Movements of Diadromous Fish in Large Unregulated Tropical Rivers Inferred from Geochemical Tracers

Walther, Benjamin D.
Dempster, Tim
Letnic, Mike
McCulloch, Malcolm T.
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Public Library of Science

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 (87Sr/86Sr) 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 87Sr/86Sr 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.

Benjamin D. Walther is with Australian National University and UT Austin, Tim Dempster is with University of Melbourne, Mike Letnic is with University of Western Sydney, Malcolm T. McCulloch is with Australian National University and The University of Western Australia.
Walther BD, Dempster T, Letnic M, McCulloch MT (2011) Movements of Diadromous Fish in Large Unregulated Tropical Rivers Inferred from Geochemical Tracers. PLoS ONE 6(4): e18351. doi:10.1371/journal.pone.0018351