Mark - Visual evidence of dead fish from a winter kill usually depends on the time span between the die off and ice off. An early or mid-winter die off usually results in no or very few carcusses due to adequate time for decomposition which occurs but is pretty slow in cold water. A late winter die off is often apparent with evidence of dead fish.
A second good way to tell if there has been a significant loss of fish is to fish the pond in early spring. A third way is if you regularly feed fish and very few or none appear when the water gets 55F -60F then loss has probably occurred. A fourth, but later in the season, way is to observe spawning or nest building of the bass and bgills.
