Sunday, December 29, 2013

Cutthroat genetics, part 2

     So, where we left off, our cutthroat researcher Kevin Rogers, along with others, put forth the theory that Green lineage fish represent the Colorado River cutthroats native to the Gunnison and Colorado, and Blue lineage fish are the Colorado River cutthroats native to the Yampa and White. When the new genetics information was combined with historical information, this was the theory that best explained what we were seeing.
     Now a couple of new questions arise. If this theory is true, is there any way to prove it? Also, if it is true, where does that leave the true Greenback - the fish native to the South Platte? Does it even exist  any more or is it actually extinct?
     Enter Jessica Metcalf again, and the Museum DNA project. As it turns out, a handful of early surveyors collected fish specimens from Colorado rivers and streams, spanning the period from 1856 to 1889. The specimens still exist, in places like the Smithsonian. For the first time in history, we have the technology to extract DNA from those specimens, perform the same AFLP analysis on the samples, and compare those results to today's populations. Metcalf published her findings in 2012:

Historical stocking data and 19th century DNA reveal human-induced changes to native diversity and distribution of cutthroat trout


Abstract

Many species are threatened with extinction and efforts are underway worldwide to restore imperilled species to their native ranges. Restoration requires knowledge of species' historical diversity and distribution. For some species, many populations were extirpated or individuals moved beyond their native range before native diversity and distribution were documented, resulting in a lack of accurate information for establishing restoration goals. Moreover, traditional taxonomic assessments often failed to accurately capture phylogenetic diversity. We illustrate a general approach for estimating regional native diversity and distribution for cutthroat trout in the Southern Rocky Mountains. We assembled a large archive of historical records documenting human-mediated change in the distribution of cutthroat trout (Oncorhynchus clarkii) and combined these data with phylogenetic analysis of 19th century samples from museums collected prior to trout stocking activities and contemporary DNA samples. Our study of the trout in the Southern Rocky Mountains uncovered six divergent lineages, two of which went extinct, probably in the early 20th century. A third lineage, previously declared extinct, was discovered surviving in a single stream outside of its native range. Comparison of the historical and modern distributions with stocking records revealed that the current distribution of trout largely reflects intensive stocking early in the late 19th and early 20th century from two phylogenetically and geographically distinct sources. Our documentation of recent extinctions, undescribed lineages, errors in taxonomy and dramatic range changes induced by human movement of fish underscores the importance of the historical record when developing and implementing conservation plans for threatened and endangered species.

     So, there are a few big game-changers here. First, the sentence about six divergent lineages. Remember the old traditional model that I described at the beginning of the last post, about the three ranges of Greenback, Colorado River, and Rio Grande cutthroats? That is out the window now. Gone. It has been replaced by this:

     We have six historic lineages of cutthroats that are definitely distinguishable from each other genetically. Two of them are believed to be extinct - the fish native to the Arkansas River (historically referred to as the Yellowfin), and the fish native to the San Juan - which were never named. There is only one population in the state - alas, in the world - that matches the historic Greenbacks collected from the South Platte watershed. So in the span of a few years, we've gone from thinking (erroneously) that we had a good  number of Greenback populations up and down the east slope, to now knowing that we only have one population that resembles the fish that were there originally. This is a huge setback for Greenback recovery.
     Even before this study was complete, our cutthroat researcher Kevin Rogers had the foresight a few years ago to realize that there was something important about this single unique population, and had already been working with our hatchery managers to build a captive broodstock of these fish in our hatchery system. So we have these fish in captivity to guard against something catastrophic happening to the stream where they live, such as a large fire and/or extreme flooding. 
     We're hopeful that our Durango counterpart, Jim White, will manage to find a San Juan lineage population somewhere, but there aren't many stones still unturned in his part of the state.
    Notice that we're being careful not to call them subspecies. This whole issue is a perfect example of the quesiton of how exactly to define a subspecies. Geographic separation is the most commonly stated element defining subspecies. But are these subspecies or strains? Ultimately, these questions are up to the US Fish and Wildlife Service, because they are the entity that determines what populations warrant protection under the Endangered Species Act. The jury is still out on that but we are expecting some direction soon.
     Another question that arises, and one that certain sectors of the angling public definitely ask is, who cares? Why does this matter? Well, to some people it doesn't matter. But, if we've got populations of fish that are unique in the world and are still persisting in the drainages that they have lived in since the last ice age, isn't that valuable? If we are doing things that are leading to the extirpation of some or all of those populations, shouldn't we do everything we can to reverse those declines that we caused? For me, the answer to both of those questions is an emphatic "Yes."
     I'll wrap it up with a nice shot (taken by Kevin Rogers) of a fish from one of my native populations. This is a population Green lineage fish, in the Colorado River basin, that does not carry a Grand Mesa haplotype - which means that we have every reason to believe that this is the aboriginal fish, occupying this stream successfully since long before our time. There aren't very many of those populations, and everything I do in terms of cutthroat conservation from here going forward will radiate out from these fish in this stream.
     Thus ends the first year of this blog, and I'm happy with the level of success. We'll end up at right about 16,000 views for the year, which may not sound like a lot but I wasn't as consistent as I could have been so I'm happy with that. The whole purpose of this is to do a better job conveying information to the folks I work for (you) and so please be sure to let me know of any topics you'd like to see me cover, either in the comments or via email at jon.ewert@state.co.us. Here's to a good 2014.


Wednesday, December 18, 2013

Cutthroat genetics for the layperson

     I thought I'd give folks a rundown of the current state of affairs in the world of cutthroat trout genetics. It is a very confusing situation. I get asked by anglers a lot about where they can go to catch a cutthroat that is native or genetically pure. The answer to that question is quite complicated and involves a lot of history. The story that I'll give you has some generalities and glosses over some details but this is an endless rabbit-hole if you get bogged down in exploring every detail. You have to take this slowly, piece by piece, for it to make sense, and hopefully I can succeed in making it understandable.
     We have to start with the world as we knew it before 2007. Up to that point we understood that there were three subspecies of cutthroat trout native to Colorado: the Rio Grande, the Greenback, and the Colorado River. Their distributions are shown below:
    Credit for all the graphics in this post goes to Kevin Rogers.  In the map above, the green area is where the Greenbacks were native (east of the Continental Divide), and so on. This is a very clean and understandable distribution of subspecies, split out along drainage divides. It is important to keep in mind that especially with Greenbacks and Colorado River cutthroat, it is basically impossible to differentiate between the two in the field. Rio Grande are a little more different than the other two, but still there is a lot of visual overlap in the appearance of all three of these subspecies. So up to this point, the fish's LOCATION has been just as important as its appearance in identifying which subspecies it belongs to.
     Greenbacks were thought to be extinct until 1957, when an isolated population was found. Other remnant populations were found in 1965 and 1970. There were no stocking records in existence for the streams where these fish were found, and the best science at the time identified them as being Greenbacks, native to the Arkansas and South Platte. This led to several decades of conservation and reclamation work in the Akansas and South Platte river basins, to reestablish populations of these fish using progeny taken from these remnant populations that were found.
     So everything was moving along more or less swimmingly until 2007. A Geneticist from CU named Jessica Metcalf published a paper that rocked the world of cutthroat genetics. She used a new technique called AFLP - Associated Fragment Length Polymorphisms - to look at the genetics of our cutthroats in a higher level of detail than anyone ever had before. This is one very important thing to be aware of when trying to follow this progression: these genetic techniques are on the cutting edge of the technology that's available, so every decade or so there are new tools available that reveal things that we have never been able to see before. Here is the abstract from her paper:

Across the great divide: genetic forensics reveals misidentification of endangered cutthroat trout populations


Abstract

Accurate assessment of species identity is fundamental for conservation biology. Using molecular markers from the mitochondrial and nuclear genomes, we discovered that many putatively native populations of greenback cutthroat trout (Oncorhynchus clarkii stomias) comprised another subspecies of cutthroat trout, Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus). The error can be explained by the introduction of Colorado River cutthroat trout throughout the native range of greenback cutthroat trout in the late 19th and early 20th centuries by fish stocking activities. Our results suggest greenback cutthroat trout within its native range is at a higher risk of extinction than ever before despite conservation activities spanning more than two decades.

