Generally describes a fish stock for which current catches and fishing pressure are close to optimal. In the Status of fisheries resources in NSW 2008–09[2], this term has the following specific meaning: ‘Fishing mortality is approximately the same as natural mortality; estimates of biomass are greater than 30 per cent of the estimated unfished biomass; catch rates have been steady for 5–10 years and/or catch rates are greater than 30 per cent of initial catch rates; length and age distributions are stable; species are fished throughout their entire geographic range’.