Sacramento-Shasta Chapter of The Wildlife Society Giant Gartersnake Symposium Classroom Session - Wednesday, September 21, 2016 The Falls Event Center, North Main Hall 8280 Elk Grove Blvd., Elk Grove, CA 8:15am – 5:00pm (Poster session/ Social 5:00 - 7:30pm) The continued efforts by the resources agencies and others involved in the research and conservation of the State- and Federally Threatened Giant Gartersnake (Thamnophis gigas; GGS) requires communication of threats and sharing of how research studies are being used to manage and conserve the species. This two-day symposium is comprised of a Classroom session with oral presentations and an optional, limited enrollment field session. This symposium serves agency and private professionals, managers, students. The session topics (6.5-7 hours of total instruction, including Q&A) outlined in the Classroom agenda include:
Identification, Natural History and Taxonomy (including distribution and habitat) Movements and Demography Diet, Health, and Threats New Methods, Conservation, and Management
The poster session/ social reception includes viewing of posters, service of refreshments & hors d'oeuvres, and continued networking, discussion of ongoing research, and exploration of collaborative opportunities.
Field Sessions - Thursday, September 22, 2016 Three concurrent locations in the Sacramento Valley will host field attendees from approximately 8am-noon (approximately 3-4 hours of instruction) where GGS conservation efforts are occurring through broad, collaborative management strategies. At each field site attendees will observe and learn about proper capture and handling methods (trapping for ongoing research or management efforts), possibly process any snakes captured, and apply field topics discussed in the classroom session from the previous day. Field instructors will discuss the challenges of managing and maintaining GGS habitat and populations in the different landscape types of each field site. Colusa Basin Mitigation Bank At Colusa, attendees will visit a recently constructed, 160-acre habitat mitigation bank in Colusa County, discuss habitat features necessary for the snake and how the site contributes to a much larger conservation area because of its proximity to other wetland conservation projects, protected properties and the Colusa NWR. Field Instructors: Eric Hansen (Independent Consulting Biologist) and Rob Capriola (Westervelt Ecological Services). Field site access arranged by Westervelt Ecological Services. Cosumnes River Preserve, Snake Marsh At Cosumnes, attendees will visit one of the last remaining semi-natural wetlands that support GGS, learn about the particularly important conservation priority of this population, and about the impacts of drought and non-native species on GGS. Field Instructors: Sara Sweet (The Nature Conservancy), Eric Kleinfelter (California Department of Fish and Wildlife; CDFW) and Laura Patterson (CDFW). Field site access arranged by The Nature Conservancy and CDFW. Natomas Basin Conservancy’s BKS Tract At Natomas, attendees will visit the Conservancy’s first (and very successful) habitat restoration and enhancement project for GGS, amid a matrix of wetlands, rice and other farmlands, and urban areas. Field Instructors: Brian Halstead (USGS), John Roberts (Natomas Basin Conservancy), and Dustin Wood (USGS). Field site access arranged by The Natomas Basin Conservancy, cooperating agencies and landowners.
Sacramento-Shasta Chapter of the Wildlife Society
Giant Gartersnake Symposium Agenda September 21, 2016 Classroom Session The Falls Event Center, Elk Grove, CA 7:00 - 8:10 8:10 - 8:20
Registration & Breakfast Refreshments Welcome and Opening Remarks
Session 1 – ID, Natural History, and Taxonomy 8:20 - 8:40 The Giant Gartersnake: A Tale of Persistence in an Uncertain World ~ Mike Casazza 8:40 - 9:00 Notes and Procedures for Identifying the Giant Gartersnake (Thamnophis gigas) ~ Eric Hansen 9:00 - 9:20 Contemporary Patterns of Genetic Structure and Diversity in Giant Gartersnakes (Thamnophis gigas) ~ Dustin Wood 9:20 - 9:40 Relations among Environmental Attributes, Potential Chemoreception, and Contemporary Occupancy of a Threatened Snake ~ Eric Hansen 9:40 - 10:00 Active Season Microhabitat and Vegetation Selection by Giant Gartersnakes Associated with a Restored Marsh in California ~ Mike Casazza 10:00 - 10:25
Morning Break
Session 2 – Movement and Demography 10:25 - 10:45 Space Use by Giant Gartersnake in Structurally Different Wetland Habitats ~ Patricia Valcarcel 10:45 - 11:05 Terrestrial Ecology of Semi-Aquatic Giant Gartersnakes (Thamnophis gigas) ~ Glenn Wylie 11:05 - 11:25 Spatial Ecology of Giant Gartersnakes in Rice-growing Regions of the Sacramento Valley ~ Brian Halstead 11:25 - 11:45 Rates of Growth in Giant Gartersnake Populations in Managed Wetlands and Agricultural Areas ~ Rick Scherer 11:45 - 12:05 Demography of Giant Gartersnakes in the Natomas Basin ~ Brian Halstead 12:05 - 1:25
Lunch Break (lunch served on-site)
Session 3 – Diet, Health, and Threats 1:25 - 1:45 Diet, Prey Preference and Selection of Giant Gartersnakes (Thamnophis gigas) from the Sacramento Valley of California ~ Julia Ersan 1:45 - 2:05 Contaminant Exposure and Effects of Groundwater Pumping on Giant Gartersnake ~ Rick Scherer 2:05 - 2:25 Update on Giant Gartersnake Health Assessments and Preliminary Mortality Findings ~ Ray Wack* 2:25 - 2:45 Demography of Non-native Nerodia sipedon in the Sacramento Valley and the Efficacy of Trapping as an Eradication Method ~ Jonathan Rose 2:45 - 3:05 Giant Gartersnakes Encountered during Construction of Water Canals for the Gray Lodge Wildlife Area Water Supply Project, Assessing the Effectiveness of Avoidance and Mitigation Measures ~ Eric Britt 3:05 - 3:30
Afternoon Break
Session 4 – New Methods, Conservation, and Management 3:30 - 3:50 Scent-Detection Dog Surveys for the Giant Gartersnake (Thamnophis gigas) ~ Robyn Powers* 3:50 - 4:10 Development of Environmental DNA Methods for Giant Gartersnake (Thamnophis gigas) ~ Gregg Schumer 4:10 - 4:30 Use of Water Budgets to Plan Giant Gartersnake Habitat Needs ~ Sara Sweet 4:30 - 4:50 Thinking in Perpetuity: Management of Giant Gartersnake Preserves ~ Eric Olson 4:50 - 5:00 Closing Remarks 5:00 - 7:30 Poster Session/Social (prepaid, or tickets available for purchase on site $12– see our merchandise table!) *Thank you to our symposium sponsors!
