Fish Explorer Logo
Colorado Fishing
Colorado Fishing
Login Usr:Psd:
Don't have an account? Register now...
spacer spacer
Go back to Main FxR Forum listings
Lake: Dillon Reservoir

CPW biologist report -- Dillon Reservoir

Post By: Ewert      Posted: 3/10/2018 9:26:06 AM     Points: 12    
Yo -- here's my report on Dillon. I'll watch this thread for one week. If you have any questions about Dillon that aren't answered in the report, post them here.

[log in for link]
 Reply by: not too old to fish      Posted: Mar. 10, 11:31:29 AM     Points: 3824    
You said they were stocking more fingerling rainbows, any sign of them thriving or surviving better than than the catchables?
 Reply by: Ewert      Posted: Mar. 10, 1:02:50 PM     Points: 12    
The rainbow fingerlings are making a huge contribution to the fishery there.
 Reply by: redleader      Posted: Mar. 10, 3:25:35 PM     Points: 544    
They were put in for forage in an attempt to improve the Brown Trout's growth and body condition.
Keep feeding time steady add some protection regs on the larger Browns and we might have another Gold medal lake someday.
 Reply by: Ewert      Posted: Mar. 11, 8:48:27 PM     Points: 12    
 Reply by: Ryan      Posted: Mar. 11, 9:09:52 PM     Points: 1340    
Interesting data. Thanks for sharing.
 Reply by: Fordo      Posted: Mar. 12, 1:26:20 AM     Points: 55    

Thanks for sharing, great report and I even got some photo credit! And thanks for the good work on giving the rainbow fingerlings and timing the stocking of the catchables differently.
I know it gets old with me constantly asking, but PLEASE put some bag limit protection on these magnificent brown trout, and PLEASE don't worry about them reducing char populations. Gill net studies and the report do not show it, but right now there are more char in the lake than anything else. They are everywhere. Find 50 to 65 feet in the winter at just about any location on the lake and there will be char, they are small, 8 to 12 inches, but they are there in massive numbers. In the summer, you can find layers of them 30 feet thick from 80 to 120 feet at just about any location. So many, that when trying to catch them deep, you'll end up foul hooking 8 inchers because the schools of small fish are so dense. Gill nets do not reveal this because they do not get deep enough. As you know, recruitment of Arctic Char is growing every season. Every year we are getting increasing numbers of mature spawners. The Char fishery is here to stay, and Ill bet my left one, and even my right, that putting bag limit protection on brown trout will never comprise the char fishery.

 Reply by: Freestone303      Posted: Mar. 12, 7:56:19 AM     Points: 442    
Is the goal of the char establishment to stabilize or crash the music population or be sustained as a fishery?

What forage is present for the rainbow and brown populations? Insect, suckers, and small trout?
 Reply by: Ewert      Posted: Mar. 12, 9:06:22 AM     Points: 12    
The goal of stocking char is to produce a unique recreational fishery not available anywhere else that makes use of the Mysis prey base that other species weren't exploiting, because they reside most of the time in habitat that rainbows and browns don't use. It is definitely NOT the goal to eliminate Mysis from the reservoir, because then obviously the char would have nothing to eat. There has never been a documented case where that has occurred. We monitor the density of Mysis in the lake, and the long-term average density estimate is about 240 Mysis per square meter of lake surface area. So if you envision that across the surface of the lake, it's a huge number.
As far as forage for rainbows and browns- yes, on all three of those, but also Mysis. One thing I didn't go into detail in the report on (I thought about adding a page on this but wanted to get the report out) is that in the past few years I've shifted to stocking the majority of the catchable rainbows for the year as late as possible. The reason for this is that it appears that if I stock a lot of catchables late, after the lake has destratified or as close to that time as possible, the rainbows can get on the Mysis, and they feed on them through the winter under the ice and come out of the winter in good condition and actually having put on a couple inches of growth. Stockers that go in during the traditional time of May-Jun-July never even get the chance to figure out that those Mysis are there, because of the behavior of the Mysis while the reservoir is stratified. So it's almost like I'm stocking the following spring's fish in the fall of the previous year. We can't do that in any reservoir with lake trout because any rainbows you stock in the fall just completely disappear by ice-out. It's just a working theory I've got going, and need a few more years of this approach to really see if it's successful. It's a huge advantage for the hatchery system because there's not much demand for stockers in the fall, and so if I've got waters where I'm actually asking for them then it's a good thing.
 Reply by: Fordo      Posted: Mar. 12, 10:15:15 AM     Points: 55    
The late stocking of the Rainbows has been fantastic. We catch 11 to 13 inch healthy rainbows all winter long by the numbers. They are strong, hard fighting, and taste much better than your typical stockers due to the mysis diet. Its very common to pick rainbows out of 40 to 50 feet that are rubust mysis eaters. Ive even found fresh water sculpin in their stomachs.
Since Jon started the late stocking, my catch rates on rainbows through the ice has raised by like ten times.
Another cool thing is folks are enjoying those late stockers during the salmon run at the snake inlet like never before. Along with limits of kokes, folks are going home with limits of nice fat rainbows. Many of those rainbows that are stocked at the Dillon marina in October will tie in with schools of salmon and follow them clear up to the snake inlet.

