Downrigger and Line/Lure Depth

[Kokanee Learning]

I recently bought a Fish Hawk X2 to better track lake temperature for kokanee. However, it has me thinking. The probe can tell the water temp. at the downrigger weight but where exactly is my dodger/lure. For example, If I let out 50/75/100 ft. of line before deploying the weight and then drop 30 ft. where is my lure at when trolling 1 to 1.5mph. Would it be lower or higher in the water column? I wonder if there's any sort of chart that explains weight of dodger/lure, ft. of line out and trolling speed to show how much the lure goes up or down the water column when attached to a downrigger. I may be overthinking this but wondered if anyone had any thoughts. Thank you.

[Sideburns]

I troll with a wide variety of dodgers and terminal tackle in shallow lakes.... A lot. Many of my 4 inch oval dodgers with a similar looking front and back lip actually dive about 10 feet when pulled at those speeds. I have checked this by trolling over a 12ft deep area without bottoming, then later bottoming when trolled over a 10ft deep area. Most teardrop dodgers will actually rise somewhat (5 feet?) , its difficult to keep them under the water after letting your line out, some cannot be trolled above 1mph without weight (or downrigger) without surfacing.

Your lure behind the dodger has a massive effect on this depth though, but that's kinda complicated and dependant on dodger style. (for example, a teardrop dodger will rise higher with a large or heavy spinner that has a lot of drag in the water. To stop this rising effect, in the past I have added split shots above the dodger, just enough to keep it under the water.... then your downrigger reading is again accurate.

When the dodger is a known diving type, I just mentally add 10ft to the downrigger reading. When trolling deeper than 30 ft, I usually run a shorter 20-30 ft setback to alleviate this problem, and it makes turning while trolling much easier!

The lower setup pictured dives about 10ft and the upper setup probably rises 3-5 ft when trolled at 1.5mph with a 100ft setback before the downrigger ball.

[Sideburns]

BTW...

I dont think your overthinking this, but the complexity here would make it very difficult to put in an easy reference chart.

[Kokanee Learning]

Interesting, and thank you for the reply. Based on the temperature readings I get, 10 ft (even only 5) can make a drastic difference in the preferred temperature zone for kokanee. What you said makes sense. I was recently in a shallow lake and was pulling 'gunk' up on my lures even though I should not have been on the bottom, but close. Next time I go out I think I will try to greatly reduce the amount of setback I do. I have read it is preferred to have a longer setback because of the boat engine scaring the kokanee. I fish out of a kayak so hopefully that will help mitigate that.

[Sideburns]

Long setbacks are certainly beneficial sometimes. The deeper your fishing, the less this seems to matter. Kinda have to choose a balance point between the efficiency of a short setback and the stealthiness of a long setback. Ive been told that the rule of 100 works pretty well. (50ft down, 50 feet back or 20 feet down, 80 feet back etc) One of the reasons I try to run short setbacks whenever possible is that I like to dangle some kind of small rotating flashers and stick some reflective tape to the downrigger ball for added attraction.
When fishing crystal clear lakes, or fish are just spooked, I like to increase setbacks to keep the boat from visibly spooking the fish and also present the tackle a little further above the fish marks so that the downrigger gear doesn't do the same. I increase setbacks all the way up to about 200 feet max occasionally. Skip the downrigger ball attractors in clear water too.

Also remember that Kokanee and trout tend to strike at things above them. I usually like to try and present my gear 5 feet above the fish marks on the downrigger.

Where do you fish lately? I'm curious what your seeing for depth and temperature this time of year.

[Kokanee Learning]

I only recently got the Fish Hawk X2. First I went to Alder, however; the fish hawk didn't work well there. I thought it may have been broke. The readings were very spotty. I think the water was very silty or something because I next took it to Ward Lake to verify it worked. It was fine there, I believe the preferred temp. of 52 was around the 30 ft or so mark, maybe a little deeper. I haven't had any luck for Kokanee at Ward though. Last weekend I drove to Deveraux Lake in Mason County. First time being there. The 52 degree mark was roughly 28 ft there. I really want to go to Merwin Lake, however it makes me a bit nervous in a kayak, even though I have a bigger one with a Pro Angler 12 if you are familiar with it. I know the water there can get rough. I need to start keeping a fishing journal to track the temps.

[Sideburns]

Last time I went to merwin, I shouldn't have ever left the launch! Spending most of the day searching the rest of the lake, we put gear back in just outside of the launch (speelai) and caught most of our fish. I think some should be starting to spawn by now at merwin though. Only been there a couple times myself, but havent seen rough weather yet.

Terrible website compared to NWFR...... ... but I follow this thread every year
https://www.ifish.net/board/showthread. ... 685&page=6

I'm curious how high in the water the 70 degree mark was? Trout cant tolerate much higher than that to feed. Do you remember what the deepest coldest temperature was? I fish a few similar size and depth lakes in the south king county area, with about 73 degree surface temps right now.

Thanks

[hewesfisher]

I chased this rabbit hole once, got all over the temp at depth thing, bought a Fishhawk TD so I could target preferred depth by temperature. I used the TD several times the first year, a couple times the second year, and hasn't been out of my tackle bag since. Have found my sonar tells me everything I need to know about where the fish are.

Great conceptual tool, but in my experience, far less practical in application. My $.02 for what it's worth.

[Sideburns]

Having never used one, 2 aspects of water temp measurement intrigue me.

