Barramundi (Lates calcarifer) year class strength
About Lates calcarifer
L. calcarifer is a long-lived, catadromous fish species that occurs throughout northern Australia. It has been selected as an ecological asset for the Fitzroy WRP because it is a valuable commercial and recreational fishery and has a critical link to flows for the recruitment and growth of juveniles. The development of water infrastructure in the Fitzroy and the associated impacts on connectivity and water quality are known to have impacted Barramundi populations.
This model, describing the flow requirements for Barramundi year class strength (YCS), draws on the work of Halliday and Robins (2007) analysing age structures of commercially-caught Barramundi. They found that increased summer flows lead to an increased Barramundi cohort size.
The purpose of the model is to analyses long times series of modelled flow to determine if the risk to YCS of Barramundi is adversely affected by proposed water resource development for the Fitzroy River (Qld).
This model, describing YCS of Barramundi 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.
This model and its default parameters were created for application in the Fitzroy River estuary, 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.
Barramundi YCS was determined using the age-structures of the commercial catch of barramundi collected bi-annually over five consecutive years in the Fitzroy estuary (2000 – 2005; n = 2112; from Halliday et al 2007). The standardised residuals from the catch-curve regressions were used to give an indication of relative YCS for barramundi aged between 3 to 11 years old. These data were then compared against summer flow (December – February) to develop a log-linear equation that calculates YCS index score:
Y = 0.7227x – 4.1011
where y is YCS recruitment index score, and x is Log10 flow volume in ML during Summer
The YCS index output by the computation can be used to determine the degree of recruitment strength in a given year:
- Strong recruitment = >0.5 YCS index
- Moderate recruitment = 0.5 to -0.5 YCS index
- Poor recruitment = <-0.5 YCS index
Strong recruitment years (>0.5 YCS index) were considered to be those required to maintain a healthy barramundi population and the greater the number of years between these events, the higher potential risk to barramundi populations.
High risk profile (i.e. potential local population failure) was defined as any year where the number of consecutive years without strong recruitment exceeded 11 years (the longevity of most barramundi).
Moderate risk profile was defined as any year where the number of consecutive years without strong recruitment was between 5 (age at sexual maturity) and 11 years.
Low risk profile was defined as any year where the number of consecutive years without strong recruitment was less than 5 years.
A binary yearly value is determined by classifying strong years successful, and all other strength as a failure. These results are then aggregated 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 data
- Summer flow period – the period to analyse the data from. Includes a data picker to define the season.
- Constants – the constants to use when applying the YCS equation, as discussed above. Includes both a and b values.
- Intermediate assessment – parameters defining the intermediate assessment results calculated by this model. This includes the annual recruitment strength (what YCS is required to provide string, moderate or poor recruitment) and the temporal risk (how many years without strong recruitment is high, moderate or low risk). Assessment results are still provided, separately to these intermediate assessment results.
- Yearly time series of YCS index score, recruitment strength and risk.
- Temporal time series of assessment results (This is seperate to the temporal risk which is included in the yearly intermediate 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.
Halliday I, Staunton-Smith J, Robins J, Mayer D and Sellin M 2007, ‘Using age-structure of commercial catch to investigate the importance of freshwater flows in maintaining barramundi and king threadfin populations. 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.