Earlier this month, biologist Peter Ward returned from visiting the South Pacific with news that he had come across an old friend he hadn’t seen in more than three decades. It happened to be a creature that scientists think may be one of the rarest animals in the world.
Allonautilus scrobiculatus is a species of nautilus that Ward and a colleague had previously discovered off of Ndrova Island in Papua New Guinea. Nautiluses are small, distant cousins of squid and cuttlefish.
They are an ancient lineage of animal, often christened a “living fossil” because their distinctive shells appear in the fossil record over an impressive 500-million-year period. The recent sighting indicates there is still much to learn about these creatures.
Peter Ward, professor of biology and earth and space sciences at the University of Washington, says:
“Before this, two humans had seen Allonautilus scrobiculatus. My colleague Bruce Saunders from Bryn Mawr College found Allonautilus first, and I saw them a few weeks later.”
Those sightings were in 1984, back when Ronald Reagan was finishing his first term as president and the oldest of today’s millennials were just starting preschool. Ward and Saunders collected several Allonautilus scrobiculatus specimens for analysis and realized that their gills, jaws, shell shape, and male reproductive structures differ significantly from other nautilus species.
“Some features of the nautilus—like the shell giving it the ‘living fossil’ label—may not have changed for a long time, but other parts have,” Ward says.
Allonautilus also sports a distinctive accessory clearly visible in photographs:
“It has this thick, hairy, slimy covering on its shell,” Ward says. “When we first saw that, we were astounded.”
This slimy nautilus turned out to be even more elusive than its siblings. Aside from another brief sighting by Saunders in 1986, Allonautilus disappeared until July 2015, when Ward returned to Papua New Guinea to survey nautilus populations.
Since nautiluses are expert scavengers, Ward and his colleagues set up “bait on a stick” systems each evening—fish and chicken meat suspended on a pole between 500 and 1,300 feet below the surface—and filmed activity around the bait for 12 hours.
“We started using this approach in 2011. This year, there were about 30 guys involved and each day we would all watch the movies from the night before at 8X speed. There were a lot of ‘ohs and ahs’.”
One night’s footage from a site off of Ndrova Island showed an Allonautilus approach the bait after a 31-year absence from Ward’s life. It was soon joined by another nautilus, and the two fought for access to the bait until a sunfish arrived on the scene.
“For the next two hours, the sunfish just kept whacking them with its tail,” Ward says.
The team also used baited traps to capture several nautiluses, including Allonautilus, at a depth of about 600 feet.
Since most nautiluses do not like the heat, the researchers brought them to the surface in chilled water to obtain small tissue, shell, and mucous samples and to measure the dimensions of each animal. They then transported the animals back to their capture site and released them.
The researchers used this information to determine the age and sex of each animal, as well as the diversity of each nautilus population in the South Pacific. Through these studies, they have learned that most nautilus populations are isolated from one another because they can only inhabit a narrow range of ocean depth.
“They swim just above the bottom of wherever they are,” Ward says. “Just like submarines, they have ‘fail depths’ where they’ll die if they go too deep, and surface waters are so warm that they usually can’t go up there. Water about 2,600 feet deep is going to isolate them.”
These restrictions on where nautiluses can go mean that populations near one island or coral reef can differ genetically or ecologically from those at another. The findings also pose a challenge for conservationists, Ward says.
“Once they’re gone from an area, they’re gone for good.”
Illegal fishing and “mining” operations for nautilus shells have already decimated some populations. This unchecked practice could threaten a lineage that has been around longer than the dinosaurs and survived the two largest mass extinctions in Earth’s history.
In September, the US Fish and Wildlife Service will decide whether to advocate for nautiluses to become a protected species under the Convention on International Trade in Endangered Species of Wildlife Fauna and Flora, or CITES treaty. Such protection could curb international trade in nautilus shells, with the aim of reducing nautilus harvests across the Pacific.
“As it stands now, nautilus mining could cause nautiluses to go extinct,” says Ward.
He hopes to see Allonautilus again, especially since he would like to study how the species, which arose relatively recently according to genetic tests, behaves differently from other nautiluses. Its rarity makes this endeavor challenging.
“It’s only near this tiny island,” he says. “This could be the rarest animal in the world. We need to know if Allonautilus is anywhere else, and we won’t know until we go out there and look.”
The work was funded by National Geographic, the National Science Foundation’s Division of Polar Programs, and the Tiffany & Co. Foundation.
Top Illustration: Nautilus pompilius (left) swimming next to a rare Allonautilus scrobiculatus (right) off Ndrova Island in Papua New Guinea. (Credit: Peter Ward)
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