The mortgage market faces a big challenge when the Federal Reserve figures out how to unload its massive $1.7 trillion portfolio of agency MBS, but anticipated widening of spreads could at least improve market liquidity. The fixed-income market has seen a sharp decline in trading volume resulting in part from regulatory issues, said Mike Fratantoni, chief economist at the Mortgage Bankers Association, during the group’s annual secondary market conference in New York this week. “Banks have been hoarding liquidity instead of providing it to the market,” he said. Average daily trading volume of MBS has dropped...