Why so Ira? I think lake water reaches lethal T before it reaches lethal dissolved O2. However, max dissolved O2 does decline as T increases, so there is some direct relationship there.
Stillwater Temps - At what temperature should we cease trout fishing?
- Thread starter Buzzy
- Start date
It would be great if we could measure O2 easily, but who among us recreational fishermen owns a dissolved oxygen sensor?
It was my understanding that the temp is one of the things that leads to low O2 and the lack of O2 is the big killer. Temps fluctuate in lakes based on the depth, so it is easy enough for the fish to find cooler waters. What they can’t find easily is O2 if it isn’t there.
Measuring O2 would also help in the situations where algae blooms have caused a spike in bacteria growth. Temp might be fine, but O2 might be low.
As @Starman77 said though most people don’t have O2 kits, let alone ones capable of measuring at different depths.
Again though, I’d like to see a study of catch and release mortality in lakes based on temperature.
I'm not aware of any good studies on C&R mortality in lakes based on temperature. Such a study would be complicated by the depth at which fishing is occurring, as the water temperature varies considerably with depth, but when fighting a fish, much of the fight is occurring at shallower depths.
The attached study is on a couple of Montana rivers and in the lab, not lakes, but I would guess that the results would be similar to a study on lakes. From this study and many others, it is clear that increased temperatures result in higher mortality rates. The study also suggests that death doesn't occur immediately, but usually within 48 hours after release. So, even if you carefully revive a fish and it swims away on its own, that doesn't necessarily mean it will still be alive 3 days from the time of release.
The attached study also points out a lot of complications in conducting such a study. Inexperience on the part of the fisherman likely results in higher mortality rates. Evening fishing on some rivers appears to result in higher mortality rates. Repeated C&R on highly pressured waters results in higher mortality rates. Predation on weakened fish will be higher, and the weakened fish will be more subject to disease, resulting in death down the line. Sensitivity to temperature varies according to fish species.
I've been thinking about buying a dissolved oxygen sensor that can measure O2 at various depths. What O2 sensor or kit do you use and would you recommend it? I've heard that a good one may cost thousands of dollars, not hundreds, and I've heard that they can be very difficult to calibrate and keep calibrated.
The attached study is on a couple of Montana rivers and in the lab, not lakes, but I would guess that the results would be similar to a study on lakes. From this study and many others, it is clear that increased temperatures result in higher mortality rates. The study also suggests that death doesn't occur immediately, but usually within 48 hours after release. So, even if you carefully revive a fish and it swims away on its own, that doesn't necessarily mean it will still be alive 3 days from the time of release.
The attached study also points out a lot of complications in conducting such a study. Inexperience on the part of the fisherman likely results in higher mortality rates. Evening fishing on some rivers appears to result in higher mortality rates. Repeated C&R on highly pressured waters results in higher mortality rates. Predation on weakened fish will be higher, and the weakened fish will be more subject to disease, resulting in death down the line. Sensitivity to temperature varies according to fish species.
I've been thinking about buying a dissolved oxygen sensor that can measure O2 at various depths. What O2 sensor or kit do you use and would you recommend it? I've heard that a good one may cost thousands of dollars, not hundreds, and I've heard that they can be very difficult to calibrate and keep calibrated.
For work we’ve been using YSI multi-parameter probes. For DO we still use the membrane style sensor which is fussy (you have to calibrate to current barometric pressure) but good. Even those are costly. What you want is a laser DO system.
With cold water fishes and temperature, you also have to be aware that their neurotransmitters only work in a certain temperature range, aside from what DO levels are. Even if the water is saturated with DO a rainbow can’t deal with 75* water. It’s like heat stroke, their brains and nervous systems stop working.
I’ve read this study and it only slightly works for lakes. Problem is you aren’t releasing fish and then making them stay in an isolated area while you observe them. Even in rivers the mortality rate of the design of the study will be higher because it doesn’t take into account movement of the fish in a system.
I don’t have an O2 measurement device personally. I also don’t worry about the C&R mortality as much as others.
While not with trout, a while back I had posted up a podcast with a Wisconsin DNR biologist talking about DO with muskies (and several ongoing studies). They found that it had nothing to do with DO since even at really high temps, the DO was still waaaay above what would be considered a minimum level required by the fish (in fact that part of the equation never was even close to lethal to the fish). I have no idea what the critical level is for trout, but I'd be willing to bet that DO isn't THE limiting factor.
Regarding lactic acid buildup, I suppose if you're using 6x and fighting fish far longer than necessary in 65+ temps, then your mortality rate is going to be quite a bit higher than the guy using 8lb and horsing them in, not taking pics and torpedoing them straight down into the water.
That's not even taking into account various populations of trout, some of which thrive (or at least can handle higher temps easier) in those warmer temps. (e.g. desert redbands).
