Eradication and Control of the African Clawed Frog (Xenopus Laevis) on Irvine Ranch Land Reserve, Orange County, California, 2003

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Eradication and Control of the African Clawed Frog (Xenopus laevis) on Irvine Ranch Land Reserve, Orange County, California, 2003

Final Report March 2004

Prepared for:

The Nature Conservancy, Irvine Ranch Land Reserve – Trish Smith The Irvine Company – John Graves, Steve Letterly, and Sat Tamaribuchi

Status Report to The Irvine Company and The Nature Conservancy. Study funded through the 2003 Irvine Ranch Environmental Enhancement Fund Program (TNC Contract #IEE110602)

U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY WESTERN ECOLOGICAL RESEARCH CENTER

Eradication and Control of the African Clawed Frog (Xenopus laevis) on Irvine Ranch Land Reserve, Orange County, California 2003

By T’Shaka A. Touré1, Adam R. Backlin1, and Robert N. Fisher2

U.S. GEOLOGICAL SURVEY WESTERN ECOLOGICAL RESEARCH CENTER

Draft Report

Prepared for: The Nature Conservancy (Contract # 11.06.02 Irvine Enhancement) The Irvine Company

1San Diego Field Station – Irvine Office USGS Western Ecological Research Center 2883 Irvine Blvd Irvine, CA 92602

2San Diego Field Station – San Diego Office USGS Western Ecological Research Center 5745 Kearny Villa Road, Suite M San Diego, CA 92123

Sacramento, California 2004

U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, SECRETARY

U.S. GEOLOGICAL SURVEY Charles G. Groat, Director

The use of firm, trade, or brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

For additional information, contact:

Center Director Western Ecological Research Center U.S. Geological Survey 7801 Folsom Blvd., Suite 101 Sacramento, CA 95826 iii TABLE OF CONTENTS Executive Summary ...... 1

Introduction ...... 1

Study Purpose ...... 3

Objectives ...... 3

Methods ...... 3 Study Area and Site Selection...... 3 Reconnaissance Surveys ...... 4 Removal Methods ...... 4

Results ...... 6 Clawed Frog Removal Results...... 9 Removal Methods Comparisons...... 9 Discussion ...... 10

Management Recommendation ...... 12 Clawed Frog Eradication ...... 13 Recommended Course of Action...... 15 Regional Land and Water Management ...... 15

Acknowledgements ...... 17

Literature Cited ...... 18

Tables Table 1. Summary of African clawed frog (ACF) presence and native species by site...... 20 Table 2. Summary of African clawed frog (ACF) removal by site and month. If no traps were set out, one day of visual surveys were conducted per month as shown...... 21 Figures Figure 1. Regional map of African clawed frog study area 2002-2003...... 22 Figure 2. Map of African clawed frog study area 2002-2003...... 23

Figure 3. Aerial photograph of Sand Canyon Reservoir...... 24 Figure 4. Photograph of Strawberry Creek...... 25 Figure 5. Photograph of Turtle Rock Creek ...... 26 Figure 6. Photograph of Turtle Rock Pond ...... 27 Figure 7. Photograph of Bommer Canyon Pond...... 28 Figure 8. Photograph of Shady Canyon Golf Pond 1 ...... 29 Figure 9. Photograph of Strawberry Pond ...... 30

Appendix Appendix 1. Contact list of organizations...... 31 iv

This report should be cited as:

Touré, T. A., A. R. Backlin, and R. N. Fisher. 2004. Eradication and Control of the African Clawed Frog (Xenopus laevis) on Irvine Ranch Land Reserve, Orange County, California 2003. U.S. Geological Survey final report. 31 pp.

v EXECUTIVE SUMMARY The African clawed frog (Xenopus laevis) is an exotic species from sub-Saharan Africa that has invaded and established populations in regions of southern California. This exotic threatens native amphibian and reptile species through increased predatory pressure and competition for food and habitat. From July 2002 through July 2003, we conducted studies on a portion of Irvine Ranch Land Reserve in the San Joaquin Hills of Orange County to: 1) determine the distribution of clawed frogs in Sand, Shady, and Bommer Canyons; 2) capture and remove clawed frogs from invaded habitats; and 3) monitor the effectiveness of various techniques used to remove clawed frogs. We sampled a total of thirteen sites, eight of which had sufficient water and habitat suitable for clawed frogs. Of the eight sites with water we detected clawed frogs in seven. The remaining five sites were in the dry creeks and tributaries. Over the course of 189 days of field work we captured and removed over ten thousand clawed frog tadpoles, juveniles, and adults. Removal methods investigated included dip nets, cast nets, seines, and baited and un-baited minnow traps. We also assessed the value of lowering the water level at a major waterbody in the study area, Sand Canyon Reservoir, to aid in clawed frog removal. We found the efficient removal of clawed frogs requires a combination of techniques. Juvenile and adults are captured in minnow traps, while tadpoles are most easily captured using cast nets. Draining Sand Canyon Reservoir dramatically reduced the subsequent capture rate of adults and juveniles. We conclude our report with recommendations regarding continued clawed frog removal. Based on our initial results, we have designated sites as primary removal, secondary removal, and monitoring site. Primary removal sites are areas where small populations of clawed frogs exist and complete eradication could be achieved with further effort. Secondary removal sites are areas where larger populations of clawed frogs exist and the level of effort necessary will be higher to achieve complete eradication. A monitoring site is an area where surveys should be conducted to detect the presence or absence of clawed frogs.

