Mary River turtle (Elusor macrurus) and white-throated snapping turtle (Elseya albagula)
About White-throated snapping turtle Elseya albagula
Elseya albagula, commonly known as the white-throated snapping turtle, is one of the largest species of chelid turtles in the world, growing to about 45 cm carapace length and is critically endangered (Environment Protection and Biodiversity Conservation Act 1999). The species is endemic to south-eastern Queensland, Australia, in the Burnett, Mary, and Fitzroy River drainages. Turtle life histories are characterised by long life spans, slow growth to maturity and multiple breeding events, typically in a defined season. In the three catchments in which the white-throated snapping turtle is found, approximately all adult females will breed in each successive year, unless the turtle has been injured or debilitated or unless the riverine habitat has been severely depleted through severe drought or excessive water extraction. This is a low fecundity species, laying only a single clutch of eggs per annual breeding season, averaging 14 eggs per clutch (Hamann et al., 2007; Limpus, 2008; Limpus et al., 2011). Age at first breeding is approximately 15-20 years (Limpus et al., 2011).
About Mary River turtle Elusor macrurus
Elusor macrurus is one of several species of cloaca-breathing turtles, which breathe underwater using specialised glands in their reproductive organs. This allows individuals to remain submerged for up to 72 hours. The Mary River (Elusor macrurus) turtle is a large freshwater turtle endemic to the Mary River in Queensland and is endangered (Environment Protection and Biodiversity Conservation Act 1999). This turtle is highly distinctive, both morphologically and evolutionarily. It is the only species in its genus.
Both Elseya albagula and Elusor macrurus have similar water requirements to support breeding events. For a potentially successful breeding year, firstly a connectivity event to allow movement for partnering / mating needs to occur between March and May. At least two weeks following this partnering connectivity (to allow for egg fertilisation), there needs be a suitably large rainfall event to soften the stream banks to allow the digging of nests and egg laying. After a potentially successful egg laying, there needs to be a prolonged period (6 months) where the banks containing nests are not inundated. The model uses site based data relating water level depth to percent of nests inundated to capture the relative impact of high flows during this incubation period.
The purpose of the model is to analyses long times series of modelled flow in conjunction with observed rainfall to determine if the risk to successful breeding events is adversely affected by water resource development (represented in the modelled flow).
This model, describing the flow requirements for spawning and egg and larval survival, has been developed using quantitative information from the literature and expert opinion. It was developed to support the Queensland Department of Environment and Resource Management’s ecological risk assessment for the Mary River Water Resource Plan (WRP) review.
This model and its default parameters were created for application in the Mary River, Queensland. However, the model parameters could be edited to suit other locations or species with similar requirements.
A potentially successful breeding year is defined as:
- Connection event for partnering (March to May: Elseya albagula; June to October: Elusor macrurus) defined as flow above a certain cease to flow threshold. The connectivity threshold can be defined as discharge (ML/d) or depth, depending on the available input time series.
- Egg fertilisation – A period of 14 days after the partnering connectivity is required for egg fertilisation before egg laying (Typically May to July: Elseya albagula; September to December: Elusor macrurus).
- Egg laying – A rainfall event of >10mm is required to soften the river bank to allow nest excavation.
- Incubation – Following the egg laying, an extended period of low flow is required to allow egg incubation (168 days: Elseya albagula; 52: Elusor macrurus) (Typically July to December: Elseya albagula; December to February: Elusor macrurus). Flow is considered during the incubation period to identify any potential inundation of nests. The potential inundation of nests is captured via a relationship between water height and potential nests inundation.
Assessment is based on considering if the partnering event has occurred, followed by an potential egg laying event and the level of potential success is represented by the proportion of banks that are not affected by inundation during the incubation period. In order for a year to be deemed successful, the max inundation threshold (set on the interface) must not be exceeded.
These binary yearly results are then aggregated to temporal assessment results, by considering the number of consecutive years without success.
Finally, the temporal results are then analysed across locations to report an overall landscape risk by considering the simultaneous occurrence of failures across the system.
- Daily depth data
- Daily rainfall data
- Partnering event – Parameters to define partnering success. Included season, cease to flow threshold and the amount above cease to flow required for partnering success
- Rainfall event – Parameters to define rainfall event success, which must occur following a partnering event. This includes the rainfall threshold and the minimum days since partnering.
- Stable water level – Parameters to define the stable water level requirement post laying. This includes the duration needed, the nest inundation curve, the inundation risk curve and the max inundation threshold for recruitment success.
- Yearly time series of recruitment success. This include intermediate results such as the inundation %, the risk level of this inundation, if recruitment was attempted and the recruitment failure reason (if applicable).
- Temporal time series of assessment results
- Spatial time series of assessment results
This plugin is written in Python and its underlying code is publicly available from the Eco Risk Projector computation repository.
Hamann M., Schauble C. S., Limpus D. J., Emerick S. P. and Limpus C. J. (2007). Management Plan for the Conservation of Elseya sp. (Burnett River) in the Burnett River Catchment. Queensland Environmental Protection Agency Brisbane.
Limpus C. J. (2008). Freshwater turtles in the Mary River, Queensland. Review of biological data for turtles in the Mary River, with emphasis on Elusor macrurus and Elseya albagula. Environmental Protection Agency Brisbane.
Limpus C. J., Limpus D. J., Parmenter C. J., Hodge J., Forest M. and McLachlan J. (2011). The Biology and Management Strategies for Freshwater Turtles in the Fitzroy Catchment, with particular emphasis on Elseya albagula and Rheodytes leukops: A study initiated in response to the proposed construction of Rookwood Weir and the raising of Eden Bann Weir. Department of Environment and Resource Management Brisbane.