Anecdotally, trout don't bite as readily when temps approach 70 anyway....I fish for most trout because I want to catch a decent number of them, so I'm out on that anyway.
Regarding lactic acid buildup, I suppose if you're using 6x and fighting fish far longer than necessary in 65+ temps, then your mortality rate is going to be quite a bit higher than the guy using 8lb and horsing them in, not taking pics and torpedoing them straight down into the water.
That's not even taking into account various populations of trout, some of which thrive (or at least can handle higher temps easier) in those warmer temps. (e.g. desert redbands).
Anecdotally, trout don't bite as readily when temps approach 70 anyway....I fish for most trout because I want to catch a decent number of them, so I'm out on that anyway.
Interestedly as the water temperature increases its ability to hold oxygen decrease while in the case of rainbow trout as the water temperature increases into the 70s oxygen needs increases.
Generally speaking, rainbow trout require dissolved oxygen (DO) about 4 parts per million (PPM). The oxygen needs for many of the so-called warm water fish are much lower than trout. For example, largemouth bass can survive in waters with DO levels of 1 ppm. In some of our lakes various folks (often associated with DOE grants, or various universities) have done water quality studies looking at such temperature and oxygen levels and stratification etc. but it can take some digging to find the information.
Something that many anglers do not realize is that in many of our popular fly waters (those shallower waters) is that as surface water temperatures climb into the 70s for any length of time even at depth will also have temperatures in the 70s. For example, on Pass lake say in mid-June at day light the surface temperature and at 20 feet can be in that 70-to-72-degree range though as the day progresses the surface temperature can increase several degrees only to fall over night. Unlike most of the clear/deeper lakes no thermocline forms so there is little cooler water at depth.
For those interested in looking at temperatures below the surface Vexilar makes a relatively cheap gadget called the Deptherm that allows measure temperature at various depths. I have found it handy in my kokanee fishing as well as tracking what is going on in those lakes I fly fish for trout.
Curt
Generally speaking, rainbow trout require dissolved oxygen (DO) about 4 parts per million (PPM). The oxygen needs for many of the so-called warm water fish are much lower than trout. For example, largemouth bass can survive in waters with DO levels of 1 ppm. In some of our lakes various folks (often associated with DOE grants, or various universities) have done water quality studies looking at such temperature and oxygen levels and stratification etc. but it can take some digging to find the information.
Something that many anglers do not realize is that in many of our popular fly waters (those shallower waters) is that as surface water temperatures climb into the 70s for any length of time even at depth will also have temperatures in the 70s. For example, on Pass lake say in mid-June at day light the surface temperature and at 20 feet can be in that 70-to-72-degree range though as the day progresses the surface temperature can increase several degrees only to fall over night. Unlike most of the clear/deeper lakes no thermocline forms so there is little cooler water at depth.
For those interested in looking at temperatures below the surface Vexilar makes a relatively cheap gadget called the Deptherm that allows measure temperature at various depths. I have found it handy in my kokanee fishing as well as tracking what is going on in those lakes I fly fish for trout.
Curt
thanks for posting...I was hoping you'd chime in here with more species specific information.
If I remember correctly, this particular bio was talking about DO in the 6-7ppm at high temps. Provided there was minimal weed growth in the area since at night, those plants use oxygen rather than make it in the absence of sunlight.
FYI, field DO meters are expensive to acquire, expensive to operate, and notoriously unreliable.
Guy, you seem to have some experience using DO meters in the field. Would you mind elaborating on this? What brands of DO meters did you use that were notoriously unreliable (I'd like to avoid buying those)?
Plants don’t use O2 at night, but they stop making it (no photosynthesis in the dark) and all the critters with gills keep breathing, so O2 typically drops overnight.
Yeah, that's what I meant to say. Thanks for the correction.
I stand corrected. I forgot that they do continue to respire, albeit at a somewhat reduced rate.
In my opinion, all brands are notoriously touchy, mostly because the meters require frequent maintenance and frequent calibration, which is best performed by frequent use by a trained and observant user.
I'm just a tramp geologist, but these things are a pain in the ass. To paraphrase the Dude: It's just my opinion, man...
Don't let me discourage you, but before you invest 2 grand or so in a basic DO meter and your first couple months' supplies, do some research. Here's a pretty good introduction in to DO meters and measurement.https://www.hach.com/parameters/dissolved-oxygen?
And lets not forget the myriad of variables which result in an ambient DO determination. If you're gonna do lacustrine water quality and you want to draw conclusions, ya gotta go all in. That means pH, DO, temperature, probably some nutrient sampllng, and replicate samples over time. Probably oughta just buy and deploy a hydrolab (https://www.hydrolab.com/) or equivalent.
Good luck.
Bambooflyguy
Legend
Powerbait, popgear and frying pans kill most trout.......