JAWS TRULY
Inter-species incident shows ecological richness of St Lucia
● For some it’s a natural marvel, for others the stuff of nightmares. A rare photo has emerged of a 2.5m Nile crocodile attacking and eating a bull shark at the mouth of the St Lucia estuary in KwaZulu-Natal. The photo confirms what scientists have only known indirectly from studies of stomach contents: that hefty Nile crocs occasionally feed on juvenile sharks.
The rare interaction, photographed during a scientific field trip in January, also highlights the upsurge in shark activity in the sixmonth period the mouth was open at the beginning of the year — the first time in 13 years. Scientists not only captured rare footage but also observed and tagged multiple sharks in the estuary mouth, which used to be a key nursery area for juvenile sharks.
The team has since written a scientific paper drawing attention to the potential ecological benefit of opening the mouth and restoring the natural habitat.
“An adult Nile crocodile (Crocodylus niloticus) was observed preying on a live neonate [juvenile] bull shark, which it swallowed whole,” the authors said in the paper, due to be published in the African Journal of Marine Science.
“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.”
Lead author Ryan Daly, a marine scientist with the Oceanographic Research Institute of the South African Association for Marine Biological Research, told the Sunday Times he hoped the picture would draw attention to the need to protect the St Lucia world heritage site. “The picture is certainly unique. There are historical records of sharks having been found [in a crocodile’s stomach] but never a record of actual predation.”
In their paper, Daly and his colleagues said estuaries were vital breeding grounds for many aquatic species. “Estuaries remain
This … provided the first photographic evidence in Africa Dr Ryan Daly Co-author of scientific report on the encounter
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 was notable for the management and conservation implications for this important estuarine system, as well as for regional bull shark populations,” they said.
Daly said he was encouraged by the number of bull sharks — also known as Zambezi sharks — observed and tagged at the mouth, further evidence of the importance of estuaries to sharks’ life cycle.
“It came as a surprise when adult Zambezi sharks were seen at the mouth on the day it was opened, as if they had been waiting for it,” Daly said in a separate newsletter article published last month.
“It came as even more of a surprise when pregnant sharks were seen entering the mouth within the first week of it being open and the first pups were found at the mouth only 10 days after it had been opened.”
Jeff Asher-Wood, St Lucia fishing tour operator, said the mouth used to be periodically opened 20 years ago. “Some scientists say it must open naturally, but there is so much more urbanisation on the water, putting pressure on the rivers coming in, that it can’t be natural. In my opinion you need to help it [open],” Asher-Wood said.