FROG MANAGEMENT PLAN FOR POND AT GREENWICH, NSW
Niche Environment and Heritage,
Description Greenwich Frog Advice
Person writing this document Frank Lemckert
Document Status Date Final Report 2nd of April 2014
Niche Environment and Heritage Pty Ltd (Niche) was commissioned to provide advice on a residential issue involving frogs at a residence in Greenwich. The swimming pool in the backyard of this residence had been turned into a pond five years earlier.
There had been no issues in regard to the pond and its wildlife until new neighbours made a complaint to Council about frog calls in October- November 2013. The pond was inspected on Tuesday 18th of February to assess its location and form, determine the species making the calls and provide advice including how to manage the number of frogs, or discourage these frogs from using the pond as a breeding site.
Adult frogs were essentially absent at the site as the breeding season was completed, but some tadpoles were still present. The locations and types of frogs using the pond were discussed along with the pond history and issues under consideration.
Discussions with Ms xxxxxx indicated that the frog causing the concern to the neighbour were the Perons Tree Frog (Litoria peronii), a species occurring in varying habitats outside of the Sydney Metropolitan area, but rarely recorded inside it in recent years.
The frogs in the Sydney Metropolitan area have suffered significant declines as a result of ongoing habitat loss and modification. The population of Perons Tree Frogs present at this pond would be considered by most conservationists as a locally and important population as it probably represents one of at best only a few remaining successful breeding populations in the Greenwich area.
The preferred management option considered is to let this rare urban breeding population persist.
If Council insists on actions to encourage the removal of the breeding population of frogs the management option is to introduce aggressive fish that will eat frogs attempting to breed in the pond as well as any tadpoles from successful reproduction. The timeframe for this to work and its final extent of success is unclear. If this is the course of action, it is recommended that fish be introduced into the pond as soon as is possible.
Purpose of this report
Niche Environment and Heritage Pty Ltd (Niche) was commissioned by Msxxx to provide advice on frog management at Greenwich. The residence at Greenwich had a swimming pool constructed in the backyard in the 1980s. The swimming pool had been converted into a “natural” pond by the owners five years previously through the cessation of filtering and chlorination and addition of aquatic vegetation. The calls of frogs had not been noticed or regarded as an issue by the owners or neighbours until October-November 2013 when a new neighbour complained to Council. Msxxx contacted Dr Frank Lemckert of Niche Environment and Heritage to provide expert advice on what could be done to manage the frog population or level of frog calls. Subsequent to that initial contact, the owners requested a Plan of Management be prepared as a basis of discussion with Council. This report forms proposals for that Management Plan.
Objectives of this assessment
This objectives then of this report are as follows:
Provide a brief background of the frogs known to be using the pond and in the Sydney area, covering their biology and current status to provide a context for their value on the site
Based on the biology, provide options for managing any frogs using the pond now and into the future
Provide recommendations as to the best course of action to be taken, based on the opinions and experience of Dr Frank Lemckert.
A site inspection was undertaken of the pond on Tuesday that 18th of February to:
a) assess the relative location and form of the pond b) determine the history of the site c) determine the species of frogs at the site and when they call d) discuss options to manage the frogs The pool was constructed in the 1980s as a standard concrete in-ground backyard swimming pool of approximately 10m X 4m. It was converted to a pond approximately 5 years ago through the cessation of filtering and the provision of aquatic vegetation to form a natural filtering of the pool. In response to the neighbours complaint and on phone advice from Dr Lemkert, 20 Australian Bass fingerlings were added to the pool in November, 2013 to discourage frog breeding and provide natural fish fauna in the pond. It is unclear if the fish have survived in the pond as they have not been seen since release. This may be due to predation by kookaburras and or vulnerability of the fingerlings in the new environment.
The pond is being used as a breeding site by frogs. A description of the frogs and their calling has identified two species to be using the site; the Striped Marsh Frog (Limnodynastes peronii) and Perons Tree Frog (Litoria peronii). It is the call of the latter species that is being heard by the neighbour. Tadpoles of this species were seen in the pond at the time of inspection and recently metamorphosed froglets of this species have been noted in the garden, indicating successful breeding by this species.
