Walleyes – Depth Vs Altitude

Rather than hijacking the blade bait discussion for the Columbia River, thought this was an interesting topic.

Most walleye anglers we chat with here are primarily mid-west region of the country. I diudn’t look up specific topo’s for MN, WI, IL, IA…but I would guess most of us here are 700′ to maybe 1200feet????? Just a guess.

Anyways, I’m really curious what type of mortality there is on walleyes in deep western lakes? I know in Colorado, we see schools of walleyes cruising at 50-70 feet down frequently. Additionally, bringing these fish up from those depth don’t seem to have the same affects as we see here coming up from 30′.
Could the altitude make the difference? Any divers on here that can give any insight to pressure differences of water at 7000 feet Vs 700feet?

Good question and great observation.

Altitude diving sometimes makes my brain fart as it’s all inverted. Attached is the USN Dive Manual Rev 7 which is the most up to date.

But, it’s slmost the opposite one would think. A diver in altitude actually requires MORE decompression than they would at sea level.

At 50 FSW ( salt water not fresh water but it’s fairly close) it would actually be the equivalent of around 40 FSW at 6000 feet. Inversely though, your decompression obligations would be that of a 70 FSW dive.

Confused? 50’ dive at sea level for 1 hr would require no deco stops. 50’ dive at 6000’ altitude (equal to 70’) for 1 hr WOULD required deco stops.

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Interesting, never even considered it.

Randy Wieland wrote:

Anyways, I’m really curious what type of mortality there is on walleyes in deep western lakes? I know in Colorado, we see schools of walleyes cruising at 50-70 feet down frequently. Additionally, bringing these fish up from those depth don’t seem to have the same affects as we see here coming up from 30′.
Could the altitude make the difference?

Yes altitude will change the pressures generated at depth.
Sea level atmospheric pressure = 14.7 psi.
9000 feet above sea level =10.51 psi.

• Pressure Increases With Depth

The weight of the water above a diver exerts pressure on their body. The deeper a diver descends, the more water they have above them, and the more pressure it exerts on their body. The pressure a diver experiences at a certain depth is the sum of all the pressures above them, both from the water and the air.

• Every 33 feet of salt water = 1 ATA of pressure

• Pressure a diver experiences = water pressure + 1 ATA (from the atmosphere)

Total Pressure at Standard Depths*

Depth / Atmospheric Pressure + Water Pressure / Total Pressure

0 feet / 1 ATA + 0 ATA / 1 ATA

33 feet / 1 ATA + 1 ATA / 2 ATA

40 feet / 1 ATA + 1.21 ATA / 2.2 ATA

66 feet / 1 ATA + 2 ATA / 3 ATA

SO, if we start at sea level and go 66 deep that = 3 X 14.7 or 44.1 psi.

If we are at 9000 feet above and go 66′ deep that =3 X 10.51 or 31.53 psi.
If we are at sea level and go 40′ deep that = 2.2 X 14.7 or 32.34 psi.

To sum up; a fish 40′ deep at sea level, is under nearly the same pressure as a fish 66′ deep, in a lake 9000′ above sea level.

BOB CLOWNCOLOR,
Not sure the decompression stops even apply to the question being asked. The decompression stops only apply to a diver breathing from a tank of compressed air. Fish do not suffer “the bends” if brought up from depth. They only suffer from over expansion of the air bladder. For a diver, this would be the equivalent of holding your breath while ascending. I definite NO-NO unless one is “free diving” (no air tank).

Glad to know I’m not the only analytical minded person on here – LOL
Makes a lot of sense on why I see scholls much deeper than around here

Huntindave wrote:

BOB CLOWNCOLOR,
Not sure the decompression stops even apply to the question being asked. The decompression stops only apply to a diver breathing from a tank of compressed air. Fish do not suffer “the bends” if brought up from depth. They only suffer from over expansion of the air bladder. For a diver, this would be the equivalent of holding your breath while ascending. I definite NO-NO unless one is “free diving” (no air tank).

Correct… I’m not a fish just a scuba diver…but thanks for the obvious. My 2nd to last paragraph I thought I explained it that at 5000’ elevation 50’ of water is equal to 40’ of water at sea level.

Like explained, Boyle’s law explains this perfectly. Obviously at a great elevation, the less pressure. Roughly 18k feet is a half atmospher…however closer to 96 miles is zero atm. It’s not linear like scuba at 33fsw or 34(?) FFW.

I personally don’t think that altitude plays a part. It’s the rapid decrease in pressure when a walleye comes from deeper water to the surface that will potentially kill a walleye. If a walleye comes from about 34 feet (10 meters)of water to the surface, pressure decreases by 1 atmosphere whether one is at sea level or at 5000 ft. and the mortality rate will be the same. The pressure will increase wherever you are at by 1 atmosphere for every 10 meters deep.