1. These things seem like great learning tools. I'm curious how wide the "fishy" band is. I'm looking for 50-60 degrees for most species.... How wide is that area in 50 fow? Late summer, early summer change that? How much variation does it take to form a visible thermocline on sonar?
etc... etc... I'm sure after Ive got a grip on temperature patterns mine would end up in the bottom of the tool box too.

2. Verification. Is the band of visible thermocline on our fish finders even accurate? What temperature range does it form at? I would love to define and verify some of the thermocline sonar characteristics I've seen. Some lakes, one in particular, the visible thermocline band will regularly widen as it cools in the evening while disappearing in other parts of the lake. Whats going on there?

Ive pondered rigging up something myself with industrial thermocouple wire deployed on the downrigger for live temperature data. I think the Lowrance hds gen3 I just got will even display custom temperature gauges. That would be cool! Wow I'm a geek!

[Kokanee Learning]

Your 2 cents is probably worth more than my 10 dollars . I still have not mastered this kokanee thing but I would agree that a expert fisherman who knows what he is doing will out fish someone with more toys. I am still in that 2nd category though. My question wasn't so much about the X2 then about where my line/dodger was in relation to my downrigger weight. Sideburns - what lakes do you fish in south king county for Kokanee? Any particular one you would recommend?

[Sideburns]

I use to fish Meridian and Sawyer for Kokanee. Then they all disappeared. Haven't seen a koke in Sawyer since 2008 and Meridian 2015. Meridian was hot in 2014 then not in 2015-2016. Dont know where they went, but wdfw still stocks both the same as they used to.

[Bilgewater]

Sideburns:

You wondered how wide the “fishy” temperature band is, and said you were looking for 50-60 degrees. For years I’ve used a Fish Hawk depth/temperature meter, recording the temps by date at five foot depth intervals, every day that I fished. This in a western Washington lake that gets to about 90 feet deep, similar to Meridian. I’ve accumulated a lot of temperature data - - spring, summer, fall, winter.

You referred to the “thermocline.” Just what it that? Well, it is defined as a narrow but distinct layer in a large body of water in which the temperature changes more rapidly with depth than it does in the warmer layer above and in the colder layer below. Soooo, just how much temp change? I arbitrarily use 10 degrees in 10 feet. I measure down to 50 feet deep because I’ve learned that the year-around temp change below that is very minimal.

My data shows that in, say January, the temp is virtually the same up and down the water column. Around 43-45 degrees. By August-into-September the temp gradient is dramatically different, with the surface being in the low 70’s and 50 feet deep getting to 50-52 degrees. By sometime in June, the distinct thermocline is often 25-35 feet deep, and it gradually moves to 30-40 feet as the water above it heats up into September. Examples:
2014 66.6 at 30 feet, 55.3 at 40 feet
2016 66.9 at 30 feet, 56.0 at 40 feet
2017 69.2 at 30 feet, 56.3 at 40 feet
2018 65.6 at 30 feet, 54.7 at 40 feet

Except for right at the surface, it takes a long time for temp changes to develop below. A very, very slow, gradual process, both during spring-summer heating and during fall-winter cooling. In both cases, the changes begin at the surface and work their way down. During the cooling phase, the thermocline is actually pushed a bit deeper for a while, oddly enough.

Keep in mind: this is for a “stable” lake. Summertime measurements in lakes with enough flow-through, including Rufus Woods and Riffe, can show no thermocline at all. Just too much mixing. And who knows what develops in shallower lakes, including Sawyer.

Another significant “fishy band” issue is adequate dissolved oxygen, particularly at deeper depths. In stable lakes, deeper parts become oxygen-deficient during the summer and fall months, below the levels at which kokanee and trout can survive. That according to WDFW and U of W surveys, American Lake and Lake Sammamish respectively. Both surveys confirm my temperature measurements and go on to conclude that those salmonoids become stressed because the water above the thermocline is too warm and the water below doesn’t have enough oxygen. The U of W study even speculates that during the heat of the summer the salmonoids are mostly confined to using only about 10% of the water column, namely the thermocline.

Some writers of fishing stuff state that the thermocline is an oxygen-rich layer, without offering any reason or logic to support such an anomaly. But that is disproven by 24 consecutive monthly samples taken by WDFW in American.

[hewesfisher]

Add Lake Roosevelt to those that "mix" and don't have a thermocline. I don't consider myself an expert at catching kokanee, in fact, I struggled with it for years and was the reason I bought a FH TD so I would know where that magic temperature was. After much frustration, I finally concluded the kokanee will be where they are most comfortable or where the food source is so that's why the TD remains in my bag.

I focus my efforts in placing presentations where my sonar shows the fish are and pay no heed to water temperature. This approach may not work in a stable lake with a thermocline, then again, it may work better. YMMV.

[Bilgewater]

hewesfisher: I agree with you, in general. In waters that “mix,” the temperature is irrelevant as it is virtually the same up and down the water column. But in stable western Washington lakes, different fish populations can complicate the “sonar only” approach. WDFW survey reports say that in American only 2 to 4% of the fish sampled by various nets and electroshocking are kokanee and trout while perch and rock bass make up 80% of the biomass. And perch can be anywhere in the water column, as shown by underwater video. They can tolerate higher temperatures and lower dissolved oxygen levels. Sorting out sonar fish is not easy for me, although at times perch will be in identifiable large schools like a bait ball. The surveys done by “experts” say that salmonoids will favor the thermocline layer, when one is well developed. However, that doesn’t assure catching anything by fishing the thermocline during the summer heat. Some speculate those fish are so stressed that they quit eating. Who knows?