Maybe they're not thanking us for all the fish. Maybe they're warning us of the consequences of our terrible abuse of Earth's oceans. Some researchers believe we'll finally get some answers... sooner than you imagine!
Muriel the dolphin has plenty to say to us... to warn us. Read her story in Come the Eventide:
https://www.amazon.com/Come-Eventide-Chris-Riker/dp/1631834525