     This paper identified a number of populations on the east slope that appeared to be Colorado River cutthroat when looked at with the new analysis. Up until that point our understanding was that these populations were Greenbacks. So the stories started hitting the popular media that seemingly incompetent biologists had been stocking "the wrong fish". What this paper did was redefine what the "right fish" and "wrong fish" are, and again, you can't tell by looking at them in the field.
     So here is what the situation looked like after the 2007 study:

     On this chart, the blue populations are what were referred to as "Lineage CR" - presumably Colorado River cutthroats. The green populations are "Lineage GB" - presumably greenbacks. We're now calling them Blue Lineage and Green Lineage, for reasons I'll explain below. But it was a major blow to find out that some of these east-slope populations did not appear to be Greenbacks after all. Especially Apache Creek down south - that was one of the original populations "rediscovered" when it was believed that Greenbacks were extinct.
     Now you have to start considering what happened with fish stocking historically in Colorado. In the early 1900's, many millions of eggs were harvested from Trappers Lake and stocked all over the state. At that time, a cutthroat was a cutthroat and all fish were considered the same from Yellowstone south. Distinct subspecies of the fish had not been recognized.  In fact, during a period when the Trappers Lake cutthroat population appeared to be struggling, Yellowstone cutthroat were stocked into Trappers to bolster the population. Up until that point, Trappers was the largest intact remaining population of pure Colorado River cutthroats, but once those Yellowstones went in, that was no longer the case.
    Another problem with that period in history is that for a long time we weren't aware of much in the way of stocking records. There was a "dark age" of fish stocking history in Colorado from about 1900 or so to 1950. Fish were dumped all over the place and no records were kept - apparently. However, Chris Kennedy, one of our colleagues who works for the U.S. Fish and Wildlife Service, has done a ton of spectacular historical forensics work and uncovered many old stocking records that were not previously known. Some of them were in old ledger books buried and literally forgotten in the basement of the state archives. He has pieced together a stocking history that shows that at least 26 million fish were reared and stocked from Trappers Lake all over the state, just from the years 1914-1925 (see below). This is also new information to us.


    
     One of the things that the 2007 study didn't really highlight is the fact that one Lineage GB population was found west of the divide, in the Gunnison Basin. You can see that one in the figure above. The presence of the Lineage CR fish east of the divide was easily explained by the new historical stocking information available to us, but there was no historical explanation for east slope fish moving west - we are not aware of that taking place on any large scale historically.
     So, in the aftermath of this study, we continued collecting genetic samples and using AFLP analysis for as many of our cutthroat populations as we could. In particular we were looking for more occurrences of Lineage GB fish popping up west of the divide. Sure enough, we found a lot of them - as illustrated here:

     In a few years' time, we had identified over 60 populations on of Lineage GB fish on the west slope. Remember that these are the fish that Metcalf's 2007 paper was treating as Greenbacks, native to the east slope. If they were native to the east slope, why would we find so many populations of these fish on the west slope? Also, here's another interesting thing: we're finding these populations all over the west slope EXCEPT for in the Yampa and White River basins (and the San Juan but that's a different story). To this day we still have not identified a single Lineage GB population from either of those drainages - everything is Lineage CR. So this has become an ever-larger question.
     Enter Chris Kennedy again with his historic investigations. He and others have also found old records of a lot of fish being raised from lakes on the Grand Mesa. In fact, from 1899-1909, we now have records that at least 29 million fish were hatched from Grand Mesa lakes and stocked all over the state, including many places on the east slope.



     So now, a new theory emerges: what if the differences that we're seeing between Lineage GB and Lineage CR fish is a difference WITHIN Colorado River cutthroats - that is, Lineage GB fish are native to the Colorado and Gunnison watersheds, and Lineage CR are native to the Yampa and White. Our historical stocking records support this theory. And if we're defining Greenback cutthroat as the fish native to the Arkansas and South Platte, then if this theory is true, Lineage GB does NOT equal Greenback. That is why we have started calling Yampa/White cutthroats "Blue Lineage" and Colorado/Gunnison cutthroats "Green Lineage", to move away from the Greenback name.

    I'm about half way through this story, so I'm going to stop it here and pick it up next week. Please be sure to let me know if you have any questions, either in the comments or by emailing me at jon.ewert@state.co.us. If something is unclear to you, I guarantee you it's unclear to other people as well and I should try to do a better job explaining.

To be continued . . . 

Wednesday, December 4, 2013

We saw this coming . . .

     Ka-boom. Through the blowing snow in Grand County this morning if you listen closely enough, you can hear the low, dull sound of an implosion taking place. It's the sound of the Granby kokanee population crashing.
     We took our last kokanee eggs of the year on Monday, the 2nd. Our spawn season ended with a whimper. The total number of eggs we took from the Granby run was 357,425 out of 432 ripe females. My optimistic prediction for this year before the season was that we might get a half million. Granby needs to produce 1.2 million eggs just to sustain itself. Preferably, we'd like to use Granby eggs to stock other waters also, but that's obviously not happening any time soon. Below is the recent history of egg takes at Granby:


     Our first indication that this was going to happen was the trend in recent years of mysis densities in the reservoir. We sample mysis every year and estimate their density per square meter of water surface area. I like to look at the four-year rolling mysis density estimate because the average kokanee in Granby lives for four years. Here is that statistic, for the entire history of our mysis surveys at Granby:

     Mysis respond positively to high water years at Granby, and get knocked back during drought periods. The low point in 2004-2006 is the response to the Granby drawdown that took place during the drought of the early 2000's. When mysis densities are low, we get much better recruitment out of our kokanee stocking because there is less competition for the zooplankton that both mysis and kokanee eat. If you look at the "good" years of egg harvest, from 2004-2009, you can see that this recovery in the kokanee population was a response to that low-mysis cycle covering roughly the same time period. What we are seeing now is the fallout from the years of high mysis densities that peaked in 2010. 2013 was a lower-water year at Granby and the mysis density estimate was 280. We responded by loading Granby up with extra kokanee - we stocked 1,450,000 rather than the normal 1 million. So hopefully we got good recruitment out of those fish this past summer, but we won't see that in the spawning run until about 2015 or '16. What concerns me now is that the downward trend in this average appears to be flattening out, and for a real kokanee recovery to take place I think we need to see this statistic drop below 500 or less. If the snow keeps piling up, Granby will have another high-water year, mysis numbers will bounce back, and this trend will start heading upward again.
     Every year we run sonar surveys of our kokanee reservoirs to get an idea of the status of the kokanee populations and to predict what the spawning runs will look like. Our research section has a dedicated boat equipped with a scientific sonar rig for this purpose. It's basically a fish finder on steroids, with a lot more definition, giving you the ability to actually count fish and estimate their sizes. There is a lot of room for error in this estimate, but the trend definitely predicts what kind of kokanee run we're going to have. Here is the recent history of sonar surveys at Granby:
     The sonar surveys have been doing a good job of predicting the following year's egg take. So, the 2012 survey was showing roughly 1/3 the number of fish that were there in 2011. Lo and behold, our 2013 egg take was roughly 1/3 of our 2012 egg take. I don't have a 2013 number from this survey yet, but when I get it we will know if we've hit the bottom or if it will get even worse before it gets better. I'm betting on the latter.
     Now, the part that no one wants to talk about. We know that competition from mysis makes it very difficult for the kokanee population to persist. What about predation by lake trout? The recreational kokanee fishery is long gone from Granby. Serious kokanee anglers go elsewhere now.  However, we still need to maintain enough kokanee to provide a prey base for the lake trout, as well as survive to maturity to provide us with eggs. This is the irony of the misguided discussions you see on the discussion boards. The lake trout guys spin their arguments as some kind of kokanee-versus-lake trout struggle, when that is absolutely not the case at all. If you don't have a healthy kokanee population, what are trophy lake trout supposed to eat?
     As I've discussed before, I run a gillnet survey of the lake trout population every May. As expected, 2013 saw a significant decline in the body condition of the large lake trout that we captured. I handled some of the skinniest large lake trout that I ever have this year. Here is a data summary for the lake trout survey:
      I set each net for 6 hours, at the same locations each year. 2011 was the first year I surveyed the lake in this way. There were a couple big differences in 2013. The first was the number of large lake trout that I caught. This number was remarkably similar in 2011 and 2012 but took a big jump in 2013. I did have one net this year that caught nine fish over 24". I had not seen that before. However, even if you remove those nine fish, we still caught twice as many fish over 24" than in the previous two years. Does that mean we have a big increase in large lake trout? This netting survey does not have the degree of accuracy necessary for me to be able to say that. There is too much variation, thus room for error, in the catch rates. In addition, the lake was lowest in 2013, so this could possibly be a reflection of the fish being squeezed into a smaller volume of water. Are the numbers of large lake trout declining? No way. But I'm saying that based on professional judgement and opinion, not on statistical analysis.
     The most telling statistic here is the last two lines. Body condition for all lake trout captured remained the same as it has the past couple years. We know that lake trout smaller than 24" make a good living off the dense mysis population. However, when they grow beyond 24" they need to at least supplement their prey with a vertebrate food item, if not switch over completely. So the drop in average body condition of large fish is the big kicker. That is a large drop over a one-year period for a fish population that by nature changes slowly. And it is statistically significant. A body condition of 73.5 is a very poor fish.
     In an earlier post I had mentioned that it appeared to me that the variation in body condition was higher in 2013 among the larger fish. That is, we caught some really skinny ones, but there were also some fish still in decent body condition. The way to see if that is true is to look at the standard deviation in body condition for the samples from each year. So, for 2011 the standard deviation in this statistic for fish >24" was 8.4. In 2012 it was 8.3. In 2013 it was 8.6. So, my initial impression was wrong, and the variation in body condition was only very slightly greater in 2013 than in past years. We just had some ridiculously skinny fish. Here's an example:

     This fish is an embarrassment. This is a starving fish. I've seen plenty of anglers' pics of fish like this over the past year. These fish are telling us loud and clear that the predator population does not have an adequate prey base to support it. 
     I know that no one wants to kill large lake trout. If this is what the anglers want out of Lake Granby then we can continue down this path. But I want to make sure that everyone fully understands that choosing not to put pressure on the lake trout population at this point in time is a POLITICAL decision and there is not a single piece of biological evidence to support it.  One thing we can't do, is increase the numbers of rainbows being stocked to prop up the lake trout, thereby substituting a cheap prey base with one that is as much as ten times more expensive. In fact, the fishing for other species is likely to decline as the starving lakers turn to anything and everything to survive on.
     Another common misconception that pops up on the discussion boards frequently is that growth rates of lake trout in Granby are slow, period. End of story. The truth is that growth rates CHANGE based on predator-prey dynamics, and we have directly observed that change. Many people are familiar with the old tags that are still in some fish in Granby. Those tags were used in a growth study in the '90's, and this is where peoples' information about lake trout growth comes from. Here is the most important information from that study, which was conducted by Pat Martinez:

     This data is old, but it reflects a time at Granby that is very similar to our situation now. In 1998 the kokanee population had crashed completely and no eggs at all were taken at Granby. The kokanee had to be restarted with Blue Mesa fish.
     But here is the take-home message from that study: Lake trout growth rates CHANGE according to conditions in the reservoir. If there is no prey for the lake trout to eat, of course they are going to be slow. But they don't have to be slow as a rule.  Imagine a scenario with one, 24" lake trout in the whole lake and a huge kokanee population. Do you think that one fish would have an extremely slow growth rate? Of course not. Its growth rate would be through the roof. This is why I get frustrated when people say, "if you kill a 30-year-old lake trout, it's going to take 30 years to replace that fish." This is dead wrong because there is a 29-year-old lake trout waiting in the wings to take that 30-year-old's place. And one less large fish to compete with will increase that 29-year-old's growth rate. So it doesn't take 30 years to replace that fish. It takes one year. Could Granby's growth rates match what we see in Blue Mesa? No way - Granby simply isn't productive enough for that, and the mysis issue will always limit the potential. But could they be faster than they are now? Absolutely.
     Here's another thing to consider. In 1994 Wayne Hubert and a couple other guys published an article called "Interpreting Relative Weights of Lake Trout Stocks." In that article, they took data from 58 different lake trout populations throughout North America, across the range of the fish. The figure below is the most important part of the article:

     It's kind of hard to make sense of but bear with me. This is a cumulative frequency distribution. The X-axis, labeled Mean Wr, is the exact same equation that I use to rate body condition in the Granby fish. What this shows is that 100% of the populations studied had an average body condition below 135. That makes sense, because a relative weight of 135 is a very fat fish. About 65% of the populations had an average relative weight less than 100, and about 35% had an average greater than that. What I'm getting at, is look where Granby falls on this distribution - at the very bottom. Our fish are skinnier than 97% of the populations in North America. In fact, we may have the skinniest lake trout in the world.

Saturday, November 23, 2013

Brookies, etc.

