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2016
SOUTHERN CROSS UNIVERSITY
SCHOOL OF ENVIRONMENT, SCIENCE AND ENGINEERING
POPULATION MONITORING OF GREEN AND GOLDEN BELL FROG
(L. AUREA)
AT THE NORTHERN EXTENT OF ITS RANGE.
JENINE DEMPSTER
1
This report has been prepared by an undergraduate student and may not have been
corrected according to the comments of University staff. The report should be cited in
the following format: Dempster, J.A. (2016). Population monitoring of Green and
Golden Bell Frog (L. Aurea) At the northern extent of its range. Unpublished Third
Year Undergraduate Report. School of Environment, Science and Engineering,
Southern Cross University, Lismore.
2
POPULATION MONITORING OF GREEN AND GOLDEN BELL FROG
(L. AUREA)
AT THE NORTHERN EXTENT OF ITS RANGE.
Prepared by Jenine Dempster
Integrated Project prepared as partial fulfilment of the requirements
of the Bachelor of Environmental Science
Southern Cross University
2016
Copyright
3
I, Jenine Dempster, consent to this report being made available for photocopying and
loan, provided that my work is fully acknowledged and that the granting of such a
licence in no way inhibits me from exercising any of my exclusive rights under the
Copyright Act 1968. I understand this licence is granted in the interests of education and
research and that no royalties are payable.
Jenine Dempster 10th
June 2016
4
Acknowledgements
I wish to thank my supervisors David Newell and Ross Goldingay for their wealth of
knowledge on the subject, patience in the field, and support during the write up. I am
also extremely grateful to Jonathan Parkyn for his help with the data analysis and
additional advice he provided. Special thanks also to Craig Taylor for organising and
supplying gear for the field work, but more importantly for some great guidance at the
start of the project. Finally to my mother Judith and my partner Mark who went above
and beyond to provide me with the support and encouragement to believe in myself.
5
Abstract The green and golden bell frog (Litoria aurea) has experienced a
considerable range reduction and population decline over the last 20 years
in NSW. Once ranging from Victoria to Byron Bay, L. aurea has now
contracted from its northern range limits. The most northern extent of L.
aurea currently exists within Yuraygir National Park NSW. These northern
populations are small and therefore prone to extinction through inbreeding,
genetic drift and other environmental factors. Consequently the populations
of L. aurea in Yuraygir National Park are considered to be of high
conservation significance. The most prominent threats to L. aurea include
predation by the plague minnow (Gambusia) and loss of breeding habitat.
The aim of this study was to continue monitoring of L. aurea populations at
the northern extent of their range. Nocturnal surveys conducted over six
night’s recorded 133 individuals, however only the 70 adult males were used
for POPAN analysis which determined abundance at 116. This is the same
estimate as previous studies; however the survey area and number of
occasions was less for this project suggesting the population has increased.
A long-term monitoring strategy is still required as there is too little
information available on life history parameters to ascertain if the numbers
observed can be interpreted as a viable population.
Key Words: Bell Frog, Litoria aurea, amphibian decline, population monitoring.
6
Contents Acknowledgements .............................................................................................................. 4
Abstract ................................................................................................................................ 5
1. Literature review .......................................................................................................... 8
1.1 Taxonomy of L. aurea ................................................................................................... 9
1.2 Biology and Physiology ................................................................................................. 9
1.3 Diet ................................................................................................................................ 10
1.4 Reproduction and Behaviour ..................................................................................... 10
1.5 Habitat requirements .................................................................................................. 10
1.6 Major threats to L. aurea ............................................................................................ 11
1.6.1 Predation by Gambusia holbrooki ............................................................................. 11
1.6.2 Pathogens ................................................................................................................... 11
1.6.3 Habitat loss and disturbance ...................................................................................... 12
1.6.4 Small Population ........................................................................................................ 12
1.6.5 Increased levels of ultraviolet radiation .................................................................... 12
2. Aims and Objectives ...................................................................................................... 13
3. Methods .......................................................................................................................... 13
3.1 Study area .................................................................................................................... 13
3.2 Climate and Rainfall ................................................................................................... 16
3.3 Survey Design .............................................................................................................. 16
