It was a beautiful day aboard Croc One, the water calm along Australia's Great Barrier Reef, the movie crew in good spirits. Philippe Cousteau Jr. and his co-host, "Crocodile Hunter" Steve Irwin, had gone there to film their Animal Planet special, "Ocean's Deadliest."

Cousteau, a multimedia conservationist and grandson of legendary oceanographer Jacques, was relaxing, doing research, when Irwin decided to go snorkeling. Not long afterward, a call came over the radio: Irwin had been pierced in the heart by a stingray barb.

"They brought him up to the dinghy and to the back of the boat," Cousteau recalls of the events last September. "It was terrible. We did everything we could to resuscitate him. It took about an hour and a half to get to (shore). ... We did CPR that whole time, switching off."

They all feared the worst, but it was not until the paramedics confirmed Irwin's death that the shock truly hit.

At 5 the next morning, the phone rang in Cousteau's room. It was John Stainton, Irwin's longtime producer and best friend.

"Would you consider finishing the film?" Stainton asked Cousteau.

There was no question in Cousteau's mind. Absolutely.

FINISHING THE PROJECT

The result is a 90-minute documentary that explores stonefish and great-white sharks, saltwater crocodiles, sea snakes and the greater blue-ringed octopus — and delivers an overarching message about conservation. Cousteau serves as the lone narrator and host, but the project is laced with Irwin's energy and irrepressible nature.

Immediately after Irwin's death, "we obviously said, 'Let's set this aside and give you guys time to grieve and deal with the family and everything that's going on,' " says Jason Carey, the film's executive producer. "But as that night went on, everybody — John, Philippe and the crew that had been working with Steve for so many years — felt it was a mission to complete the final documentary that Steve worked on."

The filming certainly was not easy. Back on the boat several days later, the crew remained shell-shocked. "I was the one who knew him the least of everybody on that boat," Cousteau says, "and I was devastated."

Cousteau had befriended Irwin, whom he admired. But the loss also brought up Cousteau's past: When his mother, Jan, was six months pregnant with him (and his sister, Alexandra, was 3), his father — famed marine biologist Philippe Cousteau Sr. — was killed in a plane crash. Like Cousteau Sr., Irwin left behind a wife (Terri), a young daughter (Bindi, now 8) and a son (Bob, 3).

"The whole thing, all the similarities — that it was on expedition, that it was a freak accident — were haunting," Cousteau says. "That immediately hit me like a freight train."

"Growing up with my father's legacy, we never felt that we had to do anything, but we were always raised to think: What could be better than to explore the wonders of the world and share that with people? To try and make the world a better place. And I guess it stuck."

FAMILY LEGACY

Cousteau, 27, keeps a trove of memorabilia in his suburban Washington, D.C. apartment — Masai spears and hunting knives, masks from Africa, a whip from Argentina, photographs from his work in Sarajevo, Bosnia, after the war and from New Guinea, where he took his first "proper" expedition at age 16. By his desk is an autographed picture of grandfather Jacques.

"My father's plan was, we were going to grow up and travel the world," says Cousteau, who speaks of the man he never met with a touch of longing in his voice. On his computer, he keeps a photograph of his father in the doomed plane.

But instead of spending 10 months in Africa exploring the Nile — which Alexandra did, as part of her father's final expedition — Cousteau grew up primarily in Los Angeles and Westport, Conn., with summers spent in Paris with family.

But he had the adventure bug sewn into his DNA, and if he wasn't certain of his future early in life, he certainly knew after that first expedition to New Guinea.

"It's my favorite place I've ever been," says Cousteau, who has since traveled extensively. "Up in the highlands, and lying on the boat at night, looking up at the sky. It was the first time I saw the Southern Cross."

After college, Cousteau and his sister founded EarthEcho International, a Washington-based nonprofit organization dedicated to environmental causes; it uses multimedia sources — from documentaries to public-service announcements — to urge action. Cousteau is also chief ocean correspondent for Animal Planet, as well as a correspondent for National Public Radio, where he takes listeners on audio expeditions as part of the station's "Living on Earth" series.

His next big expedition is planned for Hawai'i, to follow humpback whales.

"The No. 1 thing about Philippe is his devotion to his mission," says Animal Planet's Carey. "It's so obvious that he is completely and totally focused on conservation. ... That enthusiasm, Steve also had that."

Cousteau grew up watching the many hours of his father on film. "It's always weird, even to this day, to look at them," he says. "I guess I'm lucky in that regard, that we have this record of him and his work and his philosophy."

HAUNTING MOMENTS

It's a philosophy the son shares. Cousteau pushed hard to beef up the new documentary's conservation angle, and the sixth-most-dangerous species featured is humans — referred to as "the ocean's deadliest creatures" because of the effects of overfishing, pollution and global warming.

"Steve and I were both excited about this conclusion," he says. "It's a strong message about conservation, but a hopeful one, as well."

Inevitably, the film has a haunting quality. Footage of Irwin's last moments are not in the production — discussion of his death and memories of his life are saved for "Crikey, What an Adventure!" a half-hour tribute airing after "Ocean's Deadliest." But the scenes showing Irwin feel like a precursor to his death, and just as striking is his absence from the segments filmed after he died.

Although Cousteau found it emotionally painful to return to work, he counts the two days he spent filming with great-white sharks — the first shoot after Irwin's death — as particularly special.

"The stars were aligned," he says. "There were five (sharks), and they stayed with the team for most of the day. We had an amazing shoot. I felt like Steve must have been looking down on us."