Tests by the Department of Fisheries have revealed higher than normal levels of a shell disease, in
crabs recovered by researchers doing a stock assessment in the Bunbury area.
A sample of crabs collected from the outer part of Bunbury Harbour, found more than 50 blue
swimmer crabs that had developed the disease, which is caused by a naturally-occurring
bacterium.
The bacteria produce enzymes that destroy the chitin in the shell, causing it to break down and
lesions to form.
The condition is often found at low levels in crab populations.
However, the severity and high
percentage of crabs affected in the outer Bunbury Harbour location samples prompted further
investigation.
Fisheries policy and strategic services director Nathan Harrison said, so far, only crabs from Bunbury
Harbour are showing high levels of this bacterial shell disease.
“Further samples collected from Bunbury Harbour crabs have been sent for bacterial analysis and,
as a precaution, data and samples are being collected from different locations to monitor the health
of crab populations outside that area.” Mr Harrison said.
“We know the bacteria that cause this shell disease are found naturally on crustaceans and the
infection is typically non-fatal in crabs.
Environmental factors, such as water quality, can stress
crabs making them more susceptible to this infection.”
Mr Harrison said the department of fisheries was working closely with industry and relevant
agencies to deal with this situation.
“As a precaution, the Department of Health advises that recreational or commercial fishers should
not collect or consume any crabs that are damaged or have shell lesions, or appear to be in poor
health or condition, as they may be affected by bacterial pathogens or other agents which have the
ability to impact upon human health,” he said.
“As we work through this situation and carry out further investigations we will provide updates,
but for now we urge crab fishers to be vigilant.”
Anyone who sees an affected crab in areas other than Bunbury Harbour is asked to take a photo if possible (but do not retain the crab), and report the find immediately to the Department of Fisheries’ 24-hour FishWatch line on 1800 815 507.
