New online help-wanted postings on major U.S.-based Internet job boards fell in December, The Conference Board said Tuesday.

The group said its measure of online help-wanted advertising volume fell to 1.63 million last month from 1.82 million in November.

Online job ads declined in all 52 metropolitan areas for which data was available, including New Orleans, which dipped for the first time since Hurricane Katrina hit the U.S. Gulf Coast region in late August, the report said.

"A large portion of the declines in ads in November and December are seasonal declines as businesses cut back recruitment ads during the holiday season," said Ken Goldstein, labor economist at The Conference Board.

Adjusting job ads for the size of the local labor force, December's data showed San Diego leading, with 2.46 jobs per 100 persons, while Detroit fell behind all metropolitan areas at 0.55 online job ads per 100 persons.

December was the third consecutive month of declines in the data, well below the August peak of 2.13 million.

The Conference Board Help-Wanted Online Data Series measures the number of new, first-time job ads posted on more than 1,200 major Internet job boards and smaller job boards that serve niche markets and smaller geographic areas.

The group's gauge measuring help-wanted ad volume at 51 newspapers across the country is released the last Thursday of each month.