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.

Sunday, February 17, 2013

The Paul Gilbert

Ok, I'll comment on the Colorado River below Byers Canyon at Paul Gilbert and Lone Buck...I started fly fishing there back in the 70's and still fish there today.
It has been through many changes over the years from a heavily stocked river that was fished by spin fishermen using bait and lures as well as fly fishermen, to the current C&R regs.
Back in the 70's if you saw a fisherman using a fly rod, he was often fishing with live stone fly nymphs...many called them hellgramites. Despite all the stockers, you would often see people catch quality fish, especially big, pretty rainbows. Like today the best fishing was before the runoff and as the river dropped and cleared after the spring flows. Fall fishing could be pretty good too. In the 80's some habitat improvement work was done that changed the river quite a bit and it seemed to me that it took a couple of years for the fishing to rebound after the work was done. As more restrictive regulations were applied to the area over the years and fly fishing became much more popular, more and more fly fisherman became evident. Despite the popularity of that stretch, you could still catch quality wild fish with those beautiful Colorado River rainbows predominating.
Over the years I had also seen some big browns and an occasional big cutthroat caught. I remember seeing a fly fisherman catch a beautiful cutt from the riffle behind the island that is just below the Paul Gilbert area. It had to go 5 pounds!
Sadly, the impact of de-watering and warmer water at Windy Gap and Whirling Disease have really changed the river today.
The water temps have increased, insect populations have suffered and so have the fish.....especially those rainbows that everyone loved to catch. Today I catch mostly browns. While there are still some nice browns present, I see far fewer big fish and those big, wild rainbows are gone. I am encouraged to read about the current efforts to protect and improve flows in the river and the introduction of the Hofer cross rainbows. I hope to see a return of the wild rainbow trout to that stretch of the Colorado and below. Keep up the good work, Jon. I'll try to post some impressions of some of the other streams I mentioned here later.

     Ron, let's discuss this one for this week's post. I really appreciate observations like this from folks that have been on these waters for longer than I have. When I hear the same things over and over again from many different people, it becomes very revealing and enriches whatever data I may have on the fish population dynamics. 
     There is a short-term perspective to some of the things you bring up, and a long-term perspective. I'll discuss the short-term one first.
     Take a look at this report that I just put up on the web, regarding the Parshall reach. That's not the stretch of river you're referring to, but there is some stuff in this report that applies, so it's a good starting point.
     I surveyed a station on the Paul Gilbert unit this September also. I have not surveyed that reach every year - just periodically to see how it's looking. The reach that we survey starts on the western side of the large bend, where the river is very wide and shallow. We wade electrofish almost 900 feet of river, progressing upstream and ending at the steep riffle at the apex of the bend, where there is a bench on the bank of the river. This is a strange-sounding description but if you know the Paul Gilbert you will know where this is. 
     There are some difficulties with electrofishing this station that make it a tough location. The rig that I use for this consists of five electrodes. We have five people evenly spaced across the river, capturing every fish that they can. We use what's called a depletion estimate. This means that we capture every fish we can, hold them in a net pen, then do the exact same thing a second time. The depletion in the number of fish gives us the statistics we need to estimate the true population. When you do this, you're looking for something like an 80/20 split between the first pass and the second pass. This station is very challenging due to its width, and sometimes we don't get a depletion that is as good as I hope for.
     I would really like to be able to run a raft mark-recapture survey on the whole reach, where we would put the raft on the water right below the Byers Canyon bridge, and electrofish all the way down to the downstream end of Lone Buck. That would give us a much better picture of what's going on there. The best timing for this would be in the second half of September, so that this data would be directly comparable to the Parshall-Sunset data, which goes all the way back to 1981. However, there is never enough water to float a raft in this reach of river during that time of year. The input of the Williams Fork River is what makes this possible on the Parshall-Sunset reach. So, in 2013 I'm planning on using the raft in the spring instead - in late April or early May, hopefully catching the early part of whatever runoff we get, so there's just enough water to float the boat. We'll see how that goes.
    Anyway, all that aside, below is a table with population estimate information from the last three times we've electrofished on the Paul Gilbert reach.
     You can click on any of these things to enlarge them and make them readable. I was surprised to see the poor showing by rainbows, given the success we've had downstream. The number of rainbows over 14" hasn't really changed in the past decade, though, staying at very low levels. The main thing in this table that supports what you have observed is the density of quality brown trout. Right now, that estimate (13/acre) is at approximately 1/3 of what it was in 2003. This is alarming. Total brown trout biomass hasn't declined by as much, for reasons illustrated below. 
     This is the length-frequency histogram for all brown trout captured in the 2012 sample. Each bar represents the number of fish captured for a particular centimeter size group. I plotted this in CM as opposed to inches because it's easier to see the definition of the year classes this way.  The year classes are noted above the bars. These are the years that particular group of fish were born. So, you can see that 2012 had a strong year class, showing up at 9 cm. This graph also does a great job illustrating that the "quality" portion of the population, fish larger than 14" (or 35 CM) are the product of the strength of the year classes born 4, 5, and 6 years ago. Now look at the sample from the same reach surveyed in 2008. The vertical scale of the graph is the same, in order to best illustrate the difference between the two samples.

