all types of aquatic vegetation cover tended to increase in the summer. This is not unexpected, for most aquatic plants senesce as the weather grows colder. Throughout the seasons, these four ponds had similar percent coverage by the four vegetation classes, with a few exceptions.

RW-5b and FEW-3 had more coverage by emergent vegetation than the other two ponds, while PD-2 had greater coverage by floating-leaved plants than any other pond. During all seasons RW-3 was densely shaded by overhanging riparian vegetation and it completely lacked floating-leafed plants and emergent vegetation.

300 RW-5a RW-5b 250 RW-3 FEW-3 PD-2

200

150 Depth (cm) Depth

100

0 A M J J A S O N D J F M A M J J A S O N

Fig. 5. Monthly maximum depth for five permanent ponds at Lowden Ranch for April 2010 through November, 2011.

RW-5a RW-3

6 6

4 4

BBCS BBCS 2 2

0 0 EV FLP FPA OV EV FLP FPA OV

RW-5b PD-2

6 6

4 4

BBCS BBCS 2 2

0 0 EV FLP FPA OV EV FLP FPA OV

FEW-3

4 BBCS 2

0 EV FLP FPA OV

Fig. 6. Aquatic vegetation cover for spring (vertical lines), summer (grey), and fall

(horizontal lines) 2010, as well as, spring (white), summer (black), and fall (checkered)

2011 on five turtle ponds at Lowden Ranch, near Lewiston CA, using the Braun-Blanquet cover scale (BBCS). (EV = emergent vegetation, FLP = floating leaved plants with roots in substrate, FPA = floating plants/algae, and OV = overhanging vegetation)

Temperature: Temporal variation in water temperatures (surface: Fig. 7; bottom: Fig. 8) was similar across all five permanent ponds at Lowden Ranch; these temperatures tracked the seasonal changes in air temperature (Fig. 9). Surface temperatures were similar across all ponds, except RW-3, which was colder in the summers, and FEW-3, which was colder in the summer of 2011. Bottom temperatures were also fairly consistent across ponds, with the exception of RW-5a being warmer in the summer of 2010, and RW-3 and

PD-2 being colder in the winter of 2010/2011.

Amphibians/ small fish: Three amphibian species and several small fish species were captured in minnow traps in the permanent ponds at Lowden Ranch (Table 2). Bullfrog

(Lithobates catesbeianus) adults were found in all permanent ponds, while their larvae were in all ponds except RW-3. Fish were missing solely from PD-2, while Pacific

Chorus Frogs (Pseudacris regilla) were only absent in RW-3. Rough-skinned Newts

(Taricha granulosa) were rare in general and were only trapped in RW-5a, RW-5b, and

FEW-3. Anaxyrus boreas (Western Toads) and Dicamptodon ensatus (Pacific Giant

Salamanders) were also observed, but never caught in minnow traps.

Aquatic Insects: The most prevalenct aquatic insect orders in the Lowden Ranch permanent ponds were Odonata, Diptera, Coleoptera, Ephemeroptera, and Hemiptera

(Table 3). The numbers of hemipterans and coleopterans were fairly low and consistant across the ponds. In the summer dipterans had a much higher abundance in all ponds than in the fall, and RW-3 had the most dipterans. RW-3 had very few odonates and ephemeropterans, while PD-2 and FEW-3 generally had a high abundance of these taxa.

30 RW-5a RW-5b 25 RW-3 PD-2

20 FEW-3

15 Temperature 10

Fig. 7. Mean monthly surface temperature (oC) from April 2010 through January 2012 for five ponds at Lowden Ranch.

Temperatures were continuously recorded once an hour (RW-5a, RW-5b and PD-2) or every four hours (RW-3 and FEW-3).

18 RW-5a 16 RW-5b RW-3 14 PD-2 FEW-3

8 Temperature

Fig. 8. Mean monthly bottom temperature (oC) from April 2010 through January 2012 for five ponds at Lowden Ranch.

Temperatures were continuously recorded once an hour (RW-5a, RW-5b and PD-2) or every four hours (RW-3 and FEW-3).

Temperature loggers were placed in the deepest location in each pond.

