Topwater -
I believe the drop off rate has more to do with the fish being injured and escaping than marine mammal predation though both factors contribute. Suspect it is an expansion of the idea of net drop out and drop-offs associated with the commercial troll fisheries.

I too thought that 5% seemed high though to be fair last year I lost a coho after a couple hard head shakes. Upon reeling in I found two gill arches on my hook - suspect that was a drop off mortality!

I don't fish the ocean so can't comment on the frequency of "floaters" in that fishery.

Curt