On the beach clear puzzle P-087 (fishing net) and then the newly appeared P-088 (fishing rod).
You can now interact with the rod to play Piczle Fishing!

One of the catches is the elusive red herring! Once you've caught it leave the fishing mini-game.

You can now pick up this poor fish.

With the red herring in your inventory approach the bear and Score-chan will throw it.
You can now walk north.