is one piece episode 537 filler?

The episode starts with everyone exclaiming that the Mermaid Princess has been kidnapped. Luffy asks Shirahoshi why she got out of Megalo's mouth, she apologizes and asks him not to get mad at her as she starts to cry.

As someone calls Luffy filthy and heartless, Chopper urges Sanji not to turn around. Sanji realizes that Chopper's warning can only mean that the Mermaid Princess is right behind him.

Chopper tells him he is correct, but seeing the princess would without a doubt kill him if a normal mermaid made him lose so much blood before.