The level of aquatic algae in the pool has been significantly reduced by the presence of tadpoles, which feed mostly on these macrophytes. Its reduction is only aesthetic as the water itself remains of good quality. No water odour was observed.
Msxxx had also been advised that the vegetation in and around the pool might be managed as a means of reducing the appeal of the habitat to Perons Tree Frogs. Following this advice overhanging vegetation was trimmed to reduce ease of entry and emergent vegetation around the edge of the pond removed.
Biology of the Striped Marsh Frog and Perons Tree Frog
The Striped Marsh Frog is a species commonly occurring throughout southeastern Australia including Tasmania (Cogger 2000). It is known to be highly adaptable and remains common in the backyards of all urban areas. This species breeds in still or slow moving water bodies, ranging from large swamps down to buckets of water. Males call from under vegetation either in or next to the water and fight to maintain territories around those sites. Males can be heard essentially all year round (Lemckert and Mahony 2008), making a relatively soft tock sound (Cogger 2000). The females produce foam egg masses of up to 500 or more eggs that are deposited on the surface of the water and tadpoles hatch out of the eggs and wriggle into the water. Metamorphosis times are variable, but average 2-3 months.
Perons Tree Frog is a widespread species of tree frog found throughout southeastern Australia, but not Tasmania (Cogger 2000). It is a relatively adaptable species, but appears to be dependent on the presence of some form of elevated structures for their non- breeding habitat. In natural situations they inhabit tree tops through most of the year, only coming to the ground to breed or swap sites. In areas with human structures, this species is known to use those structures as substitutes for trees. The Perons Tree Frog calls from late September to early January (Lemckert and Mahony 2008), though at Greenwich in 2013 from October-January, undertaking a distinctive descending chuckle. However, in contrast to the Striped Marsh Frog, this species only breeds in larger water bodies such as dams, ponds and pools, generally not less than 8-10m across. It is widespread in cleared agricultural landscapes and areas of native forest and woodland, but it is rarely encountered in urban environments, both due to a lack of suitable arboreal habitats and, more particularly, due to a lack of suitable breeding sites.
Background on frogs and the Sydney area
The frogs in the Sydney Metropolitan area have suffered significant declines as a result of ongoing habitat loss and modification. This includes many once important populations of even common species that has resulted in localised extinctions within various areas of the Sydney Basin (Lemckert 2010). This continues a major trend in declines in frogs across Australia (Hero et al 2008) and the rest of the world for various reasons, all of which are related to human activities or human introduced diseases (see Lemckert et al 2012). After the effects of the Chytrid fungus in frog decline, habitat loss is considered to be the major action leading to current amphibian declines.
The population of Perons Tree Frogs present at this pond would be considered by most conservationists as a locally an important population as it will represent one of at best only a few remaining successful breeding populations in the Greenwich area. There are currently no OEH database records for this species within 10km of this site from the last 10 years indicating the ongoing declines of this species in inner Sydney as the required larger breeding sites have been destroyed or degraded to beyond the point of their being useable.
The following management options are presented for discussion with the owners and Council, keeping in mind that the family would like to retain it as a natural type pond in the back yard and the rarity of such sites in urban areas.
Removal of frogs: Consideration was given to the removal and translocation of the frogs using this site. This option is not feasible for three reasons.
1. Firstly to undertake such an action would require a license from Office of Environment and Heritage (OEH), as frogs are protected species, and these are rarely granted. This is because of the risk of spreading chytrid fungus, and issues with translocation.
2. Secondly, frogs are known to be extremely good at returning to their home territories and it would require the movement of frogs several kilometres from the site to ensure that they do not return, and this would still require a translocation license.
3. Thirdly, it is highly likely that new frogs would replace the removed frogs and so the problem would continue.
Discouraging pond use: This pond is being used as a consequence of it being suitable habitat for the Perons Tree Frog. The option is to provide an environment that will be less suitable for this species whilst retaining this area as a natural pond. The pond may be reduced in size to make it less attractive to the frogs, but it is unclear at what size it would no longer be used.
