FINAL REPORT 214 California Red-legged Frog Survey Mori Point and Milagra Ridge September 15, 214 Prepared by: Ruby Kwan Park Stewardship Program Golden Gate National Parks Conservancy Fort Mason Building 21 San Francisco, CA 9412 Prepared for: National Park Service Golden Gate National Recreation Area Division of Resource Management 214 California Red-legged Frog Survey 1
SUMMARY This report summarizes the results of the 213/214 seasonal surveys of California red-legged frog egg masses at known breeding areas. The goal of the egg mass survey is to determine the presence or absence of the red-legged frog at Mori Point and Milagra Ridge, and to assess trends in the abundance of winter-breeding red-legged frogs. Park Stewardship Program staff and interns conducted four egg mass surveys during the winter monitoring season on February 12, 25, March 14, and April 8. New egg masses were observed during all surveys except the last one. The peak in observations occurred on February 12, after the first heavy rains. The total number of egg masses observed this year increased at Milagra Ridge from 2 to 39, while there was a sharp decline (113 to 16) in egg masses observed a Mori Point. Egg masses were observed at all ponds at Mori Point except at the Middle Pond. At Milagra Ridge, 58% of the total egg masses observed were attached to floating vegetation close to the perimeter of the pond. It would be interesting to see if there is a correlation between the number of egg masses and the distance from the edge of the pond. As this was a particularly dry year and most of the ponds did not have water until February, breeding and oviposition which would normally begin in December was restricted to a narrow window. The dry conditions may also have impacted the frog physiologically and the stress caused by the environment may have made it less favorable for the frogs to mate, produce, and lay eggs. Fortunately, all ponds in both sites continue to serve as good breeding habitats as evidenced by the presence of egg masses in ponds found at Milagra and Mori Point. At Mori Point, the Southern and Wetland Ponds continue to be the more frequented pond while the Middle Pond is less frequented. 214 California Red-legged Frog Survey 2
1. INTRODUCTION 1.1 Natural history The California red-legged frog (Rana draytonii) is the largest endemic native frog in the western United States. It was listed as a threatened species in 1996, as the species was slowly eliminated from 7 percent of its natural range in California (USFWS, 22). Habitat loss, introduction of non-native predatory bull frogs and fish, diseases such as the chytrid fungus, and over hunting by humans are all factors that contributed to the decline of the red-legged frog in California. Currently, the red-legged frog ranges along the coast from Mendocino County in northern California to Baja, California, then inland through the Sacramento Valley into the foothills of their Sierra Nevada Mountains (Scott and Rathbun, 25). In the Bay Area, there are populations in the Point Reyes National Seashore, Lake Merced, and Golden Gate Park. In the Golden Gate National Recreation Area (GGNRA), there are populations in Marin (Muir Beach, Banducci, Tennessee Valley) and San Mateo (Mori Point and Milagra Ridge) (USFWS, 22). The red-legged frog breeds in ponds, wetlands, lagoons, and lakes. The frogs mate and lay eggs often synchronous with the first heavy rains in winter from late November through April (USFWS, 22; Fellers and Kleeman, 27). Females attach a large gelatinous cluster of eggs about the size of a grapefruit on vegetation beneath the water. Each egg cluster can contain 75-13 eggs. During this time, eggs are preyed upon by newts, salamanders, and raccoons. The eggs hatch after about three to four weeks and tadpoles metamorphose in four to five months. The peak in metamorphosis is in August. One egg mass will produce one breeding pair of frogs (Scott and Rathbun, 25). In the adult phase, the red-legged frog is preyed upon by garter snakes, predatory birds (great horned owls, hawks, great blue heron), and raccoons. The average life span for an adult frog is 2-3 years and the maximum is six years (Scott and Rathbun, 25). 