MAKASSAR, Indonesia — A fisherman found a piece of a Boeing 737 that disappeared more than 10 days ago, the first hard evidence that the plane carrying 102 people had crashed into the sea off northwestern Indonesia, a top search official said today.

The piece of tail from Adam Air Flight KI-574 was recovered yesterday in the Makassar Strait, 185 miles off Sulawesi Island’s coast, the head of search and rescue operations, Eddy Suyanto, said.

Mr. Suyanto told reporters the serial number on the yard-long tail stabilizer matched the one given to the search and rescue teams by Boeing.

No survivors or bodies have been recovered, Mr. Suyanto said.

“This morning, I would like to report the finding of a part of Adam Air,” Mr. Suyanto said, adding that the piece was discovered by a fisherman late yesterday and handed over to authorities early today.

“The part is a tail horizontal stabilizer, the right side, with a length of about one meter.”

An American Navy oceanographic survey ship arrived yesterday in an area 125 miles from where the tail piece was found to determine whether separate metal objects found on the seabed there were also wreckage from the plane. The results of the American investigation have not yet been made public.

An Indonesian vessel located three pieces of debris on the Makassar Strait seabed after local fisherman told authorities they had spotted a low-flying, unstable aircraft in the area but lost sight of it after hearing a loud bang.

The USNS Mary Sears, which has sonar and satellite imagery capabilities, was called in to see if the metal could be the remnants of the plane, which fell off radars in the area during 80 mph winds on New Year’s day, Mr. Suyanto said.