INTRODUCTION The African clawed frog, Xenopus laevis, (hereafter, clawed frog) has smooth skin, a flat and stout-body, and small head with eyes on top of the head. This amphibian has an aquatic lifestyle unlike any native California amphibian. They reside in a wide variety of

1 aquatic habitats including rivers, lakes, reservoirs, ponds, streams, creeks, swamps, flooded pits, ditches and wells. No habitat preference has been detected other than needing a consistent source of water. It is commonly found in aquatic habitats ranging from stagnant ponds to fast moving streams (Tinsley and Kobel 1996). Although, clawed frogs are essentially and primarily aquatic, overland migration has been documented (USGS San Diego Field Station Staff, unpublished data).

Its native range encompasses most of sub-Saharan Africa and the species is commonly encountered in South Africa, Swaziland, Lesotho, Zimbabwe, Botswana, and Namibia (Lobos and Measey 2002). It was introduced in the United States during the 1940’s and 1950’s as a laboratory animal for human pregnancy testing (Tinsley and Kobel 1996). Established populations in the United States occur in Virginia, Arizona, and California. The first documentation of this exotic as a feral animal in California was in 1968 in Orange County in the Westminster flood control channel (St. Amant et al. 1973; McCoid and Fritts 1993).

The clawed frog is now widely distributed in southern California. It has been documented in drainages in Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura Counties (Fisher and Case 2000; McCoid and Fritts 1980, 1989, 1993; McCoid et al. 1993; Stebbins 1985; Tinsley and Kobel 1996). Most authorities on the clawed frog believe the spread of this exotic species was, in part, due to intentional or accidental release of animals from laboratory stocks and pet animals (Crayon, in press). Aquatic habitats occupied by clawed frogs rarely contain abundant native amphibians (Mahrdt and Knefler 1972; Lafferty and Page 1997; USGS San Diego Field Station Staff, unpublished data), apparently due to predation or competition. Further, the clawed frog has been observed to rapidly reach high densities in newly created habitats, such as golf course ponds. This and other exotics represent a growing threat to native wildlife, and efforts to control their numbers and limit their spread are needed to protect species that utilize the same habitats.

2 STUDY PURPOSE The study area is located in the coastal region of the Irvine Ranch Lands Reserve comprising grasslands along with steep slopes supporting coastal sage scrub and chaparral habitat. The area also supports the only know western pond turtle population and in 1995 the first documentation of the western spadefoot in Shady Canyon was reported (LSA 1995). Subsequently, in 2001 clawed frog tadpoles were detected in rock pools (tenajas) in Shady Canyon during the development of the Shady Canyon Golf Club in 2001. The clawed frog tadpoles were detected at the same pool locations that once supported the western spadefoot toad, a listed federal species of concern, a California Department of Fish and Game (CDFG) species of special concern, Bureau of Land Management (BLM) sensitive species, and Natural Community Conservation Plan (NCCP) County of Orange target species. Due to the displacement of the western spadefoot toads specifically in Shady Canyon and the possible exotic threats within San Joaquin Hills the clawed frog was identified as a potential threat to the long-term survival of native amphibians and reptiles. In response, The Nature Conservancy and The Irvine Company identified funding from the Irvine Ranch Environmental Enhancement Project to be directed to this study.

OBJECTIVES The objectives of this project were: 1) to determine the distribution of clawed frogs in Sand, Shady, and Bommer Canyons; and 2) to reduce densities of clawed frogs from occupied habitats. These objectives were accomplished by conducting surveys and implementing eradication techniques over a course of one year. Data collected will be used to assess long-term control and monitoring protocols in order to alter the reproductive success of clawed frogs.

METHODS Study Area and Site Selection The study area for this project was Sand Canyon Reservoir and the streams that drain into it, including Shady, Bommer and Sand Canyons (Figure 1). This site is located at San Joaquin Hills in coastal Orange County. We targeted this study area because it was

3 known to be invaded by clawed frogs, and to include a variety of permanent water resources. Based on our inspection of topographic maps we identified thirteen sites with potentially permanent water (Figure 1). We then conducted initial reconnaissance surveys of these sites. Survey sites included the following habitat types: reservoir, tributary, creek, and pond.

Reconnaissance Surveys To determine the location of permanent water potentially harboring clawed frogs and identify suitable areas for trapping, we first conducted initial reconnaissance surveys of the thirteen sites. Initial surveys consisted of slowly walking the entire shoreline of ponds and reservoirs or the entire length of streams. During these visits technicians visually searched for evidence of clawed frogs (e.g., frogs surfacing to gulp air), and dip netted in suitable aquatic habitats (see detailed dip netting protocol below). We determined the precise location of each survey site in the field with a Global Positioning System (GPS), and compiled detailed notes on the distribution of standing water resources within each survey site. Those sites with clawed frogs or standing water were designated as survey sites and were later returned to for thorough trapping and removal efforts.

Removal Methods Minnow traps, dip netting, cast netting, seining, and temporary dewatering were all used to eliminate clawed frogs in the study area. Captured exotic species were euthanized and disposed of according to USGS, Western Ecological Research Center, San Diego Field Station protocols. Native species were released at the point of capture unharmed. Removal techniques used are briefly described below.

