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MadisonBoats
11-02-2010, 10:46 AM
I am sure many of you are familiar with this topic (Kármán gait-Dr. James Low of Harvard). However; I wanted to re-introduce it to others who might find it interesting. I found this topic very interesting after watching the volumes of The Underwater World of Trout.

*Basically, it surmises that trout use less muscle energy in flowing water than in slack water. It also gives them the ability to face downstream in pools.

Short (Kármán gait) video:
http://media.efluids.com/galleries/biological?medium=623

Summary [cite: The Journal of Experimental Biology 206, 1059-1073 (2003)
doi: 10.1242/jeb.00209]:

Most fishes commonly experience unsteady flows and hydrodynamic perturbations during their lifetime. In this study, we provide evidence that rainbow trout Oncorhynchus mykiss voluntarily alter their body kinematics when interacting with vortices present in the environment that are not self-generated. To demonstrate this, we measured axial swimming kinematics in response to changes in known hydrodynamic wake characteristics. We compared trout swimming in the Kármán street behind different diameter cylinders (2.5 and 5 cm) at two flow speeds (2.5 and 4.5 L s-1, where L is total body length) to trout swimming in the free stream and in the cylinder bow wake. Trout swimming behind cylinders adopt a distinctive, previously undescribed pattern of movement in order to hold station, which we term the Kármán gait. During this gait, body amplitudes and curvatures are much larger than those of trout swimming at an equivalent flow velocity in the absence of a cylinder. Tail-beat frequency is not only lower than might be expected for a trout swimming in the reduced flow behind a cylinder, but also matches the vortex shedding frequency of the cylinder. Therefore, in addition to choosing to be in the slower flow velocity offered behind a cylinder (drafting), trout are also altering their body kinematics to synchronize with the shed vortices (tuning), using a mechanism that may not involve propulsive locomotion. This behavior is most distinctive when cylinder diameter is large relative to fish length. While tuning, trout have a longer body wavelength than the prescribed wake wavelength, indicating that only certain regions of the body may need to be oriented in a consistent manner to the oncoming vortices. Our results suggest that fish can capture energy from vortices generated by the environment to maintain station in downstream flow. Interestingly, trout swimming in front of a cylinder display lower tail-beat amplitudes and body wave speeds than trout subjected to any of the other treatments, implying that the bow wake may be the most energetically favorable region for a fish to hold station near a cylinder.

kentuckytroutbum
11-02-2010, 11:41 AM
Shawn-

Thanks for the post, I didn't realize that someone had taken the time to analyze how trout hold their position behind an obstruction. I didn't want to get that technical about trout fishing.

But from what I remember of college fluid dynamics it makes sense only if you know the size and height of the obstruction, the depth of the water, the velocity, and the stream cross section. The laminar flow of water, speed, type of obstruction, etc. will determine the size and magnitude of the eddies that are created behind such an obstruction. Similar effects will occur in front of the obstruction known as the "bow wave," which can create a zone of lower velocity, and thus require less energy for trout to maintain their position in the water column, and still be accessible to their food source.

Bill

JohnH0802
11-03-2010, 01:00 PM
Shawn,
Great post. I enjoyed the technical side of it and the video.

Thanks,

John

mlstiehl
11-03-2010, 08:31 PM
Seems like you all spend to much time worrying/studying something that is fun and just not as complicated as you all want to make it;)

BlueRaiderFan
11-03-2010, 09:12 PM
I find it very interesting and not really that complicated.

MadisonBoats
11-04-2010, 10:05 AM
Seems like you all spend to much time worrying/studying something that is fun and just not as complicated as you all want to make it;)

I do spend a lot of time studying fly fishing.:biggrin: That is just my nature and when I do something; I usually go a little overboard. I find it fun understanding all the different aspects relating to fly fishing. If I did not; I would just throw fishing spinners and catch insane amounts of fish.

One thing about this topic is that it helped me target fish. I did some of the fish challenges in The Underwater World of Trout and I was completely wrong on a few of them. Also, I never expected to see trout facing downstream feeding:eek:.

If you get a chance; look at some of the video clips online of The Underwater World of Trout. I found them very interesting and informative.

kentuckytroutbum
11-04-2010, 11:01 AM
Shawn-

I agree that its fun to understand what happens to water and the trout therein.

Its been a while since I viewed the video, but from what I remember trout will face downstream especially if they're in an eddy condition such that water is flowing backwards compared to the main stream. Where there is a small protected cove.

When we were in Maine two years ago, our guide pointed this out to us, and we did catch trout in the eddies. At first, it was weird to cast downstream so that your fly drifted upstream to the trout.

Thanks again.

Bill

gmreeves
11-04-2010, 11:39 AM
Fly fishing is what you make it. Some days I like to get technical and some days I'll throw on whatever feels right and enjoy the day. That is the beauty of the sport.

BlueRaiderFan
11-04-2010, 05:00 PM
Someone was on here a couple of years ago talking about catching more trout casting down stream (confused me at the time:eek:) going up to Lynn Camp. At the time, I thought the guy had ran into an anomoly, but maybe not so much.

NDuncan
11-04-2010, 05:14 PM
Someone was on here a couple of years ago talking about catching more trout casting down stream (confused me at the time:eek:) going up to Lynn Camp. At the time, I thought the guy had ran into an anomoly, but maybe not so much.

BRF- you just made me realize something...

I can think of a spot I always fish that I kinda consider my 'lucky spot' where I always fish first on a particular stream and I almost always hook a trout on the first cast (or at least the first few), casting downstream. To me, its the best way to start a day fishing, but now that I think about it, it's usually the only time/place I will end up casting downstream. Thinking back on my success rate, I guess I should try it more often!

BlueRaiderFan
11-04-2010, 05:49 PM
I always try it after I wade through a run (I usually work a run for about 5 minutes...probably too long). Not enough time to let the previous run rest, but on occasion, it fools one.