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Species specific water requirements

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Banana prawn (Penaeus merguiensis) growth

About Penaeus merguiensis

P. merguiensis is a short-lived marine and estuarine prawn species that occurs in coastal regions of northern Australia. It has been selected as an ecological asset for the Fitzroy Water Resource Plan because it is a valuable commercial fishery and has a critical link to flows for the recruitment and growth of larvae and juveniles. Freshwater flows are required for prawn recruitment and growth in estuarine creeks. Research suggests that both prawn growth rate and commercial catch increase with increasing flow (Robbins et al 2007).

Water requirements

This model, describing the flow requirements for Banana Prawn growth, draws on the work of Robins et al (2007), determining the relationship between freshwater flows and prawn growth rate in the Fitzroy River estuary. The model represents an empirical relationship relating Banana prawn production to annual outflows from the Fitzroy River (Qld).

Model purpose

The purpose of the model is to analyse long times series of modelled flow to determine if the risk to banana prawn growth is adversely affected by proposed water resource development for the Fitzroy River (Qld).

Development context

This model, describing banana prawn growth is based on an empirical model developed for the Fitzroy River Catchment.

It was developed to support the Queensland Department of Environment and Resource Management’s ecological risk assessment for the Fitzroy River Water Resource Plan (WRP) reviews.

Spatial application

This model and its default parameters were created for application in the Fitzroy River, Queensland.

However, the model parameters could be edited to suit other locations if the underlying observation data exists to create a model of the same form.

Model description

Ecohydrological rules

Based on the data collected (from Robins et al 2007), fortnightly prawn growth and its relationship to freshwater inflow to the estuary is best represented by the nonlinear von Bertalanffy equation:

Length2 = Length1 + (L – Length1) * [1 – exp ( – {a + kc * temp + kd * temp2 + ke * flow0 + kf * flow02 + kg * flow4 } * Days + b)]

with the constants:

Days Length1 L a b kc kd ke kf kg
42 5 38 -0.0344 -0.0249 0.00297 -0.0000604 9.32E-08 -5.79E-13 5.57E-08

Flow0 is the total inflow to the estuary for the preceding two weeks and Flow4 is the total inflow during the four weeks prior to that, to account for a possible lag between the time of a flow event and the response in prawn growth.

Average daily growth is then calculated as: (Length2– Length1)/42

Assessment methods

This model produces continuous daily results (daily growth). These results are then aggregated to a binary daily result,  then to a binary yearly result, and then further to a binary temporal result based on the defined assessment parameters.

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 flow volume
  • Daily water temperature
Parameter Sections
  • Flow – Settings related to flow duration. As discussed above.
  • Constants – Settings used in the growth equation. As discussed above.


  • Daily time series of prawn growth (mm)
  • Daily time series of assessment results
  • Yearly time series of assessment results
  • Temporal time series of assessment results
  • Spatial time series of assessment results

User interface

Underlying code

This plugin is written in Python and its underlying code is publicly available from the Eco Risk Projector computation repository.


Robins J, Mayer D, Halliday I and Staunton-Smith J 2007, ‘Effects of freshwater flow on growth rates of estuarine fish In: Environmental flows for sub-tropical estuaries understanding the freshwater needs of estuaries for sustainable fisheries production and assessing the impact of water regulation, Final Report FDRC Project No. 2001/022 Coastal Zone Project FH3/AF’, Department of Primary Industries and Fisheries, Queensland Government, Brisbane.