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Developing a frog monitoring method for environmental watering of billabongs

Alisa Fisher (Waterwatch Coordinator, Melbourne Water)

Billabongs of the Lower Yarra River are watered as part of the Yarra River environmental entitlement. One of the key values of these billabongs are frogs, with ten species recorded historically across the area.

Up until now, frog monitoring has largely relied upon frog call recognition to determine which species are present. These data have usually been obtained from song recorders, which record calls for set periods and are then analysed by an ecologist. Some citizen science data has been recorded and as James Frazer, a Waterwatch Coordinator, tells us “Citizen scientists have supported the billabong program for the past 3 years, with some volunteers monitoring sites for over 20 years. That said, coverage of reports has been low at some sites so there has been a need to formalise and scale up”.

 

A screen shot from the Frog Census app showing the geo-fence around Lower Yarra Banyule Flats Billabong. Credit: Alisa Fisher.

In addition to species presence, success of the billabong watering program for frogs is determined by watering at the right time and the right amount to ensure frogs are able to complete life cycle stages and successfully reproduce. The timing and duration of watering required for breeding varies between species, and the water holding capacity also differs between billabongs. 

Effective monitoring of frogs was identified as a gap in the Environmental Water Resources strategy, with the Lower Yarra Billabongs identified as the ideal location for a pilot study.

To obtain more data on species presence, Waterwatch worked with the Melbourne Water Environmental Water team to enhance the existing Melbourne Water Frog Census app to geo-fence the Lower Yarra Billabongs. A geo-fence is a virtual boundary for a geographical area, in this case a billabong. This approach allowed us to highlight billabongs of interest (such as those about to receive water) within the app and recruit volunteer effort to these sites. 

The collaboration between Waterwatch and the Environmental Water team has two main benefits: it allows for the effective collection of data on the billabongs and communicates the environmental watering program to over 1,800 Frog Census volunteers. All citizen science data collected by volunteers is analysed by ecologists to ensure correct frog species identification.

In addition, Ecology Australia has been engaged to develop a conceptual model and monitoring protocol of frog responses to watering. This involves a combination of call identification, tadpole monitoring, nocturnal surveys and water level and quality monitoring. 

The conceptual model will guide the appropriate watering regime for each billabong, depending on what species are present, and the monitoring program will allow us to determine whether the watering has resulted in successful frog reproduction in each of the billabongs. 

The monitoring protocol will allow us to add water when the frogs need it, such as if tadpole metamorphosis is incomplete and the billabong is drying out. Further refinement of watering recommendations to specific billabongs is another benefit. As each billabong has different conditions (e.g., water holding capacity, water chemistry, stormwater inputs, time since last watered) it is necessary to monitor during watering events, until such time as we have a greater understanding of how each billabong and their frog communities respond to the watering.

Along with geo-fencing of the app, other app upgrades include a reporting function that will allow users to download frog data sets directly from the app; frog report verification which will confirm species ID and include assessor comments; and other bug fixes. The upgrade will be launched in Autumn 2021.

For more information contact Waterwatch here: waterwatch@melbournewater.com.au

This article was first published in the ESA Bulletin March 2021. 

Willsmere Billabong after receiving a much needed drink of environmental water. Credit: Alisa Fisher.

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