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.

41 comments:

  1. Jon, glad to see you blogging again and I appreciate the work you do.

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  2. I can tell you that I, for one, will take as much information as you are willing to give. I actually do look up scientific studies and read them, so having you break them down into an easier read is very nice.

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  3. Good write up!! Did you read that book on pike i gave you at silverthorne meeting a few yrs ago?

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    1. I did, yes. It's a great reference to have on the shelf and thanks again. If you're new to this blog, One "rule" that I have is that in order for me to interact with folks, they need to be using their real name. Thanks for commenting, and I hope you stick around.

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  4. Great information, I have been thinking about the bad news and I think it is about the Kokanee.

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    1. No problem. Thank you for the time you spend writing up the information and sharing the scientific work and the thinking that goes into the decisions that power our fishing adventures.
      Jennifer

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  5. Thanks again Jon, you are doing a great job. If only we could get a a slot protection for the big lakers at GM, and slot for big browns at Dillon. I would be just the happiest hwy 9 corridor angler in the valley!! The only trophy fish protection wev'e got is the slot for pike at Willy's. This region needs more big fish conservation. Thanks again. Randy Ford.

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  6. Randy, thanks for the positive feedback. The only thing that we don't agree on is the need for the slot protections that you ask for. In fact, every piece of information that I've given in the post above is strong evidence that there is no need for that, and that the fishery is thriving without it. We don't apply slot protections just so people can feel good - the data has to show us that we need it. This data is showing us the exact opposite.

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  7. Jon, Don't you want less suckers and less small lakers? A big laker at green mountian is a sucker, and subctchable laker eating machine. Those big lakers are the best thing the fishery has going for it and your graphs show there are not that many in there. I think it will soon be shown that a 28 to 36 inch laker is the heroe of the fishery. To me it seems so obvious that protecting the big lakers would result in less suckers, and less subcatchable lake trout. Every big laker kiled results in more suckers and more snall lakers. This is something i observed after Ice fishing at green mountain 72 times during the winter of 2012/2013 while taking a sabbatical from my construction business. I caught 14 lakers in the 28 to 36 inch slot. I never saw one rainbow or kokanne tail sticking out of there jaws, but i had caught them spitting out suckers, and caught them with laker tails sticking out of their jaws. I don't see anything in your graphs that supports your statement that a slot is not needed. Thanks, Randy Ford

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    1. Randy, after five years of the current regulation, catch rates for lake trout >24" in the gillnets were the highest they've ever been, suggesting that their density is as high or higher than it's ever been, and their body condition is also the best. What more could you want? The data shows a thriving fishery.

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    2. Jon, Its fantastic that GM is a thriving fishery and one of the reasons I have love to fish there. And once again I will thank you for all your efforts and transparency with us.
      I don't understand the reasoning behind not protecting the trophies only because it is shown that density is increasing. This was the same reason you gave me for not protecting the brown trout in Dillon. After taking years a to finally see improvements it seems logical to protect the good results of your work. Both fisheries need those bigger fish to ensure good fishing in the future, and at both fisheries the bigger fish are old, and take a decade or more to replace. All across the state there are protective size restrictions on desired sport fish except ours. Look at the limits on walleye and bass along the front range, or look at the slot regulations at places like Taylor, Twin, Turquise, and now Blue mesa with a one over 32". Why does Granby, Williams Fork, and Green mountian, and Dillon(aside from the Char) have to be the only fisheries that don't have protective size limits? Youv'e got protection on grand lake for lakers, but its sees the least amount of laker fisherman than just about any laker fishery in the sate. Why protect the lake trout there and not the other fisheries that us guys in the public really care about?

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    3. I mentioned willies having no protection and want to correct myself on that with its 1 over 30", At willies, its seems such a fishery should have a slot just like all the other laker fisheries in the state.

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    4. Yep,although you can't concur from one years netting results that the densities of Large fish are increasing.
      The fact is that a Lake Trout and Brown fishery is all we have left at GM due to the Gill lice and hatchery problems.
      The Kokanee have been decimated by the gill lice for many years now while the Larger sized Lake trout are in great shape.
      The last meeting at Granby was full of Anglers including locals that have been avid anglers involved in the issues decades longer than Jon's been here as a Biologist.
      Jon wanted to take the Slot protection off Grand lake and the room was unanimously against that and the slot remains on GL.
      We also ALL, "reluctantly" Jon included agreed with overwhelming support that if Granby's limit went from 4 to 8 they would add a 1 over 22" limit on larger fish. The outcome of the meeting may not have gone as Jon wanted it to and unfortunately this year the annual state of the fish meeting in Granby was cancelled and was only done in Silverthorne.
      If you did a survey of avid Anglers on Granby and Green mtn there would be overwhelming support for a one fish limit on Large Lake trout.
      It's past time that Jon and the DPW quit downgrading and failing to support our great Lake Trout Fisheries.

