CC,
(Hope you had fun on the trout fishing trip!)
I have never heard of a crawfish kill when no other (more sensitive) species were killed. But I am not an expert.
However, I think the low water levels may have been a causative factor?
If your pond was near normal pool elevation on the "winter burrowing" date, then they picked their optimum locations/depths based on that. If your water level dropped all winter, and then you got a very cold snap right before their "spring emergence" time, they may have suffered a temperature shock that was outside of their tolerance.
That is all speculation on my part.
If you want crayfish in your pond, then I would definitely consider re-stocking. You may have lost them mostly due to "bad luck", rather than due to a preventable condition in your pond.
