American Capital Agency's share of 15-year mortgage-backed securities in its portfolio rose to 42% in the second quarter, up from 34% in the first quarter, according to Chris Kuehl, senior vice president of agency mortgage investments, Bloomberg reports. 

The firm's total investment portfolio, including To-Be-Announced bonds, fell to $91.7 billion in Q2, compared to $103.6 billion in Q1.

"We’ve chosen to position the portfolio more defensively" amid volatility in rates, spreads: Kuehl said.