The bummer of the late rainbow stocking situation is that most all of those rainbows don't make it through the time period when the ice comes off and the lake re stratifies with surface temps above about 58 degrees. The problem is, Once the ice comes off and the days are longer and there is more light, the mysis retreat deeper than 60 feet. The rainbows can do well as deep as 55, but that is their barrier. It takes until the first of June for the chrominids to start hatching. So the month of may is a dreadful month for those rainbows because the mysis are inaccessible, and there are virtually no bugs for them to eat. It doesn't take but a week for them to starve and die off. A few of them figure things out, but not very many at all. Out of 100's of trips in the summer, we catch maybe a handfull of hold over rainbows. There are very very few rainbows in the lake over 13 inches.
Another very interesting consequence of the Ice off mysis retreat to deep, deep water is that many Arctic Char also lose track of them. These char will run up to the inlets during run off to feed on bug larvae that is being flushed down into the reservoir. This is creating an excellent opportunity for Anglers to catch these fish on the fly, or casting from shore. The char that run the inlets are normally in poor body condition, but they are managing to make a living in an artificial environment and adapting. Very interestingly,if you talk to people in Maine, they never see this type of activity, this also the case in Alaska and Canada, but in Greenland, many Arctic Char run from the sea, up into the Fiords during June and create amazing opportunity to catch Silver, non spawning Char out of the fresh water rivers and streams.

With everything I said about the trouble at Dillon with holdover rainbows, There is some good news. Year before last Jon stocked a batch of Cutbows that were the Hoffer strain on the rainbow half. These Hoffer cutbows are the most common holdovers I catch, something in the instincts of those hoffers allows them to find forage year round. They have stayed pretty centralized in Frisco bay where they were stocked, and didn't seem to disperse as like the regular rainbows do. The straight hoffers are the main rainbows that are tying in with the schools of 4 year old salmon and ending up at the snake river inlet in late November.
Bottom line here is that if Mr Ewert keeps giving to the reservoir with both catchable and fingerling rainbows, and timing the stocking right, this rebound of a once word class fishery will continue. The rainbows both provide forage for the big browns and Arctic Char, and the late stockers are curbing the mysis population leaving more dapnia zoo plankton for the hatchling Arctic Char and brown trout to grow to catch able size. And they give anglers something to catch when its not always easy to catch a brown trout or Arctic Char. After all, over 90% of people that fish at Dillon don't care what they catch and do not have the skill level for Browns and Char. A lawn chair, a basic rod, and some powerbait is all they need to have an enjoyable experience fishing at Lake Dillon as long as stocked Rainbow trout are present.
 Reply by: Ewert      Posted: Mar. 12, 10:30:26 AM     Points: 12    
Good points Randy, thanks. And some of that reasoning is why I'm keeping stockers at 1/3 in spring and 2/3 in fall, and not going to all fall stocking. So if I've got 30,000 catchable RBT for Dillon, I still request 10,000 of those to be spring fish.
 Reply by: panfishin      Posted: Mar. 12, 4:10:27 PM     Points: 6428    
Wow, great information...Fordo - how can you tell the difference between the Hoffer strain and the regular rainbows?
 Reply by: Fordo      Posted: Mar. 12, 8:52:01 PM     Points: 55    
They have lots of black dots, the dots extend under thier bellies and the males typically are much darker.. First pic the one on the right is a hoffer. Second pic the one fourth from the bottom is a hoffer. Third pic all the ones on the left are hoffers, bottom left is a male.
 Reply by: Fishful Thinker      Posted: Mar. 12, 9:26:43 PM     Points: 8668    
Did somebody say big browns? I like big browns...but I can catch Arctic Char a lot closer to home these days! Wink, wink...CL
 Reply by: Fordo      Posted: Mar. 13, 2:56:25 AM     Points: 55    
Hmmm. Big browns or Arctic Char?.......How about both?.......BRILIANT!!!