Karry Kyllo wrote:

I personally don’t think that altitude plays a part. It’s the rapid decrease in pressure when a <strong class=”ido-tag-strong”>walleye comes from deeper water to the surface that will potentially kill a walleye. If a <em class=”ido-tag-em”>walleye comes from about 34 feet (10 meters)of water to the surface, pressure decreases by 1 atmosphere whether one is at sea level or at 5000 ft. and the mortality rate will be the same. The pressure will increase wherever you are at by 1 atmosphere for every 10 meters deep.

Huntindave wrote:

SO, if we start at sea level and go 66 deep that = 3 X 14.7 or 44.1 psi.
If we are at 9000 feet above and go 66′ deep that =3 X 10.51 or 31.53 psi.

So at sea level the pressure decreases from 44.1 at depth to 14.7 at the surface, a net change of 29.4 psi.

At 9000′ above the pressure decreases from 31.53 at depth to 10.51 at the surface, a net change of 21.02 psi.

The fish at sea level endures a much greater change in pressure over the same time period of ascent, than the fish at 9000 feet. It would seem logical that the mortality rate would be greater as well.

Is it safe to assume the fish at sea level would then have firmer fillets bc of greater pressure exherted on it’s tasty backstraps it’s whole life? Bc I’m all about that kind of science

Huntindave wrote:

<div class=”d4p-bbt-quote-title”>Karry Kyllo wrote:</div>
I personally don’t think that altitude plays a part. It’s the rapid decrease in pressure when a <strong class=”ido-tag-strong”>walleye comes from deeper water to the surface that will potentially kill a walleye. If a <em class=”ido-tag-em”>walleye comes from about 34 feet (10 meters)of water to the surface, pressure decreases by 1 atmosphere whether one is at sea level or at 5000 ft. and the mortality rate will be the same. The pressure will increase wherever you are at by 1 atmosphere for every 10 meters deep.

<div class=”d4p-bbt-quote-title”>Huntindave wrote:</div>
SO, if we start at sea level and go 66 deep that = 3 X 14.7 or 44.1 psi.
If we are at 9000 feet above and go 66′ deep that =3 X 10.51 or 31.53 psi.

So at sea level the pressure decreases from 44.1 at depth to 14.7 at the surface, a net change of 29.4 psi.

At 9000′ above the pressure decreases from 31.53 at depth to 10.51 at the surface, a net change of 21.02 psi.

The fish at sea level endures a much greater change in pressure over the same time period of ascent, than the fish at 9000 feet. It would seem logical that the mortality rate would be greater as well.

You’re right. I used numbers at sea level in my example and perhaps I shouldn’t have since the lakes in the Midwest are at a greater altitude than sea level but then again your example of 9000 feet is an extreme altitude example and there are few if any walleye lakes at that altitude. The point I was trying to make is that if you bring a walleye up from depth with a 1 atmosphere pressure change, the odds of it’s survival are slim whether you are in the midwest or in the mountains at a higher altitude. Take the altitude of over 1800 feet (as in the case of Lake Sakakawea) to an altitude of 5400 feet or so on Horsetooth Reservoir or Chatfield Reservoir, both of which are Colorado walleye lakes. That’s an altitude difference of only 3600 feet and the difference in pressure coming up from 10 meters would be about 13.76 PSI vs. 12.05 PSI, both of which are 1 atmosphere of pressure at their respective altitudes. Is the difference significant enough to say that the mortality rate due to rapid depth change is less at a higher altitude? There may be a case to support it but I have never read any of the scientific evidence if it exists.
As far as deep walleyes on Colorado lakes as Randy refers to, I’ve caught walleyes at 80 feet deep numerous times on Lake Sakakawea. It’s all about where the food is. On Sakakawea, they will chase schools of smelt that are that deep if they have to.

Karry Kyllo wrote:

Take the altitude of over 1800 feet (as in the case of Lake Sakakawea) to an altitude of 5400 feet or so on Horsetooth Reservoir or Chatfield Reservoir, both of which are Colorado walleye lakes.

Well,,,, obviously one is going to choose lakes which bolster ones position

I have personally caught walleye from both, Greers Ferry Arkansas (604 feet) and Carter Lake Colorado (8,904 feet).

FWIW I catch 99% of my Walleye from my local river(906 feet) with an average depth of 5 feet. It is an interesting discussion but I’m not sure either “side” is entirely the “correct” perspective. It’s all good discussion and I do understand your thoughts on the subject.