PORTLAND – One man’s rubber ducky is another man’s treasure.

Curtis Ebbesmeyer, a retired Seattle oceanographer and beachcomber, has been tracking a spilled shipload of rubber ducks since thousands of them washed up on the beaches of Sitka, Alaska, and he is urging Mainers who may have found one to contact him.

Ebbesmeyer is offering $100 a duck and plans to use the information to track flotsam movement across the world’s oceans.

“I’m an ocean detective,” he said. “Beachcombers tell me about something [they’ve found], and I work backward in time to see where it came from. What’s the story behind it?”

A container filled with 29,000 plastic bath toys tumbled off a ship into the world’s largest bathtub in early 1992 during a stormy voyage from China to the United States.

Some of the toys headed toward Southeast Asia, others toward the Arctic. By 2000, some of them should have arrived in the Atlantic, but the toys have yet to be documented on East Coast beaches.

The yellow, hard plastic ducks have “The First Years” stamped into their sides.

Along with ducks, there are blue turtles that should still be blue, even after their almost 12-year journey, green frogs, and red beavers. But it’s the duckies that Ebbesmeyer yearns for the most.

The company that made the toys, The First Years, has offered up to a $100 reward to the first person who sends a picture of their duck to Ebbesmeyer.

Ebbesmeyer uses his knowledge of ocean currents, a computer model of currents in the North Pacific developed by a friend at the National Oceanic and Atmospheric Association, and an international network of hundreds of beachcombers to track the flotsam of the world’s oceans.

He keeps in touch with what’s washing ashore through a Web site, www.beachcombers.org, and a quarterly newsletter called “Beachcombers’ Alert.” His work has been featured in publications ranging from Smithsonian magazine to People.