     You can see that in 2008, the sample revealed an extremely weak - almost nonexistent - year class of fish born that year, and a pretty weak 2007 year class as well. A comparison of the 2007 year class with the 2011 year class shows that the 2011 fish were roughly three times as abundant as the 2007 fish. The population estimate in 2008 for larger fish was better, at 25 fish per acre >14", but there were not enough fish in the smaller age classes to replace the larger fish as they cycled out of the population. Hence, what we're seeing now: the lowest densities of brown trout >14" ever recorded on this reach, and on the Parshall-Sunset reach also. One reason I'm confident in this assessment is that I can show you the exact same thing in the data from down on that section. You can see it in the report that I linked above - look at the histogram from 2009. That reflects the weak year classes of that period. Any time you have fewer small fish than large fish in a population, your numbers of large fish can obviously do nothing but decline over time. Also, by looking at the graphs you can now see why in 2012, the estimates for fish per mile and total biomass increased (due to the contribution of large numbers of small fish), while at the same time the density of quality fish dropped by half.
     So, the short-term response to some of your observations is that we are just now experiencing the lull in large fish recruitment that was created by poor survival in the 2007 and 2008 year classes. You're definitely not the only one I've heard from who has noticed that the fishing over the past year was relatively poor, and I believe this is why. Luckily, as I've shown, we have strong year classes working their way up now, and over the next year or two I think that we can at least expect to get back into that range of 25 or so fish per acre >14". Not to mention that we are on the verge of seeing a significant comeback of wild rainbows, as you can see in the Parshall-Sunset report.
     The big picture aspect of some of the things you mentioned, is a little bleaker story. We know beyond the shadow of a doubt that the aquatic invertebrate community has changed on this portion of the Colorado River over the past couple of decades. That has been documented by countless anglers' anecdotal observations, as well as scientifically documented by one of our researchers, Barry Nehring, in this report:

     This study has proven to be very valuable as we have entered into conversations with water users regarding mitigation and enhancement ideas for the river as an aspect of plans to divert more water. Those negotiations all take place above my head -- mostly to my great relief -- and in a somewhat politicized arena. But the fact that we've been able to document these things has set the stage for what I think will be some generous mitigation measures that would not have otherwise been possible. Hopefully things will be looking up on the Colorado as these projects take shape over the next several years.


Sunday, February 10, 2013

A tiger muskie conversation.

From James (Gasner?? - is that you?), a couple days ago:

In the past you mentioned the possibility of stocking Tiger Musky in several lakes to control the sucker population. What lakes are you considering for this? Specifically I am interested in Shadow Mountain. What if any progress/further thought has gone into this.