A couple great questions from Keith:
   Jon-Thanks so much for doing this blog. I find it to be very infomative. I've got a couple of questions for you. First, I've found waters with large brookies to be rare and highly coveted by fisherman. Do you or does the department manage any bodies of water for trophy brookies, and if so what characteristics do you look for in a prospective body of water? The rare gems I've found with large brookies seem to be relatively small and eutrophic. Also, just out of curiousity, are hatchery fish all fed the same thing, regardless of species? I remember as a kid we had some bullheads in an aquarium that we fed Purina Trout Chow and they seemed to like it. Then again, they seemed to enjoy eating pretty much everything we threw in there. Thanks again!

Thanks Keith. We really don't have waters that are specifically managed with the goal of trophy brook trout production that I'm aware of. There could be in some other part of the state. It seems that more often, the conditions turn out to be right for brookies to get larger than average, and so we do what we can to encourage or perpetuate those conditions. I'm not aware of a regulation on any specific body of water that is aimed at trophy brook trout production. Again, there may be one somewhere that I'm not aware of. We do have the statewide regulation that allows for extra brookies to be harvested if they are under 8". For the most part, the deal with brookies is that the more harvest pressure you put on them, the better the quality is going to be. As I'm sure you know, they're very good at reproducing in Colorado.
     I've got a few bodies of water that have larger-than-average brook trout fisheries, and a couple others with some potential for that.
     There are a small number of high lakes in my area that happen to have quality brook trout, and sometimes that's just by chance. One of them, Crater Lake, I've written about previously. It has lake trout in it, that were stocked as a means to maintain constant predation pressure on the brook trout. It works there and it appears to be a self-sustaining fishery with natural reproduction of both species and brookies to over 12". 
     There's another obscure high lake that you'll have to find, or might know about already, that grows brookies to a solid 14" or so. It's not on any established trail and in fairly rugged country. It does not get a lot of visitation and so definitely doesn't have a lot of harvest pressure. It's not eutrophic, and sits in a pretty geologically sterile area. There are no lake trout. We don't stock it with anything. The only explanation I have for that one is that there doesn't appear to be a lot of good spawning habitat. So, I think that the number of brookies born every year is fairly low, and there's probably a lot of predation pressure on the ones that are born. It's relatively low in elevation as far as alpine lakes go, so probably has decent insect production, even if it doesn't get a lot of nutrient input. So the lake just seems to maintain itself at an equilibrium level of good quality. 
     Red Dirt Reservoir is an above-average brookie fishery. There are a combination of factors leading to that. First of all, it sits in a biologically-productive basin, in part because it's all cattle country. So there are a lot of nutrients going into the lake. Also, there is a lot of harvest pressure there because for whatever reason, the angling demographic of folks who use that reservoir leans toward the meat-fishing side of the spectrum. Lastly, and probably most importantly, there is a very robust population of fathead minnows in that lake. I was unaware of this until a couple of years ago when I went up there to see what the water level looked like. I went walking along the shore, and it happened to be when the fatheads were in spawning, and there were thousands of them everywhere. It seems strange that I hadn't realized they were there, but the gillnets that I use for sampling do not catch fish as small as fathead minnows, and I just hadn't noticed them before. So that combination of factors produces brookies up to 14".
     Monarch Lake is another one that has good brookies in it. I'm not aware of any fatheads there. But it gets a lot of traffic and a lot of harvest pressure. It also has browns in it, that probably keep quite a bit of predation pressure on them. It's a fairly productive lake. It doesn't drain any cattle country but it does have a ton of shoal area and submerged vegetation, etc., that provides good forage production.  I have received word-of-mouth accounts of brookies being caught there that came very close to breaking the state record but fell just short. I have not seen such a fish personally, but there are some nice ones.
     I've got two lakes that have the potential to be better brook trout fisheries than they are right now. One of those is Meadow Creek Reservoir. That lake is a classic stunted brookie fishery. There are a ton of fish up to 8" but hardly anything over that. It's one of those lakes that if you're there on the right still summer evening, at dusk the whole surface of the lake just boils with rise forms. But they're all made by tiny fish. So for 2014, I've put in a request for tiger trout for that lake. Hopefully they can perform the same function that the lakers in Crater Lake do, and thin things out a little. I haven't heard yet if my counterparts were even successful in making any tigers this fall, so we'll see about that one.
     Another one that could produce some better quality is Lower Cataract. It's got both browns and harvest pressure, but the spawning conditions must be good enough to overcome both of those pressures because the brookies are still somewhat stunted. I think that this lake is a great candidate to introduce fatheads into. The water level doesn't fluctuate because it's a natural lake, and there is a ton of shallow productive area with rooted vegetation that would be fantastic fathead habitat. So I'm looking into that. 
     So, I guess the take home message here is that for every place that has nice brook trout, the combination of factors to produce that effect is slightly different. There are common themes, but it's definitely true that no two waters are the same.

     Regarding your question about feed types in the hatchery. This is one area that I don't know much more than you do. I work closely with the hatcheries on a certain level, but on another level I am totally naive to what goes on there on a day-to-day basis. I've never had an aquaculture job, so I don't have that background. We have a spectacular group of hatchery managers that know their systems intimately and are always doing everything to stretch their production to the absolute limit. So if there is a particular feed type that works best for a certain strain or species, I'm sure they're using it. It's just a detail that I am not involved with. 
     When I got this job, one of the steepest learning curves for me was figuring out how to interact with the hatchery system. My tendency at first was to think of the hatchery as a static machine that cranks out the same number, type, and sizes of fish at the same times every year. It took me a few years to understand that this is not the case at all. In fact, no two years are ever the same in any given hatchery. The volume and temperature regime of a hatchery's water supply fluctuates every year, which can have a big impact on production. Add to that infrastructure problems or improvements, disease outbreaks, personnel limitations and various other complications, and it becomes nearly impossible to predict exactly what the output of a hatchery is going to be. So as a biologist you have to be able to have enough flexibility to adapt, take advantage of opportunities when they arise, and on the flip side, figure out how best to work around limitations or shortfalls.