Minnow traps – We used two types of double-ended minnow traps: wire mesh traps and collapsible nylon mesh traps. The funnels of the cloth wire minnow traps were modified to a larger size (approximately 35 mm in diameter). We set traps on the bottom of reservoirs, ponds and creeks where the water was at least 25 cm deep so the funnel openings were underwater. Based on the extent of standing water within the survey site, up to 35 traps were used. Sites with adequate water levels were trapped up to once per

4 month for 2-10 days; traps were emptied every other day. Traps were either baited with sardines or un-baited. Because there was no noticeable difference between baited and unbaited minnow traps, after initial trials the use of bait was discontinued.

Dip netting – We used wooden handled, nylon mesh dip nets to capture adult, juvenile, and tadpole clawed frogs in creeks, small pools of standing water, and along the shallow margins of ponds. At least 10 sweeps were made to adequately sample each potentially suitable microhabitat; however, there was no limit if clawed frogs had already been detected. If no clawed frogs were detected we moved to the next potentially suitable microhabitat. Although adults were captured by dip netting, a majority of the captures were tadpoles and metamorphs (Crisafulli 1997; Touré and Middendorf 2002).

Cast netting – We used a cast net with a 12 ft radius. This technique required two people. The net has a rope located in the mid-section that is used to cast and retrieve the net. From shore two-people would cast the net into the water, and it would open like an umbrella and slowly settle to the bottom of the reservoir or pond. The mid-section rope was then pulled to close the net around the trapped animals and retrieve the net from the water (Dahlem 1996). This technique was useful in the capture tadpoles, especially in deep ponds and away from the shoreline.

Seining – A minnow seine is a long wide sheet of netting (approximately 1.3 m wide by 5 m long) with poles attached to the ends. Seining is effective for sampling large areas of water less than one meter deep. This technique requires two people. The seine is stretched between the poles and pulled through the area to be sampled by slowly walking through the body of water. Care is taken to keep the net on the pond bottom, agitating the bottom substrate and capturing tadpoles and juveniles (Wright and Wright 1949; Crisafulli 1997; Heyer et al. 1994). This technique has limitations in deep or heavily vegetated areas and when the substrate is complex (i.e., cobble and boulder substrate). Due to its limitations seining was not used after the initial trials.

Dewatering – Because it is difficult to capture all individuals of any species in large waterbodies such as Sand Canyon Reservoir we contacted the Irvine Ranch Water

5 District to request that the pond be drained to 1) reduce the total volume of water; 2) increase the density of clawed frogs and our sampling efficiency; and 3) to disrupt the clawed frogs reproductive cycle by killing tadpoles and limiting breeding opportunities. Between October 2002 and March 2003 this reservoir was drained from 700 acre feet (with a depth of approximately 10 m) to 50 acre feet (with a depth of approximately 1.5 m).

RESULTS The surveyed sites consisted of one reservoir, two tributaries (areas where water from urban runoff flows into the reservoir), five creeks, and six ponds (the Shady Canyon Golf Club site included two ponds) (Figure 1). Eight of these thirteen sites contained water during reconnaissance surveys (Table 1). Clawed frogs were found at eight of these sites, all of which contained permanent water. Below we summarize the basic habitat and species observation data collected at each site during reconnaissance surveys. Species scientific and common names used in this report are consistent with the most current taxonomic information available (www.itis.usda.gov).

RESERVOIRS Sand Canyon Reservoir – This reservoir has a maximum surface area of approximately 50 acres with an approximate depth of 10 m and is situated in the middle of Strawberry Farms Golf Club (Figure 2). The reservoir is managed by the Irvine Ranch Water District and has a 960 acre feet capacity, drainage area of approximately 7 square miles, and an earthen dam 58 feet in height. Both, exotic (clawed frog) and native (western toad (Bufo boreas) and western skink (Eumeces skiltonianus)) species were documented in the reservoir.

TRIBUTARIES Sand Canyon Reservoir Tributary – These tributaries were dry and no amphibians or reptiles were detected within the 160 m long reach that we surveyed (Table 1).

Sand Canyon Reservoir / Turtle Rock Tributary – Creeks within these tributaries contained temporary water from urban run off; however, no amphibians or reptiles were

6 detected within the 300 m survey reach. These tributaries are within the residential community of Turtle Rock (Table 1).

CREEKS Bommer Canyon Creek (City of Irvine Southern Open Space Preserve) – We found no standing water in this creek; however, the Pacific treefrog (Pseudacris regilla) was documented here. We surveyed approximately 1,200 m of the creek (Table 1).

Sand Canyon Creek (Strawberry Farms Golf Club) – This creek runs below a cemented spillway that is adjacent to Strawberry Pond. This creek was dry and no amphibians or reptiles were detected within the 300 m survey reach (Table 1).

Shady Canyon Creek – This creek runs through a riparian corridor within Shady Canyon Golf course and adjacent Shady Canyon City of Irvine Southern Open Space Preserve. This creek was dry and no amphibians or reptiles were detected within the 500 m survey reach (Table 1).

Strawberry Creek – This creek runs through a patchy forested area upstream of the reservoir dam in the middle of Strawberry Farms Golf Club (Figure 3). We surveyed approximately 800 m of this creek (Figure 1). This stream consistently contained water, but it was only deep enough to minnow trap in select locations. We detected clawed frogs in this creek.

Turtle Rock Creek – This creek is situated in the middle of a public park, Turtle Rock Community Park (Figure 4). The creek is accessible to the public and drains into Turtle Rock Pond (Figure 5). This creek was narrow and shallow (with a maximum depth of approximately 3 meters) but consistently contained flowing and/or standing water. Both, exotic (clawed frogs, crayfish (Procambarus clarkii), mosquito fish (Gambusia affinis)) and native (Pacific treefrog) species were documented in this site.