Full Sun 25 Shade

15 Temperature 10

Fig. 9. Mean monthly air temperature (oC) in complete shade and full sun from April 2010 through January 2012 at Lowden

Ranch. Temperatures were continuously recorded once every four hours.

Table 2: Presence (1) or absence (0) of amphibians and fish in minnow traps set on five different occasions in the five permanent ponds at Lowden Ranch throughout 2010 and

2011.

RW-5a RW-5b RW-3 FEW-3 PD-2 Pseudacris regilla larvae 1 1 0 1 1 Taricha granulosa adults 0 0 0 1 0 Taricha granulosa larvae 1 1 0 0 0 Lithobates catesbeianus larvae 1 1 0 1 1 Lithobates catesbeianus adults 1 1 1 1 1 Small Fish 1 1 1 1 0

Table 3: Numbers of aquatic insects found in each of the permanent ponds at Lowden

Ranch in the summer and fall of 2010. Numbers given for the five most prevalent insect orders. Samples from three 0.5 meter kick-net sweeps

Odonata Diptera Coleoptera Ephemeroptera Hemiptera RW-5a 24 89 21 90 31 RW-5b 1 100 10 9 8 Summer RW-3 0 364 11 2 2 FEW-3 14 176 19 126 12 PD-2 16 222 13 49 4

RW -5a 11 19 8 26 3 RW-5b 4 1 14 30 2 Fall RW-3 0 81 12 9 0 FEW-3 609 18 6 252 1 PD-2 73 37 5 166 17

DISCUSSION

Monitoring the terrestrial movements of a population of Western Pond Turtles living in a lentic habitat complex has increased our understanding of these turtles’ terrestrial biology and conservation needs in the Trinity River basin. Approximately

75% of the study population made terrestrial movements each year; some of these movements were associated with nesting and overwintering, but the vast majority of movements (93%) consisted of travel between aquatic habitats. The majority of tagged turtles used multiple aquatic resources within a single year, indicating that the home range of at least some populations can include multiple water bodies separated by upland habitat. In addition, some of these terrestrial movements between water bodies were fairly long distances (> 600 m). Because Western Pond Turtles made long distance terrestrial movements between water bodies on a regular basis, it is important to maintain connectivity and limit disturbance (e.g., road construction) within complexes of aquatic habitats.

Use of an Aquatic Habitat Complex by Turtles

In an aquatic habitat complex consisting of many permanent and ephemeral ponds and two lentic environments, Western Pond Turtles made use of all environments, giving further evidence that they are aquatic habitat generalists (Holland

1994). However, the aquatic habitats were not used in equal proportion; permanent ponds were used more frequently than any other habitat, even when ephemeral ponds were available in equal abundance. Five of the seven pre-existing ephemeral ponds

74 were visited for short periods of time in the spring and early summer; in addition, one of the four newly created ponds was visited, suggesting that turtles will “explore” new habitat. Only on a few occasions did turtles use the Trinity River or Grass Valley

Creek. The upper Trinity River is not considered ideal habitat for Western Pond Turtles because of its channelized flow and cold water (Reese and Welsh 1998; Ashton et al.

2011), thus it is not surprising that the turtles used it but little.

On many occasions certain ponds (e.g., FEW-3) were used as “rest areas” between other ponds (e.g., RW-5 and PD-2). On almost every occasion that turtles moved between two ponds separated by an intermediate pond, they used this intermediate pond as a “rest area”, often remaining there for less than a week. Although

Western Pond Turtles are capable of moving long distances over land, up to 5 km

(Holland 1994), it appears from this study that they will use aquatic stop overs whenever possible. This indicates the importance of maintaining aquatic corridors among wetland patches.

Of the five permanent ponds at Lowden Ranch, RW-3 was used far less frequently than the other four ponds. Only 3 tagged turtles used RW-3 and for fairly short periods of time (6 to 35 days); in addition, no tagged turtles overwintered here.

