Friday, April 1, 2016

Turning predators into prey

Keith Greenwell had a question about the status of tiger trout in Meadow Creek Reservoir. Excellent question, Keith. Thanks for the idea. Let me back up and give you the recent history of Meadow Creek.
     
     I've got several waters that contain classic examples of stunted brook trout populations, and Meadow Creek is at the top of that list. How do I know if a population of brookies is stunted? Let me explain.
     I have surveyed the fish population at Meadow Creek three times in recent years: in 2007, 2011, and 2015. Up until 2007, we were stocking small (1.5" or so) cutthroats and catchable, put-and-take rainbows there, on top of what we knew to be a robust wild brookie population. One of the main questions I wanted to answer in the 2007 survey was whether or not the cutthroats were doing anything. As is almost always the case when you stock cutthroats on top of a dense brook trout fishery, in 2007 I found that the cutthroats weren't persisting at all. Because we don't stock cutthroats with the purpose of feeding brook trout, I immediately pulled them off of the stocking schedule for Meadow Creek. So, in addition to not finding any cutthroats, here is the size structure of the brook trout population that I observed in 2007:


     Very few fish larger than 9", and no fish over 12".  Below is the relative weight plot of the 2007 fish. If you've read any of my other posts hopefully you understand what relative weight is - a measure of "plumpness" on a scale of 100. It can be thought of as a grade of body condition.  What I saw in 2007 was modestly declining relative weights as the fish got larger, as indicated by the trend line on the graph below. 



     The X-axis in this one is size of fish in mm; I didn't convert to inches. Taken together, these two pieces of information - no large fish and declining body condition as the fish get larger - are strong evidence of a stunted population. That is, there are more fish than there is food available, and so their growth slows down as they get larger and they are having trouble maintaining or adding to their body weight. 
     Now fast forward to 2011. I don't get to lakes like Meadow Creek every year - it's not necessary. Every few years is fine unless I'm trying to accomplish something specific, as we'll see later. What was different in 2011 compared to 2007, is that now the lake had gone four years without the annual plant of 16,000 1.5" cutthroats that it had recieved through 2007.  Here is the size structure of the brook trout population in 2011:




     Now we've got lots of fish at the 7" mark and not many making it past that. Let's look at the relative weight plot for these fish:




     Average body condition for these brookies in 2011 was only 73, compared with 92 in 2007. For you statheads out there, this difference was highly significant (p< 0.01).  Also, the trend line of body condition as fish get larger now slopes downward more steeply (-0.14 in 2011  vs. -0.08 in 2007).  Stathead that I am, I like to test for significance of different slopes. These two slopes test with a p-value right at 0.10.  Being a management biologist rather than a researcher or academic, that's good enough for me. I actually tend to fixate on a p-value of 0.2 for decision-making purposes. Academics would be aghast, but I'll take 80% odds that I'm right any day, and we're not talking about life-and-death decisions here. Aside from the life and death of a few starving brookies, that is. And actually, if you look at that 2011 plot, there are three or four outliers right at the 230 mm mark that bucked the trend. Without those fish, all these parameters would have been tighter. There's a good chance that those were the cannibals in the sample. 
     Anyway, I digress. The bottom line is that the fish in 2011 were definitely worse off than they were four years earlier. And why was that? Remember that I had pulled the cutthroat plant. In all likelihood those cutthroats were providing a prey supplement that was propping up the larger brookies to a moderate extent. Also, you'll remember that 2011 was an extremely high water year. This probably played a role too, with colder water longer into the summer, and delayed insect activity making food scarce.
     So at this point I'm thinking that I need to try something else. I love tinkering with these small-to-mid-size lakes because you can really effect major change over a fairly short time frame, and it's never been very satisfying to me to simply put them on the catchable rainbow schedule and leave it at that. Put-and-take rainbows, in my mind, are the last and least-creative management option. 
     Enter the tiger trout. For those that aren't familiar with them, tiger trout are the crime-against-nature hybrid of a female brown trout and a male brook trout. Because the fish aren't very closely related genetically (not even in the same genus), you don't get huge success rates when you try to make these fish - something like 15-30% of the eggs get fertilized. So we never have them available in big numbers, but recently our guys in Denver responsible for egg trades and procurement were able to work out a deal with Wyoming, so in the future it looks like our supply of these fish will be more reliable. Apparently Wyoming has a better situation for making tigers - we don't have a captive brood stock of either brown trout or brook trout, which means that to make tigers you have to go out into the wild, collect milt from male brookies that are ripe, and get it to the eggs of female browns from somewhere else in the wild. Getting the timing and logistics of that proposition dialed in is not an easy task, and there are many opportunities for things to not work out. It's far better to have captive broodstocks available of both species, preferably in the same hatchery. 
     Anyway, the reason we want to use tiger trout in some waters is that they are apparently a good predator, and because of their hybrid genetics they're reproductively sterile. So we can have complete control over how many teeth are in a water body. They may be used to try to impact sucker populations (I'm not aware of an example of this actually working - suckers are extremely difficult to control), but more importantly, to thin stunted brook trout populations.
     So, with the help of Chris Crowder down at the Monte Vista hatchery, in 2014 I was able to get my hands on 2,000 tigers for Meadow Creek. They were stocked on July 9, 2014 and averaged 3.7". This was a relatively conservative number of fish (20/acre), for two reasons: 1. we don't have a ton of them available, and 2. you have to be very careful not to overdo it in this situation.
     We surveyed Meadow Creek again on July 7, 2015. So the tigers had been in there almost exactly one year. Below is the graph of the fish that we captured.