Seriously though, take a look at Granby. The Fork and GM. Nice Brown's are hard to come by. Take a look at south park its cutbow and rainbow haven, relatively tough to consistently catch big Brown's, especially through the ice. Dillon is a special brown trout fishery and there is no reason to compromise the rebound of a once world class brown trout fishery in fear of over predation on arctic char by the brown's. With the data that's out with Mr Ewerts gill nets studies, and Devin Olsens thesis, as well as my observations. I could write paragraph after paragraph on why it far fetched that over predation couild happen, and why nice Brown's in Dillon in the long run are good for the arctic char, but I just finished my midnight snack and beer. Time to get back in the sack.
 Reply by: Ewert      Posted: Mar. 13, 8:56:41 AM     Points: 12    
Randy, you seem to have the impression that the reason we don't have a special reg on browns is because I'm afraid they'll prey on char too much. It doesn't have anything to do with that at all. I don't think the two species interact all that much. There are a couple reasons for no reg -- first, do we have a good fishery without a special regulation? We don't need to slap a special reg on every fishery out there, in fact there's a lot of pressure not to, and we get regular complaints that our regulations are too complicated. Have you not heard the media telling you how evil all government regulation is? What if we had a rule like the feds right now, that for every new regulation we propose, we have to remove two others? What two would we remove in order to enact this one? What I'm trying to get at is that people hate regulations and the general environment is very hostile toward them.
But that's not the main reason. The main reason is what the data is telling us. As far as I can see, it's telling us that 1.) After resumption of stocking RBT fingerlings, the number of brown trout in the lake over 16" went up by a bunch, maybe as much as a 2-3X increase. 2.) right after beginning that stocking the browns reacted with big increases in body condition and they were generally pretty fat. 3.) It appears that their numbers adjusted upward to match the prey base and now they're losing body condition due to increased competition. If anyone looks at my report and has a different interpretation, I seriously want to hear it -- that's exactly the reason I put them up here. But support your arguments -- you know what they say about opinions. All of the three pictures you posted, but especially the first two, support this because they show large brown trout in pretty poor body condition. Big heads, skinny bodies. Why would we put a special reg on a fish that obviously doesn't have enough to eat? The fingerling RBT number is fixed -- 100/acre or 300,000 fish. That's not increasing, and I'm lucky if I can continue justifying it long-term. It can only support a certain number of large browns. If they make another switch onto suckers then that's an extra bonus. If we saw more evidence that was happening, then I would be interested in protecting those fish because I would love to see them making use of the huge number of suckers. But that would be something like 24", and I don't think you're talking about protecting 24 and over. It seems like anglers have this idea that a 3,000 acre lake (which is pretty small in the big picture) can support an infinite number of large fish if only they were protected correctly. That's just not the case. When fish are in poor body condition, their growth slows or stops, they don't produce as many eggs, things stagnate and you just shoot yourself in the foot. There are so few people out there who are skilled enough AND interested in harvesting a big brown trout that if a few of them do it's not some kind of emergency. There's just a little less competition for the fixed number of prey items out there. Dillon still has a ton of fish, and always will, I think, at that 14-15" mark trying to break through into the world of making a living as a predator.

