fishwife, are you certain that they are Black Crappie? Probably best to be sure what you have, but it may not make any difference in developing a plan.

Old wisdom here at Pond Boss would state not to have Crappie in a pond less than (10) acres, but over the decades we've heard all kinds of success stories and sad stories. Of course, you're saying you don't know how they got there, and that is academic at this point. In my main (4.5) acre pond, we didn't even know we had Black Crappie for many years.

If you have some funds to spend, an electro-shock survey would help develop a multi-species plan for culling and stocking.

Early in the spring is a great time to cull crappie as they hang out around structure, and you can repeatedly catch one after another.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."