Freshwater flows affect the year-class strength of 'Barramundi lates calcarifer' in the Fitzroy River estuary, Central Queensland

The age-structure of the commercial catch of barramundi in the Fitzroy River estuary, central Queensland, was examined over five consecutive years and used to estimate year-class strength (= index of recruitment). Barramundi year-class strength fluctuated and was significantly and positively correlated with freshwater flow and coastal rainfall in spring and summer. General linear models were used to identify relationships between year-class strength and freshwater variables, and explained between 85 and 90% of the variation in barramundi year-class strength. The results provide further evidence that recruitment variation in barramundi: (i) persists over time; and (ii) is significantly correlated with the volume to freshwater flowing into the estuary. We reviewed the evidence in support of the three causal mechanisms currently proposed to explain the relationship between year-class strength and juvenile barramundi recruitment; and propose an additional mechanism, that of enhanced growth rates and thus increased survival of young-of-the-year. Freshwater flow is an important driver of barramundi recruitment, and reduction in flow, through water abstraction or climate change, will potentially reduce barramundi stock size available for human harvest. As such, fishery stock assessments for barramundi should explicitly consider the impacts of variable flow on annual recruitment and stock dynamics. environmental flows, fish recruitment, otoliths.