There were several differences in environmental characteristics that may have made

RW-3 a less desirable pond for turtles. Most importantly, the average summer surface temperature of RW-3 (16.1oC) was lower than the other ponds. This cold surface temperature can be explained by the high amount of overhanging riparian vegetation, which completely obscured the pond from receiving direct sunlight to warm the surface

75 water; no other permanent pond was this extensively shaded. The cold surface temperature and lack of exposed, sunny basking sites likely prevents adequate thermoregulation for maintenance of an optimal body temperature. Western Pond

Turtles increase activity once surface temperatures reach 15oC (Jennings and Hayes

1994), thus at 16.1oC RW-3 is only barely above the point at which activity can increase. In addition to the cold temperature, turtles may not use RW-3 because of its lack of food resources. Western Pond Turtles are opportunistic foragers and have been reported to eat anuran larvae (Rana boylii) (Bury 1986). No anuran larvae were found in RW-3, while they were found in all other ponds (Pacific Chorus Frogs and

Bullfrogs). In addition, I observed fewer aquatic insects and their larvae in RW-3 compared with the other ponds, suggesting that RW-3 may not had have an ample food supply.

Turtles selected RW-5a over RW-5b for overwintering, even though these ponds were used equally when the turtles were active. The primary difference between these two ponds was the depth, with RW-5a being on average 29.2 cm deeper than RW-5b.

A deeper pond, with a greater water volume, will take longer to change temperatures, thus a deeper pond could ameliorate the effects of short periods of extreme cold temperature. By contrast, Holland (1994) found that most turtles that overwintered in ponds were in water depths less than 0.5 m.

Proportion of Active Turtles

On average 75% of tagged turtles were active (i.e., made terrestrial movements) each year (June through October). The percent of active turtles in June through October

76 was higher at Lowden Ranch than was previously observed in a pond complex in Santa

Rosa, where 25% (n=12) and 50% (n=12) of turtles moved in 1992 and 1993, respectively (Reese 1996). However, the period of terrestrial activity for the Santa Rosa turtles was much longer than for the Lowden turtles. The only month that lacked terrestrial movement for the Santa Rosa turtles was January, while terrestrial movement only occurred about seven months out of the year at Lowden Ranch. Therefore, if the entire year is examined, rather than only June through October, 75% of the Santa Rosa turtles were active in 1992, while 58.3% were active in 1993. Although the Santa Rosa turtles were active for a longer period of the year than the Lowden turtles, a similar percentage of turtles were active.

Terrestrial Distances

Individual terrestrial movements, uninterrupted by a visit to an aquatic habitat, varied from 10 to 615 m. These distances were similar to those in the agricultural pond complex in Santa Rosa, where terrestrial movements varied from 27 to 925 m (Reese

1996). In both studies, the longest terrestrial movements were between ponds rather than for nesting or overwintering on land. Previous research on nesting (Storer 1930;

Holland 1991; Rathbun et al. 2002) and overwintering (Storer 1930; Rathbun et al.

2002) distances have not found distances that exceed 615 m; nesting sites vary from 17 to 402 m from water (Storer 1930; Holland 1991; Rathbun et al. 2002), while terrestrial overwintering sites vary from 15 to 423 m from water (Holland 1994; Reese 1996). It appears that movements between ponds in a pond complex include the longest terrestrial movements that Western Pond turtles make on a regular basis. It is unknown

77 whether turtles would make these long movements in unaltered lentic habitat complexes where more connectivity may exist between wetlands. Extensive mining on the Trinity

River created a landscape of discrete dredge ponds without connectivity between them, perhaps forcing turtles to make long terrestrial movements to supplement their resource intake.

Multiple ponds must be included within the home range of most Western Pond

Turtles at Lowden Ranch, given the high percentage of turtles that make terrestrial movements among ponds and the frequency with which these movements occur. In addition, the Lowden Ponds are much smaller (maximum diameter < 75 m) than the typical home range size (hundreds of meters) of Western Pond Turtles living in large lentic or lotic environments (Holland 1994; Reese 1996; Bondi 2009). Given the aquatic home range sizes of turtles in large bodies of water, it seems reasonable that turtles living in small ponds, like Lowden Ranch, must include multiple ponds in their home range to obtain all necessary resources.

Overwintering

All of the tagged turtles that were living in lentic habitats overwintered in the ponds, with one exception, while the one turtle that was living in a lotic site overwintered on land. This is consistent with the general tendency of turtles in lentic waters to overwinter in aquatic sites, and for turtles in lotic waters to overwinter on land

(Holland 1994). One turtle overwintered on land in 2011, although it had overwintered within a pond in 2010. Shifting overwintering locations between aquatic and terrestrial

78 habitats has been documented previously (Holland 1994; Reese 1996); this behavior further illustrates the plasticity of Western Pond Turtles in their habitat use.

