A swimmer died after a rare suspected stingray attack off an Australian beach while another two people were mauled in separate shark encounters this weekend.The 42-year-old's death came more than a decade after world-renowned "Crocodile Hunter" Steve Irwin was killed when a stingray barb punctured his chest while he was filming on the famed Great Barrier Reef.The man was in waters off Lauderdale Beach some 23 kilometres from Hobart in the southern island state of Tasmania on Saturday when he "sustained a puncture wound to his lower abdomen... possibly inflicted by a marine animal", police said.He was brought onto the beach by friends but suffered a heart attack and was unable to be resuscitated, police added."It's consistent with (a stingray injury) but further investigation and examination of the deceased may be able to give a bit more of a concrete fact on that," Tasmania Police Senior Constable Brett Bowering told the Sunday Tasmanian."It's a pretty traumatic incident to see."Commonly found in tropical waters, stingrays rarely attack humans but their barbs, at the end of their tails, are coated in toxic venom which they use to defend themselves when threatened.Two shark attacksIn the first shark attack of the weekend, a man taking part in a surf lesson off the east coast suffered serious cuts after an encounter on Saturday. The 24-year-old was wading waist-deep in waters off Seven Mile Beach some 130 kilometres south of Sydney when he "felt a forceful lashing motion against his legs", New South Wales Ambulance said.He had "significant cuts and haemorrhage as well as several puncture wounds to his wetsuit and right leg... and cuts to his hand", NSW Ambulance duty operations manager Inspector Jordan Emery told reporters on Saturday.The beach was closed and authorities sought to identify the shark species involved.That attack was followed by another on Sunday off the north coast, when a teenage boy was bitten on his arm and leg while spearfishing, police said.The 17-year-old was spearfishing from a vessel off the coast of Arnhem Land in the Northern Territory when he sustained "significant injuries" to his arm, St John Ambulance told national broadcaster ABC."Obviously there's quite a large amount of bleeding that's occurred," St John Ambulance's Craig Garraway said. He said shark encounters in the NT were unusual, adding: "I've been around a long time and I'll be honest, I can't remember a shark attack."Debate on reducing shark encounters The two attacks are the sixth and seventh off Australian beaches in two months, amid public debate about how to reduce the risk of encounters between sharks and the growing number of people using the ocean for leisure.Australia has one of the world's highest incidences of shark attacks, but fatalities remain rare.There have been 13 "unprovoked" shark attacks off the vast continent's coast this year, including one death after a swimmer was mauled by a shark in the Whitsunday Islands in early November, according to data from Sydney's Taronga Zoo.There were 15 attacks - one fatal - last year, and 17 encounters and two deaths in 2016, the data showed.New South Wales hosted an international conference with marine experts in 2015 after a sharp increase in attacks across Australia that year to 22, including the death of a Japanese surfer after his legs were torn off by a shark.The state, Australia's most populous, has trialled non-lethal measures such as aerial drones to track shark movements and "smart" drum lines that alert authorities to their presence.