When it comes to finding an enemy that was practically camouflaged between thousands of other fish, the best way to handle the task, was to constantly swim and hope for the best.
They didn't have any superior technology that would help them track down a single shark, even the system couldn't help with it. So they just need to keep looking around and try to find the right shark to slaughter.
One solution would be to slaughter any shark in this area, but that can pretty much kill the environment in this twenty-kilometer-radius, it wasn't a good idea.
Seeing that the team was putting in stubborn efforts to find the murderous shark, it felt like an appropriate time for the system to intervene.
[Why do you want to kill that shark so badly? You don't even care about the rest of your stingray family]