Sixteen-year-old runaway Johnny Clinton survives a hovership crash in the Pacific Ocean and finds himself on Dolphin Island, a small coral island in the Great Barrier Reef. Dolphin Island is home to a research station dedicated to the study of the language and intelligence of dolphins.
Dolphin Island contains examples of:
- Actually a Good Idea: The researchers have an orca named Snowy delivered to Dolphin Island so they can try to train her not to eat dolphins. They drop a robotic dolphin into her pool, but Snowy isn't fooled and completely ignores it, leaving them with no choice but to use real dolphins as bait. Dr. Saha asks jokingly, "Are we going to call for volunteers?" Professor Kazan considers the suggestion, then says seriously, "I'll do exactly that."
- Alternative Number System: The dolphin number system is binary because they only have two flippers. When Professor Kazan and Dr. Keith are translating a recording of an old dolphin folk tale, they disagree about whether an object is said to be the length of 128 or 256 dolphins.
- Behavioral Conditioning: The researchers implant electrodes in Snowy's brain that cause pain when she rushes at dolphins and Electric Instant Gratification when she doesn't. Once they've conditioned her to be unable to attack dolphins, they set her free. The conditioning works so well that months later, when Snowy's mate tries to eat dolphins, she headbutts him until he swims away.
- Friendless Background: When Johnny lived in America, the trauma of losing his parents made it hard for him to form new connections. He and his classmates mostly stayed out of each other's way, except when his classmates were making fun of him for being short. On Dolphin Island, he finally opens up and befriends a boy his age named Mick Nauru, who teaches him to skin dive.
- Friendly, Playful Dolphin: The dolphins are happy to cooperate with almost anything the researchers want, including wearing a harness and towing Johnny around on a surfboard, because they see it all as a delightful game.
- Little Stowaway: Johnny is awakened at night by the sound of the hovership Santa Anna landing near his house. He goes outside to get a better look at it and decides to sneak aboard to explore, thinking the crew will quickly catch him and kick him out. Then the Santa Anna suddenly takes off. Johnny thinks about how loveless his home is and decides to stay aboard until the Santa Anna reaches her final destination in Australia. He hides in a cargo hold and eats food supplies from one of the lifeboats. His plans are cut short the night the Santa Anna crashes.
- Lost at Sea: The crew of the Santa Anna, not realizing they have a stowaway, set off in the lifeboats and are far away before Johnny can signal for help. Johnny is left floating on a packing crate. He makes a little shelter on the crate out of debris and his shirt, but he has no way of propelling himself and nothing to eat or drink. The next morning, Heroic Dolphins start pushing him towards Dolphin Island, which is about 100 miles to the west. By the time they arrive, Johnny has been on his crate for about thirty hours and is severely dehydrated and sunburned.
- Mind Control: In addition to delivering reward and punishment, the electrodes in Snowy's brain can directly control her behavior, causing her to swim in whatever patterns Dr. Saha wants. Johnny is impressed by the degree of control, but he's also uncomfortable with the idea of taking a sentient being's freedom of choice away.
- My Life Flashed Before My Eyes: Averted. Mick falls into Snowy's pool and thinks she's going to eat him, but instead she gently nudges him with her nose. Afterwards he tells Johnny, "You know, it isn't true about recalling your past life at moments like this. All I thought about was those teeth. I wondered if I'd go down in one piece, or whether she'd bite me in two."
- Nephewism: Johnny's parents died in an air crash when he was four, leaving him to be raised by Resentful Guardian Aunt Martha. When Martha learns that he's on Dolphin Island, she's happy to send over his belongings and wash her hands of him.
- Post-Victory Collapse: At the end of the book, Johnny is towed 100 miles by dolphins on a surfboard in order to summon help for Professor Kazan, who contracted pneumonia just after a hurricane destroyed the island's medicine supply and radio transmitters. After he arrives safely at his destination, the danger of what he just went through hits him, and his legs give out.
- Sapient Cetaceans: Dolphins are as fully sentient as humans. Orcas are believed to be too, although their language hasn't been deciphered yet.
- Short Cuts Make Long Delays: Downplayed. When Johnny tries to cut through the jungle, he quickly loses his way and flounders in the burrow-ridden soil. But the island is so small that all he has to do to find his way is walk in a random direction for a little while, so he only loses about fifteen minutes.
- Speaks Fluent Animal: Professor Kazan has been working to decipher and learn dolphin language. He can say several common phrases, although he admits his accent is so poor that only dolphins who know him well can understand him. Some dolphins have also been taught to understand and speak English, although they speak with their own accent and much more quickly than a human could. Professor Kazan eventually makes waterproof communication devices with buttons a human can press to issue simple commands to the dolphins.
- What Measure Is a Non-Human?: When dolphins ask humans to take their side in their war against killer whales, scientists debate what to do: should they treat both species like animals and let nature take its course, treat dolphins like humans and kill orcas to protect them, or treat both species like humans and try to enforce peace between them? They decide on the last option and have an orca brought to the research center so they can learn to communicate with her.