     Out of the three sampling occasions, the size structure of the brookies in 2015 was actually the best it's been. There were more fish in the 10" range, but still nothing making it to 12". Below is the relative weight plot. 




     The average relative weight for these brookies in 2015 was 84, so it split the difference between the 2007 and 2011 samples. However, the trend line is the steepest yet with a -0.17 slope. So even though there are more 10" fish which represents a slight improvement in the fishery, they're having the hardest time they've ever had maintaining their body condition when they get to that size - which could be a direct result of the higher number of 10" fish creating density-dependent competition and food scarcity.
     And we captured 20 tigers. This was the main purpose of the 2015 survey: to see what kind of survival and growth we had out of those 2,000 fish. To catch 1% of them with this level of sampling effort was pretty great as far as I was concerned. Their average length was 8.0", with the largest fish at 9.8".  Below are a couple photos. 




     Predatory trout will eat prey that is up to 2/3 of their own body length. So I think our survey came right at the time when these tigers were on the verge of being able to start tearing through some of the smaller brookies. I strongly suspect (maybe I should say "hope") that at least the ones pushing 10" started doing that by the end of the summer. 
     I plan to get back to Meadow Creek again in 2016. As you know I haven't been surveying it every year, but I'm very excited to track the progress of these fish. The goal will be to again get a feel for survival and growth of the tigers, get a sense of whether my stocking rate is right, and look for signs that they are in fact using the brook trout as prey. I don't expect to see improvement in the brook trout fishery quite yet; I think it will take at least a couple years of thinning by the tiger trout to see that. But when we do see that, I hope to see brookies pushing past that 12" growth barrier, and the slope of that body condition trend line should flatten out.
     I have a request in to stock another 2,000 in Meadow Creek this year. It's been approved, so apparently barring unforseen complications, we'll get that second year-class in there this year.
     So Keith, there's a long-winded answer to your question.        






Tuesday, March 1, 2016

Green Mountain timeout, part 2.

