I'm always surprised that nobody has asked the US Navy if they heard anything. It's somewhat well known that US nuclear subs hang out in the Indian Ocean, and they have big ears.
I'd assume that if they release any info on if they heard something via a sub or some sensor.....its basically burning an intelligence asset, as it can reveal information about the actual sensor and possibly it's general area. Best option would be to just stay silent and deny if asked, and refuse any FOIA request on the grounds that releasing sensor data even if its not the raw data could lessen the effectiveness of our Intel/sensor network.