Sunday, January 6, 2013

A Tale of Two Lakes.

     Here's a wonderfully simple story illustrating how straightforward field work in this profession leads to an immediate management change.
     I am blessed with a large number of alpine lakes in my area of responsibility. This includes the east side of the Gore range, the east side of the Never Summer range, the west side of the Indian Peaks, and the handful of lakes in the Williams Fork watershed. Plus a few others scattered around. Needless to say, I haven't made it to all of these lakes yet. I hope to make it to all of them before I retire.
     You're probably aware that we stock many high lakes throughout the state with cutthroats from an airplane. The vast majority of these lakes were historically fishless, usually being situated above thousands of vertical feet of various geological barriers which originally prevented the native fish in the mainstem rivers and tributaries from colonizing that far upstream. Human history has turned the tables and now the only places that are inhabitable by our native cutthroats are typically the waters upstream of these same barriers. So, stocking our high lakes serves both recreational and conservation purposes. We stock enough cutts in enough places that they are available for angling and harvest, while in some cases the conditions are right for the fish to establish self-sustaining populations, sometimes with nice spawning runs up lake inlet streams at high elevations. Actually, it seems to be more often the case that the successful spawning situations find the adult fish dropping into an outlet stream that has good spawning habitat and getting the job done there.
     We used to stock a lot more lakes than we do now, before the whirling disease crisis hit our hatchery system in the mid-'90's. At that time, much of our fish production went away for a few years while hatcheries were depopulated, disinfected, and new infrastructure providing clean water sources was built. All high lake stocking ceased for a few years. Once the hatcheries were back up and running, the high lake stocking schedule was slowly rebuilt, lake by lake. But many lakes never made it back on to the stocking schedule, for one reason or another, and remain that way today.
     While this sounds like an unfortunate development, there was a silver lining. Many of the lakes that had been stocked for years did not experience a drop in the quality of their fishing or the density of their populations. It turned out that conditions were good for natural reproduction in these lakes. Without a break in the regular stocking of these lakes, the self-sustaining potential there would never have become apparent. Conversely, many lakes became fishless again, hosting no successful reproduction at all.
     So, in my job I'm lucky to survey a handful of high lakes each year. Usually the purpose of these surveys is to verify that we are justified in either stocking a lake or not stocking it. It's a process of still getting the stocking schedule sorted out and maximized after all these years. And I've got to say, in a job that has more fun things to do than I can ever list here, these high lake surveys are at the very top, always. I consider myself unbelievably lucky to have the task of doing this. So much so, that in some part of my mind I'm always waiting for the other shoe to drop, for the bad news to come, and to find out that I'll be spending the next thirty years sitting in a cubicle in a windowless hole staring at a screen.
     I should explain that when you take a job as a fisheries biologist, you inherit a stocking schedule for all your waters. This schedule has been perused, tweaked, massaged, and altered by each biologist who had the job before you. When you are new in the job, you have no knowledge whatsoever indicating you should change anything in that schedule, so you don't. But you start collecting field data that picks up right where the previous guy left off, and you design your surveys and collect your data in a way that hopefully answers the question of whether or not there is a better way to be doing things. If you don't have data that directs you to make a change, you don't make a change.
    This past August, I recruited a handful of willing coworkers and we headed up to survey two lakes of interest, Crater and Pawnee. Crater Lake had been put back on the stocking schedule and had been receiving 2,000 1.5" cutthroats most years since 2001, while Pawnee was one of those lakes that had fallen off the stocking schedule, stocked for the last time in 1993, and had never found its way back on. I had received angler reports that Crater was full of brookies and macs. I had not ever received any reports from anyone regarding Pawnee. I was hopeful that we would find a happy, reproducing population of cutts doing fine in Pawnee.
     I was also intrigued by the report of lake trout in Crater. The combination of lake trout and brookies is not unusual in other areas of the Rockies. Lake trout were sometimes stocked in high lakes that were overrun with stunted brook trout populations to thin the brookies out, increasing the quality of the brookies that were left while at the same time providing an opportunity for a larger mac in the recreational catch. It seems that I've heard of this more in the Wind River range and other areas of Wyoming, but if this was true, it would be the only such lake in my area, to my knowledge. Also, if this report proved to be true, it didn't sound to me like there was much opportunity for those 2,000 1.5" cutthroat dropping in from the plane every year to survive. So I wanted to know if we were wasting those fish. I've seen a couple other scenarios in which we stock cutthroats into a lake with a prolific brook trout population and never get any recruitment out of them at all. That is a futile effort.
     Logistics for a high lake sampling trip are a little more complicated than a standard backpacking trip. We have to get gillnets, float tubes, and waders to the lake. That pretty much makes it a requirement to use animals of some kind. I've been on a couple Llama trips and been very impressed with the utility of those animals, but for this trip it would be Scott and Becky's horses doing the work for us.
     We made our way up the trail to a suitable base camp, at a point beyond which it seemed unwise to take the horses any farther. The following morning, after repacking gear onto our own backs, Chris and Scott headed for Crater Lake while Sean, Michelle, and I made for Pawnee.
     These lakes sit in spectacular glacial cirques with massive headwalls rivaling anything in the national park. As soon as we arrived at Pawnee, I set about getting the float tube inflated and set two 75' gillnets on opposite sides of the lake. While the gillnets soaked I cruised around the lake a bit on the float tube, then did some hiking around to check out the basin. The weather was completely still and from the time we arrived I never saw a rise on the water.
     Pawnee doesn't have much of a defined inlet. It seems that the inflows to the lake probably come from many directions, and most of it beneath large boulder and talus fields. The outlet, however, had a similar appearance to many I've seen that support spawning success. There is a beautiful small meadow immediately below the lake that the stream snakes its way through, with deep pools. I've often seen these types of places immediately below high lakes teeming with fish. The substrate was definitely on the large side and there wasn't an overabundance of good gravel, but I thought surely there was enough to get the job done. However, in all our traipsing around, we never saw a single fish. No fish in the outlet stream, no fish cruising the lake, no rise forms, nothing. We walked all the way around the lake, with good conditions for seeing into the water. And, ultimately, zero fish in the gillnets when I pulled them at the end of the day several hours later. So, I felt pretty confident in the assessment that Pawnee Lake holds zero fish.
     At camp that night, I got the report from Chris and Scott regarding what they found at Crater. It was exactly what I had expected: decent brookies up to 12 inches, a couple lakers in the 16-inch range, and no cutthroat to be found anywhere.
     Simple as that, we have a management change to make. It appears that all we've been doing stocking those cutthroats since 2001 is subsidizing the brook trout and lake trout diet in Crater Lake, while one basin over Pawnee Lake sits fishless and begging for cutthroats since 1993. Crater will no longer receive cutthroats, while Pawnee goes back on the schedule.
     That's how it works with our alpine lakes stocking program. It slowly evolves over time based on a slowly building base of firsthand information. I love the simplicity of the information combined with the significant physical effort required to get it, and the phenomenal work environment. It may not seem like much information, but it took a three-day effort to get it. I would love to do nothing but high lake surveys all summer long, but there are obviously other responsibilities, and summer flies by. This is why we can only make it to a few of them each year.
     The main unanswered question from this trip is, why weren't the cutthroats historically stocked in Pawnee Lake successful in reproducing? I've seen recruitment in lakes that appear far less hospitable. It's impossible to say. It may be a matter of one bad year in which conditions under the ice were just right for dissolved oxygen to drop to levels impossible for trout to survive. I'm optimistic that the outlet stream there will see spawners again, and cutthroats born there as well.


