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.



  1. Thanks for the very informative post, Jon. It appears the data reflects my observations about changes in the river over the years pretty well. I found the links to be very interesting and informative. It has been tough to see the river decline as it has. I'm hoping that the efforts to protect and perhaps improve flows will be successful along with your efforts to re-establish a self- sustaining population of WD resistant wild rainbows. Too bad we let the river get to this point.

  2. 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?