I can help here. Electrofishing boat isn't 100% effective to determine survival of threadfin shad after winter, until well past time to re-stock. Electrofishing open, deep water, where threadfins reside during cool months is hit or miss. If you hit, that's great. If you miss, all you know is you missed.
Wr of bass won't tell you.
Consistent water temperature readings can be of help. If water temperature drops below 42, you can pretty well expect threadfins to be gone. When water temps reach lower lethal, threadfins rise, seeking warmth. Birds have a field day, especially terns.
Otherwise, a short term gill net set can help determine. Use small mesh. So can checking stomach contents of bass via lavage.
