Nautilus shells are big business. The U.S. imports more than 100,000 of the iconic mollusk shells every year, according to a recent study by the U.S. Fish and Wildlife Service (FWS). The shells end up online or in stores around the country, where they sell for anywhere from $15 to a few hundred dollars.

But that level of trade is unsustainable, according to new research by Peter Ward, a professor at the University of Adelaide in Australia, who has been studying nautilus species for several years. Ward and other nautilus experts were in the U.S. last week for a meeting with FWS and the National Oceanic and Atmospheric Administration (NOAA) to help inform efforts that may, in the next few years, result in limiting or banning trade in nautilus shells.

Ward's message is clear. "There is no sustainable fishery for nautilus possible anywhere," he says of the mollusks, which are found only in the Indo-Pacific region of the world. "They are on the knife-edge" of extinction, he adds. His research, pending publication in PLoS ONE, shows that nautilus populations in heavily fished areas, especially the Philippines, are almost gone. Ward's most recent surveys found 10 to 15 nautiluses per square kilometer in Australia's Great Barrier Reef but almost none in the Philippines' Bohol Strait and other fishing locations, which had also been overfished of all large fish species. The new surveys follow similar findings that Ward and his colleagues reported in 2010 in Fisheries Research, which found that populations in the Philippines had declined by 80 percent since 1980 and called for the famous chambered nautilus (Nautilus pompilius) species to be listed as endangered.

Nautiluses currently have very few protections and no restrictions when it comes to international trade. The Australian government regulates the harvest of some of the Australian species, but Ward said they still turn up for sale on eBay and other sites regularly. No nautilus species currently appear on the International Union for Conservation of Nature's Red List of Threatened Species, despite earlier warnings of their decline.

Conservationists have discussed possible nautilus protections several times in recent years. The FWS in 2011 said there "wasn't enough data" to justify nautilus protections at the time but the agency has funded research into global nautilus populations and threats. The research found that more than 500,000 nautilus shells were imported into the U.S. between 2006 and 2010 but did not uncover enough information on nautilus life cycles or the full impact of international trade. Nautilus protection under the Convention on International Trade in Endangered Species (CITES) has been discussed but has not yet formally proposed.

Last week's meeting between the FWS, NOAA and nautilus scientists was an important step. "This will help inform future decision-making by the U.S. government about whether the species meets the criteria for listing in the CITES Appendices," says Claire Cassel, FWS ‎senior public affairs specialist. The service is now preparing for the next CITES meeting in 2016 and will soon publish a call in the Federal Register for public comment and additional information on nautilus populations and trade. For at least the next few years, though, the trade in nautilus shells will continue unabated.

Photos: Live nautilus by Michael Bentley. Nautilus shell by Jitze Couperus. Used under Creative Commons license

Correction: A previous version of this article suggested that CITES had not passed nautilus protections. No formal proposal has yet been made to CITES.