Well, isn't there a lot going on here? Here we have a human delegation, who may or may not have gathered to mourn the passing of the last fish. That's one way of looking at it. Another would be to say that this is a gang of travelers who have come to see the amazing and inexplicable fish body which has appeared in the middle of the desert. Who put that there? A big cat? And why on Earth are these people wearing scuba gear if there's no water?
The thing about art is that it's open to interpretation. Doomsday myths for the human race vary. Some say we'll die of drought, others of flood, and many other reasons to boot. Perhaps that's what's Haderer is saying. Nobody actually knows. Scuba outfits might even just be the latest fashion craze in whatever future he's drawn for us!