"According to a 2004 New York Times article on the subject, this particular baleen whale has apparently been tracked by NOAA since 1992, using a 'classified array of hydrophones employed by the Navy to monitor enemy submarines.' It sings at 52 Hertz, which is roughly the same frequency as the lowest note on a tuba, and much higher than its fellow whales, whose calls fall in the 15 to 25 Hertz range.
"Not only does it sing too high, it also fails to travel along any known migration route of any baleen whale species -- so other whales can't hear it, and they don't run into it along migration paths.