The acoustic team listens day and night to vocalizations and clicks. Sounds from dolphins are often noted as "undetermined dolphin species", because several different species produce very similar sounds. However, sometimes a group of animals comes so close to the vessel that the acousticians can visually confirm the detections.
In some lucky situations, the animals travel with us for many miles, as happened with a group of common dolphins that approached the ship in the late afternoon and remained with us after sunset. From the hydrophones, we appreciated how really close they were by their strong echolocation clicks, bursts and whistles. It was not a surprise when, at midnight, we looked outside and under a strong light from the ship that shone into the water, we discovered that the dolphins were still there …maybe the same dolphins we saw before.