Friday, November 15, 2013

Stocking schedule 2014

     'Tis the season of preparing my stocking requests for 2014. I try to invest as much time as I can into finely tuning my stocking schedule, and I learn more every year. It takes a few years to really start to understand what to tweak and what to leave alone.
     The way our stocking schedule works is like this: We have a centralized database (called "Trans 6") in which all the biologists submit their stocking requests. Around December 1, the database is opened to all the hatchery managers across the state, and they go through all the requests and select the ones that they can fill. Every hatchery is different in what it can produce and when. Each hatchery has a kind of "niche" that it tries to fill that it is best at. If the biologist who is making the stocking requests puts stuff in that no hatchery produces in that size, at that time, or both, then you end up with requests that don't get filled. So it's important to have a good understanding of what our hatcheries can and can't do.
     In 2013, I stocked a grand total of 3,617,620 fish into waters in my area. 2,089,096 of those fish were kokanee from Glenwood. Aside from those 2 million kokanee, 70% of the rest of my fish came from Rifle Falls hatchery. It is our biggest and most productive hatchery, and so I need to coordinate as closely as possible with them when making my stocking requests.
     In even years, we make our high lake plants with an airplane. I know that folks can get a little touchy about naming specific high lakes, so I won't do too much of that here. But I've made some changes, hopefully for the better. As I've said before on this blog, I really appreciate and want to encourage input from folks regarding alpine lakes. I have added lakes to the stocking schedule based on suggestions from anglers. I'm always looking for places we should be stocking to create a good alpine cutthroat fishery.
     One lake that I'll name is Pacific Lake. I put in a request to stock grayling there this year. Pacific hasn't been stocked for a number of years and doesn't appear to support natural reproduction. I've had several people ask me about it though, and it seems like a good place to try some grayling.
     I'd really like to track someone down who has been to Island Lake, in Grand County. I attempted to get there on a pack trip this year but didn't get past Gourd because of the weather. Island really takes some commitment to get to, as far as I can tell. We stocked it up through 1993, and haven't stocked it since. I can put it back on the schedule, but before I do that I want to know if there is a fishery there that is self-sustaining. We may not need to put it back on the schedule.
     Another thing I'm going to try is some tiger trout in Meadow Creek reservoir. I've netted that lake twice since 2007, and both times it's been loaded with stunted brookies. They top out at 10" at most, and they are in poor body condition. Tigers have been used in these types of situations to control stunted brookies. So we'll see if that works out.
     If you have any questions or input about high lake stocking and you don't want it to be seen by the general public, you can shoot me a private email at jon.ewert@state.co.us . As I was saying above, our high lake stocking program has benefitted from input I've received from high-lake enthusiasts. I can only make it to a few of them every year, and I've got a lot in my area.

Friday, November 8, 2013

Kokanee update

     Just a quick update on kokanee egg collection. Up here in my neck of the woods, things are getting off to a very slow start. At Granby, we haven't seen fish arrive in any numbers at all yet. They're still running 300 or so CFS out of Shadow dam which makes things really difficult down there. I really have no idea what to expect up there this year.
     We took spawn yesterday  - Thurday, the 7th - at Wolford for the fifth time. We had 173 ripe females in the trap, which yielded 146,000 eggs. We're now up to about 350K for the year there. Wolford has had an excruciatingly slow start. However, Thursday was our biggest day yet and felt like the run has finally started to pick up. On Monday the 4th, we took 105 spawns. Each time we spawn we clear the trap out. So from Thursday the 31st (or previous spawn day) to Monday the 4th, we had an average of 26.25 ripe females per day swim into the trap. From Monday the 4th to yesterday (the 7th), we had an average of 57.7 females per day. So the rate of activity essentially doubled this week.
     I'm very optimistic that this coming Monday will be our biggest day at Wolford yet this year. We've got Wolford covered for next year, but we would really like to see Wolford cover Williams Fork (need 360K eggs) and Granby (need 1.2 million). Last year Wolford did that. I don't know about this year, but I remain optimistic.
     We've seen nothing encouraging yet at Granby, but we're going to try to take spawn there next Thursday and see what happens. At this point there is pretty much no possibility that Granby will cover itself.

From Vanish, regarding the last post about the whitefish in Parshall:

Neat! I bet they used to be in the upper colorado. Many anglers find them to be trash fish but I really enjoy taking a trip to NW CO once a year to fish for them. They can give a pretty good tussle.

     Vanish, I agree with you that the whities get the short end of the stick from anglers sometimes. It hasn't always been that way.
     But I want to address your first statement about whitefish occurring in the upper Colorado at some point. I want to make it absolutely clear that there is NO historical account - not from John Wesley Powell, any of the original settlers, any old-time surveyor - of whitefish ever occurring in the upper Colorado. We are certain that they are not native to the Colorado River. They are native to the White and Yampa rivers. They were first introduced into the Colorado and Roaring Fork rivers in Glenwood by Colorado Fish & Game in the 1910's. Prior to that introduction, they had not lived anywhere in the Colorado.
     It may seem like a minor point, but I want to make sure that the biological significance of this is clear. Whitefish re-invading a place where they had previously lived would be a very different thing than whitefish pioneering a place they have never been. The latter scenario is the case here.
     We seem to have two distinct whitefish populations on the Colorado: one upstream of Glenwood Canyon and one downstream. I honestly can't say if the whitefish up in the Pumphouse neighboorhood really originated from the historic stocking downstream from Glenwood Canyon. Another theory that I have has to do with a trans-basin diversion that takes water from Yamcolo Reservoir, which is loaded with a native whitefish population (being a tributary to the Yampa River).  When they're running water through that ditch, it dumps into Egeria Creek, entering the Colorado River at McCoy. So, this is a trans-basin diversion. I don't know all the details but I do know that the owners of the water in that ditch use it to pay back water owed to the Colorado. So there can be a significant volume of water making that trip. It's entirely possible that larval or young whitefish from Yamcolo Reservoir have been entrained into that ditch, made their way down Egeria Creek and into the Colorado. It makes sense to me because that population of whitefish seems to have its "nucleus" in the vicinity of McCoy.
     The original stocked whitefish around Glenwood came from the White River. If the above theory is true, we have White River whitefish downstream, and Yampa River whitefish upstream. We are not able to distinguish between the two genetically at this point, but it would be an interesting question to answer in the future. It would be a great subject for someone to do a masters' thesis on.
    I can't figure out how to post PDF's on this blog. But here is a link to the Wild Trout Symposium that has an interesting article about whitefish. It's a huge document. But check out the article that starts on page 106, entitled "Becoming Trash Fish", about how people's perceptions of whitefish have changed over the past century. It's interesting stuff.