Giant Gartersnake Symposium
Page 2 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
The Sac-Shasta Chapter of the Wildlife Society thanks the following sponsors for helping make this Giant Gartersnake Symposium possible: Premier Sponsor ($1,000 level) – The Sac-Shasta Chapter of TWS expresses gratitude for the Sacramento Zoo for helping to support this symposium:
Giant Gartersnake Symposium
Page 3 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
Platinum Sponsor ($750 level) – Thank you to GEI Consultants, Inc.
Gold Sponsors ($500 level) – Thank you to our Gold Sponsors:
Sincerest thanks to these and other partners for helping arrange field site access for the field sessions:
Giant Gartersnake Symposium
Page 4 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
Oral Presentation Abstracts Presenting authors in bold
Session 1: ID, Natural History, and Taxonomy
8:20 – 10:00
THE GIANT GARTERSNAKE: A TALE OF PERSISTENCE IN AN UNCERTAIN WORLD Michael L. Casazza1, Brian J. Halstead1, Glenn D. Wylie1, Julia S. M. Ersan1, Jonathan Rose1, and Gabriel A. Reyes1 1 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 (
[email protected], 530-669-5075) Despite the considerable loss and degradation of aquatic ecosystems throughout the Central Valley, some species, such as the giant gartersnake (Thamnophis gigas) continue to persist in highly modified agricultural wetlands. The giant gartersnake is a state and federally threatened species that historically occurred in the low-gradient streams, wetlands and marshes of California’s Great Central Valley. Giant gartersnake populations have become increasingly fragmented in recent decades and persist as small clusters of populations primarily in irrigation canals and drains associated with rice agriculture and remnant managed wetlands. The current range of the giant gartersnake extends from the Sacramento Valley near the vicinity of Chico southward to the northern and central San Joaquin Valley just north of the City of Fresno. Populations south of the Delta have seemingly become more isolated and rare as rice agriculture in the San Joaquin Valley has become negligible and many wetland habitats dried under varying scenarios. This apparent loss of water on the landscape in the southern Central Valley has resulted in range contraction and minimal giant gartersnake detections. A relatively stable core rice growing region in the Sacramento Valley has provided some stability for populations in this region, but they are still at future risk given potential changes to rice production and water management. Although habitat loss remains the greatest threat to population persistence, other factors include flood control and water conveyance projects that limit water availability, maintenance activities along canals and drains, poor water quality resulting from agricultural runoff from herbicide and pesticide application, road mortality, and predation and competition by non-native species, all of which contribute to further habitat degradation and population declines. NOTES AND PROCEDURES FOR IDENTIFYING THE GIANT GARTERSNAKE (THAMNOPHIS GIGAS) Eric C. Hansen, Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 (
[email protected], 916-921-8281) The giant gartersnake (Thamnophis gigas) is a federal- and state-listed species endemic to California’s Great Central Valley. Cryptic and notoriously wary, this species is among the most difficult of California’s gartersnakes to accurately identify. Yet accurate identification is of paramount importance for assessing the distribution of rare or declining species and prioritizing management and recovery efforts accordingly. In this presentation I will provide an overview of the various guidelines used to accurately identify giant gartersnakes. Topics will include physical appearance and morphology (e.g., scale count, measurements, and ratios) and life history (e.g., range, habitat associations, and behavior), and differentiating from other Central Valley species with which giant gartersnakes are often confused. I will also provide suggestions for properly documenting the features needed in the critical step of validating species identification while avoiding pitfalls associated with misidentification. CONTEMPORARY PATTERNS OF GENETIC STRUCTURE AND DIVERSITY IN GIANT GARTERSNAKES (THAMNOPHIS GIGAS). Dustin A. Wood1, Brian J. Halstead2, Michael L. Casazza2, Eric C. Hansen3, Glenn D. Wylie2, and Amy G. Vandergast1 1 U.S. Geological Survey, Western Ecological Research Center, San Diego Field Station, 4165 Spruance Road, Suite 200, San Diego, CA 92101 (
[email protected], 619-889-0732) 2 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 3 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 Giant Gartersnake Symposium
Page 5 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
Despite the loss of 93% of historic wetlands throughout the Central Valley, giant gartersnakes continue to persist in relatively small, isolated patches of highly modified agricultural wetlands. However, severe fragmentation and disturbance activities have been shown to erode the levels and distribution of genetic diversity. Changes to genetic diversity are important for threatened species management plans, because loss of genetic diversity can reduce the long-term viability of populations and increase local and global extinction risks. On the basis of 15 microsatellite loci, we estimated population structure and compared indices of genetic diversity among populations spanning seven drainage basins within the Central Valley. Our data supported five genetic units across the present range of the giant gartersnake, and these units were largely consistent with regional drainage basins. Connectivity among genetic units was higher in northern portion of the range, and genetic diversity was significantly different and lower in the southern portion of the range. However, reductions in effective population sizes and inbreeding were detected throughout the range, suggesting that long-term maintenance of genetic diversity is not being maintained. Further management actions may be needed to ameliorate change and increase connectivity among existing wetlands to increase the long-term viability of this species. RELATIONS AMONG ENVIRONMENTAL ATTRIBUTES, POTENTIAL CHEMORECEPTION, AND CONTEMPORARY OCCUPANCY OF A THREATENED SNAKE Eric C. Hansen, Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 (
