QA,
The craws in the creek are likely over populated as there might be insufficient fish predators to keep their numbers low enough to get big. Crayfish grow amazingly fast but once they become adults (around 5 months) the growth thereafter is very slow. They can be grown to commercial lengths in one season. That is a minimum length of 3". They would rarely get larger than 5" Yours are most likely reaching lengths of 3.5 or greater in their first year. They grow slowly after that usually do not live past their second year.
3/4 in mesh will pass crayfish smaller than 3". If you are interested in capturing juveniles, insure your trap or net is of fine enough mesh to retain them. We had a crawdad pond for bait and it was stocked by nature with Orconectis Nais, the same crayfish that are growing in snrub's water. No predators so they stunted but made LOTS of 1.5" to 2" crays. We harvested them with a pool net just reaching as far as the handle would let us and then pulling it along bottom to the shore. You might try something like this in the June time frame when there should be a variety juveniles.
So I mentioned that they grow fast. Let's put that into perspective. You know how small the eggs are but lets start with the second molt when they are around .25 inches long. These are crayfish just leaving the protection of their mother when they weigh ~ 1.8 milligrams. In 5 months they can reach a mean weight of 18 grams OR 10,000 times their 2nd Instar weight!!! :0. To attain this weight they should be no denser than 1 crayfish for every 1.8 square feet. In a pond with no predators, where juveniles are stocked at this rate 24200/acre, there will be ~ 75% survival. So in a 1/4 acre unfertilized unfed crayfish production pond there should be 4538 adults weighing 179 lbs at seasons end. If we take 1/2 of those crayfish to females, then we have 2269 females. It is clear that without a harvest or predators there will be too many offspring to grow maximally the following year. If a person drained and reflooded the 1/4 production pond each year stocking only with enough inseminated females to stock the pond optimally with juveniles ... it would only require around 20 inseminated females. There are 113 times the number of females required (for reproduction purposes) at the end of the growing season.
Imagine if only 40 lbs of 3.5" females (692) over winter each yielding 300 2nd instar juveniles. This inoculates ~208,000 juvenile crayfish to the pond. By the time they reach 1" length there is potential they could weigh as much as 132 lbs. Even at 60% survival to 1" they would weigh 80 lbs even after providing forage (that was eaten by something) that is comparable to the original weight of females. But from 1" they have the potential to grow to a weight almost 64 times that. Of course they won't produce (80 x 64) 5000 lbs of crayfish because there will be attrition as they provide forage to your fish. Still, its simple to see that they can keep growing provided the support weight of 175 lbs (in the 1/4 acre pond) is not breached and because of this and their stellar rate of growth they can produce more forage than the pond could maintain all because something is cropping them. So only 700 females of the original 208,000 juveniles need to survive the gauntlet of predators. This is the challenge TJ faced in his ponds. Once a high density develops, even a small surviving (~0.33 %) proportion can sustain the population. I think you can get them under control if you have a modest weight of predators that will prefer the adults. If they do this, then the overwintering standing weight may be limited to the number your best escape cover can protect. If you are successful it will be an example others can follow to manage this forage.
For others contemplating large crayfish as forage, because of their high reproduction rate and fast growth do not give them a head start (like we do with minnows). Only introduce them after 2 or 3 years and provide a limited amount of escape cover to protect a limited weight of them from predators.
Last edited by jpsdad; 03/24/21 11:07 AM.
