My 2.5 acre pond is predator-heavy. I added 200 4 to 6 in bluegill last spring, several pounds of fathead minnows, added some "sputnik" structure and have been eradicating the flathead cats. I regular catch bass in the 14 -17 in size range, but they are kind of skinny.
I don't want to eliminate the bass but I'm fearful they have insufficient forage. Although I haven't caught a lot of bluegill there are 12 to 18 beautiful specimans nesting near the shore where I had spread pea gravel.
Now for my question. I see a lot of bass pressure near the beds and frequent splashes caused by the fight for survival. Should I fence off the bed area with snow fence or something similar. I know it would help, but I'm not sure how critical it is. Since our house is next to the pond, my wife has objected to the look of fencing sticking up in the pond.
My goal is not to raise trophey bluegill, but to have numerous large ones for family fishing outings (and ocassional fish fries). However, it is my understanding the key to a healthy pond is the proper balance between predators (bass, catfish) and prey (bluegill). Unless I dramatically increase the density of bluegill, won't the bass and cats put so much pressure on the few bluegill that are in the pond to effectively eliminate them before the predators ultimately suffer the same fate (due to lack of food)?
I'm convinced that no more than 20% of the 200 4 to 6 inchers I added last spring have survived predation.
So why wouldn't I protect the nests? How would this aid in the growth rate. Aren't the beds an invitation for the predators to "come and enjoy all you can eat?"
It's my contention that protecting bluegill nests is probably unnecessary, due to the fact that bluegill survive well long term because they are so good at what they do--produce young.
When bluegill numbers are low, the females enter each winter in a better condition due to improved food availability. This in turn improves their ability to lay lots of eggs and produce hordes of young bluegill. Having higher level predators to keep the young-of-the-year (YOY'S) in check means that you continue to allow surviving bluegill plenty to eat, so you end up with fast growth rates. Remember that humans are extremely inefficient predators. We tend to only crop off fish at the top end, so you still end up with lots of individual fish--just very few nice ones.
Now let's address your question from a slightly different angle. You asked "Why wouldn't I?". My answer to that is that if you can devise a method for fencing out the predators, there's absolutely no reason you shouldn't do that. There's no harm in it that I can see, and I'd love to see the results and how effective it may be.
You also asked if your bluegill density becomes too low, will the predators suffer. The answer to that is probably more complex than you or I can really answer. When bass have no available bluegill they will probably spend more time eating other bass, and invertebrates. Neither of these will be efficient enough to keep bass body conditions good, so you'll end up with stunting of some form. LMB stunting is not uncommon.
To summarize my feelings, I'd love to see you try some type of nest guarding device, but you should also consider improving the number of areas that the bluegill have to build nests. If you give the bluegill good nesting areas they will make sure that you end up with enough surviving fry each year.
Honestly, I think BG have such fecundity that except in rare instances (such as trying to establish an initial BG presence in a pond with mature predators), trying to impact BG nest success one way or the other is mostly pointless. Whether one successful nest has 10,000 YOY, or a hundred nests have proportionally more, most of the YOY are still going be eaten. Yet the few that survive are plenty to fill the pond will intermediate and, eventually, adult BG.
These two extremes aren't capable of being reached via Human interference; in actual practice we might be capable of affecting BG fry numbers by perhaps an order of 10. I don't think that will make much difference.
I believe the bluegill in your pond can take care of themsevles. It is when you don,t have enough predators in a pond that the growthweight suffers. For a balanced pond remember to harvest a few of the small bass each year also. Any body of water has a carrying capacity. It will grow only so many pounds per service acre .A fertile pond can handle around 300 to 400 pounds per acre of total fish. Around 30 lbs. of bass and 100 to150 lbs. of bluegill per acre should be harvested each year to maintain a balanced fishery in a fertile pond. Try laying thick brush around the spawning areas so the small fry can hide. Dead cedars work well for this.