[email protected], 916-921-8281) Habitat loss and modification are causing declines in the abundance and distribution of plant and animal species, yet robust information on which to base management and regulatory decisions for these species frequently is not available. Thamnophis gigas (giant gartersnake), a species listed as threatened under the U.S. and California Endangered Species Acts, is strongly associated with aquatic ecosystems in the Great Central Valley (California, USA), yet many important aspects of its ecology remain poorly understood. Identification of a species’ potential habitat, whether occupied or unoccupied, may inform future sampling efforts, suggest locations for experimental translocations, acquisition, or protection, and facilitate evaluations of ecological processes such as gene flow and dispersal among populations. We evaluated relations between environmental attributes and occupancy of T. gigas and characterized habitat quality for it across approximately 300,000 ha in the northern Central Valley. Occupancy of T. gigas was strongly and negatively associated with elevation and strongly and positively associated with canal density and the proportion of rice agriculture and perennial wetland. We also hypothesized that historic hydrologic and geomorphologic processes have driven soil formation in the valley, and that wetlands and their underlying soil types develop distinct hydrogeochemical signatures that might influence habitat selection by T. gigas and found a strong and previously unknown association between occupancy and soil type. We used these statistical associations between environmental variables and occupancy to map habitat quality at a spatial resolution and extent consistent with management of both T. gigas and regional land and water use. ACTIVE SEASON MICROHABITAT AND VEGETATION SELECTION BY GIANT GARTERSNAKES ASSOCIATED WITH A RESTORED MARSH IN CALIFORNIA Michael L. Casazza1, Brian J. Halstead1, Patricia Valcarcel2, Glenn D. Wylie1, Peter S. Coates1, Daniel K. Rosenberg3 1 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 2 WRA, Inc. 2169 Francisco Blvd East, Suite G, San Rafael, CA 94901 3 Oregon State University, Corvallis, OR 97331 Studies of habitat selection can reveal important patterns to guide habitat restoration and management for species of conservation concern. Giant gartersnakes (Thamnophis gigas) are endemic to the Central Valley of California, where more than 90% of their historic wetland habitat has been converted to agricultural and other uses. Information about the selection of habitats by individual giant gartersnakes is needed to guide habitat restoration. We examined activity patterns and selection of microhabitats and vegetation types by adult female giant gartersnakes with radio telemetry at a site comprised of rice agriculture and restored wetlands using a paired case-control study design. Adult female giant Giant Gartersnake Symposium
Page 6 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
gartersnakes were 15.6 (95% credible interval = 10.1–24.7) times more likely to be active (foraging, mating, or moving) when located in aquatic habitats than when located in terrestrial habitats. Microhabitats associated with cover, particularly emergent vegetation, terrestrial vegetation, and litter, were positively selected by giant gartersnakes. Individual giant gartersnakes varied greatly in their selection of rice and rock habitats, but varied little in their selection of open water. Tules (Schoenoplectus acutus) were the most strongly selected vegetation type, and duckweed (Lemna spp.), water-primrose (Ludwigia spp.), forbs, and grasses also were positively selected at the levels of availability observed at our study site. Management practices that promote the interface of water with emergent aquatic and herbaceous terrestrial vegetation will likely benefit giant gartersnakes. Restoration of native tule marshes will likely provide the greatest benefit to these threatened aquatic snakes.
Session 2: Movement and Demography
10:25– 12:05
SPACE USE BY GIANT GARTERSNAKE IN STRUCTURALLY DIFFERENT WETLAND HABITATS Patricia Valcarcel1, Dan Rosenberg2, Brian J. Halstead3, Glenn D. Wylie3, Michael L. Casazza3 1 WRA, Inc. 2169 Francisco Blvd East, Suite G, San Rafael, CA 94901 (
[email protected], 415-5247542) 2 Oregon State University, Corvallis, OR 97331 3 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 Knowledge of the spatial ecology of a species is a vital component of informed management and restoration plans, yet little is known about how animals use restored or constructed habitat. We assessed home range and core area sizes of the federally threatened Giant Gartersnake (Thamnophis gigas) within rice agricultural habitat and recently constructed wetlands developed as conservation banks for mitigation. Space use patterns were estimated from radio tracking 19 unique adult female snakes over 2 years at a site that is the center of conservation efforts for the species. We estimated home range (95% kernel density contour) and core area (50% kernel density contour) sizes and overlap between individuals. Contrary to expectations, but consistent across years, we found home ranges in the agricultural habitat were on average 80% smaller and had less variation among individuals than those in the constructed wetlands. Snakes in agricultural habitat also had greater and more uniform home range overlap among individuals. The restricted home ranges observed in the snakes in agricultural habitat suggest we need further investigation into dispersal movements and habitat connectivity to better inform regional conservation planning. TERRESTRIAL ECOLOGY OF SEMI-AQUATIC GIANT GARTERSNAKES Glenn D. Wylie1, Brian J. Halstead1, Shannon M. Skalos1, and Michael L. Casazza1 1 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 (
