An Oak Flats fisherman is calling on people to be wary of what appears, anecdotally at least, to be an increase in numbers of blue-ringed or blue-lined octopus in Lake Illawarra.
Fisherman Steve Miller said the large numbers were first brought to his attention at Berkeley but had since been told of large numbers elsewhere in the lake including the entrance at Windang.
He said one night last week, four were spotted in just 15 minutes.
"They are so small and blend in so well, that is the scary part," he said.
"They have always been in the lake but no-one has seen the numbers this high."
The blue-ringed octopuses are reputed to be among the most dangerous animals in the sea but Mr Miller said people knew little about them.
He said authorities should be warning people about potential dangers but he was getting little response and had taken it upon himself to caution people.
"I think it is sad no-one wants to do anything." he said.
Last year, the Lake Illawarra Authority decided against installing warning signs in regards to blue-ringed octopus.
A Wollongong City Council spokesman said the blue-ringed octopus was a native species commonly occurring in areas around Lake Illawarra.
"The risks of this creature are well known and publicly documented," the spokesman said.
"It is up to each individual to take responsibility regarding the natural hazards of native species in the wild."
The Lake Illawarra octopus in question is likely to be a blue-lined octopus, a close relative of the blue-ringed octopus and just as toxic.
According to Martyn Robinson, a naturalist at the Australian Museum, the blue-lined octopus occurs all around the Australian coast.
They all feed on crabs and other small crustacean and use highly toxic venom to quickly paralyse their prey so that when the catch takes place it won’t attract the attention of rivals.
‘‘The blue bands and colouring are there as a warning, but humans find the blue patterns pretty and tempt us to pick them up to show our friends.’’
Mr Robinson said as far as he was aware all but one bite had occurred on land.
It was unknown if numbers were increasing in Lake Illawarra, but with more sea water circulating in to the lake, it would create ideal conditions for the octopus as well as other marine creatures.
‘‘If you don’t pick them up you are not in any danger, if you are threatening them they go blue,’’ he said. ‘‘When not threatened they look like a rock.’’
Mr Robinson said unfortunately there can be a lot of rubbish on lake beds which create nice homes for blue-lined octopus.
‘‘One potential danger can come when kids sometimes pick up what they think may be an empty sea shell straight out of the water, shells in a sea grass bed may have one living inside.’’
‘‘They are found in many rock pools, but the message is if you see one flashing blue lines or rings don’t touch it and you should be okay,’’ Mr Robinson said.
There are several species of blue-ringed octopuses in Australia, with the most common one found in Sydney being the blue-lined octopus. All species are brown and it is only when they are disturbed that the vibrant blue markings appear as a warning. They average around five centimetres. The blue-lined octopus is found from southern Queensland to southern NSW.
• The blue-lined octopus is found on intertidal rocky shores and in coastal waters to a depth of 15metres.
• Blue-ringed octopuses are reputed to be some of the most dangerous animals in the sea.
• In some respects this is true because they have an extremely powerful venom that they use to kill their prey of crabs and small fish. On the other hand, they are very shy and non-aggressive creatures that prefer to hide under ledges and in crevices.
• Encounters with humans usually result in the octopus quickly darting for cover. It is only when an animal is picked up that it may ‘‘bite’’ and inject its paralysing venom, known as tetrodotoxin.
Danger to humans and first aid
• The blue-ringed octopuses, including the blue-lined octopus, may ‘‘bite’’ if handled but because of the small size of the injecting apparatus, the ‘‘bite’’ may not be felt.
• However, within minutes symptoms include numbness of the lips and tongue, difficulty in breathing, followed by complete paralysis of the breathing muscles.
• Victims appear to lose consciousness as they cannot respond to their name being called. However, after recovering, they have reported being able to hear everything around them. Call for help, monitor breathing and airways. Apply mouth-to-mouth resuscitation.
Source: Australian Museum