Discovery of a multispecies shark aggregation and parturition area in the Ba Estuary,Fiji Islands |
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| Authors: | Tom Vierus Stefan Gehrig Juerg M Brunnschweiler Kerstin Glaus Martin Zimmer Amandine D Marie Ciro Rico |
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| Institution: | 1. School of Marine Studies, Faculty of Science, Technology and Environment, The University of the South Pacific, Laucala, Suva, Fiji;2. Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany;3. Department of Biosciences, University of Exeter, Penryn Campus, UK;4. Independent Researcher, Zurich, Switzerland;5. Faculty of Biology/Chemistry, University of Bremen, Bremen, Germany;6. Department of Wetland Ecology, Estación Biológica de Do?ana, Consejo Superior de Investigaciones Científicas (EBD, CSIC), Sevilla, Spain |
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| Abstract: | Population declines in shark species have been reported on local and global scales, with overfishing, habitat destruction and climate change posing severe threats. The lack of species‐specific baseline data on ecology and distribution of many sharks, however, makes conservation measures challenging. Here, we present a fisheries‐independent shark survey from the Fiji Islands, where scientific knowledge on locally occurring elasmobranchs is largely still lacking despite the location's role as a shark hotspot in the Pacific. Juvenile shark abundance in the fishing grounds of the Ba Estuary (north‐western Viti Levu) was assessed with a gillnet‐ and longline‐based survey from December 2015 to April 2016. A total of 103 juvenile sharks identified as blacktip Carcharhinus limbatus (n = 57), scalloped hammerhead Sphyrna lewini (n = 35), and great hammerhead Sphyrna mokarran (n = 11) sharks were captured, tagged, and released. The condition of umbilical scars (68% open or semihealed), mean sizes of individuals (±SD) (C. limbatus: 66.5 ± 3.8 cm, S. lewini: 51.8 ± 4.8 cm, S. mokarran 77.4 ± 2.8 cm), and the presence of these species over recent years (based on fishermen interviews), suggest that the Ba Estuary area is a critical habitat for multiple species that are classified as “Near Threatened” or “Endangered.” Specifically, the area likely acts as a parturition ground over the studied period, and potentially as a subsequent nursery area. We identified subareas of high abundance and found that temperature, salinity and depth acted as small‐scale environmental drivers of shark abundance. The data suggests a tendency for species‐specific spatial use, both horizontally (i.e., between sampling areas) and vertically (i.e., across the water column). These results enhance the understanding of shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of these threatened species. |
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| Keywords: | blacktip sharks elasmobranchs hammerhead sharks neonates shark bycatch young‐of‐the‐year sharks |
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