A Predator Lurks
As it became clear to Hauser that this third creature was not a whale, in addition to how quickly it was approaching her, she began to get even more worried than she had been in the first place, thinking this potential predator was coming after her.
She finally recognized the creature that was approaching her as a tiger shark. Nan, having years of experience in the field had no doubt in her mind that this third creature was a tiger shark, and that it was probably after her.