Barramundi (Lates calcarifer) year class strength

Model description

Ecohydrological rules

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.

Assessment methods

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.

Inputs

Data

• Daily flow data

Parameter Sections

• 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.

Outputs

• 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

User interface