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    5. Randy, five years ago when I opened up the limits at both Green Mountain and Williams Fork, I looked at it as an experiment - 1 over 30 at WF and no size restriction at GM. That experiment is still going. These things take a lot of years to play out. But the hypothesis that I am testing is that there won't be any detectable difference between the two. How often do you think someone out there keeps more than 1 fish over 30"? I think it happens almost never. I don't think it would change angler behavior at all. I think that you guys place a far higher value on the biological effect of harvest regulations than they really have. 99.9% of the anglers out there who are skilled enough to catch more than one fish over 30" never keep fish that big anyway. The data appears to be telling us that higher harvest rates of small fish at GM are allowing more fish to "graduate" into the >24" size class. And that's a great thing. But one of the main things we know about lake trout in Colorado is that it is very easy for them to outgrow their prey base in a particular lake because our lakes are small and have simple food webs. So if we accumulate too many fish >24", they will become thin and stop growing, like at Granby. So if there is someone out there who keeps a few large fish each season, that doesn't hurt anything at all. They're just thinning the carrots in the row so the others can be that much healthier. You seem to be asking for a slot limit based on emotional reasons, instead of based on what the data is telling us.
      As far as CPW not supporting lake trout fisheries, that's simply exactly the opposite of the truth. The management of the fisheries in these lake trout reservoirs revolves entirely around how we can maintain a prey base that is fiscally responsible and biologically sustainable over the long term to produce trophy lake trout at a steady rate. The amount of effort we put in to try to accomplish that goal is massive, so I have no idea how that equates to a lack of support for lake trout. I know that it doesn't matter how I say that, or how many times. People choose to believe what they want to believe.

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    6. How do you figure you are getting more recruitment in larger fish?
      Your graph shows a gap of hardly any fish from 20"-24". You make a BIG deal of the better weight per length of the larger fish compared to Granby but failed to mention that Granby's under 24" fish are over 10 points heavier than same length GM fish. Since the under 24" fish are the majority of the biomass in both lakes it's easy to come to the conclusion that when you look at total biomass, Granby's Lake Trout are in better condition.

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    7. [Quote Jon]99.9% of the anglers out there who are skilled enough to catch more than one fish over 30" never keep fish that big anyway.[end quote}
      Why make an off hand exaggerated remark with absolutely no factual basis.

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    8. Thousands of angler contacts by wildlife officers and creel clerks over the years. Lots of factual basis. I know what comes next, "I never get checked." Don't go to the trouble.

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    10. here's a one in a thousand photo

      http://imageshack.com/a/img921/202/Ed6yQy.jpg

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    11. Yes, that's exactly what that picture is, and that's the very reason you have flashed that one picture around for years. Let's base our management off of one single picture that's been passed around among who knows how many people. Not to mention it's from Williams Fork, where we have a 1 over 30 reg that wasn't in place when this picture was taken.

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    13. Good points Jon.
      The guy in the picture stays in a camper for extended time at WF and is known to keep lot's of big fish, I didn't realize the picture was from prior to the new reg and found out after sending Crosby out to talk to him. The point is it only takes a few like this to damage a trophy fishery. lots of pictures of big fish killed at the bait store in Heeney, she told me she see's quite a few large ones kept. The local game warden there encourages anglers to help them reduce Lake Trout numbers with no regard to large fish. Just like gold medal rivers get special regs for the best waters, GM is a gold medal water when it comes to large lake trout and deserves the gold medal designation that the special reg supports.

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    14. Jon thank you for implementing the 1 over 30" limit at wf, although we would like to see it in the lower 20's to stay in line with where the numbers drop to the fewest it does give wf a trophy designation. Doing the same at gm would keep the regs more consistent as both lakes have many similarities and would give gm the trophy (gold medal) designation it deserves. Even Blue Mesa has s one fish limit on large Lake trout.

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    15. How do you figure you are getting more recruitment in larger fish?

