title: Movements of diadromous fish in large unregulated tropical rivers inferred from geochemical tracers.
abstract: Patterns of migration and habitat use in diadromous fishes can be highly variable among individuals. Most investigations into diadromous movement patterns have been restricted to populations in regulated rivers, and little information exists for those in unregulated catchments. We quantified movements of migratory barramundi Lates calcarifer (Bloch) in two large unregulated rivers in northern Australia using both elemental (Sr/Ba) and isotope ((87)Sr/(86)Sr) ratios in aragonitic ear stones, or otoliths. Chemical life history profiles indicated significant individual variation in habitat use, particularly among chemically distinct freshwater habitats within a catchment. A global zoning algorithm was used to quantify distinct changes in chemical signatures across profiles. This algorithm identified between 2 and 6 distinct chemical habitats in individual profiles, indicating variable movement among habitats. Profiles of (87)Sr/(86)Sr ratios were notably distinct among individuals, with highly radiogenic values recorded in some otoliths. This variation suggested that fish made full use of habitats across the entire catchment basin. Our results show that unrestricted movement among freshwater habitats is an important component of diadromous life histories for populations in unregulated systems.
authors.affiliation: Australian Research Council Centre of Excellence for Coral Reef Studies, Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory, Australia. bwalther@mail.utexas.edu
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Walther
authors.forename: Tim
authors.initials: T
authors.lastname: Dempster
authors.forename: Mike
authors.initials: M
authors.lastname: Letnic
authors.forename: Malcolm T
authors.initials: MT
authors.lastname: McCulloch
mesh_terms: D000818:Animals; D001315:Australia; D017753:Ecosystem; D005399:Fishes / Q000254:growth & development / Q000502:physiology*; D005843:Geography; D007553:Isotope Labeling / Q000379:methods*; D008018:Life Cycle Stages; D009068:Movement / Q000502:physiology*; D010037:Otolithic Membrane / Q000502:physiology; D045483:Rivers; D014329:Tropical Climate