7 PONDS Bommer Canyon Pond – This pond is situated at the base of Bommer Canyon in the City of Irvine Southern Open Space Preserve and surrounded by native vegetation consisting of willows (Salix spp.) and mule fat (Baccharis glutinosa). The pond has a maximum surface area of approximately 2.5 acres with an approximate depth of 2-3 m and drains an area of approximately 950 acres (Figure 5). Although we detected primarily exotics (clawed frogs, crayfish, mosquito fish), native (Pacific treefrogs, western toads, a western skink, a San Diego gopher snake (Pituophis catenifer), and an unidentified turtle) species were also detected (Table 1).

Shady Canyon (Turtle Pond) – This created pond is situated in City of Irvine Southern Open Space Reserve. Turtle Pond has a maximum surface area of approximately 1 acre with a depth of approximately 3.5 m. It is surrounded by native vegetation consisting of willows and mule fat. We detected no clawed frogs in this pond. However, to avoid harming western pond turtles (Emys marmorata) recently reintroduced here we did not use minnow traps. Non-target species detected included western pond turtles, Pacific treefrogs, and western toads (Table 1). This was the only pond where we did not detect clawed frogs.

Shady Canyon Golf Club Ponds – This site includes two ponds situated in a golf course, Shady Canyon Golf Club, occupying 300 acres of land with a natural riparian and foothill slopes (Figure 6). The maximum surface area for each pond is approximately 4.5 and 3.5 acres respectively with a depth of approximately 4-5 m. The ponds are within coastal sage scrub habitat and adjacent the City of Irvine Southern Open Space Preserve. We detected primarily exotic species (clawed frogs, crayfish, mosquito fish); only one native amphibian, the western toad was documented (Table 1).

Strawberry Farms Golf Club Pond – This pond is situated in a 6,700 yard golf course, Strawberry Farm Golf Club (Figure 7). This pond has a maximum surface area of approximately 1 acre with a depth of approximately 2.5 m. The site includes rolling greens surrounded by natural vegetation and hillsides studded with granite boulders and an artificially created waterfall. Although large numbers of exotics (clawed frogs,

8 bullfrogs (Rana catesbieana), crayfish, mosquito fish) were detected at this site, natives (western toad tadpoles and a western pond turtle hatchling) were also occasionally detected.

Turtle Rock Pond – This pond is situated on five-acres of land in the City of Irvine Turtle Rock Nature Center (Figure 5). The pond has a maximum surface area of approximately 1.5 acres with a depth of approximately 4 m. The pond is surrounded by native vegetation consisting of oaks (Quercus spp.), willows, and mule fat. Both exotic (clawed frogs, crayfish, mosquito fish, red-eared slider turtles (Trachemys scripta)) and native (Pacific treefrog) species were documented at this site.

Clawed Frog Removal Results In 189 total days of field work we captured and removed 10,417 clawed frogs from the project area. The composition of captures was 52% adults, 31% juveniles and 17% tadpoles. The minimum number of clawed frogs captured at an occupied site was 74 at Turtle Rock Creek, while the maximum number was 3,147 at Sand Canyon Reservoir (Table 2). We captured tadpoles at five of the occupied sites, indicating that breeding is occurring widely across the study area (the only exceptions were Shady Canyon Golf Ponds and Turtle Rock Creek). Based on the numbers of clawed frogs and rate of capture we assigned each of the thirteen sites as primary removal, secondary removal or monitoring site for future work (Table 2).

Removal Methods Comparisons There were four capture methods tested during this project. Of these all but seining was effective in capturing and removing clawed frogs from the study area.

Minnow trapping was an effective method for capturing adult and juvenile clawed frogs in deep aquatic habitats. In each of two ten day trapping efforts at Shady Canyon Golf Ponds we minnow trapped and removed approximately 1,500 adults. This translates to an average capture rate of approximately five clawed frogs/minnow trap/day. In contrast we rarely captured clawed frog tadpoles in minnow traps.

9 Cast netting was the most effective means to capture clawed frog tadpoles. In Turtle Rock Pond there were only small numbers of adults captured with minnow traps and the pond margin was too steep and deep for effective dip netting or seining. However, by cast netting in this pond we were able to capture and remove approximately 426 clawed frog tadpoles per day.

In shallow water bodies or along the margins of deep water bodies, dip netting was an effective means for capturing both juvenile and adult clawed frogs. Because dip netting is most appropriate in shallow water, it was primarily used in the creeks. However, following the draining of Sand Canyon Reservoir dip nets were highly effective for capturing clawed frogs in the small pools that remained: we captured 300-350 metamorph and juvenile clawed frogs per day by dip netting.

As mentioned above, during this first year of field work we investigated the value of habitat dewatering in the removal of clawed frogs. Following the complete draining of Sand Canyon Reservoir only small pools of water remained and we netted many clawed frogs in these areas. However, due to deep accumulated sediments the complete drying of the basin was not achieved and clawed frogs burrowed into these sediments. Although draining did not result in complete eradication of clawed frogs, comparing data from before and after suggests that densities were dramatically reduced (Table 2). For example before draining we captured approximately 133 juvenile and adult clawed frogs per day, while after draining we captured approximately 24 per day.

