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The narwhal, a kind of Arctic whale, has been called "the unicorn of the sea" because of the long, straight, often spiraling tusk that males of the species can grow. It is illegal to import the tusks into the United States because narwhals are listed by the International Union for Conservation of Nature as near-threatened.

Now the Department of Justice says it has cracked a smuggling ring that operated for nearly a decade, often shipping narwhal tusks from the Canadian Arctic over the border into Maine in a trailer with a false bottom. Two Americans have been arrested, and an indictment, provided to ABC News by the Justice Department, says they will be charged next week with smuggling and money laundering.

"The conspiracy we've alleged was over a period of 10 years, so there appears to have been enough of a market to support that length of conduct," said Todd Mikolop of the Justice Department's environmental crimes section in an interview with The Associated Press.

The indictment says Andrew Zarauskas of Union, N.J., and Jay Conrad of Lakeland, Tenn., will each face 29 federal charges for buying the tusks illegally, and two Canadian citizens - their names redacted - will face charges there for being sellers.

The indictment says that from December 2000 to February 2010, the defendants conspired to "fraudulently and knowingly import and bring merchandise, consisting of narwhal tusks, into the United States contrary to law, and to attempt to import and bring such merchandise into the United States contrary to law, and to receive, conceal, buy, sell, and in any manner facilitate the transportation, concealment, and sale of such merchandise after importation, knowing that the merchandise was imported and brought into the United States contrary to law."

Messages left for Conrad and Zarauskas were not immediately returned. The indictment cites an email in 2000 from Canada offering to sell a "5 foot narwhal tusk speciman [sic] - is in excellent condition - came from the Baffin Island area at Pond Inlet." Over the years, it says, there were dozens of FedEx shipments and more than a hundred payments.

What kind of money could be involved? A legal seller in British Columbia, Furcanada, said tusks can be more than 8 feet long and sell for $1,000 to $7,000 each.