I've talked about this before and I think that the biggest difference between the way anglers look at a fishery and the way a biologist (who's also an angler -- we all are) does is that it seems like anglers sometimes look at a fishery as a static thing that's kind of fixed in time, or could achieve some higher-quality ideal fixed-point condition if only the idiot biologists would manage it correctly. When a biologist looks at a fishery, he tends to see his information as snapshots of a PROCESS taking place. A fishery is never exactly the same from one day to the next. Fish are born and grow and die every day. It's like standing next to a slow-moving conveyor belt in a factory loaded with products and watching it pass by. So what are the TRENDS in that PROCESS, and how can we get the best possible picture of what those trends are with the most efficient use of time, so we can move on to the next one of our 600 waters that we manage? Then, once we have that information, what does it tell us about what we can do to speed up that conveyor belt, or increase the quality and/or number of the products on it? I don't know if that makes sense or not.
 Reply by: TADA32      Posted: Mar. 13, 8:57:39 AM     Points: 466    
Parvin and North Park have good browns.
 Reply by: not too old to fish      Posted: Mar. 13, 11:13:28 AM     Points: 3824    
Ewert, I want to thank you again for the posts, they are so full of facts and data on which you base you conclusions that it's hard to argue against your plans for the long term health of the lake.
I believe you had a report a couple of years ago that the biomass in Dillon was about 80% suckers. Has that changed at all and if not do you have any other solution to the suckers?
Another question I have: would the introduction of fathead minnows help with the forage base for the browns and larger predators or would that cause to much competition with the trout?
 Reply by: HookNem      Posted: Mar. 13, 7:25:38 PM     Points: 847    
Would some kind of shoreline vegetation seeding during drawdown or addition of brush or other structure help fertility in this and some of the other mountain reservoirs?
 Reply by: Ewert      Posted: Mar. 14, 8:43:21 AM     Points: 12    
I believe you had a report a couple of years ago that the biomass in Dillon was about 80% suckers. Has that changed at all and if not do you have any other solution to the suckers?

If you look at the table on page 2 of the report, you can see that suckers are down to 66% of our gillnet catch, while the percentage of brown trout has gone up. That's going in the right direction, but whether or not it's enough to really say that the suckers are declining is questionable. If it takes another drop downward this year I'll be happy about that.
You have to keep in mind that these are shoreline gillnet sets, set perpendicular to shore. The nets are 150' long, so the one or two steepest nets go to maybe 50' . So when we talk about these percentages of suckers, they're distributed in a ring around the reservoir and they don't really go much deeper than 30-40 feet. Rainbows and browns behave in similar ways, but suckers seem to be even more confined to shallow water than they are. So you have to take that into account.
When we do the deep-water netting as in 2010, 2015, and 2017, when we drop a net to anything over 60 or 70 feet, we never see a sucker in any of those nets. And it's not like suckers hang out suspended over 100 feet of water.
Anyway, I don't have a "solution" to suckers (there are a lot of them in many of our lakes), other than trying to get some of the browns to a size large enough to prey on them. That 27" fish that we got in '15 could definitely eat any sucker in the lake.
The problem with trying to force anything to eat suckers is that any predators we've got, including pike, choose suckers last. People don't give predatory fish credit for being species-selective but they absolutely are and it's been shown in multiple studies over and over. So if you're going to really get any predator to hammer on the suckers they have to be in a situation where they can't find anything else at all to eat. See my Green Mountain report.
 Reply by: elkinthebag      Posted: Mar. 14, 9:38:42 AM     Points: 1904    
Wait we stock fingerlings to feed browns but kill lakers and pike cause the eat catchable size rainbows. Can we get a shad base forage for the real fish and leave the slimers for the rookies and the kids. People hate regulations cause they are lazy. It makes it hard to fish it make it difficult to get into a lake, park and etc. most the people complaining are to lazy to pick up there own trash around the lakes. I would love to see the guys that care about are lakes and all out trophy fish potential be taken care of for once. I know money is a big issue but protect the big breeders of the fish you don't have to waste money restocking every year and let the others have there freedom on a rainbows. They are a dime a dozen and grow quick. We need a volunteer ranger program. I try to educate people that I see break regs but most are just to arrogant and could careless. But that is how they are raised. More youth programs and opportunities would be great. I volunteer on everyone I can.
 Reply by: not too old to fish      Posted: Mar. 14, 9:42:21 AM     Points: 3824    
Still looking for the answer, thanks:

Another question I have: would the introduction of fathead minnows help with the forage base for the browns and larger predators or would that cause to much competition with the trout?
 Reply by: Ewert      Posted: Mar. 14, 9:44:01 AM     Points: 12    

Another question I have: would the introduction of fathead minnows help with the forage base for the browns and larger predators or would that cause to much competition with the trout?

