Question Author
Mmmm. Thanks for tip about newts but I haven't seen any around here. Not of course that it means there aren't any.
I do have one fish that the heron didn't spot last year but he's hardly big enough to eat the masses of spawn that were laid. I know blackbirds will happily pick off the baby frogs once they get old enough to be clamouring about amongst the stones at the edges but they weren't even tadpoles.
Oh well, no doubt the frogs will try again next year.