      So strange, it's kind of like you didn't read the article at all. Well, from 2011 to 2014, our catch rate of fish >24" averaged 0.26 fish per net set, or put another way, one large fish for every 23 hours of gillnet soak time. In 2015, our catch rate for fish > 24" was 0.60, or one fish for every 10 hours of soak time. Either way you look at it, our catch rate more than doubled. Given this information, what conclusion might this suggest to a reasonable person? Here are the possibilities: the number of fish >24" is going down; the number of fish >24" is going up; the number of fish >24" is exactly the same; or the data doesn't mean anything at all. I'm not in the habit of spending my time going out collecting information and then saying that it doesn't mean anything, so for me, the last possibility is ruled out. Out of the three possibilities that are left, I'm going with the odds.

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    16. 1 year of netting results does not give you statistics.
      You said yourself it takes over 10 years to see a trend in the netting data.
      Your graphs generally always show a gap with very few fish from 19"-24" which equals slow recruitment.
      The lake is extremely overrun with cigar shaped stunted small lakers and suckers. The few large fish make a positive impact on both these problems. You should be praising and protecting these few worker bees that are helping remove overpopulated small fish including the Gill lice host's
      Some years at Granby you catch quite a few large fish in your nets others hardly any.

      After fishing GM last week I'm very thankful I live on Granby.

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    17. Yes I read the article, how else would I see the obvious bias in the fact that you make a big deal in body weight of GM fish going up when the scale starts at a pitiful 68 on the small fish there while Granbys small fish scale starts at 88.
      Thats 20 points better quality fish at Granby on over 90% of the fish comparably.

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  8. n comparing GM to Granby its important to note that you are dealing with 2 totally different aquatic environments.
    Granby's under 24" fish are over 10 points heavier than GM"s similar length fish due to Mysis shrimp that GM does not have.
    Although GM's over 24"ers are heavier they are much fewer.
    Granby is ultimately the better lake trout fishery.
    The under 24" fish comprise the largest portion of the catch at both lakes but Granbys are much healthier and better eaters.
    If you want lower quality eater size fish and a much smaller chance of a large fish that will be heavier than average go to GM.
    If you want better quality eater size fish and a much greater chance at a large fish that will most likely be lighter than a similar length at GM go to Granby.
    ________

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  10. I have been reading the discussion on the Lakers, and find it to be very educational on how we all see our fisheries. I would like to hear a little more on what the future of the Kokanee in GM. Do the gill lice die out so that in time Kokanee can flourish?

    Back to the GM Lakers, with the lack of Kokanee, what is their primary food source, Rainbows and Browns?

    Thanks for your thoughts and time.
    Jennifer Mickelsen

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    1. Jennifer, the idea is that we can knock the gill lice back by depriving them of their host. We have not tried it on a scale this large, so only time will tell.
      We will hopefully force the large lakers to feed more on suckers at Green Mountain and reduce their numbers. They do not do a good job of controlling sucker numbers in a lake as long as there are kokanee and rainbows to eat.
      Small lake trout do not ever eat algae. They eat zooplankton when they're really small, and then aquatic invertebrates such as midges and other various insect larvae.

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    4. In 3 years of helping you net Granby I never saw you check a stomach on any of the fish that didn't make it.
      As an angler interested in the biology of the lake I check stomachs of everyone I keep.
      I'm curious if you have ever checked stomachs on the small stunted lakers at gm.
      They suspend in the water column and their stomachs have green goo in them, a sharp contrast to the Healthy Granby lakers full of Mysis.

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  11. Jennifer, the largest biomass of fish in GM are Suckers, the second largest is small sized Lake trout that feed on Algae.
    Both of these species are common diets of large Lake Trout.

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  12. Jon,

    At green mountain i don't understand your theory of "thinning the carrots in the row so the others can be that much healthier" It has an enormous amount of prey base with well over 70 percent suckers. and high zooplankton levels combined with tons of small lakers. Your data from your nets clearly shows that the ratio of Lake trout that are over 32" compared to suckers and lakers under 15 inches is insane.
    The reality is that there are VERY FEW lakers in green mountain that are big. . Right now your data shows the amount of big fish compared to small fish in GM is way out of balance. It only makes sense to do what you can to keep those bigger fish in there. Changing the regs to a slot is the easiest thing you can do. All the data and info shows that the fishery needs more big fish.
    Over the years and recently I have seen many trophy fish get killed by people who luck into them. Your a fisherman and im sure you know in fishing alot of the times you would rather be lucky than good. right place, right time is everything. every once in a while there is that magic moment like one out of 30 outings, 20 + year old fish get stupid and people who do not know better luck into big fish them. People luck into 3 or 4 big fish with in a half hour. I have seen big lakers get pulled into boats and beat on the head more than you think. Ive seen 6 lake trout over 30 inches on the ice at Green Mountain between two guys. Which brings me to the tragedies to the brown troutat Dillon that are just now starting to gain momentum.

