Sesayap is an important reproductive area for one shark species.

During surveys in July–August 2023, 17 Ganges Sharks were discovered in Sesayap through observations from small-scale fishers (Grant et al. unpubl. data 2023). Lengths of individuals ranged from ~58–108 cm total length (TL) and included neonate and young-of-the-year (YOY) individuals. The known size-at-birth for the Ganges Shark is ~58–61 cm TL (Ebert et al. 2021). In these same surveys, a further ~50 fin sets from small individuals, likely including neonates and young-of-the-year, were observed in villages within the area. Fishers reported the presence of small Ganges Sharks during their lifetimes, through local ecological knowledge (LEK) interviews that included a reference photograph of the species. Research on congeneric species in Australia shows that YOY river sharks display daily and seasonal movements to remain within a relatively narrow salinity range (Pillans et al 2009; Dwyer et al. 2020).

There is no indication that YOY move into fresh- or marine water for prolonged periods (Grant et al. 2023), and thus it can be reasonably assumed that Sesayap is a pupping area and core habitat for neonates and YOY Ganges Sharks. Contemporary records of this Critically Endangered species are extremely rare (Jabado et al. 2018), so although there is no information available on mature individuals, the relative abundance of small Ganges Sharks in the area is significant for a species that otherwise appears to be extinct from much of its former range (Jabado et al. 2018). Indeed, this area potentially represents the only known viable breeding population of Ganges Shark across its global range (Li et al. 2015).