The chunk of eel flesh secured to a hefty hook sinks into the murky brown Karuah River at Allworth.
Shark researcher Nicolas Lubitz has three lines set waiting for a strike in the overcast conditions.
He is targeting juvenile bull sharks that live upstream for the first two years of their life.
The project, which includes all of the major river systems between Cairns and Sydney, aims to gather genetic information from the juvenile sharks that can be used to track their parents along the east coast.
"We have been following about 150 adults that have tracking devices on them between southern NSW and northern Queensland," Dr Lubitz, who recently completed a PhD on movement drivers in sharks and rays at James Cook University, said.
"With the genetic samples (taken from the juvenile sharks) we want to figure out whether they come back to the same rivers to give birth, sort of like turtles do with their nesting beaches."
Hunter residents are no strangers to interactions with bull sharks, with dozens of encounters reported around Newcastle Harbour and Lake Macquarie over the decades.
Bull sharks are believed to have been responsible for two fatal shark attacks in Newcastle's Throsby Creek over the past century.
A 12-year-old boy died after being bitten on the leg in 1920 and 15-year-old died from shark bite injuries in 1936.
There have also been reports of dogs and horses being taken by sharks as recently as the 1960s.
In more recent years, rowers have reported shark sightings as far upstream as Islington Park.
Concerns about poor water quality and the increased presence of bull sharks in Newcastle harbour led to the cancellation of the Stockton to Newcastle harbour swim in 2015.
The juvenile shark project that Dr Lubitz is working on is jointly funded by James Cook University, Biopixel and NSW and Queensland fisheries departments.
He said juvenile bull sharks had been found in all of the creeks and rivers between Cape York and the Hawkesbury.
"They will go as far as they can into the fresh. I've caught them almost 100 kilometres inland in little rainforest creeks and streams. As long as there is food they will go up there," he said.
While bull sharks are relatively well understood compared to some other species, scientists are keen to learn more about their behaviour, in particular their interactions with humans.
"We're doing a project looking at depredation, bull sharks stealing fishers' catches and interacting with people at tourism hot spots when people throw their food scraps overboard at anchorages," Dr Lubitz said
"We are trying to understand what brings them into areas where people are and how people can safely use environments where there are bull sharks."
Current research suggests climate change will encourage bull sharks to move further south.
While the Hawkesbury River was once considered too far south to be a bull shark nursery, numerous juvenile sharks have been found there over the past decade.
"They are starting to colonise different areas further south, but we don't really know what it would mean for them further up north in the tropical habitats. It might get warmer as well so it might displace them from up there," Dr Lubitz said.
