With a quick double beat of the 'wings', the seal that had been at the surface of the sea at Cabbage Tree Island was suddenly just about on top of us.

The animal seemed as startled about this as my scuba diving buddy and I were, the huge, wide eyes fixed on us as his otter-like body buckled into rapid twists and rolls, just inches away from our faces, flaring then beating his flippers as he rolled around while circling us fast enough to make us dizzy, his body flowing, contorting and twisting in every direction, but his staring eyes never leaving us.

There is nothing under the sea that moves and manoeuvres as insanely fast as a fur seal.

A blur lower and to our right, another seal appeared on the edge of visibility and was instantly upon us, rolling away at the last moment and somehow not making contact.

Another seal, then another, all staring with those huge black eyes rimmed with white, somehow managing to look shocked and mournful at the same time.

Their tiny, thorn-shaped ears sticking straight out add to the comic cuteness of the picture, the only thing on these animals that is not superbly, fluidly streamlined.

Sometimes it seems like a game, and that they're egging each other on, daring each other to get closer, and once in a while you'll get a glancing thwack from a solid, rubbery flipper - you can feel the animal flinching with the shock of it.

Sometimes they'll open their mouths wide and blow a small burst of bubbles or flash you a mouthful of sharp teeth, and just once in a while you'll feel an exploratory nip - they don't really have hands, so their mouths are how they explore new and interesting things in their world.

You couldn't really call it 'biting', but they do tend to run away with a guilty look in their faces when they've done it.

Animals this small-bodied, hyperactive and oxygen-hungry couldn't possibly be supreme breath-hold divers, and of all the marine mammals, fur seals do the shortest dives.

Dive times for most fur seals actually compare with those for a decent human free diver; a minute would be typical, 4-5 minutes would be a long and particularly relaxed dive.

No human is anywhere close to being so slippery or agile through the water, though.

The Cabbage Tree Island fur seals are most definitely animals living fast-paced lives near the sea's surface rather than laid-back deep divers.

The sea around the island, just out of the Port Stephens Heads, provide plenty of food for them but they must be wary of one particular predator, the Great White shark.

Our waters are a breeding ground for these sharks and deep scars on the bodies of some fur seals suggest they may have had a close encounter.

Fur seals are in the same family as the generally larger and more heavily built sealions.

As their name suggests, though, fur seals differ from sealions in having a thick, feltlike pad of incredibly soft, dense underfur beneath their coarse, water-shedding outer coat.

This luxuriant underfur traps a warm blanket of air next to the seals' skin.

The fur seal/sealion family is known as the eared seal family, and one of the most conspicuous things separating them from the 'true' seals is their tiny, almost vestigial external ears.

True seals and walruses, the other seal families, just have a small opening for an ear.

A bigger difference is the mode of swimming - the fur seals and sealions 'fly' through the water with their wing like arms or pectoral flippers, using their slender hips and feet just for steering, while the true seals have small, weaker, stubby arms and instead swim with side-to-side movements of their powerful hind legs.

The current population of fur seals in Australia is approximately 120,000, about a third as many as there were before Europeans settled here.

Fishing operations have led to near eradication in parts of Australia, for example, the Seal Rocks colony north of Port Stephens.

But seals have been protected since 1975 and are slowly increasing and re-occupying some of their former range.

At present they only visit Cabbage Tree Island during the cooler months, taking up temporary residence on the north side.

However, with populations increasing further south and overcrowding becoming a potential issue, it's hoped that they may settle permanently here and become a tourist attraction for the area.

To showcase Port Stephens' incredible water wonderland the Examiner is collaborating with local divers such as Malcolm Nobbs, Medowie marine scientist Meryl Larkin and members of the Combined Hunter Underwater Group for a new series that explores life Beneath the Surface.

Nobbs, a recreational diver and photographer from Nelson Bay, and UK marine ecologist Jamie Watts collaborate regularly on marine life articles. This article was written by the pair following a dive trip to Cabbage Tree Island, off Port Stephens.