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Government of Western Australia - Department of Fisheries

Biosecurity alerts

Carpet sea squirt

Carpet sea squirt (Didemnum vexillum) has been detected in Western Australia (WA) for the first time.

Carpet sea squirt (CSS) is a highly invasive marine invertebrate animal that can overgrow and smother native species. It can overgrow rocks, shellfish, sea sponges and man-made structures such as wharves, jetty pylons, pontoons, buoys and vessels. 

It is native to east Asia, likely Japan, and has been introduced to New Zealand, North America and Europe. 

CSS has the potential to impact oyster and mussel aquaculture, marine environments, dive tourism industries as well as increasing maintenance costs for commercial and recreational vessels. 

The aquatic pest has been detected in two locations in WA; Garden Island and at a marine facility in Henderson. The detection at Garden Island was the first confirmed detection in Australia. 

Situation update

A level 2 incident was declared on 25 January 2023 in response to the detection of CSS in WA.

On 17 March 2023 a Quarantine Area Notice was put in place for the waters adjacent to the Australian Marine Complex Common User Facility at Henderson South. Visit the DPIRD website​ to find out more.

DPIRD is working with the Australian Government Department of Defence (Defence) and the Department of Agriculture, Fisheries and Forestry (DAFF) to carry out surveillance and management activities. 

DPIRD is also working with local stakeholders and Fremantle Port Authority to manage the incursion.

Key activities currently underway include:

  • Additional vessel management procedures will be implemented at the marine complex to minimise the risk of further spread.
  • Delimiting surveys to determine the spread of CSS.
  • DPIRD is working with Defence on management activities to remove identified colonies.

What can I do to prevent CSS from spreading in WA?

Recreational boaters, fishers and divers can assist in stopping the spread of marine pests and aquatic disease by keeping their boats, trailers, wetsuits and equipment clean. 

When you clean your equipment, make sure that any bait, debris and seaweed is removed. Check wheel arches on trailers, boat propellers, fishing tackle and footwear. Do not clean in the water or allow run off to enter the ocean. 

Use soapy water to clean your boat and trailer, fishing rods and other equipment, and allow them to dry completely before using them at another location, even if it is on the same day. 

There are many native species that look like carpet sea squirt so expert taxonomic identification and molecular techniques are required to confirm the species from DNA sequencing. 

If you find unusual marine species attached to vessels, sub-merged infrastructure or in the marine environment, report it to​

More information

A CSS factsheet and FAQ​ documents are available for download.

More detailed and technical information on CSS is found at the National Introduced Marine Pest Information System (NIMPIS​).​

Alexandrium health warning

In recent years there have been two unprecedented blooms of toxic dinoflagellate algae, Alexandrium spp., in the Swan and Canning rivers.

Alexandrium algae produce paralytic shellfish toxins (PSTs) which can be concentrated by filter feeding shellfish. These toxins are known to affect a wide range of species and may bio accumulate, resulting in potential impacts on crabs, fish, birds and mammals.

Human consumption of shellfish containing high levels of PSTs can result in poisoning and may cause death.  Freezing and normal cooking processes do not destroy these PSTs.

Please do not eat mussels and remove the head, guts (mustard) and gills from blue swimmer crabs caught by recreational fishers in the Swan and Canning rivers, before freezing, cooking or eating them. All crabs must still be landed and transported whole to your home (your principal place of residence) unless you plan to eat them immediately.

Please see below resources related to Alexandrium algal blooms.

How to clean blue swimmer crabs flyer, available in five languages:

How to clean blue swimmer crabs video

Alexandrium FAQs

Alexandrium algal bloom information 

Alexandrium blooms monitoring

Blooming surprise Landscope article March 2021.pdfBlooming surprise Landscope article March 2021.pdf

Look out for caution signs installed at key Swan Canning Riverpark locations including jetties, traffic bridges, boat ramps and popular fishing locations.

Alexandrium warning sign.jpg

Don’t dump ornamental fish

Protect the environment – don’t release aquarium fish into Western Australia’s sensitive waterways.

Aquarium fish that are not native are often more aggressive than native species and can outcompete them, consuming their food and taking up their space. They can also spread disease, kill local species and damage natural habitats.

This is especially important for our cave karst system in the Cape Range Peninsular near Exmouth, where there are rare cave-dwelling species found nowhere else on earth. Having evolved in isolation, these creatures are particularly vulnerable to introduced species. The Department of Primary Industries and Regional Development and Department of Biodiversity, Conservation and Attractions have been working together to eradicate introduced fish from caves and pools in the Cape Range region to protect our unique cave species. However, for their long-term survival, further introductions must also be prevented.

If your fish are healthy but you no longer want them, give them to a pet shop, other fish owners or an organisation with an aquarium. You could also advertise them on a local notice board or on social media.

If you can’t find a new home for your fish, or if they are sick or diseased, dispose of them humanely.

If you see ornamental fish in our waterways, you can help us protect WA’s aquatic environment by emailing, or calling FishWatch 1800 815 507.

For more information, check our handy guides:

Abalone Viral Ganglioneuritis (AVG) in wild abalone in Victoria 


Victoria reported the re-occurrence of AVG in wild abalone on 04 May 2021. AVG has been detected in Australia before with previous incidents in Tasmania and Victoria, last reported in 2010.

Victoria has implemented restrictions to assist with limiting the spread of disease. Following the Victorian detection, New South Wales (NSW) detected AVG in abalone held in tanks at some Sydney retailers and actions are underway to eradicate infection from the NSW premises.


Key features of AVG

AVG is a viral disease affecting the nervous system of abalone resulting in weakness and death of the shellfish. There are no known or likely impacts for human health. AVG only affects abalone species.

AVG has not been reported from Western Australian abalone. If introduced into Western Australia (WA), AVG could have a severe impact on abalone in WA and WA’s important commercial, recreational and aquaculture abalone sectors.

To prevent introduction of AVG into WA, the import of live abalone into WA from Victoria and other States is not permitted. It’s also illegal to use abalone meat or any abalone material as fishing bait in WA.

Look out for and report disease signs in abalone

The detection in Victoria was made by a diver who noticed a cluster of dead abalone and reported their concerns. This shows the critical role industry and community members play in monitoring our aquatic environments for disease and pest threats, and reporting anything unusual.

Signs of AVG in abalone

  • You may see patches of weak and/or dead abalone that are easily removed from or fall off the reef and cannot right themselves.
  • There may be clusters where there are only empty shells present (evidence of abalone that have died and been scavenged)
  • In some abalone you may see swelling of the mouth parts or edges of the foot curling inwards, leading to exposure of clean shiny shell, but this is more common on farms.

How to report

  • Report any signs of disease in abalone to the WA FishWatch 24-hour hotline on 1800 815 507.
  • You may be asked to collect some whole abalone in a sealed plastic bag or container and record the exact location where the samples were collected. Samples should be kept refrigerated but not frozen.

Download or read the AVG fact sheet to learn more about:

  • What is AVG?
  • What are the signs of AVG in abalone?
  • How is AVG spread?
  • What you can do to help protect WA
  • What to do if you see a sick abalone

More information about AVG

Other biosecurity alerts

Current biosecurity alerts are listed below. Fishers are asked to look out for these pests and to report evidence of them to FishWatch

Marine pest alerts

Asian green mussel

Asian paddle crab

Black-striped mussel

European green crab

Japanese kelp

Northern pacific seastar

Redclaw crayfish

Spangled perch

Disease alerts

White spot disease in prawns

Biosecurity fact sheets

Indistinct river shrimp

Asian green mussel

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Last modified: 17/03/2023 9:38 AM

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