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Discovery of a multispecies shark aggregation and parturition area in the Ba Estuary, Fiji Islands

Vierus, Tom and Gehrig, Stefan and Brunnschweiler, Juerg M. and Glaus, Kerstin and Zimmer, Martin and Marie, Amandine D. and Rico, Ciro (2018) Discovery of a multispecies shark aggregation and parturition area in the Ba Estuary, Fiji Islands. Ecology and Evolution, 8 (14). pp. 7079-7093. ISSN 2045-7758

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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.

    Item Type: Journal Article
    Uncontrolled Keywords: blacktip sharks, elasmobranchs, hammerhead sharks, neonates, shark bycatch, young-of-the-year sharks
    Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
    Q Science > QH Natural history > QH301 Biology
    Divisions: Faculty of Science, Technology and Environment (FSTE) > School of Marine Studies
    Depositing User: Fulori Nainoca
    Date Deposited: 18 Sep 2018 14:28
    Last Modified: 18 Sep 2018 15:42
    URI: http://repository.usp.ac.fj/id/eprint/11028
    UNSPECIFIED

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