ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Physiological ecology of bull sharks Carcharhinus leucas in the Brisbane River

Richard D. Pillans^1,2 and Craig E. Franklin²

¹ CSIRO Marine Research, PO Box 120, Cleveland Qld, 4163, Australia
²Zoology Department, School of Life Sciences, University of Queensland, Brisbane, Australia
Email: richard.pillans@csiro.au

The bull shark Carcharhinus leucas is one of the only elasmobranchs capable of surviving for long periods of time in both freshwater and seawater. Despite this remarkable ability, large size and worldwide distribution, there is little biological information on this species. Female bull sharks are believed to give birth to 1 - 13 live young in estuaries or river mouths. Juveniles then move upriver and are probably restricted to fresh/low salinity water for their early years; however, there is no data to support this theory.

This study is investigating the movement patterns and distribution of C. leucas in the Brisbane River by tagging large numbers of sharks with plastic tags as well as using acoustic tags to track individuals. The length of time juvenile C. leucas spend in freshwater and their movement patterns within the Brisbane River have been investigated. Data are presented on four sharks tracked for between 2 – 6 weeks and over 350 tagged sharks ranging in size from 56 – 156 cm TL, of which 45 have been recaptured to date. Size at age data and growth rates of sharks will be determined from vertebral ring counts and tag-recapture data.

The physiological mechanisms that enable C. leucas to survive in both freshwater and seawater were also investigated. There were significant differences in the physiological responses to exposure to freshwater and seawater. These differences include changes in blood chemistry as well as chemical and morphological changes in key osmoregulatory organs including gills, rectal gland, intestine and kidney.

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