[email protected], 530-669-5065) Wetlands are a vital component of habitat for semiaquatic herpetofauna, but for most species adjacent terrestrial habitats are also essential. We examined the use of terrestrial environments by Giant Gartersnakes (Thamnophis gigas) to provide behavioral information relevant to conservation of this state and federally listed threatened species. We used radio telemetry data collected 1995–2011 from adults at several sites throughout the Sacramento Valley, California, USA, to examine Giant Gartersnake use of the terrestrial environment. We found Giant Gartersnakes in terrestrial environments more than half the time during the summer, with the use of terrestrial habitats increasing to nearly 100% during brumation. While in terrestrial habitats, we found Giant Gartersnakes underground more than half the time in the early afternoon during summer, and the probability of being underground increased to nearly 100% of the time at all hours during brumation. Extreme temperatures also increased the probability that we would find Giant Gartersnakes underground. Under most conditions, we found Giant Gartersnakes to be within 10 m of water at 95% of observations. For females during brumation and individuals that we found underground, however, the average individual had a 10% probability of being located > 20 m from water. Individual variation in each of the response variables was extensive; therefore, predicting the behavior of an individual was fraught with uncertainty. Nonetheless, our estimates provide resource managers with Giant Gartersnake Symposium
Page 7 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
valuable information about the importance of protecting and carefully managing terrestrial habitats for conserving a rare semiaquatic snake. SPATIAL ECOLOGY OF GIANT GARTERSNAKES IN RICE-GROWING REGIONS OF THE SACRAMENTO VALLEY Brian J. Halstead1, Gabriel A. Reyes1, Jonathan P. Rose1, Shannon M. Skalos1, Julia S. M. Ersan1, Michael L. Casazza1, and Glenn D. Wylie1 1 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 (
[email protected], 530-669-5076) Giant gartersnakes have lost nearly all of their natural habitat, and most extant giant gartersnake populations occur in areas associated with rice agriculture. The water used to grow rice is highly sought for other uses during dry years, but the effect of this reduction in rice acreage and filled canals on giant gartersnakes is unknown. We examined the spatial ecology of giant gartersnakes in rice agricultural systems to estimate the scale at which reduction in aquatic habitats is likely to affect giant gartersnakes. Giant gartersnakes generally moved short distances infrequently, but much variation in movement distances and frequencies existed among individuals. Core area and home range sizes were generally small (usually < 0.4 ha and 35 ha, respectively), and activity centers were nearly always associated with canals. Although capable of long-distance (> 1 km) movements, giant gartersnakes generally appear to remain in small core areas of activity. Water management practices that reduce local habitat availability might therefore affect giant gartersnake body condition and survival as snakes move farther in search of habitat and prey. RATES OF GROWTH IN GIANT GARTERSNAKE POPULATIONS IN MANAGED WETLANDS AND AGRICULTURAL AREAS Rick D. Scherer1 and Eric C. Hansen2 1 Conservation Science Partners, 5 Old Town Square, Suite 205, Fort Collins, CO 80524 (
[email protected], 970-484-2898) 2 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 Population models are a valuable tool in the management of wildlife populations, and estimates of growth rates are an essential component of those models. Thamnophis gigas (giant gartersnake) has been eliminated from more than one half of its former range. Although factors such as habitat degradation and diminished water quality are attributed to these declines, the trajectories of declining populations – i.e., the thresholds indicative of population health and successful resource management – have not been described for T. gigas. The correlates of habitat and environment that affect demographic parameters also remain unclear. We captured T. gigas in populations at managed wetlands and at sites embedded in agricultural settings. We used the data from individuals captured on multiple days to estimate growth rates and asymptotic size (using snout-vent-length, or SVL). We also evaluated the hypothesis that growth rates and asymptotic size varied among populations in managed wetlands and agricultural areas. Model-selection results indicated that T. gigas in agricultural areas grew more quickly than those in managed wetlands but grew to a similar asymptotic length. Estimates of model parameters also indicated variation in growth rates among individuals. These results are expected to contribute to the development of demographic models characterizing stable or increasing T. gigas populations and to identifying factors to which critical demographic rates are sensitive. DEMOGRAPHY OF GIANT GARTERSNAKES IN THE NATOMAS BASIN Brian J. Halstead1, Jonathan P. Rose1, Gabriel A. Reyes1, Michael L. Casazza1, Glenn D. Wylie1, Shannon M. Skalos1, Julia S. M. Ersan1, Eric C. Hansen2, and John R. Roberts III3 1 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 (
[email protected], 530-669-5076) 2 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 3 The Natomas Basin Conservancy, 2150 River Plaza Dr., Suite 460, Sacramento, CA 95833
Giant Gartersnake Symposium
Page 8 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
Assessment and management of wild populations requires understanding their vital rates and the variables that influence demography. Few published estimates of vital rates of giant gartersnakes exist, in part because of the difficulty in estimating vital rates of rare and elusive species. We used data collected in the Natomas Basin from 2004-2016 to estimate annual abundance, survival, and per-capita recruitment of giant gartersnakes at five sites in the Natomas Basin. Abundance of giant gartersnakes varied more among sites than among years, with annual site abundances ranging from less than 10 to more than 100 individuals. From 2004 through 2016, three populations were likely stable (< 10% change), another likely increased by more than 10%, and the other likely decreased by more than 10%. The proportion of different habitat and vegetation types had little effect on apparent survival probabilities from 2011 through 2016. Minimizing emigration in future studies of giant gartersnake demography will continue to improve demographic estimates based on capture-mark-recapture studies.