So that was the good news. Now the bad news. We've got problems at Green Mountain. They had already started by the time I got here in 2007, with an explosion of the gill lice parasite in the kokanee salmon population. From that time onward, the reliability of the kokanee run took a nosedive and has never recovered. Green Mountain used to produce a good spawning run in the Blue River as well as reliable ice fishing for silver kokes. Those opportunities disappeared after the gill lice showed up.  As far as I can tell, a few folks still get into some fish by snagging during the spawn or ice fishing for silvers, but it's extremely spotty and unpredictable.
       Because they originated in the Pacific, the gill lice that we have infect both kokanee and rainbows (also from the Pacific). They do not infect browns or lake trout. The rainbows at Green Mountain are also heavily infected and have been for years, with no reduction in infection apparent over time. There is no known mechanism of control of gill lice in a water body this size. Except for one. 
     This is an obligate parasite - meaning, it won't survive if it can't find its specific host species, in this case rainbows and kokanee. The only known biological way to reduce prevalence of the parasite is to deprive it of its host. This is one of the three reasons that, for the first time in the history of the reservoir, we are not stocking Green Mountain with any fish in 2016.
     The other problem we've got at Green Mountain is an illegal introduction of northern pike. I received some word-of-mouth reports of pike being caught beginning in '08 or so, but no confirmation with photos or any carcasses. I finally picked one up in my standard gillnet surveys in 2012.  Then I got four in 2013, one more in 2014, and in 2015 I picked up 17. That's not quite as bad as it sounds, because in 2015 I increased my gillnet effort from 24 net sets to 40. So in terms of gillnet hours, pike capture went from 0.01 fish per hour to 0.07 fish per hour. So still a low catch rate indicating a small population, but they were all the same size (22-25 inches), indicating that they are all from the same year class, born in the lake around 2012. 
     When Green Mountain spills, the volume of water going over the spillway can be big. 2015 wasn't a particularly big water year, and it spilled for 15 days at an average of 513 CFS. In 2011, which was a huge water year, it spilled for 27 days at an average of 1,141 CFS. So if pike take off in GM, we've got a huge risk of the lake dumping a lot of them into the Blue and Colorado Rivers. We do a lot of survey work downstream of GM, and we have not seen pike establish themselves at this point. 
     What's so frustrating about this is that whoever takes it upon themselves to spread fish around is probably unaware of the implications of tying these waters to the Endangered Fish Recovery Program. We have a great luxury here at the head of the basin in that we can manage these waters with recreational opportunity as the top priority. This is a luxury that we should never, ever take for granted. If the species that are problematic to the Recovery Program - northern pike, yellow perch, walleye, smallmouth - continue to turn up in these waters, it is probably only a matter of time before it is proven that fish from one or more of these reservoirs are finding their way all the way down to Rifle and causing problems in the recovery area. At that point, managing these fisheries to maximize recreational opportunity immediately becomes the second priority, and that luxury that we've enjoyed all this time disappears indefinitely, possibly permanently. All options are on the table then, including rotenone treatment of large reservoirs and closing large bodies of water to fishing.
     I know I'm preaching to the choir here.  I've communicated this message before many times, and no one who would bucket stock fish would ever take the time to read this. So this is the second reason we're not stocking any fish into Green Mountain this year. We're not going to turn that lake into yet another pike feedlot. We've got plenty of them around, and it's a ridiculously expensive way to manage a fishery. 
     Here's the little bit of good news within this piece of bad news: we're implementing a northern pike angler harvest incentive of $20 at GM. If you catch a pike there, you can take it to Heeney Marina and they'll give you a twenty dollar bill. We have got to get on top of this as quickly as we can, and enlisting the help of anglers is the best way to do it.  So I'm hoping that whatever angler traffic is lost due to the lack of stocking, is replaced by folks going after pike.
     The third reason we're not stocking fish is that we've got some production issues in the hatchery system. I rely heavily on our Glenwood Springs hatchery for a lot of my plants, and last year Glenwood came down with a disease called Bacterial Kidney Disease. It's a long story, but the point is that we can't stock fish that have been exposed to this disease, and Glenwood had to be completely depopulated and disinfected last year. So there is a general shortage of fish on the west slope as the other hatcheries try to make up for the fish that Glenwood will not have in 2016. One of the results is that I have a smaller allocation of rainbows than normal. If I cut one major reservoir (Green Mountain) out of my schedule, I am able to maintain catchable numbers at the other large waters in my area.
     One benefit taking a timeout from stocking is that this will serve as a large-scale lake trout management experiment. A couple messages that I get on a regular basis from the lake trout angling community are an almost universal lack of support for kokanee in Colorado, and and the assertion that we can have perfectly good trophy lake trout fisheries based on a sucker prey base alone. These two positions are totally misguided - and quite possibly tragic for the future of trophy lakers in this state - but we've seen over and over again that it doesn't matter how many times we try to communicate this.  Here is our golden opportunity to test these theories.  The proof will be in the pudding, and we'll see how this trophy lake trout fishery fares when both kokanee and rainbows disappear from the prey base.


