Snipe,
Of all the North American crayfish, I think the Northerns are the most beautiful cray. They are successfully cultured for food, command higher prices, and with the exception of the Rusty, stand up to fish as well or better than any other crayfish.
The number will decline as your fish mature. How much food they provide will be determined by the number of overwintering inseminated females. The key to survival, will be the amount of cover they have, but if you have adults weighing in >20 lbs in the spring, their contribution to the food chain will be significant.
You may have this link already but it has a really good image in how to sex crayfish. I couldn't find images for Northerns, but here is another link that also has a
good image. Northern males will be most easy to determine in the fall after the molt. Females must also molt in order to be inseminated and the males molt into (and out of) the "reproductive form". Males grow faster and will comprise more than 50% of the population in a pond with fish due to being able to resist predation better than females. The key is probably size. I think their claw display works to discourage fish by making them look to large to swallow.
If I do the mini 1/8 acre pond, which at this point I may not, I have given consideration to a combination male lepomis (CNBG & LES) with Northern crays. With the right balance crayfish growth and numbers will be good (like you are experiencing).
Don't know if you are eating them ... but crawfish are simply amazing. If you have a few CC, you could eat the tails and they would eat the heads as the clean up crew!
