Background: My pond is complete after about three years of construction. It is watershed fed and is now 1.6 acres and about 15' deep. The goal of the pond is to have a good YP and SMB fishery, and hopefully BT in the future. It is well established with FHM, GSH, Eastern Silvery Minnows, crayfish and PK shrimp. There is very little vegetation as of yet. The water is tannin stained from Eastern Hemlock and looks like diluted ice tea (clear but brown).
I have stocked a total of about 200 6-7" YP and 25 5" SMB between Fall of 2024 and Fall 2025 and have no proof of life after fishing and setting minnow traps. The YP should have pulled off a spawn in Spring 2025. I was hoping that I could catch their fry in minnow traps baited with dog food. I caught all of my forage species but no YP or SMB. The SMB probably haven't pulled off a spawn yet, but if they're in there they should be large enough to this Spring.
I have fished open water with live and artificial bait and done the same through the ice with no signs of life beyond the forage. I have found a total of maybe a dozen dead perch (mostly on the bottom in 2-3' depths) and no dead SMB. I'm an avid trapper and have seen no signs of otters. GBH visit occasionally but they fish in less than 1' deep (I suspect the tannin staining limits their visibility). The pond is the center piece of the property and is visible from the back windows of the house, so I'm assured there are no trespassers.
I have not installed aerators yet but ran conduit underground from the house to the pond edge in the event that I need power there in the future. I don't object to installing an aerator, but the pond is used for a closed loop geothermal heating a cooling system and I'm not clear on how destratification of the water column would impact the efficiency of the geothermal.
Recent posts by essup and others regarding DO under the ice made me consider low DO as my culprit so I tested it tonight using the CHEMetrics kit and used a digital meat thermometer from my kitchen. There is currently 22" of ice with about 16" of snow covering, although I have kept about 10% of it cleared of snow to allow some light penetration. Here are my results:
2' 36.1F 8ppm
4' 37.6F 4ppm
6' 37.2F 1ppm
These were all taken just after sunset after a clear and sunny day. Depth is relative to the top of the ice, not the bottom of the ice so 2' deep is actually a couple inches under the ice. I suspect that my ice fishing has been mostly too deep, so that is likely why I haven't caught any through the ice this winter. I'll try shallower.
I read a study that suggested a lower DO limit of 2-3PPM for YP, however it suggested they can tolerate lower concentrations temporarily without much negative effect. It also suggested that "in general, the first response of fishes to severe hypoxia is avoidance." That gives me a little reassurance that they should be able to survive my current DO levels, but would likely not be at depths below 4' for extended periods. Here is the link for those who are interested:
https://www.sciencedirect.com/science/article/abs/pii/S1095643317300879 Based on what I have read, DO levels of 5-6 or greater are ideal for SMB. Given that, my results above worry me that they may not have survived.
The reason for my post (and my sleep deprivation) is trying to figure out where my fish went. Are they dead at the bottom feeding my crayfish, or are they avoiding my efforts to find them? As I said before, I have a very robust forage base and low density stocking numbers. I expected catching them would be a little bit of a challenge, but I have completely struck out.
My plans moving forward are to fish at shallower depths until ice out, then deploy fish traps. So far all I've used are Gee style minnow traps baited with dog food hoping to catch fry. I'd love to hear the advice of others here on how to survey the pond. Unfortunately there aren't pond management companies here in New England like there are in the south, so shocking isn't a realistic option.
Also, what are recommendations on aeration given my DO numbers today? Is it required? Should I expect a complete kill of my YP and SMB has happened based on my DO numbers? How might aeration effect the geothermal system? I'm willing to accept lower geothermal efficiency for a healthy pond ecosystem.
