Is 80-degrees too hot?

Over the years, I have read lots of information provided by Biologist, Jordan Weeks. This summation of his recent podcast is the latest info we have on the “is 80-degree water too hot to safely musky fish” debate.

Enjoy the read.

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The Hot Water Debate

We've talked about hot water musky fishing plenty in the past, but after listening to fisheries biologist Jordan Weeks discuss the topic on the Musky 360 podcast, we had to reach out and ask him to do a writeup for y'all.

He has a different perspective on the topic, and we want our readers to have as much info as possible. Like we've said in the past, we're not here to tell you what to do – we're here to share what we've learned so you can make up your own mind.

Here's what Jordan had to say on the topic:

"80 degrees, or maybe it’s not? There’s more to this question than simply the reading on your sonar unit. To really understand what’s going on, several factors should be considered.

"The common narrative is that water over 80 degrees doesn’t hold much oxygen. In limnological theory that is true, warm water has less capacity to hold dissolved oxygen (DO)…but is that a reality where you fish?

"Muskellunge need a minimum 5-6 ppm (mg/L) of oxygen, below that they become stressed. Data I looked at from several Wisconsin lakes showed DO levels well above that threshold, even at 83 degrees! Some lakes showed the highest DO levels occurred in the warmer surface waters. Some stratified lakes showed that there was less DO at the thermocline where water is much cooler! Looking at this type of data for your favorite water can be helpful. Consult your local citizen scientist or water quality biologist."

Jordan and other fisheries folks use meters to measure both water temps and dissolved oxygen at the same time.

"Stressed fish don’t feed – fish hatchery personnel will tell you this. In lakes that stratify, cool water lies below warm surface water. This occurs on many lakes across the muskie range. A temperature profile can help determine if the lake stratifies. Be careful fishing these lakes, especially if you fish deep. Muskellunge inhabiting deeper cool water can be stressed by removing them from their preferred environment and subjecting them to warm surface water. A rapid change of more than 5-10 degrees can be deadly to fish. I suspect this is how most mortality occurs. Muskellunge inhabiting warmer surface waters are tempered to the ambient environment and should be less stressed if DO is adequate."

As they discussed on the podcast, it's kind of like a goldfish dying of temperature shock when you pour them from their bag into a new fish tank.

"Rivers seem to be the place folks turn to when water gets hot. Uniform temperature and high dissolved oxygen are listed as reasons. This almost always holds true. If water temperature alone stressed fish in rivers we would see massive fish kills each year when water gets hot.

"Plants give off oxygen…except when they don’t. Vegetation can boost DO when the sun is shining, however, at night plants stop producing oxygen and begin to take up oxygen in a process called biological oxygen demand (BOD). Highest BOD occurs just before sunrise. Early morning can be the time when low DO occurs in areas of vegetation and high amount of organic matter (muck bays). Remember algae is a plant and rocky areas tend to have much lower BOD."

The biggest problem is the limited amount of science available on this topic. That said, there's a lot of assumptions being made by anglers, as Jordan lays out here:

"Is your sonar temperature gauge accurate? My guess is that most units are calibrated once (if at all) at the factory, then never again. I own multiple brands. Each brand gives me a different temperature. Which is correct? Based on what I see on social media there is a world of difference between 79 and 80 degrees. What if our sonars are lying to us?

"What if different stocks (strains) handle hot water differently? What if we see floating muskies in the hottest part of the summer because that’s when they tend to float? What if 80 degrees IS the time to stop? What if other factors influence delayed mortality and what if muskies are tougher than we give them credit for? Current available research doesn’t do a good job of answering these questions. Hopefully future work does! One thing I know for sure is that it’s not as simple as a single water temperature reading."

Just some food for thought!

No one's trying to discount the anecdotal experience of guides and anglers who are on the water everyday – we just wanted to share another perspective.

The more you know.... the better you can make informed decisions!