3.4 Data analysis ................................................................................................................ 17
3.5 Additional Field work ................................................................................................. 17
4. Results ............................................................................................................................ 17
5. Discussion ....................................................................................................................... 19
5.1 Population stability ..................................................................................................... 19
5.2 Management options ................................................................................................... 20
References .......................................................................................................................... 22
Appendices ......................................................................................................................... 27
7
List of Tables and Figures
Figure 1. Blue Lake, Yuraygir National Park, NSW. Photo: J. Dempster. ................................. 15
Figure 2. Southern Swamp, Yuraygir National Park, NSW. Photo: J. Dempster. ...................... 15
Figure 3. Rainfall for 2014-2015 compared to mean. (BoM, 2016). .......................................... 16
Figure 4. Capture results for male, female and sub-adult L. aurea over six nights .................... 18
Figure 5. Colourmorphs of Yuraygir. Photos: D. Newell & R. Goldingay. ................................ 27
Figure 6. Male L. aurea on M. quinquinervia tree. Photo: R. Goldingay. .................................. 27
Table 1. POPAN model ............................................................................................................... 18
Table 2. Survivorship (phi), capture (p) and probability of entry (PENT) estimates. ................. 19
Table 3. Population estimate derived from POPAN 6 model. .................................................... 19
Map 1. Location of Yuraygir National Park and Station Creek Camping area. Source: Google
Earth, 2015. ................................................................................................................................. 14
Map 2. Location of Sampling sites, Blue Lake and Southern Swamp. Source: Google Earth,
2015. ............................................................................................................................................ 14
8
1. Literature review
The decline in abundance and diversity of amphibians is considered to be a global
phenomenon, which began in the 1970’s (Stuart et al. 2004) with the simultaneous
disappearance of frog and toad species from points widely distributed across the globe.
It was initially thought there was a single cause or that it was purely coincidental and
that local environmental factors were to blame (Barinaga, 1990). There was insufficient
data on many species to ascertain if these population declines were simply normal
fluctuations (Lewis & Goldingay, 2005) or something of more concern. It was
recognised that declines and disappearances of amphibian populations over the last two
decades however, represented a distinct phenomenon that exceeded the problematic
issue of biodiversity loss and researchers began to try and discover the cause. There are
numerous hypotheses implicated in the decline, including global warming and increased
UV-B radiation, habitat destruction, and disease (Belden & Blaustein, 2002, Pyke &
White 2001, Kriger et al. 2007). Additional factors which may contribute to localised
frog declines include pollution, salinisation and predation by introduced species (Polo-
Cavia, et al. 2016; Stockwell, 2012; Pyke & White, 2001). However, researchers have
also investigating confirmed frog declines in apparently pristine, undisturbed habitats
(Eisemberg et al. 2016; Neckel-Oliveira et al 2013). Frogs are unique in that they have
a biphasic lifecycle making them vulnerable to impacts in both aquatic and terrestrial
environments (Tinto, 2015)
Populations of Australian frogs have followed the trend of global decline with fifty of
216 (23%) amphibian species now recognised as threatened or extinct in accord with
IUCN Red List Categories and Criteria (Hero et al. 2004). Worldwide, researchers have
confirmed frog declines in abundance and diversity in both pristine and disturbed
habitats (Blaustein, et al. 2011; Skerratt et al. 2007; Stuart, et al. 2004). Stuart et al.
(2004) have stated that Australia has significantly more enigmatic declines than the
world average. The causal agents proposed at the time of amphibian declines provided
no explanation for the disappearance of species including the Mt Glorious Torrent
Frog (Taudactylus diurnal), and the Gastric Brooding Frog, (Rheobatrachus silus). It is
important to note that frogs were not even recognised as fauna in Australia until 1991
when the Endangered Fauna (Interim Protection) Act amended the National Parks and
Wildlife Act 1974 (White, 1995).
Since the mid-1970s the Green and Golden Bell Frog (L. aurea) has experienced an
extensive reduction along the south east coast of Australia, and the species is now listed
as endangered in the New South Wales Threatened Species Conservation Act 1995
(TSC) and as vulnerable in the Commonwealth’s Environmental Protection and
Biodiversity Conservation Act 1999 (EPBC). The Green and Golden Bell Frog once
occupied 134 locations ranging from Byron Bay in northern NSW, to East Gippsland,
Victoria, and west to Bathurst and Tumut (White and Pyke, 1996) this number has now
been reduced to 47 known locations. Victorian populations appear stable, however,
Gillespie et al. (2011) question the certainty of some conservation assessments that may
at times underestimate the threats to populations.
