The biggest event was at Cottesloe Beach, one of Western Australia's most famous beaches, where more than 6,000 people gathered.
They're calling on the government to stop the use of baited hooks placed one kilometre off the coast and killing certain sharks larger than three metres.
One shark has already been killed under the policy and another was found dead on a hook this morning after hooks were set off the coast for the first time yesterday.
Protester Craig Berry says the government is taking the wrong action following seven fatal shark attacks in three years.
"I don't feel it makes our beaches any safer," he told SBS. "In fact I feel more threatened by having baited hooks out there when I want to enjoy the ocean and I think a lot of people feel similarly.
"I think the number of sightings we have of sharks shouldn't be reported as horror stories, but the sign of a healthy eco system and most of our interactions with sharks are positive."
The policy was introduced after a fatal attack off Gracetown in November, and targets tiger, bull and great white sharks longer than three metres that come within a kilometre of the shore.
Sea Shepherd Managing Director Jeff Hansen says the support from people all over the world has been humbling.
"Ten years ago we may have only had a handful of people on the beach speaking out for sharks and now we've got regular people - mums, dads, average people that aren't working in conservation, talking about biodiversity, talking about apex predators and talking about the importance of sharks in our oceans," he told SBS.
"People are saying an ocean without sharks is a planet without people. We need to give them the respect they deserve and that's really humbling and encouraging to see that."
Have your say in the comments section below: What do you think of the WA government's policy to prevent shark attacks?
Earlier today, a female activist chained herself to a Department of Fisheries vessel in Fremantle as part of the protest against the shark cull.
The boat is one of two fisheries vessels being used to set and monitor baited hooks off the Perth coast.
Police say emergency services had to cut her free from the locks.
In defence of its policy, the WA government says a spike in often-fatal shark attacks has dented tourism and leisure-based businesses.
But shark expert Paul Sharp says the baited drum lines might actually increase the risk.
He says simply having the baits in the water will result in excited sharks, meaning there was a greater chance of an accident.