Lab Report: Winter 2020
Updated: Aug 1, 2020
By Rob Hale, WetMAP scientist
Geoff Brown and I (both from the Arthur Rylah Institute - ARI) have spent the past few months analysing the data collected from the WetMAP frog monitoring during 2018-20.
We have found clear benefits of environmental watering for frogs. Significantly more frogs were counted (number of frog species, total number of frogs, and numbers of individuals of each species) at wetlands that received environmental water than at dry sites. In many cases, we observed as many or more frogs at wetlands that received environmental water than those that are permanently wet. We have also found that water quality and habitat (like vegetation along the edges of wetlands) are important for frogs.
The total number of frogs observed at WetMAP sites during 2019 audio-visual surveys.
D “Dry”: Wetlands that did not receive environmental water and were dry, n (sample size) = 5
NAT “Natural”: Wetlands that only received natural water (e.g. rainfall) and contained water, n = 1
PW “Previously Watered”: Wetlands that have received environmental water in the previous year and still contained water, n = 3
W “Watered”: Wetlands that received environmental water in the spring, n = 9
PER “Permanently Wet”: Wetlands that always contain water and sometimes get topped up with environmental water, n = 4
The bold horizontal lines mark the median (middle) number of frogs we counted. The boxes around them show the amount of variation in our results as the (interquartile range: 25th to 75th percentile). For example, dry sites never had any frogs, but watered sites often had between 25 and 80 frogs depending on the visit. The vertical tails show the extremes of the data (values greater than 1.5 x interquartile range), and the black dot shows a value outside these extremes.
We are also starting to explore the relationship between frogs and the longer-term hydrological regime. While individual inundation events are important, understanding longer-term fluctuations is critical to managing wetlands. Our results so far show that different species respond differently to changes in wetland hydrology. For instance, we found:
more Eastern Sign-Bearing Froglets (Crinia parinsignifera) when wetlands contained water for more of the previous 30 days,
more Eastern Banjo Frogs (Limnodynastes dumerilii – also known as “Pobblebonk”) in wetlands with a higher proportion with water in the previous 90 days.
This could be because the tadpoles of the Eastern Sign-Bearing Froglet develop faster than those of the Eastern Banjo Frog. This sort of information can help us determine how much environmental water needs to be released so that wetlands have water in them when the frogs need it to breed.
We are preparing a technical report summarising our key findings for catchment management authorities and DELWP to help inform how future environmental flows can be managed most effectively.