Trout Survival ?

[Detour66]

With the rivers loaded with rainbow trout and the hot weather rapidly approaching what are the chances of these trout surviving the summer water temps and making it to the cooler fall weather?

[Kikofishnfool]

Warmer water contains less oxygen than colder water. As temperature rises and dissolved oxygen decreases, fish begin to experience stress. These stresses begin to set in well before the water temperature reaches lethal limits. For example, rainbow trout are said to be able to survive in temperatures up to and exceeding 77°F (24°C), but stop growing at 73°F (23° C). It stands to reason that a fish, one which is already oxygen stressed while positioned carefully in current that minimizes its energy use, will be dramatically more stressed after being hooked and attempting to fight its way to freedom. In fact, in many cases, a fish otherwise properly handled and released under thermally stressful conditions may be likely to not survive.

So how do you know when the conditions remain comfortable enough to fish your target stream without creating a lethal situation for its residents? Unfortunately, studies vary and there doesn't seem to be any one set of accepted limits. That said, there is a considerable consensus that all three major trout species (brook, brown and rainbow) begin to experience some level of stress at around 68°F (20°C), with that stress increasing rapidly as the temperature rises further. For brook trout, these limits are generally accepted to be a few degrees lower (some sources suggest as low as 65°). For many fishermen, 70°F (21°C) has become a round figure that represents the "don't fish" limit.

Of course these are merely guidelines. Water temperature is not the only determining factor of dissolved oxygen (speed of current also plays a factor, for example). Trout which spend extended periods of time living on these generally accepted thermal margins will likely have a greater tolerance outside these margins. However, 68°-70° represents a valuable limit outside of which -- provided you don't know otherwise -- trout should not be fished to.

On days when temperatures soar, and especially during extended periods of high temperatures, the catch and release fisherman should pay specific attention to stream temperatures throughout the stream he or she is hoping to fish. When temperatures in moving water exceed 68°F (20°C), it's best to call it and return another day.

[Detour66]

Great explanation... I didn't realize that C&R for trout during higher water temps can be a lethal combination which now makes sense. I have also found that trout will somehow find the coolest water. I remember seeing trout stacked up in a spot where a cooler very small spring feed stream was running into Greenwood Lake on a very hot summer day. They know how to survive.

[AndyS]

I give trout more credit than most do when it comes to survival. The water coming out of the Lamington felt lice ice water the other day. Rainbows are nuts when it comes to swimming up stream. Browns can definitely hold over pretty well.

[Almaink]

The D&R Feeder canal is now over 70 degrees and the trout have stopped biting for the most part and are very lethargic now. Once the water temps get over 70 in there the short hits start, then the follow up's, then nothing. I'm guessing with this heat wave starting today the season will be for the most part over and it's a shame most of those fish in there will die if they don't swim up or down stream and get in the rivers to find cooler water.

[Dave B.]

The D&R Feeder canal is now over 70 degrees and the trout have stopped biting for the most part and are very lethargic now. Once the water temps get over 70 in there the short hits start, then the follow up's, then nothing. I'm guessing with this heat wave starting today the season will be for the most part over and it's a shame most of those fish in there will die if they don't swim up or down stream and get in the rivers to find cooler water.

If you really want to see something that'll upset you stop by the little brook that flows under 29 and into the canal immediately north of Scudders Falls. You'll no doubt see 100's of trout packed like sardines into a very small amount of cooler water. It's the same at every little trickle trib that flows into the canal between Lambertville and Ewing/N.Trenton. Happens every year, some years worse than others. If I had a tank truck w/ aeration I'd scoop them up and hual 'em to a more suitable locale before they succumbed to the heat.