They can die from exhaustion and old age during the spawning season, they only live a year or so. I saw this in my pond. I had no predators, with predators I would expect them to be picked off pretty quick and not getting much of a chance to see them unless your population is that large. That's just one possibility of many

Goofing off is a slang term for engaging in recreation or an idle pastime while obligations of work or society are neglected........... Wikipedia