DISCUSSION When exotic plants and animals become established in new areas they disrupt the natural balance of ecosystems, causing losses in native species diversity and altered community composition (Lobos and Measey 2002). This appears to be true for the area around Sand Canyon Reservoir, where the clawed frog has become widely established and native species of amphibians and reptiles are rare. Because this region includes a mosaic of urban development and naturally preserved open space land, special challenges exist for maintaining native diversity. Based on this first year of field work we now know: 1) where clawed frogs occur; 2) their relative densities; and 3) the level of effort needed to

10 reduce their densities. To protect and recover native diversity in this urbanized landscape, habitat management, including the control of exotics, is essential.

Our trapping efforts indicate that clawed frogs have reached massive densities within virtually all permanent water bodies in the study area. Even after removing thousands of clawed frogs from some sites our captures did not decline detectably (e.g., Shady Canyon Golf Ponds, Strawberry Pond). Draining Sand Canyon Reservoir appears to have been the most successful of our efforts to reduce clawed frog densities, and this method would probably be the most efficient means to reduce clawed frog densities in any pond. However, using increased numbers of minnow traps would also enhance capture efficiency.

In the course of our work last year we also made several important observations incidental to our focused field work. First, although McCoid and Fritts (1980) previously suggested that clawed frogs are more of a nuisance than a major threat to native populations, our observations suggest that clawed frogs are limiting native populations of reptiles and amphibians in the study area. Although we observed a variety of native species, we did not detect breeding populations of these species in any ponds containing clawed frogs. In addition, it appears that even though our initial efforts did not eradicate clawed frogs, they may have reduced their densities sufficiently to benefit native species. For example, Pacific treefrogs, western toads, and a hatchling western pond turtle, were detected at ponds towards the end of our first year of work. Thus it is appears that native species will re-establish rapidly as clawed frogs are removed from the system.

The colonization of native species to created and modified habitats are an essential component of wildlife restoration and enhancement (Touré and Middendorf 2002). Where clawed frogs are present they are a major nuisance and hinder colonization by natives. In a time period when conservation groups and land managers are working to restore functioning native systems, the removal of exotics and the re-establishment of native species can be used to measure the success of these efforts.

11 The other major observation was that human activities continue to facilitate the movement of clawed frogs within the landscape (McCoid and Fritts 1980). Opportunities for clawed frog dispersal occur via water transport or silt removal. Water from invaded clawed frog habitats appears to be used to fill newly created water features, leading to the rapid establishment of new populations. For example the Shady Canyon Golf Ponds, where we captured 2885 adult clawed frogs, were newly constructed during May 2001. We have also found that silt removed from invaded ponds often contains live clawed frogs, and thus sediment removal can act as another opportunity for clawed frog dispersal. For example, following the deposition of silt in previously un-invaded areas we found clawed frogs in small rock pools and shallow creeks. Although we removed over 10,000 clawed frogs during our 2002-2003 field season, additional work is necessary to further reduce their densities and potentially eradicate some populations. In addition to the sites mentioned in this report clawed frogs were detected but not trapped in San Joaquin Hills (e.g., Crystal Cove State Park and Laguna Lakes).

By disrupting the breeding of clawed frog and establishing systematic trapping regimes their densities can be reduced. Natives should respond by recolonizing these habitats and establishing more sizeable populations. There are small patchy forested areas within Sand, Shady, and Bommer Canyons that appear to provide refugia for native species. Therefore, for most species natural immigration should prevent the need for additional management in the form of reintroductions.

MANAGEMENT RECOMMENDATIONS Based on the results of our first year of field work we recommend two parallel courses of action to control clawed frogs within the study area and beyond. First, now that we understand the distribution of clawed frogs and the relative efficiency of potential control measures, a second season of focused work to eradicate clawed frogs from ponds that are lightly invaded and further reduce densities elsewhere is needed. Second, because clawed frogs generally occupy constructed waterbodies, and water and silt management are key to their dispersal among these habitats, regional coordination among the

12 responsible parties is needed to control this problem. We can control these populations but continued removal and cooperative land and water management is necessary.

Clawed Frog Eradication Because clawed frogs are essentially completely aquatic, if we can eliminate them from a given waterbody and prevent their reintroduction, removal should be permanent. However, clawed frogs can be reintroduced if current management practices are not modified. Below we summarize our recommendations for the continued reduction and removal of clawed frogs from habitats around Sand Canyon Reservoir. Based on estimated densities from last years work we divided these sites into primary removal, secondary removal, and monitoring site. We made recommendations for each category as a group. In general, it appears that clawed frog removal will require draining of the regional permanent water habitats. Following eradication we recommend that regular draining of these sites be adopted as part of a long-term management program to promote native diversity.

Primary Removal Sites: Two sites, Turtle Rock Pond and Turtle Rock Creek, appear to contain much smaller populations of clawed frogs (Table 2). Given their small size it is likely that complete eradication could be achieved with further effort. We recommend draining these sites in early summer and keeping them dry until the following winter. The process should be repeated until no clawed frogs are captured or observed during one week of minnow trapping in the spring.

Secondary Removal Sites: Because the level of effort necessary will be higher, we discuss Sand Canyon Reservoir separately from other secondary sites.

Sand Canyon Reservoir: This is the largest waterbody in the area and has likely been the source of clawed frog introductions to many other sites. Permanent removal of clawed frogs from this region will hinge on eliminating them from this reservoir. But due to its size this will be a major undertaking. We have recommended that the reservoir be totally drained and kept dry for an entire year, and the Irvine Ranch Water District has considered this as a possibility for 2005. Concurrent drying of as many ponds and

13 connected waterbodies as possible in the region would maximize the potential for complete eradication.