A more practical option is placing fish into the pond. Fish are known to be major predators on frogs’ eggs and tadpoles and ponds with fish are generally avoided for use by most species of frogs (Lemckert and Mahony 2010). In fact, the presence of introduced fish remains a significant threat to many species of frogs in Australia as they are highly efficient predators of frogs.
The suggested fish for use in this situation are one of the big aggressive gudgeons, although they would need to be accessed legally and discussion will be required with Council to ensure that they are wiling to accept this action. Flat-headed Gudgeons appear to be the best option as this is a local fish.
Another option is to re-introduce Australian Bass. Fingerlings might need to be raised to a more advanced age before being introduced to the pond. Increased plant cover on the water surface may be required to protect them from kookaburras.
Exclusion of breeding frogs (Sept-Jan): Another option is to place a net over the pond so that the frogs cannot access the pond water to breed. It is predicted that frogs may still attempt to access the pond in the short term and that frogs will get through the netting if this is possible in some way. The net will need to remain above the water to prevent the Perons Tree Frog from laying eggs on the surface. A disadvantage of this measure is that it will exclude the use of the water by other species of fauna, including dragon and mayflies and so not be useful for birds such as ducks, kookaburras, butcher birds etc to bathe in or drink from, besides reducing overall amenity of the property.
Maintain and value the site as a “frog hotspot”: As frogs in the Sydney Metropolitan area have suffered significant declines as a result of ongoing habitat loss and modification, a management option is to leave the pond system to adapt and evolve. As stated the population of Perons Tree Frogs present at this pond would be considered by most ecologists and conservationists as a locally important population as it will represent one of at best only a few remaining successful breeding populations in the Greenwich area. Members of the Frog and Tadpole Study Group have already voiced their concerns at the removal of this frog and the consequent loss of biodiversity in an already native fauna poor landscape. It is apparent there is an ongoing decline of this species in inner Sydney as the required larger breeding sites have been destroyed or degraded to beyond the point of their being useable. This option would fit with the Council’s initiatives to encourage backyard habitat for wildlife and biodiversity aims. Better understanding of the environment and ecological benefits of wildlife (and the improved urban amenity their presence brings) is a prelude to increased tolerance of native animals.
It is recommended that Council consider with the owners:
a) The retention of the pond and its potential to provide for an important locally breeding population of Perons Tree Frogs and discuss the significance of the site with the neighbours who complained.
The much less preferred option is to commit to the reduction and likely long-term loss of the local breeding population by:
b) Introducing a suitable species of fish into the pond as soon as is possible and assess the situation next breeding season.
Cogger, H.G. 2000. Reptiles and Amphibians of Australia - 6th edition. Sydney, NSW, Reed New Holland.
Hero, J-M, Richards, S, Alford, R., Allison, A., Bishop, P., Gunther, R., Iskandar, D., Kraus, F., Lemckert, F., Menzies, J., Roberts, D. & Tyler, M. 2008. Amphibians of the Australasian Realm. Pp 65-73 In: Threatened Amphibians of the World. S. N. Stuart, M. Hoffman, J. S., Chanson, N. A. Cox, R. J. Berridge, P. J. Ramani & B. E. Young (Eds). Lynx Edicions, Barcelona, Spain.
Lemckert, F.L. 2010. The rich early history of frog research in Sydney. Australian Zoologist 36:102-106.
Lemckert, F.L. & Mahony, M.J. 2008. Core calling periods of the frogs of temperate New South Wales, Australia. Herpetological Conservation and Biology 3:71-76.
Lemckert, F & Mahony, M.J. 2010. The relationship among multiple-scale habitat variables and pond use by anurans in northern New South Wales, Australia. Herpetological Conservation and Biology 5:537–547.
Lemckert, F.L., Hecnar S.J., & Pilliod, D.S. 2012. Habitat Destruction and Modification. In Biology of the Amphibia Volume 10: Conservation and Decline of Amphibians: Ecology, Effects of Humans, and Management. H. Heatwole (Ed.). Surrey-Beattey and Sons, Sydney.