http://www.wildtroutsymposium.com/proceedings-10.pdf

Thursday, October 24, 2013

A new species in Parshall

     On September 24 & 27, we ran our annual raft electrofishing survey of the Parshall-Sunset reach, AKA the Kemp-Breeze State Wildlife Area. I always consider this to be probably the single most important data set that I collect every year, for the simple reason that it is one of the longest-running big river trout population data sets that exists in the state. Our researcher Barry Nehring was the first biologist in Colorado to start running raft electrofishing surveys, in the late '70's. He had gone up to Montana, where they had figured out how to do it. 1981 was the first year that he surveyed the Parshall-Sunset reach, so as of this year that data set is 32 years old. It's been done the same way, at the same time of year all those years.
     Speaking of Barry Nehring, I often like to say that I owe my career to a series of phenomenal mentors. I did not arrive in this job by the traditional route of attending graduate school in fisheries. Instead, three years out of college when I was trying to figure out my next move, I stumbled into my first permanent job as a wildlife officer for our agency. After five years I transferred into the biologist job. My goal was always to work as a fisheries biologist; I just arrived here via a slightly different route than most. It's not unprecedented - I've got coworkers who took the same route. But what I was getting at, is that I am constantly thankful for the series of spectacular mentors that I have worked with in the fisheries field.  These are guys that I feel so lucky for every day that I have worked side-by-side with. It's the knowledge that I was able to glean off of them that got me where I am today. Barry is one of those guys. It seems that quality mentorship may be slowly fading away in the professional world, and if that's truly the case it's a sad, sad thing.
     Anyway, I digress. I haven't worked up the data yet from the Parshall reach, but thought I would share a couple of things. First of all, it looks like the density for large fish (>14") is as low as it has ever been, and at this point may be flirting with dropping below the gold medal standard of at least 12 fish per surface acre greater than 14 inches. That is really bad news, for a reach of river that not very long ago supported densities in the neighborhood of 100 or more per acre. Numbers of rainbows in that size category are up, which is good news, but browns are way down. I don't have a precise explanation for it at the moment, but we can get into that over the winter.
     But here is the really sensational tidbit that I wanted to share for now. On our first day, the mark run on the 24th, I was working fish out of the tank and picked up this little 3-inch silvery thing. I immediately said "kokanee" because every once in a while we pick up the occasional small kokanee that got flushed out of one of the reservoirs. However, as soon as I said it, I realized that was not what I was looking at. I said, "Wait--" and the other guys on the boat looked, and three of us said in unison, "MOUNTAIN WHITEFISH !?!?"
     We have NEVER captured a mountain whitefish anywhere upstream of Gore Canyon. Thirty years of one of the most intensively studied trout rivers in this state, and not a SINGLE record of a mountain whitefish. Not just in the Colorado, but not in any tributary, any lake or reservoir, nowhere in the Blue River watershed. In the entire time I've been here, I've taken it for granted that Gore Canyon is the natural upstream barrier of whitefish on the Colorado. There are a lot of them below, and there are none above. That is simply the way that it is and what we have observed in the entire historical record. But here was this little three-inch fish in my hand that was very definitely a mountain whitefish, no question about it.
     The weird thing about it is, this is not a species that people move around. When a new species pops up in an unexpected place, it is almost always the result of either deliberate or accidental introduction by people. But I just can't see someone willfully moving mountain whitefish from a lower section of the Colorado to the upper section, and I have a hard time picturing how it would happen on accident.  I didn't know what to make of it, and chalked it up to just one of those crazy anomalies that keeps us humble. A one-time occurrence that I probably would never run across again.
     Three days later, on the 27th, we ran our recap run on the same reach. You'll never guess what we picked up right in the Parshall Hole. Not one - not two - but THREE young-of-the-year mountain whitefish. Three of them. I was just flabbergasted, and remain so today.
     So here is my theory for the moment. We just came through two extremely unusual years flow-wise. 2011 was an insanely high-water year, and 2012 was an insanely low-water year. I think that if whitefish were to make it through Gore Canyon, it would be more likely to happen during high water than low water. I'm thinking that maybe a few adults managed to find their way through in 2011. We have never run across the adults, but now we have found their offspring.
     There is a good lesson in humility for me in this. At some point over the past year, I was talking with someone who told me that their friend caught what he was sure was a mountain whitefish somewhere above Gore Canyon. I don't remember who it was or exactly where the person was fishing. But it was a secondhand report that came to me. Secondhand reports are never very reliable, and I basically brushed it off because there are many examples of incorrect species identification by anglers.  I can't tell you how many times I've talked to people who don't know the difference between a whitefish and a white sucker. So, whoever it was that told me that, if you're reading this please drop me a line so I can get those details again, and you can watch me eat a little crow.
     If whitefish proliferate in the upper Colorado, it could change the ecology of the river significantly. There would be some benefits to the sport fishery and some potential drawbacks. It will be fascinating to see if they manage to get a foothold here. If they do, 2013 will be a milestone marking the end of the "pre-whitefish" era and the beginning of the "post-whitefish" era.

Tuesday, October 15, 2013

Kokanee season

     I'm fully immersed in chasing kokanee eggs at the moment. Things are not looking quite as rosy this year statewide, and we have a good chance of coming up a bit short. By this date last year, Blue Mesa had produced 2.5 million already; prior to today, they were sitting at right about half of that, at 1.2 million. I think it's safe to say that they're not going to have another record-breaking year. Hopefully I'm wrong about that.
     Up here, things are looking decidedly worse. As for Williams Fork, all our indicators tell us that whatever run takes place will be very weak. My best estimation is that we would get about half the eggs we got in 2011 - which would be approximately 300K. That's the best-case scenario. That operation is extremely labor-intensive. If you've never seen it, I have to build an electric barrier in the river to stop upstream migration, which means that I have to hire a dedicated person to live in a camper there and monitor the thing around the clock. 300,000 eggs is not worth that much expense and manpower. So, we're not putting the trap in at WF this year. The buoy line is in and the fishing closure is in effect, but the purpose of that is to allow us to get our disease sample. We have to keep a disease history current to continue to use it as an egg source in the future. That involves getting ovarian fluids and a couple other biopsies from 60 females. Once we have that, we'll pull the buoy line. Hopefully that will happen by the 25th. We haven't seen a fish running there yet. My first year here, 2007, we took 4.5 million eggs from Williams Fork. Crazy how times change.
     Granby is not looking much better. Last year, we scraped and scraped for 800,000 eggs. That was the first time in over a decade that Granby did not provide enough eggs for itself - we need 1.2 million there to break even. Our projections for this year suggest a continued decline, and I will feel lucky if we get half a million there.
     It's also a weird year for Granby with the water regime. When the floods started happening around September 11, the water entities immediately stopped taking water through the tunnels to the east slope. There hasn't been any water going through the Adams, Moffat, or Roberts tunnels since the floods. Because of that, all of a sudden we've got a lot more water in certain places where there is never water this time of year. One of those places is below Shadow Mountain dam. It's sitting at 200 CFS right now, when normally at this time of year they're releasing 40. The only control they have on the elevations of Grand and Shadow right now is releases out of Shadow Mountain dam. Normally there is a lot of water going through the Adams Tunnel this time of year. At one brief point in September, Shadow dam was spilling 1600 CFS. Our whole kokanee trap system there is designed to handle 40 CFS, and it's always a very controlled, steady situation, except for this year. We're way late on getting a trap in the river there. So, tomorrow they're going to cut releases for us for a few hours while we jump in the river and get a trap built that can handle 200-300 CFS. When we're done they'll crank it back up and we'll stand there with our fingers crossed hoping that it holds. It's a good problem to have; I shouldn't complain.
     The one bright spot in this neighborhood is Wolford. We have every reason to believe that I'll take just as many eggs there this year as I did last year - 1.9 million. Over the past year we built a new and improved Merwin trap which corrected some of the design flaws of the original one that we used. We set it yesterday, and this morning there were 100 or so kokes in it. That's a good sign. We'll start taking eggs there on Monday, and we'll be taking every egg we can get out of Wolford. Our biggest day there last year was November 20, so we'll be sticking with it for a while, and in fact Wolford will probably be the lake that saves our bacon for kokanee up here.
     Here is the disturbing trend for kokanee in Colorado: fewer and fewer lakes are able to support them. My mantra for kokanee the past few years has been "Competitors, Predators, and Parasites." That is, I'm not aware of a single lake in the state with a viable kokanee population that has all three of those things. In my time here, I've seen both Williams Fork and Green Mountain go from one to two, and the kokanee populations at both those lakes have taken a major hit. The only lake I've got left with none of those three things is Wolford - assuming we can stay on top of the pike population there. If the pike take off, or gill lice were to get into Wolford, I'm afraid we'd be done with kokanee in this area. We keep turning away from problem reservoirs as egg sources, and it feels an awful lot like we're backed into a corner now.