Steps should also be taken to have the silt deposit, where the clawed frogs will burrow removed to an offsite landfill (with no waterbodies nearby). Upon refilling, Sand Canyon Reservoir should be minnow-trapped intensively (e.g., ten days with a hundred traps) to assess the success of draining and remove frogs that may have survived. Further plans beyond this point will depend on the number of clawed frogs observed in this initial trapping. For long-term success, intermittent draining (e.g., at least once every two to five years) should be adopted as part of a regular management scheme.

Ponds: Ponds such as Bommer Pond and Strawberry Pond contained the next largest populations of clawed frogs. Due to the smaller size of these sites, complete eradication will be more easily achievable. Priority should be given to sites that are not hydrologically connected to other invaded habitats. We recommend that a regular drying schedule be adopted (e.g., at least every two to five years) to prevent re-establishment of clawed frogs or other non-natives. At this point ponds should be totally drained and maintained dry for three to six months during the summer. Afterwards the ponds should be monitored and trapped, to determine the success of the draining program. Draining should be repeated annually until no clawed frogs are detected. When silt is removed from invaded ponds this material should be placed far from any permanent waterbody at least until the material is completely dry.

For those land managers not receptive to pond drainage, introduction of predatory fish (centrachids i.e., black crappie (Pomoxis nigromaculatus) and green sunfish (Lepomis cyanellus)) to prey upon clawed frog tadpoles and juveniles (McCoid and Fritts 1980; McCoid et al. 1993; Prinsloo et al. 1981) may achieve population reduction. Upon reduction of clawed frogs the predatory fish could be captured and removed by using gill nets.

Monitoring Sites: Some creeks and drainages are connected to habitats containing clawed frogs, but are normally dry. These sites should be sampled for clawed frogs at least once

14 annually after heavy rains that leave standing water. Sampling should be by visual encounter surveys along the entire length of each reach, using dip nets to sample pools.

Recommended Course of Action Goals: A) Identify where African clawed frogs occur vs. where they do not occur in the entire Irvine Ranch Open Space Reserve Lands as follows: 1) Locations where no clawed frogs occur 2) Locations where clawed frogs need to be controlled 3) Locations where clawed frogs are not a problem but present B) Determine the boundaries of the African clawed frog population. C) Get baseline data for African clawed frogs in the Irvine Ranch Land Reserve. D) Determine the best management plan to control African clawed frogs from spreading any further. E) Provide recommendations on the control of African clawed frogs in the Irvine Ranch Land Reserve and adjacent areas.

Steps: Conduct presence/absence surveys with minnow traps and dip netting at new locations in the coastal and central regions of the reserve. African clawed frog survey sites will be conducted in the following creeks and a reservoir: Buck Gully Creek, Los Trancos Creek, Muddy Creek, Moro Creek, Boat Creek, Canyon Acres Creek, Emerald Creek, Laurel Creek, Willow Creek, Tustin Marine Base, Rattlesnake Reservoir, Siphon Reservoir, Peters Canyon Reservoir, and San Joaquin Reservoir.

Regional Land and Water Management More generally, during last year’s field work we have seen the need for regional coordination of land and water management. We are concerned that even if we can remove clawed frogs from a given site, currently they could easily be reintroduced from nearby or even distant habitats (e.g., via dredged silt). We recommend that a formal working group composed of members of the responsible agencies and interested parties be created to address this and other habitat management issues in Orange County Watersheds. To prevent further movement of clawed frog populations the following agencies should be represented: California Department of Fish and Game, City of Irvine Public Works, City of Irvine Open Space Reserve, City of Irvine Animal Care Center, Irvine Ranch Water District, Nature Reserve of Orange County, The Irvine Company, and The Nature Conservancy.

15 As an example, it appears that water used to fill golf course ponds may arrive containing clawed frogs. We recommend that prior to translocation of water into sites capable of supporting clawed frogs, such as ponds, the water should be sampled for clawed frogs. As discussed above, silt dredging also appears to be a means by which clawed frogs have invaded new sites in the past. Simple guidelines could reduce future problems, but regional cooperation is needed. In the Sand Canyon Watershed we now know the invaded habitats, and any removal of water or silt from these habitats should follow specific procedures until this invasive species is eradicated. The clawed frog is a threat to native wildlife; however, they can be removed from this system completely, but this will require a sustained and coordinated effort.

16 ACKNOWLEDGEMENTS This project would not have been successful without support and assistance from many individuals and organizations. Funding for this project was provided by The Irvine Company and the Donald Bren Foundation through the Irvine Ranch Environmental Enhancement Program, administered by The Nature Conservancy. We thank Trish Smith and Melissa Ervin, The Nature Conservancy; Carl Ballard, Steve Habiger, Greg Hiertz, and Thomas Roberts, Irvine Ranch Water District; Sharon Heider, Cathy Tucker, and Amy Litton, City of Irvine Open Space; Joe Dillman, City of Irvine Public Works; Ron Edwards, City of Irvine Animal Care Center; and Jeff Brown, Shady Canyon Golf Course. Special thanks are due to the USGS-WERC San Diego Field Station staff for their contributions of field work, map production, and insightful dialogue, especially Denise Clark, Sara Compton, Josh Hadley, Liz Gallegos, Carlton Rochester, Roland Sosa, and volunteer Lorraine Kuemerle. We also thank Peter Trenham for his timely review and edits which have enhanced this document.