That's an excellent question. I have done a lot of thinking about fathead minnows. I've got three lakes (that I know of) that have good populations of them, and you can really see the benefit of them in the fishery. The trout are much better quality. The fishing itself can be difficult in all three of these lakes, but that's not because the trout aren't there, it's because they're very well fed and they seem to behave differently than people expect. I've heard some negatives about them too and I need to do more research on them. I've got a couple lakes in mind that I'm thinking about introducing them, but these are all smaller waters that I'm talking about. I'm not aware of a large coldwater lake that has them and whether or not they do well and/or contribute to the fishery.
 Reply by: redleader      Posted: Mar. 14, 6:29:45 PM     Points: 544    
[quote elkinthebag - Wait we stock fingerlings to feed browns but kill lakers and pike cause the eat catchable size rainbows]

Haven't you ever played a game of Goodfish-Badfish?

Predators are Oportunists not Species selective, some species may be easier targets like a fresh from the hatchery Rainbow versus a wild Sucker.
A school of Salmon may get more attention at times.

There's a good reason the only Suckers you find in places like Williams fork are Large compared to lakes like Dillon overrun with small ones.

There's plenty of evidence from anglers and Jon's own netting studies of many instances of Predators eating Suckers and their own.
 Reply by: D-Zilla      Posted: Mar. 14, 7:57:37 PM     Points: 1737    
Personally I plan to help thin the sucker population this summer. At 10 bucks a bag, it's getting awful expensive to chase lakers! I know Dillon has always had a healthy population of smaller suckers, so that is my target at least a few weekends once it opens up.

My experience up there is VERY limited though, and it's been better than 10 years since I SERIOUSLY fished that lake. Usually it's a stopping point on my way by for work.

Smaller hooks and worms still work for them? I'll help you balance the population. I hope there's no limit on them, maybe next year I'll open a bait store in Granby! (LOL)

I'd love to see more lakes with BIG browns in them, they are so hard to find in bigger sizes, that it feels like we need them. Not because I want to eat them or hang them on my wall, but because they are amazingly fun to catch!
 Reply by: shmiley1      Posted: Mar. 15, 8:39:51 AM     Points: 2503    
As the runoff gets going, the suckers will flock to anywhere water is flowing in to spawn. Im sure some inlets are more productive than others but once you find them, there should be LOTS.
There is no limit on suckers and metheods of take are alot less restrixtive in SOME places.
 Reply by: Lone Shark      Posted: Mar. 15, 10:10:47 AM     Points: 779    
I see what you did there Chad HAHA
 Reply by: HookNem      Posted: Mar. 15, 11:13:05 AM     Points: 847    
Jon Ewert, I think you might've missed my question above...

Would some kind of shoreline vegetation seeding during drawdown or addition of brush or other structure help fertility in this and some of the other mountain reservoirs?

 Reply by: JohnnyW      Posted: Mar. 15, 12:13:42 PM     Points: 627    
Any tips of how to target the Char during open water season? Never caught one before, thanks!
 Reply by: Kokanee Bro      Posted: Mar. 15, 1:05:40 PM     Points: 233    
Thanks for your posts Ewert. So many times I see CPW/Biologists attacked on this site from highly opinionated people who know nothing about the science or politics surrounding the decisions made on a body of water. It is refreshing to see the data as well as the rebuttal to those "arguments" from someone actually knows what they are talking about. You will never make everyone happy, but thanks for all you do to allow the rest of us the thrill of catching fish.
 Reply by: Fordo      Posted: Mar. 15, 2:55:20 PM     Points: 55    
Jon, What more evidence do you want? Since the increase in size distribution of brown trout raised, the sucker density went from, 80% to 66%.....Kill one brown trout, save 1000's of suckers over the lost life of that brown.
And your gill net studies show that there is just not enough browns in there to start starving each other out. How many over 20" have you caught in your nets in the last 10 years of netting? I counted 9, Correct me if I am wrong, but that's an extreme few amount out of 5 studies I counted less than 40 fish in ten years between 15" and 20". For a 3000 acre lake that is a minuscule amount of brown trout captured. Again correct me if i'm wrong for looking at this way. I just don't see how it helps one brown trout to kill the other due to less competition of food when there is so few of them to begin with. But isn't that what you are suggesting, and a main reason for not protecting them?

