I have a similar setup, but have only goldfish. They (or most of them,
that is) have survived a couple of heron attacks. Yes, they do get
spooked after such a traumatic event, but they do return to their
normal behavior in a few weeks, assuming that there are no subsequent
attacks.
I don't know any special tricks, but I just approach the pond quietly
and offer a little food once or twice each day. Eventually, they
should come around to being their old selves again. The bad thing is
that after they get back into their trusting mode, they are once again
more vulnerable to becoming a snack for the evil bird!
Good luck,
Gary