BY STEPHEN L. BERNARD

NEW YORK—Global foreign-exchange trading volume dropped for the first time since the financial crisis, according to data released Monday by four major central banks.

Average daily trading volume in October totaled $3.470 trillion in North America, the U.K., Singapore and Australia, which combined account for most of the world’s foreign-exchange activity. That is down from $3.474 trillion in April, according to reports from central banks in the U.S., U.K., Australia and Singapore. It was the first sequential drop in the semiannual survey since April 2009, though volume was still up 15% from a year earlier.

The decline from April to …