TAKE THE 70 DEGREE PLEDGE!

When the morning temperature at Mio Dam is 70 degrees or more then I will not fish for trout on that stretch of the Au Sable River, Mio to Alcona Pond. If I choose to fish that day, it will be on other streams with cooler water, further downstream for warm water fish such as smallmouth bass, or on the many lakes in the area. If I catch a trout I will let it go immediately. When the temperatures fall below 70 degrees at Mio Dam I may consider fishing the stretch again, but will do it early in the morning, at twilight, and at night. I will use a thermometer to fish runs with cooler water so the trout have a better chance at surviving catch and release. I recognize that this is a necessary practice during the hottest part of the summer, late June through mid August, and I am helping the fishery when I do it.

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Why Should I Take It?

Because trout are coldwater fish their metabolisms are designed to function best at temperatures around 60 degrees. Furthermore, oxygen levels are greater at cooler water temperatures. Thus, it is not surprising how well salmonids fight when the water temps are in this range. Their bodies are at peak performance and there is plenty of oxygen to feed their muscles. When fought fairly and released properly they should have a very high survival rate. That means somebody else gets to enjoy the magic. It also helps to build a trophy fishery. It's very unlikely that any trophy trout, let's say 20 inches and up, has never been caught before. Proper release, which includes understanding the effects of water temperature, is the key to great sport fishing.

As the water temperature rises a trout's metabolism begins to put more demands on the fish than its system can easily handle. Essentially, their body is now out of tune and there is much less oxygen to help them maintain proper function.

This becomes more of a problem at 65 degrees and by 68 degrees some studies indicate significant hook mortality. By 70 degrees the chances of surviving catch and release are very low. Many trout will die at temps of 75 degrees or more whether they are hooked or not. The effect is like running on a very hot day with a tight shirt or vest hindering one's breathing. The body exerts more effort due to the heat, but can't get enough oxygen to the muscles, including the most important one, the heart. The body cannot regulate the effects of exertion without oxygen and death occurs. Here are two charts on temperature ranges during the summer of 2001. Notice how long the temperature stayed above 68 degrees.

Some would say that it appears that the McKinley gauge, actually located at 4001, shows a cooling river. Actually that is an artifact of where the gauge is placed. In the summer months it is fairly shallow around its location so there is a greater temperature fluctuation. This is good but does not signal all clear. Notice that daytime water temperatures tend to be higher at 4001 than Mio. Also, notice that it still stays above 65 for most of the summer. Finally, DNR SFR page 16 makes it clear - tributaries and upwellings DO NOT OFFER relief.

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What About Feeder Creeks, Springs and Upwellings?

Yes, there is some cold water inflow below the Mio Dam, but page 16 of the Status of the Fishery Report makes it clear that these inflows are insufficient to offset the massive amounts of water coming in from Mio Pond. Don't believe any claims about upwelling or feeders significantly mitigating the inflow from the pond. These waters mix and the result is a warming of the river. There is far more warm water coming in than cold water seepage, much more. In addition, the river is dropping in the summer months and the sun is heating the shallow flats and runs.

The effect is so pronounced that a study demonstrated less than 1% quality habitat - water depths greater than three feet and aquatic temps below 70 degrees - for trout is available during the hottest weeks of the summer. Relaxing the parameter to 72 degrees produces about 3% quality habitat, that's about 12 acres for the 22 miles of river below Mio. Even if you find these areas many of them are little more than slivers on the riverbank, 10 or 15 feet long and perhaps two feet wide. There may be a fish there but as far as survival goes, it's where they are released. Pull a fish out of 68 degree water and release him in 71 degree water and he's likely a goner.

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Why is this not a problem above Mio?

It can be, but rarely is for several reasons. First off, the Au Sable above Mio does not have to deal with Mio Pond. It's the surface water of the pond and the overflow at the Dam that is the major culprit. (Consumers Energy installed an aerator in 2009, and there are reasons to be optimistic.) The Upper Au Sable benefits as well from large amounts of cold water inflow from feeders, springs, etc and long stretches of shade. Some areas get less than an hour of sun a day in High Summer. This is why the South Branch, tail-water like the Big Water, does not have a temperature problem.

The river here is also very shallow. This allows for quicker cooling at night. The North Branch, for example, can get much warmer than the river below Mio, but does not stay that way for long. Water temps can swing 15 degrees or more on it in a single day. These are known as diurnal changes and the Au Sable below Mio does not significantly benefit from them.

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Where Can I Read More About This?

Let's start with the DNR "The Au Sable River - Mio to Alcona, Status of the Fisheries Report" http://www.michigan.gov/documents/dnr/2007-22_225164_7.pdf.
If you like to fish below Mio then you really need to familiarize yourself with this document. It is the best source of information on the Big Water.

