Can you tell us a little about the setup you have that allows for the turtles and frogs to over winter in your pond? How long are they dormant? Do you provide an area for them to dig in somewhere underwater? How deep is your pond, and how deep underwater is the area they dig into?
I have thought of providing a large container of sand underwater just for that purpose. I have in the past had turtles overwinter in my pond, but have also lost one over the winter. It hadn't occurred to me that it may not have gotten enough to eat to put on enough reserves to overwinter. I thought the turtles did pretty well competing against the goldfish I had, but maybe not.
What type of turtles are you keeping?
I have a Western Painted turtle. As far as burying themselves in the mud all winter I know this is a common belief, but (and I can only speak for Western Painted turtles other turtles may have different habits) they don't do this. That's not to say they never dive into the mud at the bottom of the pond from time to time when frightened or being pursued, but they don't bury themselves and remain there all winter. The fact is they move around a fair bit in the winter albeit very slowly and they just crawl along on the bottom of the pond. They seem to be unable to swim when dormant, I'm not sure if that is because they can't move fast enough to paddle through the water or it has something to do with regulating their buoyancy. I know this not from watching my own turtles, but from observing them in natural pond settings that had a healthy population of turtles when conditions were such that the ice was clear enough to see to the bottom of the pond and you could see all the turtles just laying on the bottom or slowly crawling around, which is exactly what my turtle does.
My frogs on the other hand generally try to tuck themselves in somewhere like between folds in the liner or under some rocks or under a clump of dead algae or in amongst the potted lilies, and like the turtle they also seem to move around from time to time as well, however, unlike the turtle they still seem to be able to swim even in the coldest part of the winter. My pond has a 3" bottom drain and once in a while a frog may try to tuck themselves under the bottom drain dome and get sucked into my settling tank where I'll find them, and if there is still an opening through the ice on my pond I will return them to the pond and watch them swim away. If the pond is completely covered in ice I just leave them in the settling tank until a hole does open up, they are fine in the settling tank but they tend to end up in the muck at the bottom of that tank which I frankly don't think is healthy for them. When I drain that muck out of the bottom of my settling tank it has a strong smell of rotten eggs from the Hydrogen Sulphite that builds up in from the anaerobic bacterial action going on down in there where it has poor contact with the oxygen-rich water.
Besides all that, my pond is about 3,000 gallons, 5 ft deep at the deepest point, and in the winter I circulate the water through the bottom drain into the settling tank and back to the pond. The settling tank is in a pump/filter room that remains above freezing all winter, and because the settling tank has an open top it functions as my breather hole allowing oxygen in and carbon dioxide and what not out.
The turtles dormant period last at least 5 months, and usually only takes food from my hand from May to the end of September. So there are about 7 months where he may not be eating much or nothing at all, so it's really important for me to make sure I feed him as much nutritious protein-rich food as I can when I can. Besides the mealworms, I feed him salmon and shrimp, and he gets some turtle sticks and fish pellets and the occasional other bugs I happen to catch and feed him. Oh, also in the spring the two female frogs both lay a cluster of eggs and when they start hatching out little tadpoles the whole things disappears pretty fast, so I imagine he gets his share of them too.
maybe one of these days... wife did get me this little guy to fill my void.
