Actually, there was another important reason why Qiu Tu switched the target of the encirclement from the Whale Shark to Xie Yue.
That was... harvest.
The character of a creature affects its actions.
A naturally cautious creature and one with an arrogant, conceited personality will act completely differently when facing the same situation.
For example... Larilo. Because of her somewhat cautious nature and preference for keeping an ace up her sleeve, her "regional center" would not be carried on her person or hidden within her main body.
This was both to retain a sliver of hope for turning the tables in the face of danger,
and to preserve a lifeline for her in case an Evil God invaded and captured her.
Similarly with the Whale Shark, whose nature was to fear death and crave life, would 100% also have hidden his regional center.
But Qiu Tu was different. Although he was cautious, he had a strong desire for control.
Therefore, he would carry his regional center with him.