PUGET SOUND, Wash. –  To check on the health of the giant Pacific octopus population in Puget Sound, an unusual census takes place every year. Volunteer divers, enlisted by the Seattle Aquarium, take to Washington's inland waters to look for their eight-tentacle neighbors.

THE BIGGEST IN THE WORLD

Weighing as much as 150 pounds with tentacles that can span up to 20 feet, the giant Pacific octopus lives up to its name. It's the biggest octopus in the world, and it calls the waters off Seattle home, part of its vast range over the Pacific Ocean.

"The Puget Sound offers good habitat, water temperature and an abundant food source for them," said Kathryn Kegel, a Seattle Aquarium biologist.

Known as one of the smartest creatures in the sea, the giant Pacific octopus leads a relatively short life, between three and five years. They are terminal maters, meaning once they mate, they die soon after.

Let’s start with the biggest: the 888-foot USS Oriskany. Diving the world’s largest artifcial reef is all my buddy and I talk about on the drive from Orlando to Pensacola, Florida. So we’re a bit disappointed when we learn our frst dive will be on the rubbly remains of the 315-foot San Pablo.

As we soon find out, we should have been excited. “We have hundreds of dive sites, but until Oriskany no one knew about our diving,” says Capt. Douglas Hammock, at the helm of H2O Below as we pull away from the marina. “San Pablo is actually a great dive.”

When San Pablo exploded of Pensacola’s coast in 1944, locals conjured tales of espionage and foreign spies, and dubbed the wreck the “Russian Freighter.” But Franklin Price, a maritime archaeologist with the Florida Department of State, explains during our briefing what really happened to the ship. “It was a refrigerated cargo carrier that brought bananas up to Boston from Central America for years. It was torpedoed in 1942 at the dock in Puerto Limon in Costa Rica by a Nazi U-boat.” Franklin says that the ship was refoated and towed to the United States in 1944, and blown up during a top- secret government mission. The facts about San Pablo’s sinking were revealed only a few years ago, so the moniker Russian Freighter still persists among local divers.

A new study has shown that the dottyback, a small predatory reef fish, can change the colour of its body to imitate a variety of other reef fish species, allowing the dottyback to sneak up undetected and eat their young.

The dottyback also uses its colour-changing abilities to hide from larger predators by colour-matching to the background of its habitat -- disappearing into the scenery.

The research, published today in the journal Current Biology, reveals a sophisticated new example of 'mimicry': disguising as a different species to gain evolutionary advantage.