Holdovers or Migrating Fish?

Many fishermen ask me how you can tell a holdover from a migrating striper. The simple answer is you can't.

This skinny schoolie, landed on a Zoom fluke on
a quarter ounce jighead, was one of  many
fish landed tonight in a backwater location.
Is it a holdover or a migrating fish? I just
don't know.

There are a few things you can look for.  Migrating fish might have sea lice on them, especially if caught along the high surf of the ocean in April. However, I've caught many along the oceanfront with no lice.  Holdovers might be caught somewhere near fresh water where they hold up for the winter.  These areas can be backwater ponds or rivers that flow into the ocean.  But, migrating ones can also be found  there in April as they are drawn to these warmer backwaters where food is more plentiful.
I have landed staggering numbers of schoolies (close to 200 fish)  in the last week. I found scarse numbers of them along the oceanfront, yet the backwaters I've fished have been crawling with them. At first I thought these were all holdovers, but I am unsure. I've never found this many holdovers at this time of year in these places so I am beginning to think I might be finding a mix of holdovers and new fish.
But, I just don't know.