Habitat-use strategies of young barramundi (Lates calcarifer) in a heavily modified landscape.

Barramundi (Lates calcarifer) is a facultatively catadromous species that migrates between saltwater and fresh water to complete its life cycle. Modified riverine landscapes may limit these migratory paths and alter the environmental cues that migratory fish rely on to trigger migration. This study aims to determine the timing and prevalence of migration strategies of L. calcarifer in modified habitats and to identify the environmental parameters associated with these movements. Historical habitat use was interpreted from mean otolith Sr:Ca ratios as a proxy for ambient salinity. In this study, 27.9% (range: 16.1%-50.0% per year) of L. calcarifer exhibited catadromy, which is lower than what has been found for this species in other regions. Juvenile L. calcarifer adopted a catadromous strategy either early in life or not at all. Across the nine cohorts represented in the study, the fraction of catadromous individuals showed a moderately positive trend (r = 0.34-0.50), though not statistically significant, with wetter and cooler wet seasons. In the modified landscape of the Burdekin basin, North Queensland Australia, other factors may influence the likelihood of barramundi adopting a catadromous life strategy. Habitat connectivity is crucial for the viability of wild L. calcarifer populations and associated fisheries. Freshwater management should consider the timing required for juvenile L. calcarifer to access freshwater habitats and consider further interventions to improve habitat connectivity.