     I thought I would discuss this a bit for this week's post. For those of you that don't know how we're structured, the biologists in the aquatics section are divided into management biologists (which is what I am), who cover a specific geographic area, and the research group, headquartered in Fort Collins. These guys don't have a specific geographic area of responsibility. Their function is to answer bigger-picture questions across the state to help us manage or waters as effectively as possible. So each of them has various research projects going on all over the state. They are assigned to specific subject areas. So, for instance we have a researcher dedicated to native cutthroat issues, one for eastern plains fishes, one who specializes in physical habitat work in rivers, and so on. I'll be sharing some information that our lake and reservoir researcher, Jesse Lepak, conducted last year. 
     One of the questions that we asked Jesse to work on is to investigate the utility of tiger muskie as a sucker control agent, and how to most effectively do that. The proliferation of white and longnose sucker is a constant frustration to those of us that manage coldwater reservoirs. For many of these reservoirs, white and/or longnose suckers make up 60-80% -- or sometimes more -- of the total fish population, by both number of individuals and total biomass. You can't help but wonder what the sportfish productivity of a water could be if that much biomass wasn't tied up in sucker bodies, which really don't benefit the system at all. Out of the large reservoirs that I cover (Dillon, Green Mountain, Wolford, Williams Fork, Granby, Shadow), Shadow Mountain is the worst in this regard. The whole thing is unintentionally designed to be prime sucker habitat. It is a shallow, flat pan, almost entirely 15-17 feet deep. It fluctuates very little - which is usually a good thing, and is actually relatively productive. However, unfortunately most of that productivity is tied up in suckers, as far as the fish population is concerned. Below is the length-frequency histogram for both brown trout and white suckers from 2011 (I don't have all the 2012 data entered yet but it's very similar).

     As you can see, white suckers dominate the fish population both in numbers (329 captured, or 67% of the total catch) and in size. The size distribution of the two species is really interesting in Shadow, because there's not much overlap - the browns don't get much beyond 14", and the white suckers really take off beyond that size. It's obvious that the browns can't get "on top" of the white sucker population.
     So anyway, Shadow is a great candidate to try to do something to change the white sucker population structure and see if we can get a positive response out of the sport fish community. When you spend time on that lake, it just seems made for tiger muskie, with a lot of the type of habitat that these fish prefer. 
     Enter Dr. Lepak. Over the past year Jesse collected tiger muskie (TGM) from a handful of places around the state to see what they're actually eating. Below are some slides for a presentation that he gave to us at a staff meeting a couple weeks ago.

     The slide above shows the locations that TGM's were collected, and how many were captured at each water. As you can see, it's hard to get a large sample of them, but he did end up with a decent number. Jesse took tissue sample biopsies from each fish captured to perform stable isotope analysis. This is a fantastic tool which looks at the molecular composition of a fish's body tissues and tells you what food items have made up the fish's diet throughout its whole life. At the same time, Jesse also collected rainbows and white suckers from each lake for use in the analysis.

     Above is the result of the stable isotope analysis. The TGM's that Jesse and his crew collected had consumed 20% white suckers and 80% salmonids. About half of the salmonids were stocked rainbows, the other half unknown, but they were likely wild browns or other wild trout in these lakes. We've known from other studies that esocids have been observed to preferentially feed on salmonids even if another type of fish is present in greater numbers, but this is the most direct observation we've had of what our TGM's are eating. 

