2014 california red-legged frog egg mass survey summary report

2014 California Red-legged Frog Survey 1

FINAL REPORT 2014 California Red-legged Frog Survey Mori Point and Milagra Ridge

September 15, 2014

Prepared by: Ruby Kwan Park Stewardship Program Golden Gate National Parks Conservancy Fort Mason Building 201 San Francisco, CA 9412

Prepared for: National Park Service Golden Gate National Recreation Area Division of Resource Management


SUMMARY

This report summarizes the results of the 2013/2014 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 20 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.


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 70

percent of its natural range in California (USFWS, 2002). 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,

2005). 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, 2002).

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, 2002; Fellers

and Kleeman, 2007). Females attach a large gelatinous cluster of eggs about the size of a grapefruit on

vegetation beneath the water. Each egg cluster can contain 750-1300 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, 2005). 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, 2005).

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 2013/2014 breeding season.

1.2.1 Mori Point

Mori Point is a 110-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.


In November 2004, 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, LS05 and LS06). In 2007, the

Middle Pond was modified to hold water longer

and the Wetland and Southern Ponds (LS08 and

LS07) were created through excavation

(Wetland Pond is also known as the Northern

Pond). In 2009, the Middle Pond was modified

again to incorporate a bentonite lining into the

base of the pond to prolong the ponding period.

In the 2003/2004 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 (LS05),

Middle Pond (LS06), Southern Pond (LS07), and

Wetland Pond (LS08) have been surveyed for

CRLF eggs each season, thus this report only

examines data from the four aforementioned

ponds.

1.2.2 Milagra Ridge

Monitoring at Milagra Ridge began in the

2000/2001 winter season. Egg mass surveys are

completed annually in an abandoned oxidation pond constructed by the United States Army sometime

prior to the mid 1950’s (MC01) (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, 2000).

FIGURE 1. A map of ponds at Mori Point and Sharp Park.

FIGURE 2. A map of sampling area at Milagra Ridge.


Back in 2000, 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, 2000).

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, 2000). In 2009, 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.


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.

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.

FIGURE 4. Mori Point. Total number of California red-legged frog egg masses observed at each pond. Sixteen egg masses were observed in the 2013/2014 breeding season.

2

8

6

0

1

2

3

4

5

6

7

8

9

10

Willow Pond (LS05) Middle Pond (LS06) Southern Pond (LS07) Wetland Pond (LS08)

# o

f C

RLF

egg

mas

ses


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 (R2 = 0.01,

n=10, p=0.698, α=0.05). 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 2007 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.

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 2007 following their completion and there has been a steadily increasing trend since. There was a significant decline in egg mass observations in the 2013/2014 season.

0

10

20

30

40

50

60

70

2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 2012/13 2013/14

# o

f C

RLF

egg

mas

ses

Monitoring season

Willow Pond (LS05)

Middle Pond (LS06)

Southern Pond (LS07)

Wetland Pond (LS08)

FIGURE 6. Mori Point. Abundance of California red-legged frog egg masses observed overtime (Note: only since 2007 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.

3 12 3

23

35 28

128 130

113

16

0

10

20

30

40

50

0

25

50

75

100

125

150

2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 2012/13 2013/14

Total rain

fall (in.) #

of

CR

LF e

gg m

asse

s

Monitoring season

# of CRLF egg massesTotal rainfall (in.)


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,

2007). 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, 2003).

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 red-

legged 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, 2002).

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 20 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 (R2 = 0.045, n=14, p=0.466, α=0.05), suggesting that the amount of rainfall did

not influence egg mass abundance. Likewise, there is no significant relationship (R2 = 0.001, n=7,

p=0.941, α=0.05) 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.


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., 2013). 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, 2007). 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 8th.

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.

27

81

53

40

39

31 35

61

12

68

51 43

20

39

0

10

20

30

40

50

0

10

20

30

40

50

60

70

80

90

100

2000/01 2002/03 2004/05 2006/07 2008/09 2010/11 2012/13

Total rain

fall (in.) #

of

CR

LF e

gg m

asse

s

Monitoring season

# CRLF egg masses

Total rainfall (in.)


Amphibian reproduction is highly vulnerable to variations in temperature and the amount and timing of

precipitation (Carey and Alexander, 2003). 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., 2008). Warmer temperatures have shifted the

phenology of spring and summer breeding frogs (Carey and Alexander, 2003). 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 50/50 ratio between open water and

vegetation before the breeding season.