Friday, February 5, 2016

Green Mountain timeout, part 1.

     I'll start with the good news about Green Mountain before getting into the bad news.  Last June, I spent four days out there running gillnet surveys.  We set 40 gillnets in random locations all over the lake, for six hours apiece. Over the course of that survey we handled 86 lake trout. These lakers looked the best that I have seen them at Green Mountain over the past decade. Below is the size distribution of the lake trout that we caught.
     Out of all the times I have run gillnet sampling on Green Mountain, 2015 gave us the highest catch rate of fish greater than 24", and the average size of all the lake trout caught was the largest. In the four years prior to 2015, when running these surveys, I caught an average of one lake trout over 24" for every 23 hours of gillnet soak time (we have 8 gillnets fishing simultaneously, so each day we're out there we get 48 hours of gillnet soak time). In 2015, I caught one for every 10 hours. 
     Also, when we look at relative weights of lake trout, fish over 24" at Green Mountain are in consistently better condition than fish under 24". Below is the relative weight plot from 2015 to illustrate that. Body condition for fish less than 24" averaged 72.1, while fish larger than 24" averaged 95.7. In fact, we have seen this relationship - increasing body condition as the fish get larger - for all of the past 5 years there. However, the difference between the two groups in 2015 - 23.6 points - is the largest gap that I have observed there. Another way to put it would be to say that the trend line on the graph below has the steepest slope out of any of the years that I have surveyed GM.
     All this information means a lot more when you compare it with other lakes. At Granby, fish over 24" have consistently POORER body condition than fish under 24". Below is the relative weight plot for all the Granby lake trout that I have weighed (899 fish) from 2011-2015. 
     Across all those years, relative weights for the Granby fish less than 24" was 82.7, and for fish larger than 24" was 77.1. I have searched our database and run this calculation for many of the lake trout waters across the state including Jefferson, Taylor, Ruedi, Twin, Turquoise, Blue Mesa, and Williams Fork (of course). The fact is, Granby is the ONLY lake trout fishery in the state that sees a consistently lower (and statistically significant if that matters to you) body condition in large fish than in small fish. 
       Here's how it works out in pounds of fish. Based on these length-weight relationships, the average 30" fish at Green Mountain weighs 10 lbs., while a Granby fish of the same size weighs 8.6 lbs. A 36" fish at Green Mountain averages 18.6 lbs., while a Granby fish of that size averages 15.1. And if you take it up to 40", a Green Mountain fish will average 26.7 lbs., while the Granby fish weighs in at 21. The result of poor body condition in these large fish is extremely slow-or zero- growth in length over time, and less egg production. The population seems to become "decadent" in a way, like an overgrown forest that has suffered from a lack of disturbance and renewal. We've all seen what that results in. 
     You may remember that we changed the harvest regulation at Green Mountain Reservoir beginning in January of 2011. We increased the bag limit of lake trout to 8 fish of any size, separate from the bag limit of other trout. There is no size restriction of any kind on the 8 fish bag.  In the years since that regulation change, I regularly ask the game wardens as well as other folks around Green Mountain if people are taking advantage of the 8-fish bag on lake trout and harvesting limits of them. The answer has always been that they absolutely are. As far as we can tell, anglers have been taking full advantage of the increased bag limit there since we enacted it.
     I'll take this opportunity to point out a statement that I wrote in the 2010 issue paper which proposed to increase the lake trout limit:

"This population should easily sustain increased harvest rates, and may exhibit increased quality as a result of the thinning effect that increased harvest may produce."