     So now that we have that information, we can run what is called a bioenergetics model. This one is a quick thumbnail version, but gives us a realistic scenario of what a TGM consumes throughout its life, up until it's 14 years old and about 22 lbs. in weight. Jesse cut the TGM's some slack on this one and went with a 70/30 trout-to-sucker ratio in the diet as opposed to the 80/20 that he actually observed. He used Parvin Lake temperature data, just because it's a heavily studied lake and was the one that had the best temperature information available. Temperature is important in these models because it tells you at what speed fish consume and use their food items. The cost column is an accounting of how much it costs our agency to raise and stock the trout that the TGM eats throughout its lifetime. 
     The bottom line is that by the time the TGM in this particular scenario is 14 years old, it has consumed $462 worth of hatchery-stocked trout. Over that same period of time it has consumed 165 suckers. Or, you could say that we're paying that TGM $2.80 for every white sucker that it eats. If I had the time, I could remove a whole lot more than that for a lot less money.
     There is a bright side to all this. In order to force TGM's to eat more suckers and not eat stocked trout, all you have to do is stop stocking trout. It's obvious to me from this information that if you really want TGM's to hammer the whiter sucker population, that's a necessary step. So, to give the original question a very long-winded answer, I would still like to go down this road at Shadow. I would think of TGM as a biological "treatment" that we would be applying to the lake, that would play out over 10 years or so, to be followed by a reduction in TGM density and the restoration of some level of trout fishery there.  Here are the main hurdles as I see it:

  • We have to get permission from the US Fish and Wildlife Service to do this. This is because Shadow is on the west slope, in the Colorado River basin, and drains into the endangered fish recovery area (eventually). I believe that I can make a very good argument with the Service that they should allow this in Shadow, because of the extremely remote chance that a TGM from Shadow would make it down into the endangered fish reach -- and even if that did happen, one of the great beauties of TGM is that they are sterile hybrids, incapable of reproduction. I've made some inroads on getting this permission, just through informal conversation at this point. But it seems promising.
  • Numbers. To date, we have always had to obtain our TGM's from out of state. It seems that we have never had a reliable source, and when we do get them it's never as many as we would like. To do it right at Shadow, we would need roughly 13,000 fish (10/acre). In 2012, we stocked 11,874 TGM's in the WHOLE STATE. I don't believe I would be able to persuade all my counterparts in the entire state that I deserve all of the TGM's that we could get in a given year. But -- we're working on this one. My counterpart to the east, Ben Swigle, has imported pure muskellunge into the state and is attempting to raise them to spawning size in a private water on the east slope. If all goes well, we may have the means to make our own TGM's before too long. If and when this happens, hopefully this quantity issue will be resolved. Our fingers are crossed on this one.
  • Public buy-in. We need to get the acceptance of people who like to fish Shadow. It may not be the most valuable fishery in the world (or in Grand County, for that matter), but it does get its share of traffic. Some of those people will not be thrilled that we're going to cease the stocking of trout there for a decade or so. I suspect that the recreational fishing traffic that would be lost would be replaced with a different set of anglers coming specifically to pursue the TGM, but it would probably not be as many people, and it's tough to say whether or not the economic activity would be equivalent.
     Then there's the issue of Grand Lake. We haven't yet discussed at all the fact that there is free movement of fish between Shadow and Grand. It would be foolish to assume that TGM wouldn't at least occasionally move through the channel and check things out over on that side. We're having some good success with a new strain of rainbow fingerlings that we've been stocking in Grand, and I wouldn't want this TGM project to interfere with the progress that we're making there. My gut feeling is that because of the difference in habitat, the occurrence of TGM turning up in Grand Lake would be fairly minor and rare, but what about if that's the only place where trout are available, and they figure that out? What if Grand Lake became a magnet for the TGM's just because of the presence of trout there, and they didn't do their job in Shadow at all? Maybe that's a far-fetched scenario, but it does warrant some consideration.

So that's pretty much where my thinking is at the moment on the subject. If you're a Shadow Mountain regular, I'd love to hear your thoughts. 

Sunday, February 3, 2013

Your turn

All right, I've posted about a smattering of subjects and tried to make it diverse. There are a lot of you reading this but no one is commenting. I started this blog to stimulate conversation, so let's have some. You tell me what you want to talk about. Fire away.