They don’t seem to be surfacing in any particular pattern, but they do seem to be coming up when their nets are nice and full.
She grabs her gun, and then when she sees a lull Mulberry tries to run up to grab a wagon and get away.
As she approaches the closest one however she hears the splash of water behind her. Instinctively she jumps into the wagon to hide. The mare doesn’t take a chance to check, but she is almost certain that it’s one of the fish-ponies, especially since it sounds like it’s messing with one of the barrels nearby.