Swimmers have been warned to swim between the flags after dangerous sharks were caught at some of Australia’s most popular surf beaches.

A 2.3m great white shark was pulled ashore at Mermaid Beach on the Gold Coast about 12.30pm (AEST) on Friday after getting caught in a shark net.

Just two days earlier another great white was caught off Rainbow Bay, also on the Gold Coast.

Surf Life Saving Queensland duty officer Kevin Dunn said swimmers should avoid known risks at this time of year.

“Don’t swim before sunrise and not after sunset,” Dunn said.

“Definitely don’t swim where you see a lot of bird and bait fish in the water or in murky and overcast conditions.

“People are better off swimming in a patrolled area where lifeguards or lifesavers are on duty.”

Dunn said the sharks were following whales migrating south and were hunting whale calves and bait fish.

While the netting program was efficient, people shouldn’t fall into a “false sense of security”, he said.

Estuaries and canals were also dangerous places to swim because they may be the haunt of bull sharks.

“Bull sharks are the worst in the canals,” Dunn said.

“People need to observe the signs and warnings.”

Sea World Gold Coast director of marine sciences Trevor Long said the most threatening sharks were bull, tiger and great white sharks. But if caught, they should not be killed but released back to sea.

“I don’t like to see them killed,” he said.

“Small sharks under 1.5m aren’t threatening to the bathers.

“I’d rather see them tagged (for research) and released alive.”

A total of 12 great white sharks have been caught in shark nets off Gold Coast beaches since 2003.

Great whites are expected in the area over the next month.