9
Consequently, the populations of L. aurea in Yuraygir National Park are of great
significance in relation to the conservation of the species. Due to the decline in regional
populations, combined with the apparent isolation of the known populations in Yuraygir
these populations may be amongst the most threated of all known populations of the
species (Frankham, 2015; Luquet, 2015; Goldingay, 2008). The small size of these
populations indicates that L aurea will be particularly vulnerable to local extinction.
Further to this, MtDNA and microsatellite data collected by Burns et al. (2007) has
shown that more isolated northern populations of L aurea are highly differentiated from
those in the south demonstrating some genetic divergence. This may indicate that the
Yuraygir population is significant management unit. Colourmorphs of the Yuraygir
population certainly suggest some genetic variation from those populations located in
the south (Appendix 1). Further studies are required throughout Yuraygir NP to confirm
results of previous studies and to provide continued monitoring of the L aurea
populations in YNP to conserve all viable populations throughout the extent of their
geographic range (Goldingay 2008).
1.1 Taxonomy of L. aurea
Bell frogs are a distinct group within the Australo-Papuan hylid genus Litoria. There
are seven species within the group listed in Pyke and White (2001) comprising of
Southern Bell Frog (L. raniformis), Yellow Spotted Tree Frog (L. castanea); Moore’s
Frog (L. moorei), Dahl’s Aquatic Frog (L. dahlia), Striped Burrowing Frog (L.
alboguttata), Spotted Thighed Frog (L. cyclorhynchus). Litoria aurea can be
distinguished from similar species by its granular free skin, conspicuous toe and finger
disc and absence of spotting or marbling on the hide side of the thigh, with colouration
on its back being a distinctive feature.
1.2 Biology and Physiology
Green and golden bell frogs are one of the largest frogs in Australia with adult females
growing between 70- 85mm snout-vent length (SVL) whereas adult males reach 55-
70mm (White and Pyke 2001). The dorsal colouration of L. aurea ranges from
chocolate brown to dull olive to bright emerald green or brown, with coppery-gold
blotches on the back. The dorsal surface is smooth with a yellow dorso-lateral fold
extending from the eye to the groin. The belly and ventral surfaces of the thighs are
white and coarsely granulated. There is a pale or cream stripe which runs from above
the nostril over the eye and tympanum. The tympanum is distinct and gold in colour.
There is a distinctive area of blue-green colouration surrounding the groin and upper
thighs. Webbing is absent in the fingers, whereas the toes are almost entirely webbed.
Reproductively mature males have swollen thumbs, as a result of the development of
dark nuptial pads, which are used to clasp females during amplexis.
Green and golden bell frogs are possible the most highly fecund species of Australian
Frog with egg spawn masses averaging 3773 eggs (Pyke and White 2001). Tadpoles
hatch in approximately two days with development from tadpole to metamorphling
occurring between 2-12 months depending on climate. Tadpoles are not easily
characterised, as descriptions vary considerably from green with golden streaks
(Fletcher, cited in Pyke and White, 2001)), dull brown or dirty yellow (White 1995).
10
pinkish grey with yellowish fins (Frogs of Victoria, 2015) or a metallic golden lustre
(Hamer, cited in Pyke and White, 2001). Obviously this is not a reliable method for
identification, therefore body markings are usually used such as a distinctive canthal
stripe which flanks tadpoles > 1cm SVL. Other identifying features include a dorsal fin
extending nearly halfway up the back, lateral eyes and the mouth disc has to rows of
upper labial teeth, with three rows of teeth in the lower labium.
1.3 Diet
The diet of tadpoles varies with age, consisting of algae, organic detritus and bacteria,
progressing to a more carnivorous diet as they mature. Adult bell frogs are known to eat
a variety of invertebrates and small vertebrates with White (1995) suggesting that adults
will consume any moving prey that will fit in its mouth, including conspecifics and
other frog species. Frogs have been found to consume more during the warmer months,
however this corresponds with breeding season which Humphries (cited in Pyke and
White, 2001) states reduces foraging behaviour. Clearly more research is required in
this area if management plans are to be designed effectively.
1.4 Reproduction and Behaviour
Breeding occurs in the warmer months from Oct-Mar with male bell frogs calling to
attract females, while partly submerged in water. These vocalisations play an integral
part in the social and mating behaviour of frogs (Bleach, et al. 2015), as calls may not
only be intended to attract females, but also alert other males of their presence (Pyke
and Osborne, 1999).