1.2 Surveying The Park Stewardship Program (PSP) monitors egg masses at Mori Point and Milagra Ridge, both sites located in Pacifica, San Mateo County. The goal of the egg mass survey is to determine the presence or absence of the red-legged frog at Mori Point and Milagra Ridge, and to assess trends in the abundance of winter-breeding California red-legged frogs. This report provides a summary of survey results for the 213/214 breeding season. 1.2.1 Mori Point Mori Point is a 11-acre coastal land parcel with a matrix of coastal shrub and wetland vegetation, and provides habitat for the California red-legged frog. Adjacent to Mori Point is the Sharp Park Golf Course, managed by the City and County of San Francisco, and both are contiguous sites within the Sanchez Creek/Laguna Salada watershed (Figure 1). The frogs utilize the ponds and waterways at both locations for breeding although dominant wetland features are primarily inside Sharp Park. 214 California Red-legged Frog Survey 3
In November 24, the U.S. Fish and Wildlife Service, the Golden Gate National Parks Conservancy, and the GGNRA collaborated to construct two seasonal ponds at Mori Point to provide amphibian habitat and foraging areas for the San Francisco garter snake (Willow and Middle Ponds, LS5 and LS6). In 27, the Middle Pond was modified to hold water longer and the Wetland and Southern Ponds (LS8 and LS7) were created through excavation (Wetland Pond is also known as the Northern Pond). In 29, the Middle Pond was modified again to incorporate a bentonite lining into the base of the pond to prolong the ponding period. In the 23/24 winter season, PSP began surveying the ponds for red-legged frog egg masses during the winter season, typically from December to April. Egg mass surveys have occurred at seven locations, which were selected based on historical presence-absence data. The most dominant bodies of water, Horsestable Pond and Laguna Salada, have been surveyed since 1999 by the San Francisco Recreation and Parks Natural Areas Department. However, egg mass surveys are not completed annually at Laguna Salada, and infrequently at the Horsestable Pond and Sanchez Creek. Since their construction, the Willow Pond (LS5), Middle Pond (LS6), Southern Pond (LS7), and Wetland Pond (LS8) have been surveyed for CRLF eggs each season, thus this report only examines data from the four aforementioned ponds. FIGURE 1. A map of ponds at Mori Point and Sharp Park. 1.2.2 Milagra Ridge Monitoring at Milagra Ridge began in the FIGURE 2. A map of sampling area at Milagra Ridge. 2/21 winter season. Egg mass surveys are completed annually in an abandoned oxidation pond constructed by the United States Army sometime prior to the mid 195 s (MC1) (Figure 2). Open water is present for only a portion of the year fed directly by rainfall and surface runoff. Water leaves the pond via evapotranspiration, seepage, and is drained through a series of pipes and is from an existing drainage system (Fong and O Neill, 2). 214 California Red-legged Frog Survey 4
Back in 2, it was determined that the oxidation pond does not retain water long enough, whether in normal or dry years, to allow the red-legged frog tadpoles to metamorphose (Fong and O Neill, 2). Under normal conditions, the pond would be entirely dry by June while metamorphosis takes place well beyond this time. This posed a significant threat to the mortality of the red-legged frogs (Fong and O Neill, 2). In 29, repairs were made to the drainage system to prevent excess leakage thus slowing down water loss. 2. METHODS Egg mass surveys were conducted mid-february through April in three to four week intervals to avoid sampling an egg mass twice. In order for a survey to be conducted, the water in the ponds had to be clear in order for the surveyor(s) to see the egg masses. The ponds that had water (Willow and Wetland Ponds) were unofficially monitored for eggs on January 16 but no eggs were observed. After the first heavy rain in February, all the ponds contained water. Surveys started on February 12 and occurred during daylight hours on February 25, March 14, and April 8. This season, surveys were conducted by PSP staff and interns. The ponds were surveyed twice for eggs by two separate surveyors making independent passes around the pond going opposite directions. This method was