17 LITERATURE CITED

Crayon, J. J. (In press). Species account: Xenopus laevis. In Lannoo, M.J. (ed.) Status and Conservation of U.S. Amphibians. Smithsonian Institution Press Washington, DC.

Crisafulli, C. M. 1997. Chapter 6. A habitat-based method for monitoring pond-breeding amphibians, pp.83-111. In Olson, D. H., W. P. Leonard, and R. B. Bury (eds.) 1997. Sampling Amphibians in Lentic Habitats: Methods and Approaches for the Pacific Northwest. Northwest Fauna Number 4. Society for Northwestern Vertebrate Biology. Olympia, Washington. 134 pp.

Dahlem, T. 1996. How to make & mend cast nets. Great Outdoors Publishing Company. St. Petersburg, Florida. 96 pp.

Fisher, R. N. and T. J. Case. 2000. A field guide to the reptiles and amphibians of coastal southern California. Website: http://ratbert.wr.usgs.gov/fieldguide/

Heyer, W. R., M. A. Donnelly, R. W. McDiarmid, L. C. Hayek, and M. S. Foster. 1994. Measuring and monitoring biological diversity. Smithsonian Institution Press, Washington, D.C. 364 pp.

Lafferty, K. D. and Page, C. J. 1997. Predation on the endangered tidewater goby, Eucyclogobius newberryi, by the introduced African clawed frog, Xenopus laevis, with notes on the frog's parasites. Copeia 1997:589-592.

Lobos, G. and G. J. Measey. 2002. Invasive populations of Xenopus laevis (Daudin) in Chile. Herpetological Journal 12:163-168.

LSA Associates, Incorporated. 1995. Orange County Western Spadefoot Survey. Unpublished report on file at USGS San Diego Field Station. 14 unpaginated pages.

Mahrdt, C., and F. Knefler. 1972. Pet or pest? Environmental Southwest 450:2-5.

McCoid, M. J. and T. H. Fritts.1980. Notes on the diet of feral population of Xenopus laevis (Pipidae) in California. The Southwestern Naturalist 25:272-275.

McCoid, M.J. and T. H. Fritts. 1989. Growth and fat body cycles in feral populations of the African clawed frog, Xenopus laevis (Pipidae), in California with comments on reproduction. The Southwestern Naturalist 34:499-505.

McCoid, M.J. and T. H. Fritts. 1993. Speculation on colonizing success of the African clawed frog, Xenopus laevis (Pipidae), in California. South African Journal of Zoology 28(1):9-61.

18 McCoid, M.J., G. K. Pregill, R.M. Sullivan. 1993. Possible decline of Xenopus populations in southern California. Herpetological Review 24(1):29-30.

Prinsloo J. F., H. J. Schoonbee, and J. G. Nxiweni. 1981. Some observations of biological and other control measures of the African clawed frog Xenopus laevis (Daudin) (Pipidae, Amphibia) in fish ponds in Transkei. Water Southern African 7:88-96.

St. Amant, J.A., F.G. Hoover, and G.R. Stewart. 1973. African clawed frog, Xenopus laevis (Daudin), established in California. California Fish and Game 59:151-153.

Stebbins, R. C. 1985. A Field Guide to Western Reptiles and Amphibians: Field marks of all species in Western North America, including Baja California, 2d ed., Houghton Mifflin Company, Boston. 336 pp.

Tinsley, R. C. and H. R. Kobel. 1996. The biology of Xenopus. Clarendon Press, Oxford 440 pp.

Touré, T. A. and G. A. Middendorf. 2002. Colonization of herpetofauna to a created wetland. Bulletin of the Maryland Herpetological Society. 38(4):99-117.

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19 Table 1. Summary of African clawed frog (ACF) presence and native species by site.

Site Name Latitude/Longitude1 ACF Water Native species seen at site Present Present Sand Canyon Reservoir N 33.64611 Y Y western toad (Bufo boreas) W 117.79669 western skink (Eumeces skiltonianus) Sand Canyon Tributary N 33.64552 N N — W 117.79861 Sand Canyon /Turtle Rock N 33.64234 N N — Tributary W 117.79843 Bommer Canyon Creek N 33.62885 N N Pacific treefrog (Pseudacris regilla) W 117.80592 Sand Canyon Creek N 33.63878 Y Y — W 117.79518 Shady Canyon Creek N 33.62812 N N — W 117.79588 Strawberry Creek N 33.63878 N N — W 117.79518 Turtle Rock Creek N 33.63179 Y Y Pacific treefrog (Pseudacris regilla) W 117.80615 Bommer Canyon Pond N 33.62993 Y Y Pacific treefrog (Pseudacris regilla) W 117.80621 western toad (Bufo boreas) western skink (Eumeces skiltonianus) San Diego gopher snake (Pituophis catenifer) Unidentified turtle Shady Canyon (Turtle Pond) N 33.62284 N Y western toad (Bufo boreas) W 117.79077 Pacific treefrog (Pseudacris regilla) western pond turtle (Emys marmorata) Shady Canyon Golf Ponds N 33.62949 Y Y western toad (Bufo boreas) W 117.79739

N 33.62685 W 117.79512 Strawberry Pond N 33.64752 Y Y western pond turtle (Emys marmorata) W 117.79367 Turtle Rock Pond N 33.63340 Y Y Pacific treefrog (Pseudacris regilla) W 117.80540

1All GPS coordinates presented in WGS84.

