Prawns return to Perth rivers

July 5, 2016 by Samille Mitchell, Sciencenetwork Wa, Science Network WA
Prawns return to Perth rivers
The restocking project sought to not only bolster prawn populations but provide answers as to what was limiting their natural recovery and how they respond to different water conditions. Credit: S Allen

Prawns are returning to WA's beloved Swan and Canning Rivers thanks to a recent restocking program that has now seen 4.5 million juvenile western school prawns (Metapenaeus dalli) released into the iconic waterways.

A multi-agency project hopes to restore the prawn fishery by boosting their population.

Prawn populations plummeted between the 1950s and the 1970s but no one was exactly sure why.

The city waterways had become polluted and suffered macroalgae blooms, yet despite active management in the 1960s and 70s to remove industry, close landfill sites and reduce point source pollutants as well as ongoing work to improve the health of the river, the have not recovered.

The restocking project sought to not only bolster prawn populations but provide answers as to what was limiting their natural recovery and how they respond to different water conditions.

Effort to restock started in November 2012 with community volunteers engaged through Prawn Watch to catch egg-carrying female prawns in the shallow waters where they congregated to spawn.

The pregnant females were placed in carefully controlled aquaculture tanks at the Australian Centre for Applied Aquaculture in Fremantle, where they released their young.

The tiny hatchlings then remained in the aquaculture facilities for three weeks—enough time to grow to a size at which they could avoid simply drifting on the currents as plankton and instead bury into the sand for safety.

Prawns return to Perth rivers
Broodstock collecting on the Canning River. Credit: K.Trayler

The juveniles were then released in the same waters from which their mothers were taken. The restocking occurred in batches over four years, culminating in the biggest restocking this year, when almost two million prawns were released.

Monthly sampling of prawn populations has been undertaken by Murdoch University since the restocking program began in an attempt to learn more about the prawns, their recovery, predation and how they react to environmental variables such as salinity, temperature and oxygen.

It will take a few more months before the extensive monitoring dataset is fully analysed, Department of Parks and Wildlife Rivers and Estuaries Division principal scientist Kerry Trayler says.

But she says preliminary assessment indicates the population is increasing, despite ongoing fishing pressure.

"We think this project is making an impact," Dr Trayler says.

"Obviously releasing prawns into an environment in which the community is inclined to go out and catch your stock has some downfalls."

"Yet, despite that fishing pressure, we are seeing improvement in the stock since the project began."

Explore further: Science maximises prawn restocking success

Related Stories

Science maximises prawn restocking success

March 8, 2016

Murdoch University scientists involved in a project to restock the Swan and Canning Rivers with Western School Prawns have identified a key predator of the juveniles and are using their research findings to maximise prawn ...

Prawn restocking program put to the test

February 6, 2014

Researchers from Murdoch University, led by Professor Neil Loneragan and Dr James Tweedley, have joined the latest effort to boost prawn populations in the Swan-Canning estuary.

Prawn spawn secrets unlocked in 3D images

May 16, 2016

Discovering the secrets of how one of the world's most popular prawn species produces sperm and transfers it to create the next generation could help free aquaculture from reliance on brood stock from the wild.

Fishery bounce back informs on seagrass importance

August 22, 2013

Insights into the impact of cyclones on tiger prawn habitats in north Western Australia has demonstrated the resilience of the species, as well as underscored the importance of protecting seagrass for fisheries production ...

Recommended for you

Meteorite source in asteroid belt not a single debris field

February 17, 2019

A new study published online in Meteoritics and Planetary Science finds that our most common meteorites, those known as L chondrites, come from at least two different debris fields in the asteroid belt. The belt contains ...

Diagnosing 'art acne' in Georgia O'Keeffe's paintings

February 17, 2019

Even Georgia O'Keeffe noticed the pin-sized blisters bubbling on the surface of her paintings. For decades, conservationists and scholars assumed these tiny protrusions were grains of sand, kicked up from the New Mexico desert ...

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.