Moments later I watch as a dorsal fin cuts the surface, an exclamation mark against a swath of blue. A frenzy of flippers and flukes follows, rising in unison and creating their own wake as they torpedo through the water. From the bow of the National Geographic Venture, the call goes out: ''Orcas off starboard side!''

We spot the orcas near Wallace Island in the Strait of Georgia on day four of our 14-day cruise aboard the newly launched 100-passenger National Geographic Venture. Purpose-built for these narrow waters, with a shallow hull and a raft of expedition equipment, this is NG Venture's maiden voyage from Seattle to Sitka.

Our final tally is 11 orcas - males, females and juveniles across two family units. Sometimes they surface in quick succession, their black and white ''paint work'' and grinning mouths lending a comical air. Other times they disappear, only to re-emerge on the opposite side of the bow, a spontaneous cheer the only reaction to such magnificence.

Given the misleading name ''killer whale'' by ancient sailors, orcas belong to the oceanic dolphin family. Once hated as vicious killers, tides have now turned as researchers are discovering that these playful, intelligent creatures live in complex societies, with strong cultural connections.

''Our critically endangered southern residents live in tight-knit pods organised along matrilineal lines,'' says on-board naturalist Victoria Souze. ''The older females pass knowledge and culture to the younger animals.''

We learn that there are three ecotypes of orca in the Pacific Northwest - salmon-eating southern and northern residents, mammal-eating Bigg's (or transients) and an elusive off-shore group. Although they belong to the same species, Orcinus orca, genetic studies indicate that residents and transients divided into separate groups more than 100,000 years ago.

''With a current population of just 76, the southern residents are among the most at-risk marine mammals in the world,'' says Souze. ''Contaminated waters and loss of wild chinook salmon are the major cause.'' At the time of publication, another three southern resident orcas had died.

Souze shares stories about Blackberry (J27), who looked after his little brother Mako (J39) when their mother died and Tahlequah (J35) who carried her dead newborn on her head for 17 days. ''With numbers at a critical, 30-year low, it's as if they know how valuable each new baby is.'' And that's why I've chosen a small-ship expedition cruise, to travel with heart and purpose, to learn about the fragile threads that hold the natural world together, and to see firsthand the impacts of human folly. Through Lindblad Expeditions' support of global stewardship programs such as Pristine Seas and Alaska Whale Foundation, passengers can bring positive change to the places they visit.

Led by National Geographic photographers, naturalists and undersea specialists, we'll trace the Inside Passage of British Columbia and Alaska. Following a similar route to John Muir's 1899 Harriman Expedition, we'll bypass busy ports in favour of smaller, out of the way places.

While kayaking on the smooth waters off Sucia Island, I see my first sea otter, a fluff of whiskery cuteness, tiny paw raised in a classic high-five. Wallace Island delivers harbour seals and black-tailed deer, woodpeckers and river otters, all packaged in forest and flowers so soft you could fall asleep on them.

Unlike Muir, who travelled by steamer ship, the NG Venture is built with luxury as well as function in mind, accommodating 100 guests in 50 outside-facing cabins. While the public areas are bright and spacious, and my balcony cabin is as elegant as a boutique hotel, the real thrill comes from visiting places inaccessible to big cruise ships.

We spend a full day at Alert Bay, a small town on Cormorant Island where a community of Kwakwaka'wakw First Nations people invites us to attend a gift-giving festival known as a ''potlatch''. After dancing and feasting on barbecued wild salmon, we are led to the community's sacred burial ground to view the wooden totem poles.

Giving and sharing is a big part of Kwakwaka'wakw culture, sharing food, sharing culture. Walking through the town, with its hand-painted murals of salmon and orcas, we see that stewardship is also paramount. One sign reads: ''Friends don't let friends eat farmed salmon''; another, ''I support the occupation of Swanson fish farm'', in reference to the recent 285-day sit-in by concerned community members.

Souze follows with a discussion about open-net salmon farms, the damage they cause by spreading diseases to wild populations and the knock-on effect to the salmon-eating southern resident orcas. ''About 70 per cent miscarry from starvation,'' she says.

And with these words, this journey becomes bigger than us. We've been handed a message stick - from traditional custodians, the oceans and the wild creatures themselves. The message is clear: when apex predators are at risk, so are we all.

Our crossing into Alaskan waters is heralded by a forget-me-not mauve cocktail - in honour of Alaska's state flower - and the arrival of three small pods of orcas. ''These are probably mammal-eating Bigg's orcas,'' says Souze. ''Smaller pods make more efficient killers.''

Silent assassins, these orcas roam from Alaska to northern California eating everything from harbour seals to minke whales, sea lions to dolphins. Later, we'll add our photos to an online database, but for now we watch in awe as one of the groups breaks away to give chase to a pod of Dall's porpoises. ''A family of six orcas needs to kill at least 12 seals or porpoises each day,'' says Souze, brushing aside any sentimentality we may have.

As we cruise further north everything gets greener, bolder and wilder. One day, crossing the tumultuous waters of Icy Strait by Zodiac, I fill my notepad with sightings of tufted puffins and stellar sea lions, sea otters and bald eagles. Returning to our ship we watch as a mother and baby humpback frolic against a burnished sky, the water dripping down their sides like spun gold.

Early next morning, we enter Glacier Bay accompanied by three Tlingit guides, their arms and voices raised to the heavens as they ask their ancestors to grant us safe passage. Pushing through brash ice - turquoise to mint to neon blue - we pause in front of the yawning face of Margerie Glacier, its crystalline wall topped with peaks of whipped meringue.

I turn to my husband, his face aglow with the life force that only wilderness (and freezing temperatures) can bring. We laugh at the antics of harbour seals, their chubby bodies sliding about on ice floes like sausages in a pan, and stare in wonder as a blizzard of black-legged kittiwakes fills the sky.

Day 12 arrives in a rush of ice and thunder as we make our way towards Dawes Glacier, our Zodiac threading a cautious path through the slurry of newborn bergs. Bobbing beneath the glittering cliffs we hear the stupendous roar - ''white thunder'' to the Tlingit people - before a skyscraper of crystals collapses into the fiord below.

Like most of the freshwater glaciers in Alaska this one is receding; faster than natural processes can explain, faster than scientists have predicted. ''A journey through Glacier Bay is a journey back in time,'' says park ranger Julia Allshouse. ''When explorer Captain George Vancouver came through in 1794, Glacier Bay was mostly covered by a thick ice sheet.'' Even more sobering, Muir Glacier has retreated at least 50 kilometres since John Muir visited in 1879.

The sky is the colour of cloudberries as we cruise out of Icy Strait. A pod of orcas follows like stealth bombers, while a humpback breaches off the bow. Far below, the water churns with marine microbes - fungi, algae and plankton - a nutrient-rich broth twirled to the surface by incoming king tides.

As the water rushes in, salmon hitch a ride - driven by an urge to return to the river where they were born. On land, hungry black and brown bears pace the waterways, tummies rumbling after long months of hibernation, while in the distance the Tongass National Forest stands sentinel over all. All the invisible threads are still connected. But for how much longer?

In the words of Muir, ''When we try to pick out anything by itself, we find it hitched to everything else in the universe.''