Thursday, January 30, 2014

Tough times in Parshall

     I've done some processing of the data that I collected on the Parshall reach of river and it's not great news. This is the reach of river that we have a long-running historic data set for, going back to 1981. I survey two miles of river there every September, starting in the split channels upstream from the Parshall Hole, and continuing on downstream into the BLM Sunset parcel. We end it at the big irrigation diversion there. This reach of river has really been struggling the past several years and I can't put my finger on the exact reason why. Here are the population estimates in fish per mile greater than 6" (rainbows and browns combined) going back to 2000:

     Here are the rainbow population estimates:

     2012 was the year that we finally saw good success with the HXC's. Rainbow numbers came down in 2013 but I'm optimistic that the overall trend will be upward in the coming years. A quick comparison of the two figures shows that rainbows still make up only approximately 4% of the total trout population of fish greater than 6". Anglers have been reporting better catches of rainbows since 2012, but you have to remember that rainbows are approximately 10 times more vulnerable to being caught than browns are. So you can have a population that is 90% browns and 10% rainbows, and because of the greater catchability of rainbows, an angler may perceive that there are equal numbers of the two based on his catch rates. 
     Here are the density estimates of "quality" browns (over 14"), by surface acre of river. To me, this is the most disturbing statistic:

     As you can see, this is the lowest estimate we've had in recent history for fish >14". This reach of river has really been struggling in this regard. At this point it's barely maintaining the minimum standard for a gold medal-designated fishery. In 2010, we captured more than twice as many browns over 14" on that reach of river than we did in 2013. The gold medal standard is at least 12 fish per acre over 14", and at least 60 lbs./acre of total trout biomass. Speaking of biomass, here are the estimates from recent years:

     This is the only parameter that we saw an increase in 2013 - albeit a small one at that, and well within the margin of error for these estimates.
     So when I've got data like this that shows a lot of doom and gloom, one of the first things I do is ask myself if there is some way that the data could be wrong, and that it is not reflecting true trends in the population. The biggest reason for it to be totally wrong would be if during some years there is some large-scale movement of fish out of the reach, and in some years the opposite. But we know that for the most part browns don't move large distances. Most movement studies that have been done with trout in rivers show that a very small percentage of fish move large distances, but most fish live their whole lives over a relatively small reach of river - a mile or a few. The way that I control for timing of movements is by running this survey as close to the same dates as possible every year - right around the third week of September. The reason why it works best at this time is that the water has cooled enough that it's not overly stressful on the fish, and it's still early enough that major spawning movements and concentrations are not in full swing yet. 
   The other thing that makes me think these trends are real is best illustrated in the biomass estimates. The trend was downward every year from 2007 to 2012. If there was a large amount of error in this estimate, there would be a lot more variation - it would bounce around more. 
     I'm interested in hearing from folks who fish the Kemp-Breeze a lot, to know if their angling experiences match what I'm seeing in this data. Are you catching fewer browns over 14" than you did just a few years ago? Has the average size of fish that you are catching become smaller? 
     So let's assume this is all real, and speculate as to the reasons. We know there is functionally no harvest taking place there, because it's a catch-and-release area. There is a ton of fishing pressure, but there always has been. I definitely don't believe that there was more pressure there in 2013 than there was three, or five, or ten years ago. This reach of river doesn't have extreme temperature problems because it's right below the Williams Fork confluence, which cools it down during the hottest portion of the summer.
     One thing that always lurks in the back of my mind is the impact of anchor ice in certain winters. Last winter was a great example, when we had weeks of brutal cold, around 30 below every night. During times like that, you can go look at the riffles right around the Parshall Hole and see the anchor ice covering the cobble. That has to have some form of impact. It's difficult to get an idea of how flow varies from year to year in the dead of winter, because the flow gauges in the area are off for the season. 
     I also wonder if it's a forage issue. We know that since the early '80's, we've lost the giant stonefly hatch that used to be prolific there. That species isn't the only one that's gone - our studies have found a whole list of invertebrate species that have disappeared from this reach of river. But these extirpations happened gradually over the past 30 years - it's reasonably safe to say that they had already occurred at the times in the previous decade when biomass was twice what it is now and when densities of quality trout were far higher. Also, there is evidence that does not support the forage limitation theory: the fact that body condition of the fish is consistently good. Not spectacular, like we have seen at Radium, but good. 
     It could be a habitat degradation issue. There are sections of river that are utterly featureless, and at 150 CFS on these sections the river is 200 feet wide, ankle deep, and contains nearly zero fish. Whether or not the physical habitat has slowly been degrading over time is a question that I don't have an answer for. 
     Anyway, I'm interested in hearing your thoughts on this, so let me know if you've got any opinions. Thanks.


  1. Thanks for sharing Jon. Hopefully it will turn around in Parshall soon. Out of curiosity, where did you glean your stat on rainbow vs. brown catchability? I'd like to read the paper/report if you have a citation for it.

    1. Devin, I don't have a specific citation for the establishment of that in general, I know it's out there somewhere but it's just one of those things I've heard discussed so many times that it's ingrained. In this reach of river though, the example we have is that when Barry Nehring was doing research on the effectiveness of special regulations (before Whirling Disease came along and changed the course of his career), he intensively studied this reach, and it included some thorough creel surveys. The creel survey showed that the number of rainbow trout being caught and released was approximately 50X what the electrofishing population estimate was, and the number of brown trout being caught was approximately 5X what the pop. estimate was. Don't quote me on these numbers but that's roughly what it was. So in other words, every rainbow in the reach was being caught about 50X per year, and every brown was being caught about 5X per year. It's all in our research library in FtC. Barry's reports from the '80's and '90's are just a priceless gold mine of information on fish population dynamics in our rivers at the time. I've got my own paper copies, and I'm not aware that they've ever been digitized by anyone.

    2. Thanks Jon. I'll have to see if I can dig them up before I leave town at some point.

  2. Hi Jon, I met you and volunteered on the 2nd Blue River shock. I just now came across your blog while searching for information on the Char in Dillon Res. I have been catching up on all the previous blogs from last year and I just want to say that I really am enjoying reading them. Please keep it up, as I like to be informed of the state of our local fisheries. Thanks.

    1. Thanks Corey, I appreciate the interest. Tell your friends.

  3. I have fished the Parshall area a hand full of times and I have noticed catching mostly smaller browns and a few 13-16" rainbows. It is a very featureless section of river and I think the upper age classes of brown trout might have move to more suitable structure(up or down river).