The first year at my pond, without gamefish, produced thousands of tadpoles of many species...mostly bullfrog. It was not uncommon to see a few floating tadpoles (dead or dying), maybe not daily, but close. You are probably seeing the results of the normal mortality rate.
Also, with the existence of predators in your pond, tadpoles are not a favorite meal and the tadpoles may be being hit and spit out left to suffer and die. This is just a guess.
Side Note: I thought for sure we would be sweeping up frogs off the drive way, out of the shop, and mowing more frogs than grass, but they seem to leave the pond and disappear very effectively. I might have noticed a few more baby toads in the front yard than normal, but, all in all, their exodus was mostly unnoticed. They might lose their bad taste as they turn to hopping and become bird, snake, raccoon, and possum meals as well.