FIGURE 8. Mori Point. Number of California red-legged frogs egg masses observed at each pond by survey date.

2

3

4

1

6

0

1

2

3

4

5

6

7

2/12/2014 2/25/2014 3/14/2014 4/8/2014

# o

f C

RLF

egg

mas

ses

Willow Pond (LS05) Middle Pond (LS06) Southern Pond (LS07) Wetland Pond (LS08)


5. LITERATURE CITED Alverez, J.A., Cook, D.G., Yee, J.L., van Hattem, M.G., Fong, D.R., and Fisher, R.N. 2013. 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. 2003. Climate Change and Amphibian Declines: Is There A Link? Diversity and

Distributions. 9(2): 111-121. Cook, D.G., and Jennings, M.R. 2007. Microhabitat Use of the California red-legged Frog and Introduced Bullfrog in

a Seasonal Marsh. Herpetologica. 63(4): 430-440. Fellers, G.M. and Kleeman, P.M. 2007. 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. 2000. Milagra Ridge Oxidation Pond Management Plan. Golden Gate National Recreation

Area. 19 p. Scott, N. and Rathbun, G. 2005. California red-legged frog PowerPoint presentation. Livermore, CA. April 2009. U.S. Fish and Wildlife Service. 2002. 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. 2008. Long-term United Kingdom Trends in the Breeding Phenology of the

Common Frog, Rana temporaria. Journal of Herpetology. 42(1): 89-96.


APPENDIX 1: Pond level summary

FIGURE 9. Mori Point. Average max water depth (feet) at each pond from July 2013 to July 2014. 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 2014. Since there were multiple readings per month for certain months, the average depth is calculated.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

0.5

1

1.5

2

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3.5

4

4.5

July September October November January February March April May June July

Total rain

fall (in)

Ave

rage

max

wat

er

de

pth

(ft

)

Middle PondSouth PondWetland PondWillow PondTotal rainfall (in)

FIGURE 10. Milagra Ridge. Average max water depth (meters) at each pond from June 2013 to June 2014. Since there were multiple readings per month for certain months, the average depth is calculated. Pond level was not monitored between June and December 2013.

0

0.5

1

1.5

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4

0

0.05

0.1

0.15

0.2

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0.3

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0.4

0.45

0.5

June December January February March April May June

Total rain

fall (in.)

Ave

rage

max

wat

er

de

pth

(m

)

Average max depth (m)

Total rainfall (in)


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.: C (at 1 m) F

Water Temp.: C (0.5m out) F

Habitat: Natural Altered 1 2 3 4 5

Type: Lake Pond Emerg. Wetl. Ditch Stream Seep/Spring

Drainage: Permanent Seasonal

Watershed: Natural Grazed Logged Urban Agriculture Other

Substrate: Silt Sand (<2mm) Pebble (2-75 mm) Cobble (75-300mm) Boulder (>300mm) Bedrock

Survey Length: m

Survey Width: m

Aver. Depth: m

Max Depth: m

Water Flow: 0 <1 fps 1-5 fps 5-10 fps >10 fps

Visibility (m): Emergent Vegetation: %

Submergent Vegetation: %

Open Water: %

Dominant Emergent Vegetation:

Dominant Submergent Vegetation:

Fish Present: Yes No

Species and Approx. Number:

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)

Gosner Stage

Comment

Y N

Y N

Y N

Y N

Y N

Y N

COMMENTS (e.g., surveyed route, habitat conditions, observation, conditions):

CRLF_eggmass_datasht_v2009.doc Rev. 11/09


APPENDIX 3: Survey Map


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\2014 CRLF Monitoring Season This report: 2014_Mori_CRLF_report_final_20140915.docx Data used in this report: mp_CRLF_egg_mass_data_2014.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\2014 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_2014.xlsx Pond level data: J:\Community Programs\Bldg 34 Files\Park Stewardship\Restoration\SITES\Milagra Ridge\mr_pond\ mr_pond_data.xls

2014 california red-legged frog egg mass survey summary report

Documents

redlegged frog ranges

breeding redlegged frogs

presence of egg masses

total egg masses

new egg masses

northern california

california usfws

total number of egg