Some fish, like this black drum, make curious thumping sounds that can trigger the buoys’ detection software. The sounds are created when the fish strikes its own swim bladder using bones or muscles.
False alarms such as these are why the auto-detection buoys route their detections to human analysts for final approval. The buoys are intentionally programmed to accept sounds that aren’t an exact match for a typical right whale call. That way, the buoys avoid ignoring right whales that happen to sound a little unusual. Experienced listeners at the Bioacoustics Research Program identify the false positives and remove them from the data used to warn ship captains to slow down.