Connecting the dots: tracking bull sharks from a provisioning site into the species’ river parturition sites in Fiji

Context For sharks, information on the location and usage of critical habitats is rare. Marine protected areas (MPAs) have great potential to benefit shark populations but these rarely protect a species throughout its life stages or all critical habitats. The latter often includes parturition sites. Aims Pregnant bull sharks from the Shark Reef Marine Reserve in Fiji were tracked into riverine systems during three parturition seasons. Methods We tagged 31 female bull sharks with acoustic transmitters and placed acoustic receivers in the Rewa, Sigatoka, Navua and Ba Rivers on the island of Viti Levu between 2016 and 2018. Key results Fourteen bull sharks were detected by receivers placed in the four rivers for few, typically consecutive days during parturition season. Bull sharks were detected in the Rewa River during all three parturition seasons whereas sharks were detected in the Navua River only during the 2017/2018 season. Conclusions We have shown that Fiji’s rivers are critical for the completion of the bull shark’s life cycle. Implications Fiji has recognized the importance of conserving its population of bull sharks. Our results call for the implementation of protective measures for the species’ critical habitats.