20 Table 2. Summary of African clawed frog (ACF) removal by site and month. If no traps were set out, one day of visual surveys were conducted per month as shown.

Total ACF Total ACF Total ACF Total ACF Total ACF Survey month (adult/juvenile/ tadpoles Sites adults Juveniles tadpoles trap /survey removed) and trap days removed removed removed removed days Aug ’02 (0/846/1) 5 days Sept ’02 (0/375/0) 2 days Oct ’02 (40/1003, 0) 10 days Jan ’03 (172/157/0) 10 days Sand Canyon Reservoir 477 2,625 45 52 3,147 Feb ’03 (188/0/0) 5 days Apr ’03 (11/43/0) 5 days June ’03 (24/37/17) 5 days July ’03 (42/164/27) 10 days

Aug ’02, Feb, ’03, July ’03 (visual surveys Sand Canyon Tributary ———3 0 only) 1 day for each month shown

Aug ’02, Feb ’03, July ‘03(visual surveys Sand Canyon /Turtle Rock Tributary ———3 0 only) 1 day for each month shown

Aug ’02,Oct ’02, Nov ’02, Apr ’03 Bommer Canyon CreekJune ’03, July ’03 (visual surveys only) 1 day — — — 6 0 for each month shown

June’03, July ’03 (visual survey only) 1 day Shady Canyon Creek ——— 2 0 for each month shown

Aug ’02 (0/155/0) 2 days Strawberry CreekOct ’02 (40/230/0) 5 days 51 404 12 7467 June’03 (11/19/12) 2 days Jan ’03, Feb ’03, Apr ’03, May ’03, June’03, Sand Canyon Creek July ’03 (visual surveys only) 1 day for each ———6 0 month shown

Aug ’02 (2/7/0) 2 days Turtle Rock CreekNov ’02 (40/0/0) 10 days 64 10 0 22 74 Feb. ’03 (22/3/0) 10 days Aug ’02 (55/48/26) 2 days Oct ’02 (45/15/0) 2 days Nov ’02 (601/0/0) 10 days Bommer Canyon Pond 889 63 776 26 1,728 Apr ’03 (13/0/0) 2 days June’03 (84/0/170) 5 days July ’03 (90/0/580) 5 days

Aug ’02 (visual survey & dip netting) 1 day Shady Canyon *(Turtle Pond) — — — 20 June’03 (visual survey & dip netting) 1 day

June’03 (1532/50/0) 10 days Shady Canyon Golf Ponds 2885 50 0 20 2,935 July ’03 (1353/0/0) 10 days Jan. ’03 (102/4/0) 5 days Feb. ’03 (385/29/0) 10 days Apr ’03 (16/5/0) 2 days Strawberry Farm Golf Pond 1,001 84 77 32 1,162 May ’03 (73/21/0) 5 days June’03 (4/9/15) 5 days July ’03 (421/16/62) 5 days Aug ’02 (1/0/0) 2 days Turtle Rock PondFeb. ’03 (26/1/0) 6 days 52 1 851 10 904 July ’03 (25/0/851) 2 days

Figure 1. Regional map of African clawed frog study area during 2002 and 2003 on Irvine Ranch Land Reserve.

Figure 2. African clawed frog survey and removal locations for 2002 and 2003. All study sites are within the Sand Canyon Reservoir Watershed, coastal region of Orange County. Dots mark ponds and reservoirs. Lines mark stream/tributary reaches sampled.

Figure 3. Sand Canyon Reservoir aerial photo taken in 1994. There have not been any structural changes to the reservoir since the taking of this photograph. No more recent aerial photos were available through USGS terra server (http://terraserver.microsoft.com).

Figure 4 Photograph of Strawberry Creek taken in October 2002. Photo is looking towards the southwest.

Figure 5. Photograph of Turtle Rock Creek taken in October 2002. Photo is looking towards the north.

Figure 6. Photograph of Turtle Rock Pond taken in November 2002. Photo is looking towards the northeast.

Figure 7. Photograph of Bommer Canyon Pond taken in November 2002. Photo is looking towards the southwest and the Bommer Canyon ridge line.

Figure 8. Photograph of Shady Canyon Golf Pond 1. Photo is looking towards the southeast and Shady Canyon.

Figure 9. Photograph of Strawberry Pond taken in September 2002. Photo is looking towards the northeast.

30 Appendix 1. Contact list of organizations.

The Irvine Company, John Graves, Steve Letterly, & Sat Tamaribuchi 550 Newport Center Drive Newport Beach, 92658

The Nature Conservancy, Trish Smith Irvine Ranch Land Reserve 2883 Irvine Blvd Irvine, California 92602

City of Irvine Animal Care Center, Ron R. Edwards 6443 Oak Canyon Irvine, California 92618

City of Irvine Open Space Reserve, Sharon Heider & Cathy Tucker One Civic Center Plaza P.O. Box 19575 Irvine, California 92623

City of Irvine Public Works, Joe Dillman 6427 Oak Canyon Irvine, California 92618

Irvine Ranch Water District, Greg Heiertz 15600 Sand Canyon Avenue Irvine, California 92618

Nature Reserve of Orange County, Lyn McAfee 15600 Sand Canyon Avenue Irvine, California 92618

Shady Canyon Golf Course, Jeff Brown 90 Shady Canyon Drive Irvine, CA 92603