Session 3: Diet, Health, and Threats
1:25 – 3:05
DIET, PREY PREFERENCE AND SELECTION OF GIANT GARTERSNAKES (THAMNOPHIS GIGAS) FROM THE SACRAMENTO VALLEY OF CALIFORNIA Julia S. M. Ersan1, Brian J. Halstead2, Erica L. Wildy3, Michael L. Casazza2, and Glenn D. Wylie2 1
California State University, East Bay, 25800 Carlos Bee Blvd, Hayward, CA 94542 (
[email protected], 530-669-5081), in collaboration with 2 U.S. Geological Survey, Western Ecological Research Center, 800 Business Park Drive, Suite D, Dixon, CA 95620 3 Department of Biological Sciences, California State University East Bay, Hayward, CA 94542 The introduction of exotic species can change the trophic dynamics of native species. The giant gartersnake, an endemic predator in the Central Valley of California, is listed as threatened due to the conversion of its once vast wetland habitat to agriculture. Further contributing to this snake’s changing ecology is the introduction of non-native prey species resulting in a diet that is almost completely comprised of exotics. I conducted behavioral trials in a laboratory to access prey preference and selection of naïve neonates. Results from olfactory trials suggest that native species elicit the highest response from neonates and results from consumption trials suggest that other factors contribute to prey selection. I also examined prey selection of a broader age class of giant gartersnakes in the wild by analyzing trap by-catch and regurgitated gut contents of snakes in four basins in the Sacramento Valley of California to determine whether these snakes actively select their prey or if they are simply consuming what is abundant. Results show that despite the domination of non-native anuran and fish species in the available prey community, giant gartersnakes most strongly selected native Sierran treefrogs (Pseudacris sierra) metamorphs. Giant gartersnakes also were more likely to select introduced American bullfrog (Lithobates catesbeianus) adults over all tested introduced fishes. Managing prey communities to increase native amphibian abundance within the giant gartersnake’s range might benefit populations of this rare snake. CONTAMINANT EXPOSURE AND EFFECTS OF GROUNDWATER PUMPING ON GIANT GARTERSNAKE Rick D. Scherer1, Eric C. Hansen2, L. Arriana Brand3, Raymond F. Wack4, Robert Poppenga5 1 Conservation Science Partners, 5 Old Town Square, Suite 205, Fort Collins, CO 80524 (
[email protected], 970-484-2898) 2 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 3 Conservation Science Partners, 11050 Pioneer Trail, Suite 202, Truckee, CA 96161 4 Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA 95616 5 California Animal Health and Food Safety Laboratory, University of California, Davis, CA 95616 Thamnophis gigas (giant gartersnake) is critically imperiled in the San Joaquin Valley (SJV), where populations have declined or are missing from formerly occupied habitats that otherwise appear to retain suitable physical characteristics (e.g., presence of water, sufficient hydroperiod, emergent vegetation, and terrestrial refugia). Physical characteristics, however, may not be the only drivers of T. gigas occupancy in Giant Gartersnake Symposium
Page 9 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
the SJV, and there is some evidence that poor water quality may be impacting T. gigas and its prey. Recent drought and resulting surface water depletion and concentration of potentially hazardous heavy metals in the perched water table may also pose an immediate threat to regional population persistence. Maintaining a water supply that is both reliable and of a quality adequate for sustaining wildlife is of paramount importance to meeting the goal of long-term persistence for T. gigas. Beginning in 2012, groundwater pumping was used to maintain water in the wetlands used by the population at the Volta Wildlife Management Area. To address concerns regarding potential negative impacts associated with groundwater quality, we began collecting water samples, tissues from prey species and T. gigas, and demographic data on T. gigas in 2010, prior to the initiation of pumping and continued collecting samples through 2015. We use these data to evaluate the effects of groundwater pumping on water quality, metal concentrations in prey and T. gigas, and survival probability for T. gigas. UPDATE ON GIANT GARTERSNAKE HEALTH ASSESSMENTS AND PRELIMINARY MORTALITY FINDINGS Raymond F. Wack, Senior Veterinarian,, Wildlife Health Center and Sacramento Zoo, School of Veterinary Medicine, University of California, Davis, CA 95616 (
[email protected], 916-808-8808) As a veterinarian involved in several different GGS field studies, I have been conducting systematic health assessments on snakes throughout their range for over 5 years. This presentation will cover health related findings including establishment of hematology/plasma chemistry reference ranges, radiographic findings, parasitology, and information gained from a limited number of necropsies. DEMOGRAPHY OF NON-NATIVE NERODIA SIPEDON IN THE SACRAMENTO VALLEY AND THE EFFICACY OF TRAPPING AS AN ERADICATION METHOD Jonathan P. Rose1 and Brian D. Todd2 U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620 (
[email protected], 530-669-5075) 2 Department of Wildlife, Fish & Conservation Biology, University of California, Davis, One Shields Ave, Davis, CA 95616 1