started this monitoring season and the purpose is to ensure consistency between two samples, detect any inconsistencies between surveys if any arose, and monitor the sampling methods for accuracy. For each new egg mass, data collected about the mass included the egg mass shape (sphere, ½ sphere, or rectangular), egg mass dimensions, water depth at egg mass, location of egg mass relative to the water surface, the type of vegetation to which the egg mass is attached to (twig, tule, cattail, etc.), and the Gosner life stage. Each egg mass was assigned a number in order of appearance to help keep track of the number of egg masses. The number count restarted at 1 for each separate survey. The vegetation near each observed egg mass was flagged and marked with the date and the egg mass number to avoid recounting the egg mass in subsequent surveys if it did not hatch after three to four weeks. The location of the egg masses at each pond was mapped by drawing a point on an aerial map of each pond. FIGURE 3. Restoration intern John Doyle with the Park Stewardship Program records egg mass data at the Milagra oxidation pond. 214 California Red-legged Frog Survey 5
# of CRLF egg masses The number of adult red-legged frog observed incidentally during the course of egg mass surveying was also recorded. The number of adults and egg masses observed of other frog species (commonly the Sierran tree frog) were also recorded. Data related to environmental and habitat conditions were also recorded. This includes, the weather, wind speed, air and water temperatures, average and max water depths, dominant vegetation, percent emergent vegetation, submergent vegetation, and percent open water. The pond level was continually monitored once a month after the end of the winter survey season. See Appendix 1 for max water depth data for each pond during the egg mass surveys. See Appendix 2 for a copy of the GGNRA Egg Mass Datasheet. See Appendix 3 for a copy of a map that is complementary to the datasheet. Copies of the datasheets were sent to the GGNRA Aquatic Ecologist. Egg mass data and pond level data were entered into and analyzed in spreadsheets specific to PSP. 3. RESULTS AND DISCUSSION 3.1 Abundance Mori Point This season, surveys indicated the presence of a red-legged frog population and breeding activity at all ponds at Mori Point except at the Middle Pond. Breeding was most concentrated at the Southern and Wetland ponds (Figure 4). A total of sixteen egg masses were observed. 1 9 8 7 6 5 4 3 2 1 8 6 2 Willow Pond (LS5) Middle Pond (LS6) Southern Pond (LS7) Wetland Pond (LS8) FIGURE 4. Mori Point. Total number of California red-legged frog egg masses observed at each pond. Sixteen egg masses were observed in the 213/214 breeding season. The total number of red-legged frog egg masses observed at each four ponds declined from the previous season (Figure 5). This trend was further emphasized in comparison the total number of egg masses observed at Mori Point (Figure 6). In addition to egg mass totals, the total rainfall (inches) is graphed and each value represents the total rainfall from July through June of each year. 214 California Red-legged Frog Survey 6
# of CRLF egg masses # of CRLF egg masses 7 6 5 4 3 2 1 Willow Pond (LS5) Middle Pond (LS6) Southern Pond (LS7) Wetland Pond (LS8) 24/5 25/6 26/7 27/8 28/9 29/1 21/11 211/12 212/13 213/14 Monitoring season FIGURE 5. Mori Point. Number of California red-legged frog egg masses observed at each pond. Monitoring at the Southern and Wetland Ponds started in 27 following their completion and there has been a steadily increasing trend since. There was a significant decline in egg mass observations in the 213/214 season. 15 125 # of CRLF egg masses Total rainfall (in.) 128 13 113 5 4 1 75 5 25 35 28 3 23 16 12 3 24/5 25/6 26/7 27/8 28/9 29/1 21/11 211/12 212/13 213/14 Monitoring season 3 2 1 Total rainfall (in.) FIGURE 6. Mori Point. Abundance of California red-legged frog egg masses observed overtime (Note: only since 27 have all four ponds been monitored). Total rainfall is given in inches and represents the rain that fell from July through June of a given year. Although the rainfall total was lower during this season, based on a regression analysis, there was no significant relationship between rainfall totals and the number of red-legged frog egg masses (R 2 =.1, n=1, p=.698, α=.5). However, there are two factors that may have skewed egg mass data thus confound the analysis results. First, the four ponds did not exist until 27 and second, even after the ponds were established it took a couple of years for the vegetation to establish and the exposed habitat may have been a deterrent for breeding frogs. 