Curious seal pups born to the colonies this summer dart from the shallows to the depths, pausing to check out the swimmers who've arrived via boat to visit them.

Perhaps it's the doll eyes or the fixed smiles but the Australian and long-nosed fur seals that call Barunguba home, dual named as such since 2021, look like they're enjoying themselves.

The youngest are puppy-like in their playfulness as they dip repeatedly into the paths of swimmers, seeming to welcome humans into their hidden paradise.

At least, "they like us" was my take away from diving at the NSW National Parks and Wildlife Service reserve nine kilometres off the coast of Narooma in December.

Leading the tour was Francois Van Zyl, who has dived in the area and taken tours to the island for almost 10 years.

"Most of the stuff that's underwater doesn't want to be anywhere around you," Mr Van Zyl said.

"The awesome thing with seals is they naturally gravitate towards you because they're curious.

"It's like they're teenage siblings, always wanting to play and annoy each other."

Prior to starting Underwater Safaris, Mr Van Zyl was a field officer on Montague Island for several years. He was diving with seals recreationally from his home country, South Africa, before that.

"I feel very fortunate to be able to experience what I do on a daily basis," he said.

"Every single time you put your face underneath the surface you get to possibly experience something or see something new."

Snorkelling and diving is most popular on the South Coast from December to May when the water is warmest. As well as seals, pot-bellied seahorse, Port Jackson sharks, manta rays and hundreds of species of fish are spotted regularly in Montague Island's waters.

Humpbacks and southern-right whales migrate past the Narooma coastline from September to November. From the tours, the ocean giants can often be seen breaching the water as they make their way south.

Photographer Sitthixay Ditthavong and I watched dolphins swimming in the wake of the boat as we travelled from the island in December.

Rob Harcourt, an honorary professor of marine ecology at Macquarie University, said fur seals were not present at all in NSW in the 60s, having been hunted in the thousands in the early years of European settlement.

Professor Harcourt said populations of both Australian and long-nosed fur seals, also known as New Zealand fur seals, had been recovering steadily since being granted full protection in 1924.

Montague Island was recognised as a breeding site in 2011, after previously being considered a stop-over spot for male seals on the move.

Professor Harcourt said the last time they'd conducted a count there had been about 25 pups born to each species on Montague Island during the breeding season.

"The island's an interesting place because even though they're large enough to be established breeding colonies, they're still relatively small," he said.

"But there's a lot more seals of both species on the island because it's a major haulout for male fur seals that come up from Victoria and Tasmania where the larger breeding colonies are."

Professor Harcourt said they'd tracked seals to South Australia, as far as New Zealand, to Sydney Harbour and back to Montague Island.

On land, the more than 150-year-old Montague Island Lighthouse is still operational. NSW National Parks and Wildlife Service is now the keeper of the protected reserve.

Amy Harris, a NSW parks ranger, said the 82-hectare island was big enough to also support a number of seabirds, including some they'd only discovered nesting on the island in the last decade.

Nine species of seabirds now nest on the island, including little penguins, short-tailed, wedge-tailed and sooty shearwaters, silver gulls, crested terns and the recently discovered Gould's and white-faced storm petrels.

Prior to its designation as a nature reserve in the late 80s, native species' survival on the island was far less certain.

Goats and rabbits were among the pests threatening native species, introduced as survival food for people shipwrecked in the 1800s.

An eradication program saw noxious weeds and feral pests removed and the island was deemed vertebrate-pest free in 2009.

Ms Harris said the island had since become a hub for biodiversity, its bird species also the subject of research projects aimed at improving understanding of populations. They include placing little trackers on birds to gather data on what their migration patterns look like.

"We're certainly doing our best to manage and uphold the biodiversity," she said.

"It's an incredible place."

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