Saturday, September 28, 2013

Used and abused

     Hi folks, and sorry for the long break. Summer just becomes a wave of activity that builds and builds and doesn't really crest until kokanee spawn is over with. I have every intention of continuing this blog; there just hasn't been time over the summer.
     I had a great summer, but it ended too soon as always. Every summer I wish I made it to more high lakes, although I did squeeze in one last pack trip at the end of August. 
     We ran our annual population survey of the Blue tailwater below Dillon on Friday the 16th and Monday the 19th of August. It's two days of work because we use a mark-recapture survey. I like surveying this section during the second half of August because I feel that we're getting a relatively clear picture of the resident fish population. If we wait until September or October, it's always hard to know how much the data is influenced by seasonal movements of browns getting ready to spawn. And when you're working on a section of river immediately below a dam, if there's a seasonal upstream concentration of adult browns, then all your data will really tell you is that the browns are getting ready to spawn.
     In higher-water years, if there is at least 150 CFS coming out of the dam after August 15, we put the electrofishing raft on the river and run the survey starting at the power plant bridge and end it at 7-Eleven, which is 0.7 mile. If it's a low-water year, such as 2012 and 2013, we wade electrofish a smaller reach, starting at the USGS gauge and working upstream to the power plant bridge. So, the low-water station is a portion of the high-water station. 
     This summer was a weird time for the Blue tailwater, because releases were pegged at minimum flows for a very long time. For August, 58 CFS is about half of the 25th percentile of flow. On December 10, 2011, flows dropped to near the minimum release of 50 CFS and stayed there until just the past couple of weeks. There had been brief periods of marginally higher releases, but the river never exceeded 200 CFS during that time, and in 2012 and 2013 there were no flows that ever resembled a "runoff" period. The last time the river exceeded 200 CFS was August 15, 2011.
     I want to be clear up front here and point out that I'm not trying to run down the Blue tailwater or be insulting. It gets a huge amount of fishing pressure and generates a lot of economic activity. It is the most accessible, visible, and urban of all our gold-medal trout rivers. But during such a long period of constant flow, the Blue tailwater resembles an aquarium more than any river I've ever spent time on. We know that the forage base is very sparse, and my belief (I don't have solid data to back this up, but we're moving in the direction of doing a study on this) is that at those low flows there are very few mysis - maybe even none - getting entrained in the tailrace. It's also really cold during the growing season. So between the cold temperatures, lack of food, and insanely high fishing pressure, growth rates in the fish are extremely slow. I stock brood culls from the Glenwood Springs hatchery there, and unfortunately that's really the only thing that maintains a large-fish component to the fishery there. 
     During this year's survey, I thought the rainbows were in particularly rough shape. So much so, that on the recapture day I designated an official photographer to document the condition of the fish. So here's a "rogues' gallery" of rainbows from the blue. I'm dead serious when I say that these fish have it pretty rough. Be sure to click on the pictures themselves so you can see close up the full gnarliness of the situation.






     There is literally not a single fish in that reach with a clean jaw. The other thing going on, that I hadn't really seen before, is shown in the pictures below. Massive abrasion starting from the upper jaw and sometimes extending all the way back nearly to the dorsal fin. I really have no idea what causes this. It's only on the brood cull rainbows, and not at all on the browns. The only thing I can think of, is that they have such a hard time finding anything to eat, that they're rolling rocks looking for food, causing the abrasions. Maybe that's a stretch, but it really baffles me. I'd  be interested in hearing anyone else's ideas.





Sunday, June 9, 2013

Summer break

     We finished up Granby last week and got started on Green Mountain. At Granby we ended up capturing exactly 200 lakers in our 32 net sets, for an average of 6.25 fish per net. That falls right in there with the past couple years. We did have one net though, where we picked up NINE fish over 30". We've never seen that while we've been using this sampling scheme. It was astounding. We just happened to hit a big group of them travelling together, I guess. Any other time we pick up big fish, they're by themselves, or maybe there are two of them. Never nine of them.
     This is our third year of running the six-hour gillnet sets at Green Mountain. We set a new single-net record on Thursday with 18 lakers in one net. The previous record was 9 fish. We also picked up a 14- and an 18-pounder.
     Another day on Green Mountain tomorrow, and then I'm going to be off for the rest of the week, camping with family visiting from out of state. Hope you're enjoying this warm weather as much as I am.
     James W - those are great questions and I'll get into them soon. I never know how much people are interested in the hardcore analytical side of things but I love discussing it, so stand by on that.

Sunday, June 2, 2013

Granby spring netting

     We've been running our gillnet surveys on Granby. I've got a sampling scheme set up where I set gillnets (150 feet long, six feet tall) in 32 random locations all over the lake for six hours each. We typically set 8 of these per day, so it's four days of work on Granby. We got two of those days done this week, Tuesday and Wednesday, and then we had a couple days of horrendous wind. So we were sidelined Thursday and Friday. We'll be out there again tomorrow and Tuesday to finish it off.
     The idea behind running 32, 6-hour net sets in random locations was something that I started working on a few years ago. The traditional way to sample our reservoirs is with overnight gillnet sets, in which the nets are always set on shore, extending out into the lake, perpendicular to the shoreline. If my goal is to know what the trend in the lake trout population is, and have a good amount of statistical confidence in the data, setting a small number of shoreline gillnets (like 6 of them) overnight does not do a good job answering that question. Now, I have a set of 32 independent samples that tell me a lot more about the lake trout population. There are a lot of different statistics that I get out of this sample design, but the one that should tell us the most about trends in lake trout density is the average number of lake trout captured per net.
     This is only the third year that I've sampled the lake in this way. In 2011, the average lake trout catch was 6.4. In 2012, it was 5.3. Right now, with only half the netting done, it's 7.5. We don't have a way to directly measure the actual number of lake trout in the lake, but 5 or 10 years from now, if the average catch is twice, or half, what it is now, we can safely assume that the density of lake trout in the lake has either doubled or declined by half (with a certain degree of error in these estimates, of course).
     I keep using the word "density" for a reason. Even if I run this survey at the same time every year - or at the same water temperature - the biggest variable that I have no control over is the volume of the reservoir. So, for instance, this year on our first day the water was at 8233', which is 30 feet lower than it was when we did this in 2012. So even though I'm setting nets in the same locations (mostly - some of my locations are out of the water and so I have to use alternate ones), those locations are all 30' shallower than a year ago. So it changes the distribution of the fish, but it also changes the density. If you have the same number of fish and put them in a smaller volume of water, the catch rate should go up even though the number of fish is the same - because the density of fish is higher. So, when I get into the analysis of this data later on, I'm going to experiment with correcting for reservoir volume at the time of the netting, and see if that yields numbers that make sense.
    So here are a few photos, courtesy of Mike Kline. Here's the biggest fish we've picked up so far, weighing in at 20.5 pounds:

     This fish did have a fresh meal in its throat, so we investigated:



