The use of thermometers

[Daniel Podobed]

This will be the first year I'm fishing with a digital thermometer full time. I'm hoping to get much more detail oriented with my fishing experiences and recording as many details as possible in a journal. I've done this to a lesser extent the past 2 seasons and it has proven to be invaluable with certain scenarios. Now I'm trying to put all the missing pieces together.

I've read some basic guidelines and have used common sense in regards to warm water temperatures. I was looking for any advice regarding thermometers, their readings, and how it affects trout behavior, and the various waterways and any specifics for them, ie- Freestone vs. Limestone etc.

Any thoughts on this would definitely be great. I think by not using a thermometer I was putting myself at a disadvantage. I'm not yet sure *will know by next season*, how much of one I was putting myself in.

[Alex Steczka]

I started using a thermometer this winter to figure out a starting set-up of my flies. If the water is in a cooling trend, I will start the day with the anchor on the first dropper and a nymph or egg on point. If the water is warming, I'll start out with the anchor fly on point and a nymph or a midge on dropper(s).
Even in a cooling trend, if it's a sunny day, I might add a dropper in the afternoon.I want to present something a bit higher in the water column, especially if I notice insect activity.
This "system" improved my takes/hookups significantly.

Tight lines, Alex

[Alain Barthelemy]

Two book references:
Joe Humphreys Trout Tactics (the bible).  Must read.  The only book you really ever need to read.
Rich Osthoff's No Hatch to Match and Active Nymphing (innovative, tactical solutions to unique situations)

Measuring temperature

I use a plain old glass thermometer with alcohol in it.  It takes longer to get a reading, but the readings are more consistent and reliable.  The infrared ones are great for quick readings, but they measure surface temperature and seem to jump around a lot.  It is best to take water temperatures in moving water, out of direct sun.  The best way is to put your thermometer on a string and just toss it in.  I carry my thermometer in the vertical slots on my Confluence pack.  The thermometer should be immersed for about 2 minutes. The standard thermometers also give you air temperature.

Uses of water temperature

- To determine whether conditions are suitable for fishing.
- To find areas of more favorable temperature that fish might seek out.
- To record events or temperature-induced feeding binges (Osthoff's term).

General trends in temperature ranges

The three main species vary a little bit in terms of optimal temperatures, but they are all basically best from 50 - 65deg F.  In this range, a trout's metabolism goes in to high gear and it needs to eat.  This is the same thing that happens to humans; if you exercise for a while, you have to eat.  At the lower end of the range, trout may start out a morning in slower water and wait for hatches before moving to faster water.  Near 65, trout may feed in current, but start to feel uncomfortable and seek out turbulent areas with more oxygen. 

I consider low temperatures to be from 32 - 43 deg F.  In this range, trout are likely to sulk in deep pools, especially until early afternoon.  Towards late afternoon, you may see them feeding more actively.  They sulk in deep pools to guard against surface and shelf ice and cold winds near the surface.  They also use the stream's depth for protection for predators.  In the winter, otters and mink quickly realize that trout are stacked up in deep refuges.  In my experience, even if the water is around 40, but there is a cold NW wind, the fishing will be slow.  If the water is 40, but there is a 50+deg F wind blowing, trout may rise to dry flies.

Transitional temperatures are from 43 - 50 deg F.  At this temperature, nymphs become active and the trout know it.  A thaw or warm spring rain can raise the water temps to this level.  This is a great time to fish some lesser food items (cranefly larvae) in the drift.

Above 65 deg, the ethics of fishing to potentially stressed fish come in to play.  It is best to fish in the early morning hours, as the water will be coolest at this time.  This is when the night fishing game heats up.

Many people don't realize that the seasonal air and water temperatures form a parabola around their lowest winter recordings.  This means that quite often the temperatures in November are similar to those in March.  The photoperiod in these time frames is also similar.  Thus fall tactics are often the same as early spring tactics.

Alain

[Bob Streb]

The #1 tool in my guide bag