Sunday, February 24, 2013

Grab bag

From Mark - 
I hope you are able to establish a reproducing rainbow population in the river. I, too, remember the old days. Jon, when will you have the updated survey of Lake Granby posted? I will be very interested in the body condition of the Macks. The pictures I am seeing of big fish posted on various fishing forums are very disturbing. I have not caught any big fish this winter, but even the small ones seem very skinny. Is there reason for concern, or do you think this is a result of high water, low water years?

I'm working on getting the Granby report together. But, the short version of the story is that things are not good. I am expecting a full collapse of the kokanee in Granby this year. The main piece of evidence pointing to that is in the graph below. We run sonar surveys on the lake every year, and each year's sonar survey gives us a prediction of what the kokanee run will look like the following year. The numbers are an estimate of the total number of pelagic (open-water) fish in the reservoir. There is a lot of error inherent in the estimate, but it does serve as a good indicator.

You can compare  that with egg takes over the same period of time:

   We appear to be headed for a repeat of the 1998 situation when there was no spawning run at all and no eggs taken. I think we'll be lucky if we take half a million eggs this year. 
     I've seen some of those pics of macs this year too, and it looks like a return to the bad old days of the late 90's, when the fish were embarrassingly thin. It won't  show up yet in my netting data though, because I run the surveys there in late May. So the May 2013 data is where that should show up. Yes, there is reason for concern, and yes, it is what we can expect from the wet/dry weather pattern. Any of you that are Granby anglers - what do you think we should do? We've seen repeated examples now that we can't seem to keep the food web in balance through a high water cycle that lasts more than a couple years. The combination of mysis booms and lake trout booms during those times create an environment that is just too hostile for the kokanee to be able to hang in there. Yet, without a good kokanee prey base, the lake trout will be in pathetic body condition forever, and growth among larger fish comes to a screeching halt.

From Lee - 

Jon, Not here to argue about adding more Mackinaw to other lakes but in the example of Dillon Res. I agree that lakers would desimate the small Kokanee in that lake. You suggest that Lake Trout then be left with nothing to sustain the population. Although there is not a DPW survey on Dillon, isn't that lakes biomass made up of mostly suckers? Have your studies shown that lakers prey on suckers, trout, or salmon more? Thanks man. We all appreciate your insight and find this blog helpfull.

     We've got plenty of data on Dillon, I just haven't made up one of those reports for the website yet. I've been netting it every other year. Yes, there are a lot of suckers in Dillon. Last summer when I ran nets there, the catch was 76% suckers. In 2010 it was 78% suckers. However, there are many examples of lakes where there are plenty of suckers and lake trout that are basically starving. Granby, for one. We're seeing a decline in body condition of large lake trout (which means little or no growth is taking place) in Granby as the kokanee population declines. There are plenty of suckers in Granby - 54% of the catch in the overnight gillnets last time I ran them there. So - if suckers are the most common kind of fish in Granby, why would the lakers be losing weight as the kokanee population declines, instead of just switching to suckers, and maintaining their weight? The answer is that they don't prefer suckers, and in fact seem to avoid eating them even when food is scarce. Below is a graph showing the results of a diet study of lake trout food items that Pat Martinez and Brett Johnson did a while back, and it supports what I'm saying. I'm not aware of a single example of a lake in Colorado in which lake trout actually controlled the sucker population. If anyone else is, I would like to hear about it.

From BC - I love the idea of stocking the tiger muskie in Shadow Mountain on multiple levels. I have a few questions about the process and what it did to Parvin lake. I have been fishing Parvin for 15 years or so and have seen the lake change quite a bit in those years... for the better. 
When Tigers were put in Parvin were trout stocking stopped? Or would your attempt be the first of it's kind?
How many tigers were put in Parvin to achieve the results that were accomplished? The results I saw were a dramatic size increase in all of the trout as a whole. 
How long do tiger muskie last at that elevation? What have you seen from the fish in parvin, big creek, and joe wright? 

