Habitat details as listed in assessment
The Scalloped Hammerhead is a coastal and semi-oceanic pelagic shark, found over continental and insular shelves and in deep water ranging from intertidal areas and the surface to at least 1,000 m depth (Compagno et al. 2005). Horizontal migration is observed from inshore bays to a pelagic habitat as this species grows. It has been observed to be highly faithful to particular diurnal core areas (Holland et al. 1993) and sometimes form large schools which migrate to higher latitudes in summer (Stevens and Lyle 1989). This species segregates by sex, with females migrating offshore earlier and at smaller sizes than males. Adults spend most of the time offshore in midwater and females migrate to the coastal areas to have their pups (Bass et al. 1975, Klimley and Nelson 1984, Branstetter 1987, Klimley 1987, Chen et al. 1988, Stevens and Lyle 1989). Nursery areas are found in shallow inshore waters, while the adults are found offshore (Compagno 1984, Holland et al. 1993, Kotas et al. 1995, Lessa et al. 1998). Neonates and juveniles are known to shoal in confined coastal pupping areas for up to two years before moving out to adult habitat (Holland et al. 1993). The species is viviparous with a yolk-sac placenta. Only the right ovary is functional. In Taiwanese (POC) waters, ovum development takes approximately 10 months and ova reach a maximum diameter of 40-45 mm. The number of oocytes in the ovarium can be as many as 40-50 per female (Chen et al. 1988). The gestation period is around 9-12 months, with birth in spring and summer. The average number of embryos in the uterus ranges from 12-41 and females pup every year. Newborn size ranges from 31-57 cm (Castro 1983, Compagno 1984, Branstetter 1987, Chen et al. 1988, Stevens and Lyle 1989, Chen et al. 1990, Oliveira et al. 1991, 1997, Amorim et al. 1994, White et al. 2008). Maximum size is reported by several studies, 370-420 cm total length (TL) (Ebert et al. 2013) and ranged from 219-340 cm TL for males and 296-346 cm TL for females (Bass et al. 1975b, Schwartz 1983, Klimley and Nelson 1984, Stevens 1984, Branstetter 1987, Chen et al. 1988, Stevens and Lyle 1989, Chen et al. 1990). Males mature between 140-198 cm TL and females at around 200-250 cm TL (Compagno 1984b, Branstetter 1987, Chen et al. 1990, Carrera and Martinez 2007, White et al. 2008). Branstetter's (1987) growth study in the Gulf of Mexico found asymptotic length for both sexes of 329 cm TL and 253 cm fork length (FL), with an index of growth rate of k = 0.073 y<sup>-1</sup>. Piercy et al.'s (2007) more recent study used FL rather than TL and suggested faster growth, with asymptotic length of 214.8 cm FL for males and 233.1 cm FL for females, with an index growth rate of k=0.13 year<sup>-1</sup> for males and k=0.09 year<sup>-1</sup> for females. It is unclear whether these differences are related to sample size, methodology or changes resulting from a density-dependent compensatory response to population depletion. The nearest studies on life history traits of this species have been undertaken in the Eastern Indian Ocean. White et al. (2008) estimated females and males to mature at 228.5 cm TL and 175.6 cm TL, respectively. Age at maturity was estimated at 13.2 for females and 8.9 years for males (Drew et al. 2015). Based on these data, generation length was estimated at 24 years.