     I'm not making the claim that my recent data at Green Mountain is unequivocal proof of the above statement, and that my data isn't subject to any of the possible pitfalls of such a data set. However, I will say that this data gives me good confidence that the probability of the above statement being correct is far higher than the probability of it being incorrect.
     This is the stuff that a fisheries biologist bases his/her decisions on, in combination with other sources of information such as public input.  One of the main purposes of this blog is to try to fully expose the reasoning that goes into my - and any biologist's - fishery management decisions.  Even though it goes on in my head and across countless spreadsheets and databases, it's a public process. It's what you pay me to do when you buy a fishing license. And  for that, I have to say a heartfelt "thanks" because I love my job very, very much. Entering my tenth year here, I still have to pinch myself nearly on a daily basis and make sure I'm not dreaming. I consider myself to be extremely lucky to have this job.
     Anyway, I digress.  What I was getting at is that I think there is a little bit of an information gap in the world when it comes to making the details of this stuff accessible to the public. It mainly appears in the pages of specialized scientific fisheries journals that people typically don't have easy access to. I believe one reason that there's not that much of it out there is because as a group, we biologists tend to assume that there is not general interest among the public in this level of detail. But I think that there is a sector of the angling public that is interested in as much detail as we're willing to take the time to give. It may not be the majority of license buyers, but a decent slice of them, I think.  That's the group of anglers that this blog aims to serve. There will always be a majority of people who have no interest in the fact that there is a lot of effort, consideration, and decision-making behind each and every fish that they find on the end of their line.  I'm not going to reach those people no matter what, and that's fine.
     There's a selfish motivation to do this also - it makes me a better biologist to work this stuff out in written form. Makes me consider things more thoroughly and carefully.
     I'm going to hold off on the bad news about Green Mountain until my next post.

Sunday, January 24, 2016

2015 favorite fishing moments

     Greetings all, and welcome to 2016. One of my goals this year is to revive this blog. I'm committing to posting once a month. I started out with weekly posts, then slipped to every two weeks, and now I'm going to try monthly posts. I should be able to sustain that. 
      The main reason I lost motivation with the blog is that in 2014 I held a couple of public meetings in which I was attacked and publicly crucified, and that was followed by this article in the Denver Post a year ago, which was a very thinly veiled personal attack aimed squarely at me.  From my perspective, it appeared that the ultimate reward for making an effort to communicate with those that I serve was to be publicly called out as a liar on the pages of the biggest printed media outlet in this state. I've got to be honest -- that was a devastating blow to take.  
     In addition to being accused of lying, what might have been even more brutal was to be accused of not being an angler.  This is a common tactic used by some people when there are no factual arguments to be made, and it's not just directed at me.  There have been many instances around the state in which my coworkers have been branded as "non-anglers".  The purpose of such claims is to cast us as some kind of entity which is "apart" and does not act in the best interest of recreational anglers because we apparently have no idea what recreational anglers want.  These claims have no basis in any kind of factual information.  It is simply impossible to land in this job without being an avid lifelong angler.  I don't even know why someone would want this job if that wasn't the case. It's not particularly easy, and it doesn't pay as well as countless other professional pursuits. However, if fish are the most fascinating creatures in the world to you and you've always been enthralled with their pursuit, it's the best job you could possibly have.
     So enough rambling. People who desire to be personal enemies to me have clearly identified themselves, and it's time to move on. But if I remain silent, I allow them the last word in defining who I am to the world at large.  I realize that these people are a "vocal minority" and many others have reached out to me to express that they find this blog to be valuable. So it's for these folks that I choose to continue with it.  So on that note, here are some of my favorite angling memories from 2015.

     In June, our family's schedules resulted in my youngest son Ben and I having the house to ourselves for a few days. I decided to make it a fishing odyssey.  One evening we were up at Meadow Creek Reservoir to try to catch the evening bite. I'll never forget the sound of Ben's voice as he exclaimed, "what the heck?!?!" as he hooked a sizeable brookie on his kastmaster. He was sure he was snagged for a second, until he realized it was moving. He proceeded to outfish me that evening, for the first time ever.
     The next day, we headed out on an overnight backpack. We take family backpack trips every summmer, but this was the first time that just Ben and I had set out. We headed for a promising lake in hopes of dining on brookies cooked over the fire. It was early in the summer, and the trail was not easy, with downed trees, some snowbanks, and lots of mud in the shady areas. However, we were rewarded with hungry, aggressive fish and we did enjoy that brookie supper. In the morning Ben was excited to get back out there and catch a few more before we packed up. Once again, he caught more fish than me on the trip.