In the event that amplexus between male and female L. aurea has occurred, egg spawn
masses become evident within 72hours. Breeding is generally restricted to ephemeral
ponds, which contain submergent and emergent aquatic vegetation.
1.5 Habitat requirements
Green and Golden Bell Frogs can be found in almost every type of still to slow moving
fresh water body, including farm dams, wetlands, swamps, creeks, lakes, lagoons,
constructed ponds and ephemeral ponds. Social cues such as the scent of conspecifics
may also play a key role in habitat selection in this species with not all of the above
habitats utilised when available (Pizzatto et al. 2016). Bell frogs have been known to
inhabit a vast range of heavily disturbed and moderately disturbed habitats. A
requirement is the presence of diurnal basking habitat which generally consists of
emergent aquatic vegetation or rocks. Litoria aurea are generally an aquatic species,
despite its classification as a Hylid; however male bell frogs were observed calling
whilst sitting in small trees (Appendix 2) and Typha orientalis during this study in
Yuraygir National Park, supporting the Hylid classification.
Bell frogs may seek shelter during the day amongst vegetation adjacent to or within the
vicinity of permanent water-bodies, for foraging. Over wintering habitat generally
consists of piles of rocks, vegetation or litter in which bell frogs can seek shelter for
hibernation during the colder months of the year (White and Pyke, 2015).
11
One of the largest known extant populations of L aurea in NSW occurs in the Greater
Sydney region and inhabits sites of high levels of disturbance (White and Pyke 1996).
Many of the largest populations can be found in these disturbed sites and this has led
some to postulate that this may be preferred habitat rather than no other habitat is
available and the frogs are forced to live in these areas due to loss of suitable habitat.
Research by Kearney et al. (2012) has also found that Green and Golden Bell Frogs
have a greater tolerance to salinity than other Australian anuran species with an 85%
larval survival rate in sodium concentrations of 16%. This may help the GGBF to
colonise habitats as refuges from competition and predation.
1.6 Major threats to L. aurea
1.6.1 Predation by Gambusia holbrooki
Listed as a key threatening process which has known or likely implications for the
Green and Golden Bell Frog under the Threatened Species Conservation Act 1995 is
predation by Gambusia holbrooki or the Plague Minnow. Gambusi holbrooki is a
voracious predator that feeds on both eggs and young tadpoles, while also preying on
tadpoles at later stages in their development (NPWS, 2003). Although White and Pyke
(2001) stipulate that the breeding success of L. aurea requires the water body to be free
of Gambusia and other predatory fish, there have been observations of successful
breeding in the presence of Gambusia (Hamer, et al. 2002; Goldingay and Lewis, 1999).
The size of the water body and the presence of aquatic and emergent vegetation in
addition to the density of fish, will determine the level of impact Gambusia has on Bell
Frog breeding efforts.
1.6.2 Pathogens
Chytrid fungus (Batrachochytrium dendrobatidis) possibly the most well-known of frog
pathogens implicated as one possibly cause for the decline of amphibian species across
the globe (Goldingay, 2008; Newell et al. 2013). In Australia it has caused the
extinction or decline of up to 17 frog species (Department of the Environment, 2012)
and this trend does not appear to be slowing. Batrachochytrium dendrobatidis which
causes chytridiomycosis was listed as a key threatening process in 2002 under the
Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act). The
bacteria effects the keratinised epithelia such as the skin of frogs and mouthparts of
tadpoles causing the skin to become tough and less permeable to water and essential
salts leading to eventual death.
Salinity levels may offer some benefits in precluding the fungus (Osbourne cited in
Goldingay, 2008) with Threlfall et al. (2008) suggesting fluctuating salinity in addition
to heavy metals copper and zinc may provide fungicidal benefits. This is supported by
Stockwell et al. (2015) who revealed that exposure to sodium chloride concentrations
>2ppt significantly reduced chytrid infection loads in Bell Frogs. Additionally it has
been suggested that antimicrobial peptides from skin glands on the bell frog may help to
control infection (Rollins-Smith et al. 2011).
12
Myxosporean parasites have been found in the liver and brain of Green and Golden Bell
Frogs (Hartigan et al. 2011). Originally thought to have been introduced with the Cane
Toad (Bufo marinus) it has since been discovered that the parasite carried by our native
frogs was not introduced by the toads but rather it is a native strain that has been
amplified by the susceptible invasive host species. The parasite has been found to cause
axonal lesions which interfere with neurological function and result in behavioural
changes such as lethargy and failure to breed in the Green and Golden Bell frogs
(Hartigan et al. 2011).