Next comes Rollin Reineck's report on trout habitat on the Au Sable below Mio. Here it is Rollin's_Report

Mr. Reineck's outfit is called Affiliated Researchers. Check out their website at www.affiliatedresearchers.com

This is not just a problem on the Big Water. Andy Nuhfer has done great work on this topic at several sites above Mio Dam. Here's his recent report Au Sable temperature summary 1990-2009-FCS.pdf

Here are several links to sites that discuss water temperature and trout survival:

Wyoming Press Release on C&R and Water Temp: http://gf.state.wy.us/services/news/pressreleases/07/07/12/070712_1.asp

Wisconsin TU C&R Guidelines: http://www.wisconsintu.org/CPR/tabid/64/Default.aspx

Pennsylvania C&R Guidelines: http://www.fish.state.pa.us/fishpub/summary/release.html

Here are some pdfs that you can download:

Nuhfer_&_Alexander_on_Brook_Trout_and_C&R_Mortality

Rainbow_Trout_&_Water_Temps

Ontario_C&R_Guidelines

Hiwassee_River_Management_Plan

Salmonid_Behaviour_&_Water_Temperature

Dotson, T. 1982. Mortalities in trout caused by gear type and angler-induced stress. North American Journal of Fisheries Management 2:60-65.

Eaton, J.G., J.H. McCormick, B.E. Goodno, D.G. O'Brien, H.G. Stefany, M. Hondzo, and R.M. Scheller. 1995. A field information-based system for estimating fish temperature tolerances. Fisheries 20:10-18.

Hunsaker, D., L.F. Marnell, and F.P. Sharp. 1970. Hooking mortality of Yellowstone cutthroat trout. Progressive Fish-Culturist 32:231-235.

Klein, W.D. 1965. Mortality of rainbow trout caught on single and treble hooks and released. Progressive Fish-Culturist 27:171-172.

Wydoski, R.S. 1977. Relation of hooking mortality and sublethal hooking stress to quality fishery management. Pages 43-87 in R.A. Barnhart and T.D. Roelofs, editors. Catch-and-Release fishing as a management tool. Humbold State University, California cooperative Fishery Research Unit, Arcata.

Wehrly, K.E., L. Wang, and M. Mitro. 2007. Field-based estimates of thermal tolerance limits for trout: Incorporating exposure time and temperature fluctuation. Transactions of the American Fisheries Society 136:365-374.

We will add more information as we find it.

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What Can I Do To Promote This?

First off, if you're fishing to keep trout then the 70 Degree does not apply. As long as you follow the creel laws there's no problem trout fishing at this time.

If, on the other hand, you are a catch and release fisher then start watching the water temperature gauge below Mio Dam http://waterdata.usgs.gov/mi/nwis/uv?04136500 starting about the middle of June. If the morning temp is 20.7 Celsius (70 Degrees) then forego fishing below Mio for that day. Check it again the next morning and if it has dropped below that then, if you wish, fish it. Keep in mind that trout are still very vulnerable to the effects of warm water so subdue them quickly and release them immediately.

Many fishers are now leaving the Mio water alone in July and the first part of August altogether. A good compromise is a morning temp of 68 degrees and fishing only in the evening - that gives a released fish the cooling night to recover. The fact is that trout fishing, especially for bigger fish, is not particularly good at this time.

If you want to trout fish then go above the dam to the mainstream, south or north branches. Fish the early morning Tricos, Isos and Cahills in the evening, or try you hand at mousing. This is not a bad time to check out other rivers in the state as well. There are plenty of trout streams that never have significant problems with water temperature. Give 'em a try when Mio heats up.

A number of folks are also taking advantage of the fabulous smallmouth bass fishing that starts in Alcona Pond and runs the whole river to the mouth of Lake Huron. One hundred fish days and 20 plus inch smallies abound on the river. There is also quality pike, largemouth bass, and pan fish action to be had. Several trout guides have significantly improved their business by pursuing smallies during these Dog Days.

This is a relatively short period, four to six weeks, and you'll be fine usually by the third week of August. The White Flies (Ephoron Leukon - not Photons) indicate the water is cooling.

If enough folks take the 70 Degree Pledge then hundreds, probably thousands of trout are spared a needless and unintended death. That means more survive for the Ephoron hatch and September's Streamer Blitz. It also raises the number which will make it to a second year in the river. In the long run this should produce more trophy fish.

Learn all you can about water temperature and trout survival. Educate your friends. Practice peer group pressure. Demand that guides and fly shops observe it as well. Together we can all improve the Mio trout fishery.

It is irresponsible to promote catch and release trout fishing on the Big Water when the morning temps are 70 or greater. No informed, ethical person would do it.

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Is Anything Being Done About This?

Yes, Consumers Energy, they own Mio Dam, installed an aerator last summer. Here's an article Mio_Bubbler

We're pleased with their efforts. Consumers has done a lot of things in the last ear that have really benefited the river. There's an op-ed on the Anglers' site Click_Here about Consumers fine efforts in 2009.

The Sierra Club and Fishpond are giving away 70 Degree Pledge Thermometers. At the Michigan Fly Fishing Club's 2009 Fly Fishing Expo in Warren, Michigan they gave away 200 of them.

The Fisheries Division of the Michigan Department of Natural Resources (MDNR) has agreed to link to this website so fishers in the Great Lake State can learn more about water temp and trout C&R survival.

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Is This A Problem On Other Rivers?

Yes, the Manistee and the Muskegon both have tail-waters that overheat the river in the summertime. At Hodenpyle, Consumers put in a bubbler that causes colder water to rise up the column and cascade over the Dam. Early returns indicate that it works. They are also doing the same thing at Croton Dam on the Muskegon. The bubbler system was installed at Mio last summer.

Rivers out west suffer greatly from high water temperatures. In some cases rivers are closed to fishing because of it.

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THESE GUYS WILL THANK YOU!