  1. Great information. Since your time is limited in getting into the high mountain lakes and streams, I was wondering if it would be worthwhile to setup a mechanism for the general population to provide you general information. I believe with minimal training you could assemble a group of willing volunteers to do fish surveys, rudimentary water quality (i.e. ph, DO) and food sources (e.g. stomach contents, or bug activity). This volunteer information could assist you in deciding which waters might need a more thorough scientific investigation.
    Keith G

  2. Keith, I do get some feedback and trip reports from some anglers and it's always greatly appreciated. The information that's most useful to me coming from the public is even simpler than you suggest - species, catch rates, lengths, and weights if possible tell me a lot. Most of our high lake stocking occurs only every other year, and so if folks are paying attention to the size distribution of the fish, there are often two or three distinct size groups in the lake that are easily identifiable if enough fish are caught. The number of size groups that are present is very handy for me to know. If folks are visiting lakes during potential spawning times (May - July), any reports of observed spawning behavior are very helpful as well.

  3. I've had feedback from some folks that they are unable to post in the comments section. I thought I had it set so that anyone can, but I'll have to play around with that some more. In the meantime though, if you have a comment or question just email me directly at and I will paste it here.

  4. Thanks for the work Jon. I think I will start writing down things about my trips to send to the various biologists in charge of those lakes. Do you believe the other biologists will be as receptive of the information as you are?

    1. Absolutely they would. I have folders on my computer listed by lake, where I file any tidbit of information that I receive from anyone. It's all helpful. If you're in an area where you don't know who the biologist is, drop me a line and I'll shoot you their email address.

    2. I absolutely agree with Jon on this. Any angler information is helpful, and the more information the better. This includes sizes, numbers and species of fish and if you happen to keep track of it, the total amount of time you and companions fish. I've found that angling surveys can often pick up an age class (usually small fish) in some of the high mountain lakes that the gill nets may miss. I also file any information I receive by lake and it can highlight problems to help me prioritize where I need to sample, or simply show that planting was successful.

      Kurt Davies
      Aquatic Biologist
      North Park and Poudre Drainage

  5. Thanks for the read! I'll put Pawnee on the list for 4 years from now. Speaking of life span....What do you think the mean life span is for these high lake fish?

    Please let me know when you plan on doing a survey to Gourd. I want to know what's up with this lake.

  6. Life span in these high lakes -- probably 6,7,8 years on average. However, in 2009 we netted a 21-inch rainbow out of Stone Lake, and the last time rainbows were stocked there was in 1994. But maybe there was some reproduction . . . hard to say. It was definitely a rainbow though. It was very surprising.

  7. Do you manage the stocking of backcountry lakes in RMNP or is that managed by the Park?

  8. James, that is managed by the park. Because most of those lakes were originally fishless, they do very little (or maybe none) stocking of high lakes. The ones that have good fishing are self-sustaining and were stocked at a time when their management philosophy allowed for it.

  9. Ah, just found your blog, had occasionally read the CF thread. Love the story here. A friend of mine had fished Pawnee a few years ago. No dice.

    Interesting to see I know some of the people who read this!

    1. Thanks, and welcome. Glad to have you along.