Data from: Discovery of a multi-species shark aggregation and parturition area in the Ba Estuary, Fiji Islands

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 semi-healed),
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.