214 California Red-legged Frog Survey 7
The dry conditions this past year may have impacted the frog oviposition by other means. In a study of red-legged frog movement and habitat use, more frogs moved towards breeding ponds during the onset of heavy rains (Fellers and Kleeman). Furthermore, red-legged frogs breed when the water temperature is cool in the winter in comparison to water temperatures in the spring and summer (Cook and Jennings, 27). There is a possibility that a later start in the rain season and the persistence of warmer temperatures this year may have delayed red-legged frog breeding. As a result, breeding and oviposition which would normally begin in December, was restricted to a narrow window from February to April. Aside from altering the cycle, the drought could also have had a physiological impact on the red-legged frog, creating stressful conditions that affected the reproductive output of the population (Carey and Alexander, 23). There was water in the Willow and Wetland ponds between November and January but the Southern and Middle ponds were completely dry until February which is late into the winter season. Oviposition typically starts in November/December; however, conditions may not have been favorable for the redlegged frog to lay eggs. Although the Willow and Wetland Ponds had water between November and January, eggs were not observed until February after the first heavy rain. The observations this season supports the current consensus that the presence of water in the pond is not as much of a cue for the frog to lay eggs as the first rain event (Scott and Rathbun, 22). Despite the decline, the silver lining to this season s observations is that egg masses were consistently observed at three ponds, indicating that the red-legged frog is still present at Mori Point and is using the provided ponds for breeding. The Southern and Wetland Ponds continue to be the favored habitat for the frogs while the Middle Pond is less frequented. Milagra Ridge Like Mori Point, the number of egg masses observed at the Milagra oxidation pond fluctuated over time. However, unlike the trend observed at Mori Point, the total number of red-legged frog eggs at Milagra increased between this and the previous season from 2 to 39, despite a lower rainfall amount (rainfall is based on a period from July through June of the following year) (Figure 7). A regression analysis indicates that there is no significant relationship between the number of egg masses and total rainfall (R 2 =.45, n=14, p=.466, α=.5), suggesting that the amount of rainfall did not influence egg mass abundance. Likewise, there is no significant relationship (R 2 =.1, n=7, p=.941, α=.5) between the number of egg masses and the average max water depth of the pond from November through April, suggesting that the amount of water in the Milagra Ridge pond also did not influence egg mass abundance. The aforementioned analyses support the idea that as long as there is water, the red-legged frog would use the pond for oviposition. 214 California Red-legged Frog Survey 8
# of CRLF egg masses 1 # CRLF egg masses 9 81 Total rainfall (in.) 8 7 68 61 6 53 5 51 43 39 39 4 4 3 27 35 31 2 2 1 12 2/1 22/3 24/5 26/7 28/9 21/11 212/13 5 4 3 2 1 Total rainfall (in.) Monitoring season FIGURE 7. Milagra Ridge. Abundance of California red-legged frog egg masses observed over time in the oxidation pond. Total rainfall is given in inches and represents the rain that fell from July through June of a given year. The condition of the Milagra Ridge pond may be a factor that contributed to the increase in egg mass abundance observed this season. In a comparative study of red-legged frog oviposition sites, egg masses tended to be found in shallow water near the shore (<1 m) in habitats where vegetation was restricted to a narrow zone near the