The troll is meant to be a protector and good luck charm, modeled after a similar statue placed surreptitiously by a steelworker on the old span after the 1989 Loma Prieta earthquake.
The new statue forged by an unknown artist was installed at an undisclosed location, Bay Area Toll Authority spokesman John Goodwin told the San Francisco Chronicle in a weekend story.
The original troll was removed from its perch on Labor Day in preparation for the demolition of the old bridge and will likely be housed in a museum or park, but plans were still being finalized.
The new, $6.4 billion portion of the Bay Bridge opened to traffic on Labor Day, nearly 24 years after the Loma Prieta earthquake damaged the old span.
Construction was years behind schedule and billions of dollars over budget amid political fights over its design and engineering challenges.
Goodwin said the new troll, with an axe in one hand and a hammer in the other, is somewhere inside the new bridge but its whereabouts will be kept secret.
"A new troll appeared, as these things happen, on Labor Day, under the cover of darkness," Goodwin said.