The introduction of non-native watersnakes to central California presents a novel threat to many native aquatic species, especially the threatened Giant Gartersnake (Thamnophis gigas). The northern watersnake (Nerodia sipedon) and the banded watersnake (N. fasciata) are very similar ecologically to Giant Gartersnakes, and therefore likely represent novel competitors should they expand into Giant Gartersnake habitat. We sampled the N. sipedon population in Roseville, California over four summers from 2011 – 2015, and estimated abundance, survival, and individual growth rates and body condition. We found that the N. sipedon population had a low annual survival rate from 2013 – 2015 (< 30%), and declined from an estimated abundance of 126 snakes to 75 snakes during this period. Growth rates were lower than those reported from native populations, and snake body condition also declined from 2011 – 2015. Large adult females (> 600 mm SVL) were commonly captured in 2011, 2013, and 2014, but none were captured in 2015. Declines in the surface area of the wetland, and lower capture rates of prey species suggest that the recent drought was the cause of observed declines in this non-native population. We integrated data from the Roseville N. sipedon population with published demographic data from native populations of N. sipedon to construct a population model for this species. We used an Integral Projection Model (IPM), which lends itself well to modeling watersnake biology because many vital rates are size-dependent and individuals are difficult to accurately age. We used elasticity analysis to identify the survival and growth of young individuals as the life-stage transition that has the greatest influence on the growth rate of the population, followed by the survival of reproductively mature females. Analysis of snake capture data showed that aquatic funnel traps capture all life stages, but preferentially select intermediate sized snakes. We also used stochastic population simulations to evaluate the effect of trapping effort on the probability of watersnake populations going extinct. Simulations indicated that even for scenarios where populations have a high intrinsic growth rate, trapping could drive populations to extinction. Ensuring a high probability of eradication will require a substantial trapping effort sustained over a period of several years. Giant Gartersnake Symposium
Page 10 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
GIANT GARTERSNAKES ENCOUNTERED DURING CONSTRUCTION OF WATER CANALS FOR THE GRAY LODGE WILDLIFE AREA WATER SUPPLY PROJECT, ASSESSING THE EFFECTIVENESS OF AVOIDANCE AND MITIGATION MEASURES Eric Britt1, Jeff Mitchell1, and Karen Swaim1 1 Swaim Biological, 4556 Contractors Place, Livermore, CA 94551 (
[email protected], 925-455-8770) In this study, we report on the effort made by biologists to document the impact to the giant gartersnake (Thamnophis gigas) (GGS) during the reconstruction of a water conveyance canal in Biggs, California, in which GGS habitat and winter hibernacula were unearthed by construction activities. Snakes were encountered during pre-construction surveys and during construction, throughout their winter inactive hibernation phase to spring emergence. Giant gartersnakes were the most abundant snake species we captured and were typically found near deteriorating concrete structures including farm turnouts, culvert headwalls, and rip-rap adjacent to water control structures. Deep crevices and burrows were visible along the canal banks and became more numerous in the weathered areas surrounding the structures, however, our attempts at using scope cameras to locate snakes before construction activities were unsuccessful. Most of the successful GGS relocations occurred as the result of close observation by biological monitors who were in direct communication with equipment operators. The numerous drains and intersecting canals with slow-moving water and emergent vegetation present in this area of dense rice agriculture represented relatively high-quality habitat for GGS.
Session 4: New Methods, Conservation, and Management 4:50
3:30 –
SCENT-DETECTION DOG SURVEYS FOR THE GIANT GARTERSNAKE (THAMNOPHIS GIGAS) Robyn M. Powers1, Katherine Ayres1, Eric C. Hansen2, Alexandra Thiel1, Monica Hemenez1, and Lauralea Oliver1 1 H. T. Harvey & Associates, Cal Poly Technology Park, Building 83, Suite 1B, San Luis Obispo, CA 93407 (
[email protected], 805-756-7423) 2 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 The giant gartersnake (Thamnophis gigas) is federally and state listed as a threatened species and is endemic to California’s central valley. Giant gartersnakes require wetlands for foraging, upland areas for basking and summer shelter, and higher-elevation refugia for winter brumation. Giant gartersnakes are visually elusive and often occur in low-density populations making them difficult to detect, particularly when they are sheltering. As such, detection challenges have resulted in a poor understanding of occupancy throughout much of the species’ range. H. T. Harvey & Associates tested the efficacy of using scent-detection dogs to recognize and alert to giant gartersnake scent and distinguish it from the scent of sympatric snake species. When tested in a field setting, two detection dog teams performed with a positive predictive value of 91% for scent above ground and 87% for scent below ground. After determining that the dogs could detect giant gartersnakes and distinguish them from sympatric species with low error, they were used for surveys of the species in the Grasslands Ecological Area in Merced and Fresno Counties. Two detection dog teams surveyed along canal banks and also on ponds from a kayak. The dogs detected giant gartersnake odor on eleven occasions. These areas will be studied further with environmental DNA testing and trapping. The use of scent-detection dogs may offer an efficient and innovative survey approach, enabling the detection of giant gartersnakes both in their aquatic habitat and in upland refugia.