shore (Alverez et al., 213). Additionally, in a study of red-legged frog habitat use, red-legged frog egg masses occurred almost exclusively in shallow water attached to unattached, floating, dead biomass (Cook and Jennings, 27). Before the pond at Milagra Ridge filled with water, tule and cattails were removed and piled in the pond. When the pond filled, some of the cut biomass was distributed throughout the area particularly near the edge of the pond. More than half (58%) of the egg masses observed were attached to cut vegetation while the remaining eggs were attached to the ground or on standing vegetation. This leads to the speculation that the increase in egg masses at Milagra may be due to the increase in surface area available for egg mass attachment and the ease of access to this biomass, despite a later start to the season and lower pond level this season. It would be interesting to see if there is a correlation between distance from the edge of the pond and the number of egg masses observed. In doing so, it can help inform restoration and habitat management of red-legged frog ponds in terms of where vegetation should be cut or replanted to most benefit the frog. 3.2 Phenology Over the three month monitoring season, observations of red-legged frog egg masses were the highest in February in the Southern and Wetland Ponds which coincided with the time when the pond first held water (Figure 8). At Milagra Ridge, observations were also highest during the two observation periods in February. New egg masses were not observed at Mori Point and Milagra Ridge during the last survey on April 8 th. 214 California Red-legged Frog Survey 9
# of CRLF egg masses 7 6 5 4 3 2 1 6 4 3 2 1 2/12/214 2/25/214 3/14/214 4/8/214 Willow Pond (LS5) Middle Pond (LS6) Southern Pond (LS7) Wetland Pond (LS8) FIGURE 8. Mori Point. Number of California red-legged frogs egg masses observed at each pond by survey date. Amphibian reproduction is highly vulnerable to variations in temperature and the amount and timing of precipitation (Carey and Alexander, 23). Both temperature and precipitation are triggers for frogs to breed and migrate towards breeding habitat. In a study of breeding phenology of the common frog Rana temporaria, the reproductive cycle of R. temporaria is occurring 9 days earlier since 1992 as a result of temperature increases over time (Scott et al., 28). Warmer temperatures have shifted the phenology of spring and summer breeding frogs (Carey and Alexander, 23). This begs to question if the breeding season for winter breeding frogs, such as the red-legged frog, would occur later into the year given the persistence of warmer temperatures during drought years. At Mori Point and Milagra Ridge last season, egg masses were observed in December. This year, there was a two month delay. It would be interesting to monitor, or analyze if the data is available, the start time of the breeding season of the red-legged frog at Mori Point and Milagra Ridge to detect any changes of this event. 4. CONCLUSION This past season was a particularly dry season with the ponds at Milagra and Mori not holding water until late winter in February. Despite a late start in the breeding season, the California red-legged frogs managed to breed and lay eggs in all of the known breeding habitats at Milagra and Mori Point, although no eggs were observed at the Middle Pond this season. Continued habitat maintenance and restoration is need to protect the red-legged frog, especially if dry conditions such as those experienced this past season is to persist for years to come. Habitat maintenance includes removing non-native tule and cattails, and removing vegetation necessary to promote a 5/5 ratio between open water and vegetation before the breeding season. 214 California Red-legged Frog Survey 1
5. LITERATURE CITED Alverez, J.A., Cook, D.G., Yee, J.L., van Hattem, M.G., Fong, D.R., and Fisher, R.N. 213. Comparative Microhabitat Characteristics at Oviposition Sites of the California Red-Legged Frog (Rana Draytonii). Herpetological Conservation and Biology. 8(3): 539-551. Carey, C. and Alexander, M.A. 23. Climate Change and Amphibian Declines: Is There A Link? Diversity and Distributions. 