    At Dillon I have seen stringers of these old 18" browns that finally made over the 15 inch hammer handle hump. I think you have done a heck of a job at Dillon with your good management of stocking fingerling rainbow trout, catch able trout both in spring and and fall and fingerling arctic char. We have seen the beginning of a nice rebound. But more than you think, The fruits of your labor are leaving out the boat ramp and banks on stringers and those will take many years to replace. And maybe worse then angler harvest. This fall we had a whole year class of those big browns that were 20 to 30 inches die off due to a massive infection of saprolegnia fungus. I witnessed over 60 dead browns between 20 and 30 inches and over.
    In the spring up to about the second week of june, I have seen more stringers than you might think of these big browns during that 5 or 6 day hot period leave the lake on the boat ramps and banks. These browns are a size that we have not seen in Dillon for many years and most these anglers do not know better. You have made the fishery rebound and finally those browns that are something special are getting bigger. Please put protection on them for a while during this beginning of a rebound. Trust me, the large brown trout in Dillon will never overpopulate and comprise the Arctic Char and Kokanne. Please believe me on that. Im not asking for much. At both Dillon and Green Mountain I'm asking you to do something inexpensive and easy to promote conservation and appreciate the rebound at Dillon, and protect something that is wild and special
    At GM its clear there is an imbalance, Im just asking you to once again to do something simple and easy and good for the future.

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    1. Randy, thanks for your input, I greatly appreciate it. I don't want to get too far into Dillon here because this post wasn't about Dillon. But I will say that the saprolegnia fungus that you see on big browns is on them because they are dying of old age and they have no immune system left. It's the same thing as dying kokanee. The fungus isn't killing them, it's infecting them because they're dying and not fighting it off. Big, old browns die during spawn season.
      Sometimes I get the impression that anglers think that if only we have protective regs on everything, then big, old fish will live forever and just keep growing indefinitely. That's simply not the case, especially with browns. They die of old age. Happens every spawn season. We've done lots of aging studies on browns in rivers all over the state, and aged thousands of fish. It is rare to find browns older than 5 years old. A few fish turn up that are 7 or 8, but those are rare. In a lake, you may have fish up to 10 or 12, but that's going to be about it. So that's your window of opportunity to grow a fish to a large size. If there is a lot of feed for them, they'll get big. If there's not, they'll just stall out around 15".
      I see people saying so often that it takes many years to replace a big fish - people love to throw out 30 years or whatever. It's just not true. That would be the same thing as going to a high school graduation, watching the kids graduate, and saying, "It's sad to see them go - we won't see another class graduate for another 18 years."

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    2. A big difference in the life span of a Brown to a Lake trout so please don't generalize. at Granby we have proven that it takes many years to replace a big fish and that they do live to be over 30 years.
      Multiple recaptures even on fish tagged at 16"s 15 years later were only 21" to 23".
      Don't forget that we helped Jake tag over 5000 fish and study recaptures.

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    3. I see people saying so often that it takes many years to replace a big fish - people love to throw out 30 years or whatever. It's just not true. That would be the same thing as going to a high school graduation, watching the kids graduate, and saying, "It's sad to see them go - we won't see another class graduate for another 18 years."

      So prior to Graduation they get picked off with an 8 open limit so very few graduate in the first place, better keep studying those graphs.

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  15. Jon, your high school graduation analogy is something I don't understand. Luckily at Dillon you are giving those brows something so they can graduate, before you started giving you hardle any graduates, thanks to your giving we are seeing more and more. Now that theu have finally got the diploma why allow them to get whacked? Using that anology on green mountain it makes even less sence to me. Your graphs show that by far most the fish in GM do not graduate, they stay in high school. You have very few fish that have made it to college, got jobs and became a productive members of the population. When there so few of them, why have bag limits that allow them to be killed by the numbers? The fishery is extremely out of balance with to many grade schoolers and not enough graduated productive members. A population needs graduates, and GM doesn't have many at all, in this case your anology doesn't hold water. PLEASE consider at least some sort of size restrictions to your 8 fish bag limit. You can't manage a fishery with all taking and no giving and expect any good results.No more fgiving of bows and kokes, and the most extereme bag limits to take. Your doing nothing at GM but taking. Somewhere, and somehow, you have to give. Keeping those bigger fish in there is the easiest and least expensive way you have to at leasst give something to the fishery. Your seeing great success at Dillon due to your giving with lots of stocking of fish, and extremely protective bag limits on Char.
    Now that you have taking kokes and bows away from Green Mountain, Please consider giving something.

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