Bull shark Carcharhinus leucas recruitment into the St Lucia Estuary, South Africa, after prolonged mouth closure, and the first observation of a neonate bull shark preyed on by a Nile crocodile Crocodylus niloticus

Abstract

Estuaries provide critical nursery habitat for juvenile bull sharks Carcharhinus leucas, as they have the ability to withstand a wide range of salinities. St Lucia is the largest estuarine lake in Africa and was once a key nursery for bull sharks until a prolonged and near-continuous period of mouth closure and drought between 2002 and 2021. The estuary mouth was opened for the first time in 13 years on 6 January 2021, and, within 10 days, bull shark pups recruited into the estuary. On 16 January, an adult Nile crocodile Crocodylus niloticus was observed preying on a live neonate bull shark which it swallowed whole. This observation provided the first photographic evidence in Africa and highlighted a unique interaction between these species, which are top predators in the freshwater and coastal environments, respectively. Estuaries remain important nursery habitats for bull sharks in the region and we assembled the known records of bull shark occurrence in all South African estuaries. In summary, the rapid recruitment of bull shark pups into St Lucia Estuary is notable for the management and conservation implications for this important estuarine system, as well as for regional bull shark populations.