9(2): 111-121. Cook, D.G., and Jennings, M.R. 27. Microhabitat Use of the California red-legged Frog and Introduced Bullfrog in a Seasonal Marsh. Herpetologica. 63(4): 43-44. Fellers, G.M. and Kleeman, P.M. 27. California Red-Legged Frog (Rana draytonii) Movement and Habitat Use: Implications for Conservation. Journal of Herpetology. 41(2): 276-286. Fong, D. and O Neill, S. 2. Milagra Ridge Oxidation Pond Management Plan. Golden Gate National Recreation Area. 19 p. Scott, N. and Rathbun, G. 25. California red-legged frog PowerPoint presentation. Livermore, CA. April 29. U.S. Fish and Wildlife Service. 22. Recovery plan for the California Red-legged Frog (Rana aurora draytonii). U.S. Fish and Wildlife Service, Portland, Oregon. 173 p. Scott, A.W., Pithart, D., Adamson, J.K. 28. Long-term United Kingdom Trends in the Breeding Phenology of the Common Frog, Rana temporaria. Journal of Herpetology. 42(1): 89-96. 214 California Red-legged Frog Survey 11
Average max water depth (m) Average max water depth (ft) APPENDIX 1: Pond level summary 4.5 4 3.5 3 2.5 2 1.5 1 Middle Pond South Pond Wetland Pond Willow Pond Total rainfall (in) 4. 3.5 3. 2.5 2. 1.5 1. Total rainfall (in).5.5 July September October November January February March April May June July. FIGURE 9. Mori Point. Average max water depth (feet) at each pond from July 213 to July 214. The South Pond, one of the most productive ponds did not have much water between November through March. The Middle Pond did not have water until February 214. Since there were multiple readings per month for certain months, the average depth is calculated..5.45.4.35.3.25.2.15.1.5 Average max depth (m) Total rainfall (in) June December January February March April May June 4 3.5 3 2.5 2 1.5 1.5 Total rainfall (in.) FIGURE 1. Milagra Ridge. Average max water depth (meters) at each pond from June 213 to June 214. Since there were multiple readings per month for certain months, the average depth is calculated. Pond level was not monitored between June and December 213. 214 California Red-legged Frog Survey 12
APPENDIX 2 GGNRA Egg Mass Datasheet Date (mm-dd-yyyy): Begin Time (PST-Military): Total Time (Min): Observer(s): General Location: NPS Location ID: County: UTM: Weather: Clear Overcast/Fog Pt. Cloudy Mostly Cloudy Rain Beaufort Wind: <1 1-3 4-7 8-12 13-18 19-24 >24 Air Temp.: (at 1 m) C F Water Temp.: (.5m out) C F Habitat: Natural Altered Type: Lake Pond Emerg. Wetl. Drainage: 1 2 3 4 5 Ditch Stream Seep/Spring Permanent Seasonal Watershed: Natural Grazed Logged Substrate: Silt Sand (<2mm) Pebble (2-75 mm) Urban Agriculture Other Cobble (75-3mm) Boulder (>3mm) Bedrock Survey Survey Aver. Max Water Flow: <1 fps 1-5 fps Length: m Width: m Depth: m Depth: m 5-1 fps >1 fps Visibility (m): Dominant Emergent Vegetation: Fish Present: Yes No Emergent Vegetation: % Dominant Submergent Vegetation: Species and Approx. Number: Submergent Vegetation: % Open Water: % Species ID # # Egg Masses Mass Shape (sphere, ½ sphere, rect) Mass Dimensions (cm) Water Depth (cm) Egg Mass Depth (cm from bottom) Stranded? Egg Attachment Type (e.g., twigs, cattail, tule) Y N Y N Y N Y N Y N Y N COMMENTS (e.g., surveyed route, habitat conditions, observation, conditions): Gosner Stage Comment CRLF_eggmass_datasht_v29.doc Rev. 11/9 214 California Red-legged Frog Survey 13
APPENDIX 3: Survey Map 214 California Red-legged Frog Survey 14
APPENDIX 4: Data Locations All information pertaining to the CRLF data used in this report can be located here: Mori Point J:\Community Programs\Bldg 34 Files\Park Stewardship\Restoration\SITES\Mori Point\mp_wildlife\mp_crlf\214 CRLF Monitoring Season This report: 214_Mori_CRLF_report_final_214915.docx Data used in this report: mp_crlf_egg_mass_data_214.xlsx Pond level data: J:\Community Programs\Bldg 34 Files\Park Stewardship\Restoration\SITES\Mori Point\mp_pond\ mp_pond_data.xls Milagra Ridge J:\Community Programs\Bldg 34 Files\Park Stewardship\Restoration\SITES\Milagra Ridge\mr_wildlife\mr_crlf\214 CRLF Monitoring Season This report: There will be a shortcut to this report linking to storage under Mori Point. Data used in this report: mr_crlf_egg_mass_data_214.xlsx Pond level data: J:\Community Programs\Bldg 34 Files\Park Stewardship\Restoration\SITES\Milagra Ridge\mr_pond\ mr_pond_data.xls 214 California Red-legged Frog Survey 15