Before going out into coastal environments, juvenile bull sharks usually stay inside rivers, shielded by mangroves, when they are young and more vulnerable to predators. Until previously, experts thought that they obtained their nutritional needs from crustaceans and fish that graze on mangrove environments rather than saltmarshes.
The research, which was the first of its type, looked at the value of estuarine ecosystems as feeding grounds for juvenile bull sharks in the Clarence River, in New South Wales’ Northern Rivers District.
Tissue samples were taken from 55 young bull sharks caught by commercial fishermen and evaluated. The samples were compared to primary producer samples and organic matter collected from various sites along the Clarence River using a complicated scientific procedure known as’stable isotope analysis.’
Dr. Vincent Raoult of the University of Newcastle, a co-author of the study, described the findings as “surprising.”
“We discovered that once these young bull sharks reach roughly four years of age, they migrate to the estuary’s entrance and feed on fish and other species that rely primarily on vulnerable salt marsh habitats,” Dr. Raoult explained.
“Bull sharks are predators that feed on herbivores such as fish that devour saltmarsh rather than the primary producers tested in this study.”
“Mangrove environments made a little contribution to the diet of young bull sharks, which was surprising.”
Under attack from climate change
Dr. Raoult was both interested and disturbed to learn that saltmarshes are more nutritionally significant in a juvenile bull shark’s diet than mangroves.
“Saltmarsh is under jeopardy. It is vanishing in Australia and throughout the world as a result of coastal development and climate change “Dr. Raoult expressed his thoughts.
“It’s believed that we’ve already lost half of the world’s salt marshes.”
“We call saltmarsh a ‘coastal primary producer,’ since it supports a variety of creatures including crabs, elasmobranchs, and teleost fish, which are then preyed on by juvenile bull sharks.”
Informing adaptive management strategies
This study will help to inform adaptive management techniques targeted at mitigating climate change’s effects.
Dr. Yuri Niella of Macquarie University’s School of Natural Sciences, the paper’s lead author, stated that the saltmarsh must be protected from additional threats.
“These habitats are crucial not just for bull sharks but also for a variety of fish and crustacean species in the Clarence River,” Dr. Niella stated.
“This suggests that restoring saltmarsh ecosystems there might benefit not just bull sharks, but also enhance economic profit from improved fisheries catches.”
“Knowing how important estuarine ecosystems are to the creatures that live in these locations may help drive focused management decisions that benefit both people and wildlife.”
Estuarine, Coastal and Shelf Science published the study.
