Unexpected opportunity uncovers the secret life of giant mud crabs
An unexpected PhD opportunity has led to new research uncovering how one of Australia's most valuable fisheries species moves between oceans and estuaries, providing new insights that could help shape the future management of mud crab populations.
CQUniversity researcher William Dantas Charles has completed his PhD exploring the movement and habitat use of the giant mud crab (Scylla serrata), helping fill critical knowledge gaps about how the species behaves in the wild.
Focusing on Queensland's east coast, William's research reveals how giant mud crabs move throughout their life cycle and respond to fishing pressure, producing findings that are already contributing to peer-reviewed publications and advancing knowledge of the iconic species.
The research comes as fisheries increasingly aim to balance sustainability with demand, with giant mud crabs supporting commercial and recreational industries and contributing more than 1,000 tonnes to Australia's annual catch each year.
Originally from Brazil and now based in Rockhampton, William said the mud crab project at CQU wasn't what he initially expected to study.
"Mud crabs really chose me, not the other way around," William said.
"When I arrived at CQUniversity, my supervisor suggested the mud crab project because it suited my background.
"I hadn't worked with crustaceans before, but I decided to take on the challenge, and it turned out to be one of the best decisions I've ever made."
Over four years, William set out to answer a deceptively simple question: where do giant mud crabs go? The answer, it turns out, is far more complex than expected.
His research followed mud crabs across their entire life cycle, from larvae drifting offshore to adults living in estuaries, revealing how their movements are shaped by habitat, fishing pressure and competition between females and males.
"Giant mud crabs have a surprisingly complex life cycle," William said.
"They move between the ocean and estuaries, and their behaviour can change depending on environmental conditions and human pressures like fishing."
Using numerical modelling and acoustic tracking, William mapped crab movements in unprecedented detail.
He found the distance offshore where female crabs release their eggs can determine whether larvae successfully return to coastal habitats, a critical factor in maintaining healthy populations.
His research also showed fishing pressure can reshape crab populations.
"When large dominant males are removed, it changes how other crabs use the habitat," William said.
"It can affect competition, distribution and breeding opportunities."
The study also uncovered subtle differences in how male and female mud crabs use estuarine habitats, improving understanding of how the species interacts with its environment.
While the findings advance scientific understanding, they also have clear real-world applications.
Giant mud crabs are one of Australia's most valuable fisheries species, supporting commercial and recreational industries while also holding cultural significance for many coastal Indigenous communities.
William said the research provides practical information that can support more informed fisheries management and habitat protection.
"Understanding how mud crabs move and use their environment is essential," William said.
"They play an important role in estuarine ecosystems and in connecting ocean and coastal environments."
Associate Professor Nicole Flint leads CQUniversity’s long-running mud crab research program and said she was proud to be William’s supervisor during this PhD project, as a great example of the applied research we're undertaking at CQUniversity.
"From the beginning, William embraced a project completely outside his previous experience and made it his own," Associate Professor Flint said.
"The quality of his work is reflected in the high quality publications coming from the project, and it's fantastic that he's continuing this research as a postdoctoral fellow at CQUniversity."
William has more than 15 years' experience in environmental science, previously working on projects spanning fisheries, water quality and environmental impact assessments in Brazil. He is now continuing his research as a postdoctoral research fellow at CQUniversity.
Reflecting on the journey, William said the experience exceeded his expectations.
"I've been so lucky. Every part of my PhD was fantastic," William said.
"I had the chance to learn new skills, work with amazing people and study an incredible species.
"I couldn't have written a better story, and I hope this research helps protect the species for the future."
