Dead crabs on SW beach ‘worrying’ to authorities

Investigations are under way to determine why 500 blue swimmer crabs washed ashore dead at Belvidere Beach last week.

The Department of Primary Industries and Regional Development Fisheries Division has been investigating the event following a report to FishWatch made by a member of the public on Thursday.

Based on observations and preliminary analysis of the crabs, Fisheries scientists believe it may be an isolated event.

Samples have been sent to the department’s Fish Health Unit for analysis, but the cause may not be known for up to seven days depending on the testing undertaken.

Recfishwest operations manager Leyland Campbell said the incident was a “worrying sign”.

“Blue swimmer crabs are one of our most important recreational species, so we have a clear interest in determining the cause,” he said.

Fisheries supervising scientist of aquaculture and aquatic biosecurity Mike Snow said the department was concerned by all fish kills but they were not uncommon.

“There are around 30-40 fish kill events in WA each year and they can occur anywhere in our fresh and marine waters at any time,” Dr Snow said.

He said data collected from monitoring stations in the area indicated “high flow levels of freshwater into the system and high levels of suspended solids prior to the event”.

“A high influx of organic matter and its subsequent decay is likely to have contributed to a state of low dissolved oxygen in association with the estuary sea bed, from which the crabs (unlike the fish) have been unable to escape.”

The crabs had been dead for a number of days before they were found, which Dr Snow said made testing difficult, but said the involvement of disease was unlikely.

The department urged people to not collect, handle, or move any dead crabs.

Any fish kills should be immediately reported to the FishWatch 24 hour hotline on 1800 815 507.