                                        

     In August, we took the best family backpack trip we've ever had. It was one of the last weekends of summer and in the scramble leading up to the school year there were many things on the to-do list. Instead, we scrapped it all and hit the trail for a couple of nights. It was one of the most beautiful hikes we've done. On the second day we headed for one of my all-time favorite lakes, off trail and packed with aggressive cutthroats. This lake doesn't get stocked, and sustains a fantastic fishery solely through natural reproduction. The boys experienced their first-ever "double," pictured below, where they both had fish on at the same time. I won't forget that moment.  




     My sons are finally at the age where they've got some good stamina and enough physical ability that they can now get deeper into the woods than they've gone before, and I'm very excited about our adventures in the coming years.
     
     In September, I took a day and bushwacked in to my favorite low-elevation rugged canyon creek. The fishing is fantastic for a mix of browns and wild rainbows ranging from 8 to 14 inches. Ironically, on this particular day the rainbows were taking nymphs and the browns were all about the dries. It never takes long to get into "the zone" on this creek, and for a few hours the whole rest of the world just melts away. I don't seem to need days like that as often as I used to, but I'm always amazed at how much my batteries recharge when I take the time to do it.

     Over Christmas break, despite the brutal cold we dragged my Dad out and we did a little ice fishing on Willow Creek Reservoir. Although we grew up fishing a lot, southern Kansas never offered much in the way of ice fishing opportunities, and it was my dad's first time ever on the ice. We barely lasted an hour out there because the wind came up, but at least we got out there, on a day that seemed too cold to do anything.



     For me, the enjoyment of fishing has always been about the place just as much as it is about the fish. And increasingly, in the past few years, it's been about appreciating those places with my sons. So with luck I'm looking forward to a 2016 filled with more such memories, and here's hoping that everyone is able to enjoy such special times. 
     I'll get back to talking about fish populations with my next post. I would like to get some feedback on what topics folks would like to read about in 2016. So please don't hesitate to make comments here, or drop me an email at jon.ewert@state.co.us. Thanks!

     

Monday, March 2, 2015

Still alive . . .

     Howdy folks, sorry for the extended break. Hope 2015 finds you well. I still intend to keep this going - just probably not at a weekly pace. For now, check out my updated report on the Colorado River at Parshall, posted here:

http://cpw.state.co.us/Documents/Fishing/FisheryWaterSummaries/Summaries/Northwest/ColoradoRivernearParshall.pdf

     So take a look at that. Hopefully it will stimulate some discussion. If you have any thoughts/comments/questions, either post them here or shoot me an email at jon.ewert@state.co.us. Hope to hear from you.

Monday, March 3, 2014

State of the Fish

     I have scheduled my annual "State of the Fish" meetings for this month. On Tuesday the 18th we'll be at the Frisco library, in the Buffalo Mountain Room, at 6:30. On Wednesday the 19th we'll be at the Granby public library, also at 6:30. These meetings will follow an open format, and we'll talk about whatever waters folks are interested in talking about. There are a few regulation items I'd like to discuss, if anyone in attendance is interested:

  • Grand Lake lake trout
  • Granby lake trout
  • Dillon char
     I hope to see lots of folks come out for these. I'll stick around for as long as anyone wants to hang out and discuss things.

     Aside from that I'm having trouble coming up with topics for posting right now. I need some ideas from you folks. 

     February was a ridiculously warm month, and these reservoirs are not going to make it to April 1 with the ice on if this weather keeps up. Things are changing fast. It's looking like the earliest ice-out I've seen since I've been around here. I wish that wasn't the case because I'm not going to be ready for it before April 1.

     I'm headed up to Laramie for our annual American Fisheries Society meeting/conference, which is always a great experience, with lots of information being exchanged and new ideas being born.