Some of the terrestrial movements between ponds seemed to be associated with movements to a preferred pond for overwintering. For example, one turtle spent the majority of both summers in Hamilton Pond (a slow flowing lotic habitat), but moved to a lentic habitat to overwinter. In addition, movement to overwintering ponds may explain the increased number of turtles moving in September and October 2011.

Nesting Movements

Female terrestrial movements in May through July could have been associated with nesting. In 2010 most females moved in June and there were very few movements in July; however, in 2011 female movement was fairly constant across June and July.

One possibility is that the nesting season was later in 2011 than in 2010, causing some females to make terrestrial journeys later. Average air temperature and pond surface temperatures were slightly colder in June of 2011, possibly causing slower egg development and hence a delayed reproductive season. An alternative explanation is that turtle movement in July was affected by construction at the site. On July 15th, 2010 construction began at Lowden Ranch and there was heavy equipment at the site

(although not within the ponds). This activity may have limited female movement, or females could have been forced to nest closer to the ponds.

Conservation Implications

This research highlights the extent to which Western Pond Turtles will utilize multiple ponds in a pond complex, and the importance of maintaining connectivity

79 among aquatic habitats. Given that 65-70% of tagged A. marmorata traveled overland each year to utilize alternate aquatic habitats, a landscape view of A. marmorata populations is warranted. Cagle (1944) classified turtles into three different groups: 1) turtles that frequently move onto land and among adjacent water bodies; 2) turtles that are occasionally on land, but do not make regular overland movements; and 3) turtles that rarely come onto land. Only for the first group does home range include multiple aquatic habitats; Western Pond Turtles in lentic habitats along the Trinity River appear to belong to this first group.

Conservation efforts in these types of lentic systems should focus on preserving multiple wetland complexes and the upland habitat they are imbedded in, rather than individual wetlands and their surrounding buffer zone. Joyal et al. (2001) advocated for a landscape approach to wetland conservation for Spotted and Blanding’s Turtles. Like

Western Pond Turtles, both of these species made yearly terrestrial journeys to utilize multiple wetland habitats. For species that include multiple wetlands within their home range, it is particularly important for connectivity to be maintained among these aquatic resources, for seasonal differences in habitat quality (e.g., foraging, mating, basking) may exist that make the use of multiple aquatic resources essential. The terrestrial movements of Western Pond Turtles between aquatic resources were as long as 615 meters; therefore, activities disrupting migration corridors (e.g., road construction) between ponds separated by at least this distance should be avoided.

In light of Western Pond Turtle declines, it is important know if turtles will use newly created aquatic habitat and what factors make aquatic habitats suitable for

Western Pond Turtles. This study showed that Western Pond Turtles will quickly find and use new aquatic habitats if they are created. In 2011 at least four Western Pond

Turtles used the Settlement Pond and two turtles used the slow moving side channel R-

2, both of which were created by Trinity River Restoration Program in 2010. If TRRP or other organizations are going to create additional lentic habitats, I suggest the following pond characteristics to favor Western Pond Turtles: 1) The ponds must be ephemeral to prevent Bullfrog reproduction (Bullfrogs typically require permanent water for reproduction), for Bullfrogs are likely reducing turtle recruitment by eating young turtles (see Chapter 1). It would be best to build ponds far enough away from already existing Bullfrog habitat, that Bullfrogs will not colonize the ephemeral ponds en masse each spring (~250 m). 2) In order to provide aquatic habitat as long as possible, ponds should be made that do not go dry until August/ September. Western

Pond Turtles can estivate or move to other water sources when ponds go dry. 3) Ponds should have warmer water (e.g., not connected to the cold hyporheic zone of the Trinity

River). 4) Overhanging riparian vegetation shading ponds should be limited.

Conclusions

In summary, over a two year period most Western Pond Turtles moved overland, often frequently, between different aquatic resources. These movements between aquatic habitats are the longest terrestrial movements that Western Pond

Turtles make on a regular basis (Storer 1930; Holland 1991; Reese 1996; Rathbun et al.

