Abstract
Sharp declines in numerous shark populations around the world have generated considerable interest in better understanding and characterising their biology, ecology and critical habitats. The scalloped hammerhead shark (SHS, Sphyrna lewini) is subject to a multitude of natural and anthropogenic threats that are often exacerbated within the coastal embayments and estuaries used during SHS early life stages. In this study, we describe the temporal and spatial distribution, age class composition, and reproductive biology of SHS in the Rewa Delta (RD), Fiji. A total of 1054 SHS (including 796 tagged individuals; 101 of which were recaptured) were captured from September 2014 to March 2016 in the RD. A majority of the captures in this area were neonates and young-of-the-year (YOY) (99.8%). Significant seasonality in patterns of occurrence of both neonates and YOY individuals suggests a defined parturition period during the austral summer. Between the seven sampling sites in the RD we also found significant differences in SHS neonate catch per unit of effort, and average total length of individuals. According to the data, the RD is likely to represent an important nursery area for SHS up to one year of age.
Highlights
In 2010, the global fishing mortality of sharks from catches and discards was estimated to be in excess of 1.4 million tonnes[1]
A local ecological knowledge survey conducted by Rasalato et al.[19] documented the regular occurrence of hammerhead sharks in the Rewa Delta (RD)
A preliminary survey conducted between February and May 2012 reported the capture of 82 juveniles in the area, suggesting that the RD could serve as an important nursery area for SHS20
Summary
In 2010, the global fishing mortality of sharks from catches (both reported and unreported) and discards was estimated to be in excess of 1.4 million tonnes[1]. Characterisation of critical habitats, such as nursery areas, is vital to understanding shark ecology and in turn informing effective management and conservation planning for shark species. Viviparous mature females produce 13–31 neonates of 42–55 cm total length per litter after a gestation period of 9–10 months[14] This species has been documented to show natal philopatry[12]. This study focused on developing a more detailed understanding of the reproductive biology and critical habitat of the SHS in the RD, Fiji This multi-year study from September 2014 to March 2016 provides an important summary of the following aspects of the SHS population in RD: spatial and temporal patterns in catch per unit effort (CPUE), temporal trends in parturition period, and key morphometric parameters including total length
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