Hungry, angry bottlenose dolphins appear to be turning against their porpoise cousins in a war for food and 'fun' This footage shows two groups of Atlantic spotted dolphins facing off in a noisy (and squeaky) confrontation. Courtesy Dolphin Communication Project Hunger Games? British wildlife experts are pointing to a rise in dead porpoises being washed up, often killed by hunger and brutal bottlenose dolphin attack. WE'VE all gone "aawww" at scenes of dolphins rescuing swimmers and leading sailors to safety. But new evidence is emerging of a much more brutal streak to their character. Some scientists speculate our finned friends are turning upon each other in a "tribal" war over over-exploited fish stocks. It's bullying bottlenose versus the smaller and timid harbour porpoises and Risso's dolphins in their own version of the "Hunger Games." But not all the evidence supports this. The bottlenose dolphins are not eating those they kill. And they're killing species of porpoises - such as the squid-eating Risso's dolphin - that don't even compete for the same food stocks. So what's going on? A group of fishermen in Brazil spotted a baby dolphin struggling with a plastic bag and decide to save it. Watch as their kid gesture is repaid in full. Courtesy Globo "They could be doing it for fun," dolphin expert Nick Tregenza told New Scientist magazine. Bottlenose dolphins can be deadly creatures. They are fast. Agile. Intelligent. Their sonar can "detect" weak spots in their opponent, guiding their attack. These qualities have long been lauded for the manner in which they are used to protect their young from predators such as sharks. Fight for survival ... Dolphins are no longer "just victims." Now they're going on the attack. Here a killer whale is pictured attacking a bottlenose dolphin off the Mexican coast Source: Supplied There are other signs of recalcitrant behaviour, too. Dolphins in Cornwall have been seen to be picking up stones from the sea floor and lifting them to the surface - where they would throw them. "They were thought to be throwing stones at seals on rocks not far away," Tregenza said. Speculation for the behaviour ranges from food wars through to a growing "cultural" trends among some dolphin pods that regards killing to be "fun." It also could be an expression of frustration: Tregenza said the bottlenoses may have been trying to help the other, weaker, dolphins - only to become angry when they didn't respond. Dolphins are struggling to find enough food as fishing boats roam ever further in a bid to meet growing demand. Here a pod of up to 120 bottlenose dolphins frolic on Sydney Harbour.