2002). This frequent use of multiple aquatic habitats may indicate that when living in small ponds in a pond complex, turtles need to visit multiple ponds in order to meet all

81 resource requirements. Further research over a longer time period could indicate whether the use of different aquatic habitats to obtain all resources is essential for survival (landscape complementation) or if it simply improves resource acquisition

(landscape supplementation) (Dunning et al. 1992); if the former, the vast majority of turtles would be expected to utilize multiple aquatic habits; if the latter, some turtles would likely be fairly sedentary, while others move among multiple ponds. Regardless,

Western Pond Turtles will frequently utilize multiple aquatic habitats if they are available; thus it is essential to preserve terrestrial habitat between water bodies. In addition, there is extensive regional variation in Western Pond Turtle behavior.

Terrestrial movement should therefore be further studied in lentic habit complexes outside the Trinity River Basin, especially before management decisions are made concerning pond connectivity and the creation of new ponds.

REFERENCES

Aldridge, H.D.J.N. and R.M. Brigham. 1988. Load carrying and maneuverability in an

insectivorous bat: a test of the 5% “rule” of radio-telemetry. Journal of

Mammalogy 69:379-382.

Amezaga, J.M., L. Santamaria, and A.J. Green. 2002. Biotic wetland connectivity-

supporting a new approach for wetland policy. Acta Oecologica 23: 213-222.

Ashton, D. T., J.B. Bettaso, and H.H. Welsh. 2011. Comparative ecology of western

pond turtle (Actinemys marmorata) populations on the free-flowing south fork

and regulated main fork Trinity River: Demography, size and body condition

comparisons, thermal ecology, and spatial dynamics - Final report to the Trinity

River Restoration Program. USDA, Forest Service, Pacific Southwest Research

Station.

Beaudry, F., P.G. de Maynadier, M.L. Hunter Jr. 2009. Seasonally dynamic habitat use

by Spotted (Clemmys guttata) and Blanding’s Turtles (Emydoidea blandingii) in

Maine. Journal of Herpetology 43: 636-645.

Bondi, C.A. 2009. A comparison of Western Pond Turtle (Actinemys marmorata)

movements in perennial and intermittent portions of a northwestern California

river system. Thesis, Humboldt State University, California, USA.

Burke, V.J. and J.W. Gibbons. 1995. Terrestrial buffer zones and wetland

conservation: a case study of freshwater turtles in a Carolina Bay. Conservation

Biology 9: 1365-1369.

Bury, R.B. 1986. Feeding ecology of the turtle, Clemmys marmorata. Journal of

Herpetology 20: 515-521.

Bury, R.B. 1972. Habits and home range of the Pacific Pond Turtle, Clemmys

marmorata, in a stream community. Dissertation, University of California at

Berkeley, California, USA.

Cagle, F.R. 1944. Home range, homing behavior, and migration in turtles.

Miscellaneous Publications Museum of Zoology, University of Michigan 61: 1-

34.

Davis, C.J. 1998. Western pond turtle (Clemmys marmorata pallida) winter habitat use

and behavior. Thesis, California State University, San Jose, California, USA.

Dunning, J.B., B.J. Danielson, and H.R. Pulliam. 1992. Ecological processes that affect

populations in complex landscapes. Oikos 65: 169-175.

Hampton, M.A. 1995. Current status of fish habitat. In: R. L. Ridenhour (Ed.).

Proceedings from the Trinity River Restoration Program colloquium. American

Fisheries Society, Weaverville, California, USA, pp. 4-6.

Hayes, D. W., K. R. McAllister, S. A. Richardson, and D. W. Stinson. 1999.

Washington State Recovery Plan for the Western Pond Turtle. Wash. Dept. Fish

and Wildlife, Olympia, pp. 66.

Holland, D.C. 1991. A synopsis of the ecology and current status of the western pond

turtle (Clemmys marmorata) in 1991. Unpublished Report U.S. Fish and

Wildlife Service, National Ecology Resource Center, Fort Collins, Colorado.

Holland, D.C. 1994. The Western Pond Turtle: habitat and history. Prepared for the

Oregon Department of Fish and Wildlife and DOE/BP. Report #62137-1,

Bonneville Power Administration, Portland, Oregon.

