The weeklong search for an award-winning U.S. poet who disappeared while hiking up a volcano on a remote Japanese island has yielded no clues and authorities will scale down the search, a police official said Tuesday.

University of Wyoming professor Craig Arnold, 41, was reported missing April 27 after he failed to return from a hike on the tiny island of Kuchinoerabu-jima, about 30 miles off the coast of Japan's southern Kyushu island.

"We have not found anything, including his belongings," local police official Yoshiyuki Kuzuhara said.

About 40 people — including policemen, firefighters and rescue workers — were involved in the search for Arnold, along with search dogs and a police helicopter. But Kuzuhara said the search operation will be scaled down after Wednesday.

A U.S.-based search-and-rescue organization sent four people to Japan to keep up the search.

The trained searchers from an organization called 1st Special Response Group arrived Tuesday night. Their strategy will be to look carefully for Arnold's trail and then pursue any signs, said David Kovar, founder of the nonprofit organization based in Mountain View, California.

"They are expert in following the sign of human passage through the terrain," Kovar said. "If you think about aboriginals or Native Americans who were known for following signs of people going through a landscape, this is sort of the modern version of that."

Japanese authorities say they had ruled out Arnold being either inside the volcano's crater or at the barren top of the mountain. U.S. military aircraft were involved in the search during its first day.

Kuzuhara said the mountain has no hiking trail, and the locals hardly go there.

"People come to our island for fishing, not for hiking," he said.

The island, with population of just 150 people, is mostly covered by dense vegetation. It is about seven miles long and three miles wide and dominated by the 1,800-foot volcano, which last erupted in 1980.

Arnold had been traveling all over the world, working on a book about volcanoes. He is the author of two award-winning books of poetry and was in Japan through the U.S.-Japan Friendship Commission's Creative Artists Exchange Fellowship.

He grew up in a U.S. Air Force family and lived four years on the Japanese island of Okinawa, where the U.S. military has a base.