Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Where have all of the small trout gone ?

Back again to the 35 acre lake our fishing club rents. Over the past two years we have been stocking trout to see if they will make it through the summer heat. Surface temps around 75-77 degrees on the hottest days with temps 65-67 degrees at the bottom - 20' foot depth. We know some of the trout survive the summer because we have caught them in the fall - although they are a little scraggly looking compared to when they are caught in the spring and early summer.

So with that background - here is my question : We have stocked aproximately (1000) 8-10" trout and (65) 17"-20" trout over the past two years. The issue is we seldom catch one of the smaller trout but do catch the larger trout from time to time. With a stocking ratio of small to large trout of 15-1 that doesn't make a lot of sense. We asked local Fish and Wildlife for their take and they said with the large amount of 8-12" LMB we have, they think they are eating the small trout. There are eagles and cormorants that visit the lake, but could they put that much of a dent in the trout ?

Your thoughts appreciated.

They should make it through those temps although you might have some loss and wouldnt know it if the fish sink when they die...which they usually do. Also when the trout get stressed they can go to the surface and the eagles will pick them off....otters take their share as well...and so do the cormorants and LMB. So count on a good number of them disappearing because of predation (usually 30 percent but perhaps more because of the bass).

My lake is 12 to 13 feet deep but mainly 8 feet, temps hit 78 to 80 degrees this summer for about 2 to 3 weeks, I never saw a floater and never saw a fish at the surface, any trout I did catch would only fight for about 10 seconds and if released would go belly up and die within a few minutes so the heat was hard on them - but must have found some cold spots to chill out.

Im basically doing the same as you with my 6 acre lake but have learned a few things...ie. put and take, encourage everyone to fish them out and don't put any back when you catch them, they will get hook shy and/or die when releasing them in hotter weather so catch and enjoy them that's why they are there.

Secondly, because you have LMB Id only be stocking large trout 1.5 and 2 pounds, and I would stock in the fall just before ice up (only if you ice fish), and stock first thing in the spring, then get to fishing before the hot wx comes...and like I say keep every one of them.

As a side note I've been ice fishing my lake for the last 3 weeks and haven't caught a fish, Ive watched eagles slamming my fish all summer long and Ive caught 2 otters and shot several others but I know they've been hard on my fish (I put 500 fingerling specks, 200 8 to 10 inch specks, 700 1 to 2 pound rainbows, and 70 2 to 3 pound rainbows, lake is also full of pumpkin seeds and about 7 LMB about 6 inches mid summer). Anyway, I dropped a camera in the lake and am seeing tons of trout...I just guess Im a bad ice fisherman...

A poor quality vid

In deeper ponds, just because the water is cold enough in the deep water doesn't mean that there is enough O2 for them to survive. Especially if the water clarity is not 12 feet or so to get sunlight down below the thermocline. Pond Star, if you want to help manage the 35 acre lake, they really should buy a reliable O2 meter with a longer depth probe to be able to read O2 levels down 15 feet or so.

Interesting video - good way to find out if your trout are still down there.

Esshup

Can you recommend a brand of O2 meter to purchase ? That sounds like something we should be doing. Being uneducated in this area, I will need to bone up on what the numbers I see mean as far as if there is enough oxygen.

I have only used YSI brand. First one IIRC a 550 that used a membrane. To use it first you have to make sure that the membrane stayed moist when not in use, and then you had to move the probe at a certain speed (inches per second) to get it to read correctly. You couldn't just drop it in the water and leave it there. Also, when I first turned it on, it took about 15 minutes to stabilize before I could get accurate, repeatable readings.

I purchased an Optical YSI O2 meter. YSI ODO is what it was called. It's now out of production but they have comparable units. Again, you have to keep the probe in a moist environment (a rubber cap comes with it that you leave a bit of moisture in when stored) but the biggest advantage to me was it gets repeatable readings a minute or two after turning it on, and I don't have to re-calibrate it every 6 months or so. I check it, and it's never been out of calibration. I also don't have to keep it moving to get good readings like I did with the YSI 550. The ODO also has an easily removable probe, the 550 had a probe that was hard wired to the unit. I can use a short or long probe depending on the water depth, but I purchased a 10 meter probe when I purchased the ODO and it's been on the unit since purchase. It has come in handy to read deeper lakes and ponds. I was worried that I'd run out of probe length if I only had the 3 or 4 meter one.

They aren't cheap though. Maybe others (Snipe, Lusk, Cody, etc.) can chime in with what they are using.

As for readings, for warmwater fish, no less than 5 mg/l and for trout no less than 7 mg/l. It is very dependent on water temp. Saturation levels will vary according to temp. Many species of fish can tolerate lower O2 levels, but those figures I gave you are what I consider minimum levels. Adding O2 to the water without paddlewheel agitators, surface agitators or diffusing pure O2 into hauling tanks is a struggle once O2 levels drop below 4 mg/l. It's a LOT easier to keep it above 5 mg/l than to bring it up over that once it crashes below it.

Thanks esshup - will wait and see if any of the other guys chime in on this. Not inexpensive I see !!

What are your thoughts on whether a 12" LMB will eat a 8,9, or 10" trout ?

This is what I use, its inexpensive but I cant get deeper than the length of my arm though the ice, in the summer I dive to the bottom and take readings.

https://www.chemetrics.com/product/...0EoN88ISE7D5erk9QfC0EFDrcFjZb1FG0CQemsH6

In my 6 acre lake in the summer my lake is over 9ppm most of the spring/summer/fall, I usually measure during the day but should try at night as well.

In the winter last year my lake went down to 2ppm late winter so I opened up a small area with an aerator and my trout made it. The area was only about 40 feet in diameter but seemed to do the trick. The sunfish had no issues at most depths but the trout stayed up high near the ice when I checked with cams.

"What are your thoughts on whether a 12" LMB will eat a 8,9, or 10" trout ?"

I think conventional wisdom says LMB can eat other fish about 1/3 of their length, but someone correct me if I'm mistaken.

If correct, a 12" LMB could maybe eat a 4-5" fish, but the 5" would be on the upper end of capability.

Sunil's "rule of thumb" is usually pretty good guidance.

However, I think trout may break the rule. Trout are almost perfectly gullet shaped (fusiform). They also do not have any spiky rayed fins.

Personally, I would not be shocked at all to see a 12" LMB attempt to eat an 8" trout. If you have a few bass over 12", then I think they might even try for a 10" trout if they were feeling particularly feisty on that day?

I am pretty sure the momma bass did not give their babies a lecture about not biting off more than you can swallow!


(I am definitely NOT an expert on this topic. Just have watched bass on many occasions try to eat things that were ridiculously large for the optimistic bass.)