You talked about slapping special regulations, Isn't a a one over 20" on Arctic Char a a pretty extreme special regulation? Why isn't a 15 to 22 inch brown as valuable as a tiny Arctic Char?. I can catch several arctic char out there almost any day I want. I get skunked all the time on the hunt for a big brown. If a guy catches a 3 or 4 year old Arctic Char of which there a ungodly amounts of, by all means throw it back. But catch a 7 to 15 year old Brown trout of which there are extremely few of, kill it!!!, In fact go ahead and kill 4 of them!!! This just does not make sense to me, There is a small window of time every year when the select few large fish run up the 10 mile and stage at the inlet. More times than you think Ive watched a group of guys who were dunking nightt crawlers walk out of there with more large brown trout than were caught in 2 years worth of gill netting.
Ive asked you probably 100 times about protecting browns, on gthe phone, in person, and on e-mails. I do it because this is my opinion developed after spending 300+ days on the lake in 2017, 240, in 2016, and 195 in 2015, and 75 days in 2014 since I opened my guide service. I believe with everything I got, its a terrible thing that there is no protection on these brown trout. Have you ever seen the movie Shawshaink Redemtion? Ultimately, he got his library books from the state government after a letter a week for like 10 years. I figure if i keep asking enough, maybe one day you will say ef it, Im sick of hearing from this guy and put a slot regulation, or at least a one over regulation for browns on Dillon.

Dillon is loaded with shorline vegetation. There are 4 different types of plants in Dillon that are very prolific. Frisco Bay, parts of the Blue inlet, South Dillon Bay, Giberson Bay, and north Dillon Bay get so much weed growth, that anything less than 12 feet of water is almost unfishable after the third week of July.

I don't see any arguments, or attacking going on here. What are you referring to? Its been a great discussion with lots of great information. Jon asked us for our opinion, and that's just what im giving him, This type of discussion is the whole reason he put up the report. I've seen alot of threads with uninformed Jamokes whos opinions contradict the CPW. This isn't one of them.

If you want the arctic char in open water, hit the inlets during runnoff, and then during the summer, target them just like a guy would target eater sized lake trout during the summer at Granby. Be ready for some frustartion, your going to be attempting to pull 8 to 12 inch fish out of 55 to 120 feet of water. If you want the sexually mature larger fish, Here is a huge hint.

[log in for link]

 Reply by: shmiley1      Posted: Mar. 15, 8:13:05 PM     Points: 2503    
I dont always agree with the strategies put in place eigther. I do try to respect them tho. Ive been to meetings, i have spoken and have heard others speak their mind too. Its gotta be tough at times, especially comming from some of us more involved people.We are very lucky Jon is as interactive with the public as he is.

We have...( and this is just the very simplified list)
What the trophy hunters want.
What the meat fisherman want.
What the conservative/protective fisherman want.
What tourist want.
What families want.
What the feds want.
What the governing angencies want.

What is best for the body of water and what it can support long term. This alone could be many possible solutions that may or may not line up with ANY of the "wants".
Not to mention the number of waters managed.. He prolly has to go through this with them all. Its not an "ok, they want this..make it so" type of decision.

By no means do i think you should stop your campain or stop collecting data to back it up. You do a GREAT job of looking after your waters. I wish more people would do the same.
Is meant more as a little general insight for the less involved/informed. I know ive been pretty pushy on him myself before.

 Reply by: Kokanee Bro      Posted: Mar. 15, 8:57:30 PM     Points: 233    
Fordo, I wasn’t talking about this specific conversation. More that in many other conversations I have seen on this site, the cpw/biologists are attacked without them their to defend themselves or the way they do their job. This is by far the most pleasant I have ever seen this conversation go. Sorry if you felt that was an attack on you. I probably should have made that more clear.
 Reply by: bron      Posted: Mar. 15, 9:09:43 PM     Points: 18253    
Very nicely done Jeremy

Back to top...