Ranaviruses while not frequently encountered in Australia are listed on the World
Organisation for Animal Health (OIE) as a notifiable disease which may help control
the introduction of pathogenic strains to the country.
1.6.3 Habitat loss and disturbance
Habitat loss and disturbance has been identified as one of the major threats facing the
Green and Golden Bell Frog (Goldingay, 2008; White and Pyke, 2008). Development
along the east coast of NSW has removed and fragmented up to 60 per cent of
freshwater wetlands (OEH, 2016), which are the frogs preferred habitat. Pyke and
White (2001) have reported that the majority of populations are now found in highly
disturbed areas possibly because these sites are all that remains of former breeding
habitats. Fragmentation can isolate frog populations, increasing the impacts of
inbreeding, limiting evolutionary potential and predispose populations to extinction
(DEC, 2005)
The site selected for this study was historically used for sand mining and cattle grazing
which has seen the development of sand blowouts in the area and trampling of aquatic
edge vegetation. The gazetting of the area as a National Park in 1980 (Australian
National Parks 2016) has seen the gradual regeneration of vegetation, however cattle
continue to occupy the site. The site has been protected from farming and development
that has occurred along the east coast due to its distance from major roads and towns.
This may have protected the population from threats such as disturbance and pollution
which affect other populations.
1.6.4 Small Population
Small populations created through habitat disturbance are subject to rapid demographic
fluctuations resulting from variations in birth and death rates. Environmental
fluctuations that cause a variation in food supplies, predation, disease, or competition,
combined with natural catastrophes such as fires, floods, storms or droughts can result
in the complete extinction of small populations that simply do not have the numbers or
genetic variability to withstand such events (Williams, Nichols, & Conroy, 2001)
1.6.5 Increased levels of ultraviolet radiation
Exposure to ultraviolet-B (UV-B) radiation has been implicated as a contributing factor
in the global decline of amphibians (Belden & Blaustein, 2001). Increased levels of
13
UV-B due to ozone depletion has been found to cause damage to DNA and reduce
photolyase levels which can repair such damage (Goldingay, 2008). Bell Frogs appear
to be less vulnerable to the harmful effects as eggs do not remain on the surface of the
water and hatch within about 3 days therefore receiving limited exposure to the
radiation (van de Mortel & Buttemer, 1996).
.
2. Aims and Objectives The aim of this study is to continue monitoring of the known L. aurea populations to aid
the conservation and population recovery of the species
Continued monitoring of previously known habitat of L. aurea to conduct
population surveys
Conduct nocturnal surveys at previously identified sites (Blue Lake and southern
swamp) during breeding season
Mark recapture method using PIT tagging and processing (measurements of
snout-urostyle length, weight, and sex determined)
.
3. Methods
3.1 Study area
The study was conducted in Yuraygir National Park (YNP) in North-eastern Australia
between November and December 2015. YNP occupies 21500 ha which extends 70km
along the coastline between the Corindi and Clarence Rivers and is one of the largest
undeveloped stretches of coastline in NSW (NPWS, 2016). The study area included
known L. aurea habitat at Station Creek which had previously identified by Goldingay
and Newell (2005). The rationale behind the selection of these sites was to continuing
monitoring of L. aurea populations at the most northern limit of their geographic range.
Two water bodies were surveyed using SM2 sound meters (Wildlife acoustics, 2016)
whilst Blue Lake and the southern swamp were surveyed using active search utilising
mark recapture methods.
The first documented report of L. aurea in YNP were from observations made by
Clancy in 1980 (Clancy, 1996) when a single individual was sighted. Later surveys
(Lewis and Goldingay, 1999) observed 10 or less individuals. The most recent study by
Goldingay and Newell (2005) identified >100 male frogs from two sites. For this study,
surveys were confined to these same two sites, Blue Lake and the Southern Swamp
(Map 1 & 2), with casual observations of ephemeral ponds.
14
Map 1. Location of Yuraygir National Park and Station Creek Camping area. Source: Google
Earth, 2015.
Map 2. Location of Sampling sites, Blue Lake and Southern Swamp. Source: Google Earth, 2015.