     I can partially answer some of these questions, but most of them deal with waters outside my area and I don't know any of the finer details. I can basically give you stocking information. Kurt Davies has been looking at this blog from time to time, so if he sees this he may be able to chime in. Parvin has been stocked with TGM on three occasions - 2001, 2002, and 2003. It was stocked with 200, 60, and 60 fish in those years respectively. It's only 67 surface acres. Since 2001, there have been 190,000 trout of many different kinds stocked there. Parvin is the place where our researchers test new/different strains of rainbows in a small lake setting to see how they will perform after being stocked. So, just looking at those numbers, I suspect that the presence of a handful of tigers there is a fairly minor afterthought. They have plenty of access to trout and with those kinds of densities, I'm sure that they haven't had to resort to eating suckers much. I remember some information about which rainbow strains have a greater tendency to avoid predation by esocids, and I suspect the whole reason for stocking the TGMs there may have been for the purposes of that experiment. Whatever change you saw in the trout fishery was much more likely to be a result of the experimentation with different strains. Hofer crosses are much faster growing than most other RBT strains, and your observations of increases in quality trout probably correspond with the time when we started working with those strains. But that's just speculation on my part. 
     Regarding your question of whether or not trout stocking stopped and if this would be the first use of TGMs in this particular way, as far as I know it would be. We typically stock them in much smaller lakes than Shadow, and continue to feed them hatchery trout. With this new information and the budget issues facing our agency, I just can't justify that scale of a TGM feedlot operation if we continued stocking trout there.
     Big Creek and Joe Wright I really can't comment on; I'll let Kurt do that if he wants to. But the short answer, is that I just showed you what we've seen at Parvin, Big Creek and others: that stocked trout are making up approximately 80% of the TGM diet. As far as age information goes, TGMs up to 14 years old were captured in that particular study.
 Again, from BC - Would the density of tiger muskie be at a level that would be worth while to target for your average fisherman? It seems as though mostly tiger muskie in Colorado are used for a sole purpose of thinning out undesirable fish and not managed for sport fishing due to the density they are stocked. Would you anticipate trying to make a viable tiger muskie fishery out of the lake? or have it work it's way back to a salmonid fishery...... if all worked out as planned/hoped. It seems like Utah (pinewood lake and newton lake) and New Mexico (bluewater lake and quemado lake) are keeping up with the high tiger muskie concentration in these lakes. 

     I would start out at 10/acre and see how that worked. I think that would definitely be a good density to support sport fishing opportunity, and in fact it would be necessary to create that opportunity, as a way to offset the declining trout fishery that we would see. You have to keep in mind that TGM are going to be a low-density fish no matter what you do. They can't raise them much larger than 8" or so in hatcheries because they start eating each other.  And yes, the intention would be to have the lake slowly work its way back to a mainly salmonid fishery, once the TGMs were successful in reducing sucker numbers and TGM numbers then became less dense. But there would be a few TGM's hanging on in there for a long time.

     On another note, let's look at the snowpack situation. I'm always amazed at how everyone thinks everything is hunky-dory after a single good storm. So I'm going to put up some snowpack graphs, that do not include this weekend's storm, but they give a good big-picture representation of where we're at. First, let's look at the last drought period, 2001-2003:

     You have to enlarge this to see what the lines are. The smooth, red line is average snowpack here in the Colorado River basin. The point of this graph is to show that the worst drought year, 2002, was bookended by years (2001 and 2003) that were not that bad. Now, let's look at last year and this year as they compare with 2002:

This year is the dark blue line, and I'm comparing it here to last year and 2002. 2012 and 2002 were more or less equivalent as you can see here.  This storm will have the effect of MAYBE getting us up to the 2012 line for the date. What I'm saying is, the difference between this drought and the last drought is that 2002 had decent years on both sides of it. We are headed in the direction of two 2002's in a row. One decent storm is not going to get us anywhere near an average snow year. We need a storm like this every three or four days all throughout March to get us there. Is the weather pattern going to change that dramatically? I'm no meteorologist, but I'm certainly not putting any money on that. This is why all the predictions for reservoir levels this coming summer are so dire right now, and you shouldn't be lulled into thinking that everything is OK just because we had a storm. This graphing tool is a lot of fun to play with and is available to anyone, online at 

Anyway, good conversation folks, thanks to those of you who chose to comment. Keep it coming; I want to hear from you. I'm going to ask again though, to use your real names. Let's be real people talking about real things. That is the biggest problem as I see it with the fishing bulletin boards - everyone loves being an anonymous troll. Also - forgive the formatting funkiness on this post; there is just some stuff that I'm not figuring out as far as formatting goes in this application.


  1. I wish I fished the lakes in your area. I've fished a few but nothing consistently. It would be awesome if you could get the other biologists to run this kind of blog.

  2. Hey Jon, I decided I do have a question for you! Why do we choose to stock non-native trout species such as rainbow trout instead of ONLY stocking native cutthroats?

  3. Hi John thanks for the reply on the Tiger Muskie. I am really hoping that you plan comes to fruition. As far as the lake trout are concerned in Grandby is what your seeing a cyclic problem? Every few/many years we can expect an imbalance? Or is there a greater concern such as what you are seeing at Blue Mesa and a serious management approach needs to be taken. Also, in Colorado do we have any good self sustaining lake trout lakes or do all of them need to be fed with kokanee or rainbows?

    Bennett Colvin