State Street Corp., net profit dropped 71 percent in the fourth quarter and its shares fell steeply Tuesday as the company announced its after-tax unrealized losses more than doubled.

The firm, one of the world's largest asset managers said its fourth quarter net income was $65 million or 15 cents a share compared with $223m, or 57 cents in the same period in 2007.

The Boston-based group said in a statement after-tax unrealized losses in the investment portfolio rose to $6.3 billion at December 31., up $3.0 billion from September 30, 2008.

Shares of State Street slumped $19.25 or 53 percent to $17.10 in the New York Stock Exchange on Tuesday morning. The bank received a $2 billion government bailout in October.

State Street expects operating earnings to remain flat in 2009, according to the statement.