Jennings, M.R., and M.P. Hayes. 1994. Amphibian and Reptile Species of Special

Concern in California. California Department of Fish and Game technical report,

Inland Fisheries Division, Rancho Cordova, California, USA.

Jones & Stokes. 2004. Western Pond Turtle Habitat Management Plan. December. (J&S

04254.04.) San Jose, CA. Prepared for NASA Ames Research Center, Moffet

Field, CA.

Joyal, L.A., M. McCollough, and M.L. Hunter Jr. 2001. Landscape ecology

approaches to wetland species conservation: a case study of two turtle species in

southern Maine. Conservation Biology 15: 1755-1762.

Mitsch, W.J. and J.G. Gosselink. 2007. Wetlands, 4th ed. John Wiley & Sons, Inc.,

New York.

North Coast Regional Water Quality Control Board and U.S. Bureau of

Reclamation. 2009. Channel rehabilitation and sediment management for

remaining Phase 1 and Phase 2 sites. Master EIR – EA/EIR

ODFW (Oregon Department of Fish and Wildlife) 2006. Oregon Conservation Strategy.

Oregon Department of Fish and Wildlife. Salem, OR.

Rathbun, G. B., N.J. Scott, and T.G. Murphey. 2002. Terrestrial habitat use by Pacific

Pond Turtles in a Mediterranean climate. The Southwestern Naturalist 47: 225-

235.

Rathbun, N.S., N. Siepel, and D. Holland. 1992. Nesting behavior and movements of

Western Pond Turtles, Clemmys marmorata. The Southwestern Naturalist 37:

319-324.

Reese, D. A. 1996. Comparative demography and habitat use of Western Pond Turtles

in northern California: the effects of damming and related alterations.

Dissertation, University of California at Berkeley, Berkeley, California, USA.

Reese, D. A., and H. H. Welsh. 1997. Use of terrestrial habitat by Western Pond

Turtles, Clemmys marmorata: implications for management. In: Van Abbema,

J. (Ed.). Proceedings: Conservation, Restoration, and Management of Tortoises

and Turtles - An International Conference. New York Turtle and Tortoise

Society, pp. 352-357.

Reese, D.A., and H.H. Welsh, Jr. 1998. Habitat use by Western Pond Turtles in the

Trinity River, California. Journal of Wildlife Management 62: 842-853.

Roe, J.H. and A. Georges. 2007. Heterogeneous wetland complexes, buffer zones, and

travel corridors: Landscape management for freshwater reptiles. Biological

Conservation 135: 67-76.

Semlitsch, R.D. and J.R. Bodie. 2003. Biological criteria for buffer zones around

wetlands and riparian habitats for amphibians and reptiles. Conservation

Biology 17: 1219-1228.

Semlitsch, R.D., and J. Jensen. 2001. Core habitat, not buffer zone. National Wetlands

Newsletter 23: 5-6, Environmental Law Institute, Washington, D.C.

Storer, T.I. 1930. Notes on the range and life history of the Pacific Freshwater Turtle,

Clemmys marmorata. University of California Publications in Zoology 32: 429-

433.

United States Department Interior. 2000. Record of Decision for the Trinity River

Mainstem Fishery Restoration Final Environmental Impact

Statement/Environmental Impact Report. United States Department of the

Interior, Weaverville, California, December.

Whigham, D.F. 1999. Ecological issues related to wetland preservation, restoration,

creation and assessment. The Science of the Total Environment 240: 31-40.

APPENDICES

Lines do not represent the actual paths taken by the turtles and the location of the arrow tip within water bodies is arbitrary.

Appendix A. Movements for turtle #204.

Appendix B. Movements for turtles #201 (green), #208 (blue), and #206 (red).

Appendix C. Movements for turtles #205 (blue), #202 (red), and #302 (green).

Appendix D. Movements for turtles #203 (red), #209 (blue), and #248 (green).

Appendix E. Movements for turtles #210 (red) and #304 (blue).

Appendix F. Movements for turtles #225 and #212.

Appendix G. Movements for turtles #214 (blue) and #220 (red).

Appendix H. Movements for turtles #222 (blue) and #223 (red).

Appendix I. Movements for turtles #225 (red) and #212 (blue).

Appendix J. Movements for turtles #226 (red) and #232 (blue).