Giant Gartersnake Symposium
Page 11 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
DEVELOPMENT OF ENVIRONMENTAL DNA METHODS FOR GIANT GARTERSNAKE (THAMNOPHIS GIGAS) Gregg Schumer, Cramer Fish Sciences – GENIDAQS Division, 3300 Industrial Way, Suite 100, West Sacramento, CA 95691 (
[email protected], 916-231-1681) Formerly distributed throughout the lower portions of Badger Creek in southern Sacramento County, the local range of the Badger Creek giant gartersnake (Thamnophis gigas) population has apparently shrunk in recent decades to include only the isolated marsh forming at the confluence of Badger and Willow Creeks at the Cosumnes River Preserve (CRP). Commonly referred to as Snake Marsh, this isolated population represents the core of core giant gartersnake density within the eastern Delta. Recent analyses suggest that this population represents the highest genetic diversity throughout the species’ extant range. As such, this population has become an important element of conservation planning, which relies not only on the persistence of this population for maintaining genetic diversity, but also as a potential gene bank to be used for repatriating snakes to areas of former occupation in the highlycompromised San Joaquin Valley. Over recent decades, this population has been subjected to threats ranging from the expansion of invasive water primrose (Ludwigia hexapetala), which has filled in giant gartersnake open-water foraging habitat with a dense monoculture of live primrose and its accumulated biomass, to water shortages limiting available habitat during the snake’s crucial active season. This presentation highlights the history of known giant gartersnake distribution throughout the Cosumnes River watershed, efforts to identify and ameliorate potential causes of decline, and the relevance of this population to the rangewide conservation of the species. USE OF WATER BUDGETS TO PLAN GIANT GARTERSNAKE HABITAT NEEDS Sara Sweet1 and Eric Kleinfelter2 1 The Nature Conservancy, 13501 Franklin Blvd. Galt, CA 95632 (
[email protected], 916-683-1767) 2 California Department of Fish and Wildlife, North Central Region, 1701 Nimbus Road, Rancho Cordova, CA 95670 Although some giant gartersnake locations seem to have a reliable water supply due to agriculture, many others do not. Severe droughts and climate change could also imperil water supply for giant gartersnake populations that have been relatively safe to date. Land managers and policy advocates both need to have defensible estimates of giant gartersnake water needs, whether to finance and implement giant gartersnake management, or to ensure giant gartersnake needs are incorporated into statewide allocations. The water budget approach is an empirical method to supply this information need. It was central in successfully predicting and thereby avoiding a disastrous water shortage at Snake Marsh, home to the Badger Creek population. This water budget approach can be applied in many other locations to safeguard the supply of water for giant gartersnake. THINKING IN PERPETUITY: MANAGEMENT OF GIANT GARTERSNAKE PRESERVES Eric Olson, Center for Natural Lands Management 27258 Via Industria, Suite B, Temecula, CA 92590 (
[email protected], 760-731-7790) Recovery of the threatened giant gartersnake (Thamnophis gigas; GGS) depends on the establishment and perpetual management of protected suitable habitat. Appropriate land-use restrictions, sciencebased management, and adequate perpetual funding are all essential. The Center for Natural Lands Management (CNLM) manages two properties within the Natomas Basin—Prichard Lake and Willey Wetlands (Preserves)—that are protected by conservation easements and funded by endowments that form a foundation for success in the long-term protection of these sites. However, many challenges arise after areas are protected or mitigation sites developed for the benefit of GGS. These challenges include novel species invasions, native species habitat alteration, vegetation community succession and management, securing water delivery and maintenance of water distribution systems, and site-specific challenges related to preserve location and design. CNLM, in nine years of managing GGS habitat, has tackled these challenges and adapted to changing circumstances in an effort to provide the best possible Giant Gartersnake Symposium
Page 12 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
habitat for the GGS within the Natomas Basin. This presentation will provide the history of Preserve management and a retrospective on the issues that may not be considered fully during the development of Preserves, and future actions and research that may be necessary to continue the success of GGS Preserves.
Chapter Announcements Celebrate our 50th Anniversary with us! Sat. Oct. 15-Sun.Oct. 16, 2016 We’re hosting a campout and potluck at the historic Camp Pollock on the American River Parkway (467 Del Paso Blvd, Sacramento) to celebrate our 50th. We're aiming for a reunion-like atmosphere, and welcome past board and chapter members and their families, as well as community members to celebrate with us for the evening in a relaxing and fun way, with BBQ, sharing TWS anecdotes or perspectives over s'mores, kid’s conservation movie & wildlife tracking activities, photobooth, and much more! Our flier (with details) can be viewed here (and is attached); RSVPs requested by Mon., Oct. 3, 2016 here.
Natural Resources Symposium - Friday, November 4, 2016, Casa Gardens in Sacramento Call for presentations & Save the Date! Are you conducting biological or ecological research, management, restoration, or conservation activities in the Sacramento-Shasta Chapter Area? Are there regulations, policies or programs that wildlife professionals should hear about? Join us to exchange information, ideas, results, and progress of your work on natural communities, wildlife, and plant species. Please send 350 word abstracts to
[email protected] by Monday, Sept. 26, 2016 (plan for 20 minute talk).
Chapter Elections are approaching for 2016! We are looking to break into 2017 with a full
Executive board – there’s lots to be done to make our chapter great! We’re looking for someone to engage our northern parts of our 23 counties (Northern Representative), so if you live in the tip-toppity counties of our chapter area, we’d like you to share Chapter happenings up north, and let us know how we can better serve those areas. We are hopeful to have a tech-motivated person interested in web design to assist us with beautifying our website – and/ or serve as our Technology Chair. We also are seeking someone to assist with administering our Scholarship program! Many more options available – planning your next trainings or workshops with the Professional Development Committee, graphic design for new schwag, Conservation Affairs Committee – you make your chapter what you want! Please contact us at
[email protected] and help us do more to serve you!
Follow our chapter on Instagram from your account, or tag using @SacShastaTWS. We are also promoting our 50th anniversary with the tag #SacShasta50!
Subscribe to our mailing list!
Giant Gartersnake Symposium
Check us out!