Blue lake (Figure 1) is a large coastal lagoon situated within a dunal complex with
Paperbark forest (Melaleuca quinquinervia) dominating the western boundary of the
lake. The eastern side of Blue Lake generally consists of swamp She-oak (Casuarina
glauca) forest. The perimeter of Blue Lake consists of emergent vegetation including
cumbungi (T. orientalis), common reed (Phragmites australis) and Sawsedge (Gahnia
15
clarkei), a sparse distribution of spikerush (Eleocharis acuta) and Blue water lily
(Nympaea capensis). Submergent vegetation identified consists of stonewort (Nitella
sp.) and yellow Bladderwort (Utricularia australis).
Figure 1. Blue Lake, Yuraygir National Park, NSW. Photo: J. Dempster.
Southern Swamp (Figure 2) connects to Blue Lake at its southern end when there is
sufficient rainfall and is ~ 0.3 ha in area to a depth of ~ 1metre. The western edge
vegetation consists of G. clarkei with M. quinquinervia. Aquatic vegetation is similar to
that found in Blue Lake.
Figure 2. Southern Swamp, Yuraygir National Park, NSW. Photo: J. Dempster.
16
3.2 Climate and Rainfall
The annual mean rainfall the Mid North Coast is 1669.5 mm, most of which falls during
the summer months. Summer temperatures are warm, averaging between 19 and 27°C
and winter temperatures range from minimums of seven to daily maximums of 19°C
(Bureau of Meteorology, 2016). The previous summer’s rainfall was above average
(Figure 3) which may have influenced numbers observed during sampling.
Figure 3. Rainfall for 2014-2015 compared to mean. (BoM, 2016).
3.3 Survey Design
The sampling design was structured into three sessions between 2 November 2015 and
8 December 2015, with three consecutive nights surveyed within each session. The
sessions were selected on the basis of suitable weather conditions and the availability of
staff. Minimal rainfall (2.8mm) was experienced in the five days preceding the survey.
Surveys were separated by intervals of 7- 27 days so that gains and losses to the
population could occur, although the period between the initial and second survey was
insufficient to demonstrate this. The population was assessed as closed at the time of
sampling. Catch Mark Recapture (CMR) data was obtained using the methods of
Goldingay and Newell (2005). The lake and swamp including adjacent vegetation were
traversed just after nightfall, both on foot and with kayaks. Pre-recorded calls of L.
aurea and mimicry were used to elicit responses from unseen males, and frogs were
then located by eye-shine from head torches.
Frogs were captured by hand and nets in separate plastic bags and their GPS location
documented and also placed in the bag. Frogs were then taken back to a central location
nearby for processing. Individuals were implanted subcutaneously with a passive
integrated transponder (PIT) tag and the entry site sealed with medical grade
cyanoacrylate (Vetbond) adhesive (3M, 2016). The PIT tag number, sex, weight, snout–
vent length and capture location for all individuals was recorded before release at their
0
50
100
150
200
250
300
350
400
450
500
Rai
nfa
ll (m
m)
Month
Woolgoolga Rainfall
Rainfall
Mean
17
initial capture location. Sex was determined on the basis of the presence of dark nuptial
pads in males. Surveys took between 2.5 and 5.5 h per night depending on the number
of captured frogs.
All bell frogs captured were handled in coherence with frog hygiene protocols (NPWS,
2003).
3.4 Data analysis
Program MARK was used to analyse the data collected from six nights of nocturnal
surveys. MARK provides parameter estimates from marked animals when they are re-
captured at a later time and tests models of the variables that influence these parameters
(Colorado State University, 2016). These parameters include; apparent survival (phi),
which is the probability of individuals surviving between capture and recapture,
captures (p), the availability of capture, probability of recapture (c), probability of entry
(PENT) the probability of individuals entering into the population for this occasion and
finally abundance (N) which is the total number of animals entering the site during the
sampling period that survive until the next sample time. N is sometimes referred to as
the super population or hypothetical/theoretical population.
The Akaike Information Criterion (AICc) was used to compare models and corrected
for small sample size (Burnham and Anderson 2002). Models were ranked from
smallest to largest AICc value with the top ranked model showing the best fit to the
data.
Only adult male Bell Frog data was used in the analysis.
3.5 Additional Field work
Songmeters were installed at the sampling sites in addition to two meters which were
placed at a nearby artificial dam which was previously identified as habitat and an
adjacent wetland to obtain population estimates and possible identification of new
habitat. Surveying of fish species in the Lake and swamp were also undertaken to
establish the abundance of fish species in the study site that may impact on tadpole
survival. Ephemeral Ponds in the vicinity were also assessed for presence of Green and
Golden Bell Frogs as they have been utilised for breeding there in the past. During the
sampling period no evidence of breeding was detected at any of the ponds. This may be
due to insufficient rainfall required to maintain water in the ponds. Further surveys are
required to establish if GGBF are still using these ephemeral ponds as breeding habitat.