     It was a big white sucker. Interesting. Here is what we know about Granby right now: The prey base for large macs has become increasingly sparse the past couple years. The kokanee population has taken a huge dive, and we're not stocking as many rainbows as we used to. We know that suckers are definitely not the preferred food item for lake trout, but obviously if that's the only thing available to them, that's what they'll eat.
     I've been thinking a lot about body condition in these lakers. In every other fish population I deal with, when prey is scarce, you can see it very clearly in the body condition of the fish. For comparison, if you look at all the brown trout larger than 14" in a certain reach of the Colorado River, they tend to be all skinny or all fat. There's not that much variation in the body condition. What I'm seeing right now at Granby is that some of the lake trout look skinnier than any lake trout that I've handled to date. But some of them (like the one above) are in perfectly fine body condition. Here's a good example of one of the skinny ones we've seen:

     That is a very skinny lake trout. Nearly starving, I would even venture to say.  So I guess what I'm saying, is that under conditions of sparse forage, it appears to me that the variability of body condition in large lake trout in Granby increases. It seems that a portion of them successfully switch to other prey items, and some of them don't seem to do that at all. I don't know if that seems like a relevant, much less profound, conclusion or not, but I can say that this is not the way that any other trout population that I've seen behaves. It's fascinating, and I wish I knew what determined which fish are successful and which ones waste away. When I get the data worked up, we'll see if my hypothesis about increased variability holds true.



Sunday, May 26, 2013

Stonefly heaven

     I don't have a lot to report on this week. I was on the river all day (for fun) and I'm somewhat fried now. The giant stones are popping on the Colorado. Such a wonderful thing to see. I went down and checked on Friday and didn't see a thing, but today they showed up. At Pumphouse they were still seeming a little groggy and unsure, and I suspect tomorrow will be the big day. It's uncanny how often they hit at Pumphouse right on Memorial Day weekend.
     This week we finished up pike trapping at Wolford and Green Mountain. Got 14 out of Green Mountain, none of which were smaller than about 24" - a good sign. At Wolford we ended up with about 66 fish, all but one of them from last year's spawn.
     We also ran our standard gillnet survey at Wolford this week. From that, and from the pike trapping, I've got a couple of observations on Wolford this spring. First, the kokanee are still looking excellent and we should see another great year for summer kokanee fishing once the water clears. Second, I have seen more large (20" and larger) brown trout in Wolford than I've seen in my time here. Should be a good year for large browns there also.
     I'm about to nod off. Please make comments and let me know what you want to hear about. Ron Fletcher - you had asked about Muddy Creek below Wolford. I'll just say this: It's a nice place. That is all.

Sunday, May 19, 2013

Waiting for the reservoirs to fill

     We've been in a little bit of a holding pattern for the past week. It's time to start my annual spring reservoir netting surveys, but I decided to delay these a little bit in order to run the nets at a time when the reservoir elevations are at least a little closer to what they have been in the past. If the reservoir elevations are extremely different, it will be harder to draw solid conclusions when I compare this year's data with past years. But we'll get started this week, beginning with Wolford. We've been spending our time over the past week mostly running pike traps in Wolford and Green Mountain.
     So, I'll answer a few recent questions. From an anonymous poster on another website:

"Why can folks put feeders on the river in close proximatey (sic) to public waters?"

     Well, the real answer to this question is because it has never been outlawed. I can think of many reasons to do so. I personally don't agree with this practice at all. However, to propose such a regulation would invite a tussle of political maneuvering the likes of which I, as a lowly field biologist, have no desire to engage in. I could certainly provide some very solid arguments for why this practice is detrimental to the wildlife of this state in the big picture and the long run. But the impetus for passing such a regulation would have to come from an organized group of sportsmen from outside this agency. Unfortunately, our sportsmen are not all that organized, and at times that really costs the wildlife of this state. Not trying to be controversial or un-politically correct here, just calling it as I see it, personally.

 "Why then cannot I use corn or such to shoot deer or ducks over? "

     Because enough people thought it was unethical to do this, and passed regulations and/or statutes to outlaw this practice. But the analogy you're drawing here is more similar to chumming fish, which is also illegal. But where do you draw the line between feeding a free-ranging fish population in a river and chumming fish? Therein lies the rub.

"Are there the same 2 week regulations?" 

     I don't understand this question.

"Why is this allowed at all...shooting food into the river? Do they feed what they want? re they regulated as to what feed they can use?" 

     Again, it's allowed because it's never been disallowed. There are no regulations regarding what type of fish feed people can throw into a river. I'd be glad to discuss this topic further, if anyone is interested in doing so. Please comment.

Here's another:

"I read your comments abouth the Blue River in the Denver Post. You said the aquatic life in the river is just not up to supporting a quality fishery and that the lower section, down towards Green Mountain is especially barron. My observation of the Blue is that there are long sections of river that are just gravel and have no structure. I would think dumping a bunch of good sized rocks in those sections would increase insects and the fish they support. I see alot of the same featurelss water on the Platt downstream of Deckers. Are there any plans for streambed impovements on these rivers. It seems to me that improving what we already have access to is just as important as getting more access. "
     Thanks for the comment Homeboy. Please use your real name. This is a good question. I don't disagree that some of the sections of the Blue downstream from Silverthorne have poor habitat quality. I'm sure that those sections would benefit from habitat improvements, to a certain extent. I am not aware of any immediate plans to do habitat work on these sections, but it certainly may happen in the future.
     However, I don't believe that physical habitat quality is the limiting factor on the trout population on the Blue. I have lots of good data that shows that slow growth is a consistent trait of this trout population, in multiple locations on the river. Slow growth is not caused by a lack of physical structure. It's caused by a lack of food availability. You're suggesting that working on the physical habitat would increase insect densities. The focus of a physical habitat project in a river is to improve the trout habitat, not necessarily to improve insect production. Those are two different things. Cobble riffles are generally the best habitat for insect production (at least, the kind of insects that are desirable for trout and us), and I can show you plenty of featureless, cobble riffles on the Blue that are just fine insect habitat (but poor trout habitat). But, that doesn't change the fact that the insects are sparse there. What I'm getting at is that I think it's more of a nutrient/chemical issue of some kind than it is a physical habitat issue. 
     On the Colorado, there are many places where the trout habitat is awful- the river is far too wide for the amount of water in it and there are vast, featureless cobble riffles. There is a far higher density of both insects and trout - and far better growth rates in the trout, even though the habitat is very poor. It's an interesting comparison to the Blue.
     Another important thing to think about, is that there are some sections of the Blue - the one that comes to mind is the section from Boulder Creek down to Columbine Landing and the Highway 9 bridge - where there is no shortage of good, quality trout habitat. It's got plenty of deep runs and pools that are difficult to wade at any flow. There is a ton of large object cover. And the trout population there is really no better off than the population in the sections with poorer habitat. The density is a bit higher as a result of the better structure, but the quality of the trout themselves is no better. They still grow very slowly, and do not often reach very large sizes. 
     I'm not saying that there is no place for doing some in-channel work on certain sections of the Blue. I just think that if we do, we need to be very realistic about what the potential benefits of that work would be. It's not going to magically produce a high density of quality-sized trout. It would produce a higher density of skinny, 8-10-inch browns.
     I've had a lot of discussions with various folks about how we could go about directly addressing the productivity issue on the Blue, and we've got some ideas floating around. They're pretty preliminary though.

Now - I covered two specific topics in this post. Did I contradict myself between the two topics? You tell me.