Hot Water - releasing muskies

[jasonvkop]

Whats the temp for lakes getting too hot to fish; 80 degrees?

[Will Schultz]

80 is a good general rule but even fish overhandled or overfought in 78 degree water are going to be very stressed and mortality will increase dramatically.

[spnplugger]

Will,

Why is that so? Not doubting your answer in the least. Is it because their metabolism is at it's highest? Or because there is a greater difference between surface water temp, and deeper water temp? Thanks for your answer

Charlie

[Duke]

Its all about the O2 - hotter water holds less dissolved oxygen, so its like the equivalent of high altitude on our bodies/breathing. Muskies require relatively high DO to keep pumping, compared to bass etc. The combined effects low DO, high level of exertion, and especially greater size of the fish (related to level of exertion) increase the risk of unsuccessful release.

[Will Schultz]

Good question Charlie, I don't think anyone on here has ever asked why mortality increases.

The reason for increased mortality comes down to one main factor, warm water doesn't carry as much oxygen as cooler water. Fish, especially bigger fish like muskies, fight hard while being caught. The lower oxygen level in the water doesn't allow respiration to exchange gasses (oxygen for carbon dioxide) fast enough. If carbon dioxide levels remain high for too long it will cause mortality. The build up of carbon dioxide during the fight is greatly increased when the fish is removed from the water for any length of time (obviously because it can't breathe out of the water).

A second issue is that in most lakes and slower rivers there is no cool oxygen rich water for the fish to rest after being captured. Below a certain level in all waters there will be some cool water but during summer this water is very low in oxygen.

[Will Schultz]

Its all about the O2 - hotter water holds less dissolved oxygen, so its like the equivalent of high altitude on our bodies/breathing. Muskies require relatively high DO to keep pumping, compared to bass etc. The combined effects low DO, high level of exertion, and especially greater size of the fish (related to level of exertion) increase the risk of unsuccessful release.

HAHAHAHA... Duke types faster than me!

[hemichemi]

Thinking outside the box, here...

Anyone ever thought about carrying a small DC aerator (like for an aquarium), and hanging the aerator hose over the side in the water to help revive fish after capture? Maybe mount the hose on a long stick, and use it to aerate the water around the fish while it's being held in the net in the water.

[Will Schultz]

Thinking outside the box, here...

Anyone ever thought about carrying a small DC aerator (like for an aquarium), and hanging the aerator hose over the side in the water to help revive fish after capture? Maybe mount the hose on a long stick, and use it to aerate the water around the fish while it's being held in the net in the water.

I'm pretty sure you would also have to cool the water to increase the oxygen carrying capacity. What happens when the fish swims away from this oxygen righ water? The best bet in hot summer water is to stop fishing muskies and start bass, walleye or perch fishing.

[hemichemi]

OK; we could bring a water chiller along, too...

Yes, the concentration of DO would still be low, but if it were constantly being replinished around their gills, the concentration becomes far less important (in my imagination, anyway) than the flux of O2 (amount per unit time per unit volume) available to them.

I agree; when it's too hot, we should refrain. But what I suggest could be used at any temp to speed their resuscitation...

[Will Schultz]

In the fish haulers they use liquid oxygen instead of a bubbler system. If you had a livewell filled with cool water and were using liquid oxygen it would be a great resuscitation system.

Best advice is to land them fast and limit out of the water time to zero, especially when the water gets warm. Once we have consistent temps in the 80's we all need to ask ourselves which is more important - catching a fish or preserving the resource.

[spnplugger]

Will & Duke,

Great answers! Thank you. Two last questions--does this include lakes like Murray, which are spring fed (or so I'm told)? Or does the thermocline not allow the fish to reach the cooler, more oxygen rich waters to recover?

Charlie

[hemichemi]

Will & Duke,

Great answers! Thank you. Two last questions--does this include lakes like Murray, which are spring fed (or so I'm told)? Or does the thermocline not allow the fish to reach the cooler, more oxygen rich waters to recover?

Charlie

Charlie,

Even though the water below the thermocline CAN hold more dissolved O2, it typically is O2 deficient, because it doesn't mix with the upper layer of the thermocline which has access to the atmosphere. The condition persists, with O2 levels declining, until turnover occurs in the fall.

[Will Schultz]

This applies to any water. Even in spring fed situations the cooler water settles and never gets a chance to mix with the oxygenated waters in the upper layer. I've heard people try to reason that in a big river there is no thermocline so they're not pulling fish up from cooler water into warmer surface water. In fact a big river is just as bad because the water temp is pretty uniform which means all of the water column is low in oxygen.

[kid coulson]

Cant fish get temperature shock as well.Like a deeper water fish say hanging in 65* water gets wrestled up to say 80* surface water in a matter of a few seconds. ??

[Will Schultz]

Cant fish get temperature shock as well.Like a deeper water fish say hanging in 65* water gets wrestled up to say 80* surface water in a matter of a few seconds. ??

They make that move all the time under normal circumstances chasing food. The difference in the oxygen content, from the 65 to 80 degree water, is where the stress is going to come from. Being brought up and held at the surface is nearly as bad as putting them on the bottom of a boat.

I know people will say "the fish swam away just fine", I'm not killing fish by fishing in hot water. No you probably aren't killing every fish you catch but mortality rates from angler caught muskellunge are 5-20% in normal circumstances. If we then add in 82 degree water temps mortality rates likely increase to 20-50%.

"If they swim away they're going to live" - wouldn't that be nice... we know that isn't true though. You may never know which fish liced and which fish didn't survive the catch and release process because these fish aren't always going to die in the net unless they bleed out from a hooking injury. They're going to die in a few hours when their body simply can't reover from the stress. The next question is why don't we see floaters all over the place? Well... dead fish don't always float, they are only going to float when their swim bladder keeps them buoyant.