4. Results Overall a total of 133 frogs (70 males, 9 females, 54 sub-adults) were captured on six
occasions. Across the study, 34 frogs were captured on the first occasion, 57 on the
second and 42 on the last. Fifteen sub-adults were not tagged due to their small size
<40mm
18
Figure 4. Capture results for male, female and sub-adult L. aurea over six nights
Overall 133 frogs were captured, however, only the 70 adult males were used for this
analysis.
POPAN design
Analysis with the POPAN design showed that the best-fitting model was that in which
survival (phi) and capture (p) were constant over time and the probability of entry (Pent)
was time varying (Table 1). Model averaging was applied to estimate parameters.
Survival was estimated at 0.69, capture as 0.49, and the probability of entry varied from
0.11to 0.41(Table 2). Abundance was estimated for the six survey occasions at 116
individuals (Table 3).
Table 1. POPAN model
Model AICc Delta AICc AICc
Weight
Model
likelihood
No. par Deviance
{p(.)phi(.)pent(t)} 190.3996 0.0000 0.9991 1.0000 8 -123.0975
{p(t)phi(t)pent(t)} 208.9427 18.5431 0.00009 0.0001 17 -128.8280
{p(.)phi(.)pent(.)} 9921.3953 9730.9957 0.00000 0.0000 4 9617.1282
{p(.)phi(t)pent(t)} 10028.3489 9837.9493 0.00000 0.0000 12 9704.7209
0
5
10
15
20
25
2/11/2015 3/11/2015 11/11/2015 12/11/2015 7/12/2015 8/12/2015
Fro
gs c
aptu
red
Sampling Date
Males
Females
Sub-adults
19
Table 2. Survivorship (phi), capture (p) and probability of entry (PENT) estimates.
Real Function Parameters of {p(.) phi(.) pent(t)} 95% Confidence Interval
Parameter Estimate Standard Error Lower Upper
1:Phi 0.6894977 0.0627640 0.5555613 0.7977639
2:p 0.4901386 0.0768582 0.3447374 0.6372278
3:pent 0.1136285 0.0600647 0.0383060 0.2920777
4:pent 0.3316840 0.0722907 0.2075477 0.4846585
5:pent 0.4105663E-010 0.3938780E-008 -0.7678953E-008 0.7761067E-008
6:pent 0.3196601E-008 0.7849900E-005 -0.1538261E-004 0.1538900E-004
7:pent 0.4110918 0.2848553 0.0692998 0.5502291
8:N 99.166886 12.981581 81.453955 134.85557
Table 3. Population estimate derived from POPAN 6 model.
Gross Population Estimates of {p(.) phi(.) pent(t)} 95% Confidence Interval
Grp. Occ. N*-hat Standard
Error
Lower Upper
1 0 115.93050 15.424874 89.420565 150.29967
5. Discussion
5.1 Population stability
Surveying and continued monitoring of population abundance is important to
comprehend exactly what is being lost and for the design and implementation of
management plans to conserve species throughout a species geographic range. This is
especially important for small and disjunct populations such as the one in Yuraygir
National Park, which may be genetically different and at risk from inbreeding
depression, genetic drift and other environmental conditions (Luquet, et al. 2013;
Goldingay and Newell, 2005).
We sampled a population of Green and Golden Bell Frogs at Yuraygir National Park in
northern NSW to establish if the population has increased, decreased or remained stable
during the 12 years since the last study. This study follows on from surveys conducted
20
by Goldingay and Newell between 1998 and 2004 at the same site. Abundance
estimates by Goldingay and Newell was calculated using the Peterson method at <100
adult male Bell Frogs. This method uses the assumption the population being closed at
the time of sampling and that and that individuals have an equal chance of being
captured. These assumptions may over estimate numbers and should be taken with
caution. For this study abundance was estimated using Program MARK using the
POPAN design and compared the estimated abundance to previous CMR data. Initial
results revealed the population has remained the same as 2005 abundance estimates and
is therefore stable, however, the size of the sampling area during this period was half
that previously surveyed and the number of sampling occasions was substantially less,
with only six survey nights compared to the 31 of Goldingay and Newell in 2005. When
considering these limitations we may confidently say that the population has increased
over the past 12 years, possibly doubling in size.