Page 13 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
Poster Presentation Abstracts AN IMPROVED TRAPPING STRATEGY FACILITATING STATISTICALLY RIGOROUS SPATIAL AND HABITAT OCCUPANCY ANALYSES FOR THE GIANT GARTERSNAKE (THAMNOPHIS GIGAS) Eric C. Hansen1 and Brett G. Dickson2 1 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 (
[email protected], 916-921-8281) 2 Conservation Science Partners, 11050 Pioneer Trail, Suite 202, Truckee, CA 96161 Some of the most important management questions regarding giant gartersnake (Thamnophis gigas) relate to its habitat use, including the general habitat type (e.g., freshwater marsh, flooded rice, canal/ditch) and finer-scale features that can be affected by habitat management and preserve design (e.g., plant species composition, percent cover, bank slope, water depth). Spatial occupancy modeling is a powerful and reliable statistical methodology that can inform these questions, and that requires a rigorous field methodology for data collection. Because most spatial occupancy models assume that sampling units (i.e., snake traps or traplines) are independent, the conventional high-density, linear trapping strategy typically used is not ideal for this task because traps set along a common trapline are not truly independent of one another. To facilitate spatial occupancy modeling with optimal reliability and precision, we designed a stratified random trapping strategy that increases the number of independent sampling units by dividing traps among many 10-trap “clusters” rather than a few 50-trap traplines. Using ArcGIS and ground-truthing in combination, we randomly distributed the trap “clusters” among predetermined habitat strata of interest (e.g., marsh vs. open water) within all feasibly trappable areas at each study site. Initially designed for long-term performance monitoring at the Sutter Basin Conservation Bank (SBCB) in Sutter County, this strategy was also employed at the Willey Wetland Preserve (WWP) in southern Sutter County and the Volta Wildlife Area (VWA) in Merced County. In 2010, our pilot year using this strategy, capture rates within random trap “clusters” did not differ significantly from those observed at concurrently deployed 50-trap traplines used for control, indicating that snake detectability was not compromised in the process of increasing sample independence, and suggesting that a greater quality of information may be gained through stratified random trapping efforts in comparison to the traditional 50trap transect approach. Studies conducted through 2016 suggest that the probability of detection at these same sites using a stratified random sampling method is comparable to or higher than that of the 50-trap approach, thus facilitating a higher number of sites from which to analyze covariates of occupancy. STATUS AND DISTRIBUTION OF THE GIANT GARTERSNAKE (THAMNOPHIS GIGAS) IN THE SAN JOAQUIN VALLEY, CALIFORNIA Eric C. Hansen, Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 (
[email protected], 916-921-8281) The giant gartersnake (Thamnophis gigas) is a federal- and state-listed species endemic to California’s Great Central Valley. Historically associated with low-gradient streams and the wetlands and marshes of the valley floor, giant gartersnake populations in the San Joaquin Valley are experiencing precipitous declines associated with deteriorating habitat quality and perennial wetland loss. Once plentiful in areas such as Mendota, Los Banos, and Volta and presumed extirpated from areas to the south, giant gartersnakes are recently known from only a small number of localities in the central San Joaquin Valley. Studies funded by the Central Valley Project Conservation Program and Central Valley Project Habitat Restoration Program from 2006-2008 suggested that contemporary giant gartersnake populations were limited to areas south of the San Joaquin River, and that populations at Mendota Wildlife Area and Grasslands Ecological Area had declined more rapidly than expected. At this time, with the exception of Volta Wildlife Area in Merced County, all historically-occupied giant gartersnake habitats appeared to contain only sexually mature adults, indicating a skewed size distribution typical of declining or senescing populations. Studies funded by the Central Valley Project Habitat Restoration Program, California Department of Fish and Wildlife, and the Bureau of Reclamation in 2015 and 2016 suggest that giant gartersnakes may now be extirpated from all but Volta Wildlife Area. Though water quality may play a role, a lack of water during the snake’s critical spring and summer active season provides perhaps the Giant Gartersnake Symposium
Page 14 of 15
September 21, 2016
Sacramento-Shasta Chapter of the Wildlife Society
simplest explanation for this decline. At present, only Volta Wildlife Area appears to support a giant gartersnake concentration characterized by a relatively normal age/size distribution. This concentration occurs in Field 10, one of the only places within the region possessing ample water during the giant gartersnakes’ spring and summer active season during California’s recent drought. STATUS AND RELEVANCE OF THE GIANT GARTERSNAKE (THAMNOPHIS GIGAS) AT THE COSUMNES RIVER PRESERVE Eric C. Hansen1 and Sara Sweet2 1 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 (
[email protected], 916-921-8281) 2 The Nature Conservancy, 13501 Franklin Blvd., Galt, CA 95632 Formerly extending throughout the lower portions of Badger Creek in southern Sacramento County, the range of the Badger Creek giant gartersnake (Thamnophis gigas) population has apparently shrunk in recent decades to include only the isolated marsh forming at the confluence of Badger and Willow Creeks at the Cosumnes River Preserve. Commonly referred to as Snake Marsh, this isolated population represents the core of core giant gartersnake density within the eastern Delta. Recent analyses suggest that this population exhibits the highest genetic diversity throughout the species’ extant range. As such, this population has become an important element of conservation planning, which relies not only on the persistence of this population for maintaining genetic diversity, but also as a potential gene bank to be used for repatriating snakes to areas of former occupation in the highly compromised San Joaquin Valley. Over recent decades, this population has been subjected to threats ranging from the expansion of invasive water primrose (Ludwigia hexapetala) to water shortages limiting available habitat during the snake’s crucial active season. This presentation highlights the history of known giant gartersnake distribution throughout the Cosumnes River watershed, efforts to identify and ameliorate potential causes of decline, and the relevance of this population to the rangewide conservation of the species. VARIATION IN AGE AT FIRST REPRODUCTION AND FECUNDITY IN GIANT GARTERSNAKES Rick D. Scherer1 and Eric C. Hansen2 1 Conservation Science Partners, 5 Old Town Square, Suite 205, Fort Collins, CO 80524 (
[email protected], 970-484-2898) 2 Consulting Biologist, 4200 N. Freeway Boulevard, Suite 4, Sacramento, CA 95834 Although recent progress has been made in our understanding of the demography of giant gartersnakes, we still have little information on demographic rates related to reproduction. From 2009 to the current field season, we captured females from across the contemporary range of the species. We conducted radiographs on over 200 females and recorded counts of the number of fetuses in each female. We use these data to explore variation in size at first reproduction and average fecundity across individuals.
Giant Gartersnake Symposium
Page 15 of 15
September 21, 2016
