How much is too much?
With all the increased capacity, some question whether there will be enough demand to fill the ships, especially since expedition cruises are generally longer and more expensive. A 12-day Scenic Antarctica cruise has a brochure price starting at just under $16,000.
Maloney said Scenic did research before it decided to create its first cruise product.
"The boomers are coming of age," he said. "The boomers don't want their grandmother's bus tour. They want experiential. They want engagement. They want discovery. They want enrichment."
He added: "Increasingly the responses, the research, the signs that we look for point to this sort of product being very attractive."
Others said the expedition category offers something different to the experienced cruiser.
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Linda Allen, owner of Cruises by Linda in Harrison, Ark., said, "What we've seen is the general cruise market has a small segment of people who are saying, 'I've been to several places around the world; I want to experience something very different.'"
Sven-Olof Lindblad said expedition fits the trend of people collecting experiences rather than objects as they get older.
Observers cite several other factors supporting demand, which will need to expand to accommodate at least 10 ships on the drawing boards, including two Hurtigruten vessels at 600 passengers each.
"It is very explainable [why] this category is growing," Hurtigruten CEO Skjeldam said. "Traditional cruising has a very high growth rate. Regular travel is more commonplace. A certain percentage of that [market] wants to go where other people aren't."
Also, Skjeldam said, more people are up for adventure and activity as they age.
"People are getting younger at heart," he said. "Sixty is the new 50, and 70 is the new 60. A lot of people coming into retirement have been traveling much more than their counterparts 15 years ago."
Some predict that demand will also be boosted by global sourcing. Several modern expedition lines have a customer base outside North America. Scenic was founded 20 years ago in Australia. Ponant draws North Americans, but many of its customers are French.
Ecotourism interest is another driver of expedition cruising. Several companies make an effort to adopt environmentally friendly practices. As one example, Hapag-Lloyd uses rechargeable electric motors on the zodiac boats on its expedition ships the Hanseatic and the Bremen.
One travel seller who has long served the expedition market expressed some ambivalence about all of the new capacity.
"In some ways, it's expanding the market, which may or may not be good," said Jean Pickard, a Virtuoso agent at SmartFlyer in Atlanta. "That depends on how many people you believe should be in either Antarctica or the Galapagos. [In] places like that, I don't know that more product is a good thing. It's a fine line between how much money do you take in before you end up ruining the product completely?"
Cruise lines say they're aware of the potential to spoil the party. They abide by the guidelines set by the IAATO in Antarctica and are on the forefront of environmental awareness.
Some lines, in addition to building ships, are expanding in other ways. Lindblad recently paid $20 million to acquire control of Natural Habitat, a land-based ecotourism and adventure travel company. And Ponant bought parts of Travel Dynamics International, a provider of enrichment programs on small cruise ships.
Pickard said that as larger, well-financed companies become attracted to the expedition segment, there's the potential for the pioneers of the business to get shouldered aside.
"I was in the Galapagos last November," she said, "and that was always a traditional market with small boats, with expedition ships, and then Celebrity comes in, and then Silversea comes in. I don't care if they're only 100 passengers, it's a whole different ball game."
But she added that newer luxury operators can do a fine job walking the line between luxury and expedition, citing a cruise on a 284-passenger Ponant ship in Alaska as an example.
Fairly large by expedition standards, the Ponant ship is still small enough to get into shallower waters and protected areas, and flexible enough in its itinerary to accommodate serendipity.
One night around dinner time, Pickard said, the ship went into a bay and found itself surrounded by 50 to 100 humpback whales. "The captain shut down the engines and we just stayed there," she recalled. "You can do things like that on a smaller ship."