Sub-adult numbers increased from three (Goldingay and Newell, 2005) to 42. This may
be explained by higher than average rainfall during the previous summer breeding
period. The increase in rainfall decreases the chance of ephemeral ponds, which are
preferred breeding habitat, drying out before metamorphosis of tadpoles. Substantially
less females were tagged, with only nine adult females captured over the six survey
nights. These findings are consistent with previous work, from multiple sites, that
identified an apparent skewed sex ratio in Green and Golden Bell Frog populations
(Goldingay & Newell, 2005).
5.2 Management options
The population of L. aurea at Yuraygir National Park appears to have increased over 12
years. Continued monitoring should be undertaken, as the populations may still be at
risk of future declines and here we present a method that would allow this to occur at
intervals such as once every 5-6 yrs
There is too little information available on life history parameters to ascertain if the
numbers observed can be interpreted as a viable population. Putative suggestions of a
population increase, recommend that monitoring should continue every 5-10years.
Although the sampling method demonstrated here would be adequate to assess further
population fluctuations, this was part of a larger CMR study being conducted and the
extended sampling timeframe used by these researchers would be more a more
representative example of the population.
Unlike most Green and Golden Bell Frog populations, the population in YNP is located
in a relatively undisturbed site which could be used for comparable studies with other
populations. Increases in abundance found here may not be representative of a species
increase in other areas and the success of the YNP population may be used to determine
habitat requirements for L. aurea at other sites.
The likely incidence of Chytrid fungus (Batrachochytrium dendrobatidis) present in the
YNP population is also worth further investigation to determine the impact on survival.
As the site is affected by ocean salt spray future research may focus on findings by
21
Stockwell et al. (2015), which suggest an increase in salinity provides fungicidal
benefits to the species.
One approach to increase breeding success at the site would be the installation of
artificial ponds adjacent to the study sites which may overcome future decreases in
breeding success when ephemeral ponds do not retain sufficient water during dry
periods, which are expected to increase with the impacts of climate change.
22
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27
Appendices
Appendix 1.
Figure 5. Colourmorphs of Yuraygir. Photos: D. Newell & R. Goldingay.
Appendix 2.
Figure 6. Male L. aurea on M. quinquinervia tree. Photo: R. Goldingay.
28
Estimates of Derived Parameters
Gross Birth+Immigration Estimates of {p(.) phi(.) pent(t)}
95% Confidence Interval
Grp. Occ. B*-hat Standard Error Lower Upper
---- ---- -------------- -------------- -------------- --------------
1 1 13.492395 7.2457751 5.0303326 36.189400
1 2 39.384596 9.0126917 25.293901 61.324916
1 3 0.4875118E-008 0.4677067E-006 0.1307099E-010 0.1818285E-005
1 4 0.3795686E-006 0.9321208E-003 0.1644067E-009 0.8763165E-003
1 5 48.813578 11.895892 30.484798 78.162415
Net Birth+Immigration Estimates of {p(.) phi(.) pent(t)}
95% Confidence Interval
Grp. Occ. B-hat Standard Error Lower Upper
---- ---- -------------- -------------- -------------- --------------
1 1 11.268183 6.0257856 4.2165719 30.112603
1 2 32.892074 7.1582635 21.576489 50.142010
1 3 0.4071458E-008 0.3906056E-006 0.1091624E-010 0.1518542E-005
1 4 0.3169970E-006 0.7784614E-003 0.1373044E-009 0.7318564E-003
1 5 40.766695 10.075962 25.294626 65.702631
Population Estimates of {p(.) phi(.) pent(t)}
95% Confidence Interval
Grp. Occ. N-hat Standard Error Lower Upper
---- ---- -------------- -------------- -------------- --------------
1 1 14.239934 5.6518841 6.7287546 30.135698
1 2 21.086584 6.2868991 11.901510 37.360304
1 3 47.431224 7.0001976 35.572345 63.243539
1 4 32.703717 6.0395225 22.841026 46.825091
1 5 22.549137 5.6597709 13.890939 36.603974
1 6 56.314272 11.882475 37.407743 84.776493
Gross Population Estimates of {p(.) phi(.) pent(t)}
95% Confidence Interval
Grp. Occ. N*-hat Standard Error Lower Upper
---- ---- -------------- -------------- -------------- --------------
29
1 0 115.93050 15.424874 89.420565 150.29967