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Posts: 154
Location: Appleton, WI | Article:
http://www.pnas.org/cgi/content/abstract/0708159105v1?maxtoshow=&HI...
The authors use trout, but one of their key points is that since fast growth rates are associated with what they call a bold genotype (aggressive fish). These fish can be removed from the population very quickly from fishing pressure because they will hit the minimum size for keeping more quickly than more passive fish. This will remove these fish from passing the aggressive nature on during spawning. |
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Posts: 32886
Location: Rhinelander, Wisconsin | Assuming, naturally, they have not yet done so in previous spawning attempts, and assuming that the fish are exposed to angling pressure that is exactly equal to the population dynamic discussed, and assuming CPR at more than 95% is not the case.. |
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Posts: 8780
| Delayed mortality probably takes a greater percentage of those fish which are caught than those which are not. But then the more agressive fish are probably more agressive in their spawning behavior, which means...
I think it means lots of muskie anglers really need to go fishing about now, myself included! |
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| sworrall - 2/26/2008 12:04 PM
"Assuming, naturally, they have not yet done so in previous spawning attempts"
This comment is very bad logic and based on science from a 100 years ago. The reality is what should occur naturally is the biggest aggressive fish get to pass on their genes for their entire lives or they reach a point where they can no longer breed. The small fish are then not able to breed or get eaten. What we have today is that small fish get to pass on their genes for their entire lives because they are protected by size limits. The smaller the waterbody and greater the fishing pressure the faster this occurs.
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Posts: 32886
Location: Rhinelander, Wisconsin | The 'accelerated evolution' debate again.
What if the ENTIRE adult population is for all intents and purposes 'protected' to the large degree as it would be in a system with say...a 54" limit? How about 48"? OK, even 40" because as I said before 95% or more of the muskies caught (all sizes) are released? Are you telling me that the smaller fish are smaller because of genetics that will pass on and create a 'small muskie' gene pool with a 40" limit? 45" limit? Of course, now we are back to 'it depends on the water'.
Sure, this argument could be used to try for a larger size limit, but it's the wrong approach for a number of reasons. this argument could also be used to try to implement a slot limit, but because of social pressure that slows or nearly stops harvest of slot sized muskies, that too may not be effective.
'Size selection represents an indirect mechanism of selection against rapid growth rate, because individual fish may be large because of rapid growth or because of slow growth but old age.'
May be either, and in the case of, say, Green Bay Muskies, it isn't just 'rapid growth genetics' that makes the fish large. Muskies were planted there since 1983, that's now 25 years. A DNR report says the fish grow faster there than in 8 other sampled waters in MN and WI, so does that mean the Green Bay fish are 'more aggressive'?
Rapid growth rate is not, according to the top Muskie management folks and scientists, necessarily a formula for creating a trophy muskie population. Comparative slow growth and old age at low density, good water chemistry, and good forage produces the big girls. In the case of Muskies, by the time a fish reaches 50" that fish has spawned multiple times and is already in it's teens somewhere, hardly a young fish, but if harvest is allowed at 34", a fish from the Bay could be kept two years before spawning the first time. So which is worse, a 34" limit....or a 54" limit that allows ONLY the largest fish to be harvested?
Fast growth early in a fish's life doesn't always equate to trophy size. In fact, the opposite can be true. There are many waters in the US where the muskies grow very quickly and die quite young ( Like Cave Run in Kentucky), and very large fish are rare as a result. Since most of these systems are 100% stocked 'put and take', accelerated evolution isn't a likely scenario.
'This comment is very bad logic and based on science from a 100 years ago. The reality is what should occur naturally is the biggest aggressive fish get to pass on their genes for their entire lives or they reach a point where they can no longer breed. The small fish are then not able to breed or get eaten.'
What would eat the 'small gene' muskies, and when? How would a Muskie know that a fish that can't reach 55" is a 'small' growth fish and select that fish as a meal while it's still small enough? Wouldn't even 'small growth' muskies be too large very quickly to be a preferred or even semi-opportunistic meal for a 'larger' muskie? Would not a 'small growth' muskie be able to eat a fast growth muskie if the year classes are seperated by enough time? What if while 14" potential 58" fish fall prey regularly, and how would anyone know? Why wouldn't a 'small' muskie not be able to spawn? The larger fish wouldn't allow it? How? Successful spawning takes place with muskies at a few years old. How does any large fish stop a 37" 7 year old female from reproducing? How does angling pressure select for that fish to be, or not to be, a potential future trophy?
I'm suggesting the model in the experiment posted doesn't apply well to the real world C&R muskie fisheries today, 100 year old science aside. |
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| Steve
I think there are a couple of different things going on here which are sort of getting jumbled up in little details.
One point seems to be that allowing the removal of the genes of fast-growing aggressive fish (through angler harvest) will eventually lead to a population of fish whose genetics make them less inclined to aggressively bite. This theory is supported by research done on other fish.
The other point seems to be that harvesting the largest individuals will eventually lead to a population of fish whose genetics make them less inclined to reach a some maximum theoretical size (limited, of course, to the characteristics of the body of water they inhabit, as you point out). Like the aforementioned, this theory is also supported by research done on other fish.
Your point about fast-growth vs. reaching some theoretical maximum potential size is well-taken and probably relevant to muskies (i.e., fast-growth does not equal maximum potential size). However, the effect of a global 95% musky release rate is not, in my mind, relevant since the 5% that are harvested are probably skewed towards the higher end size range of a musky population. Would you agree?
BTW, I think delayed mortality is a non-issue since, presumably, the mortality rate would follow normal distribution patterns and, therefore, should not unduly influence any specific size range of musky caught (unless CPR is harder on larger individuals in a musky population).
To me, the most important questions in play here are whether: 1) clipping-off the largest individuals in a musky population (via harvest) will adversely impact the genetics of the overall population over time; and, 2) whether harvesting of muskies that are aggressive 'biters' will adversely impact the genetics of the overall population over time by leaving non-aggressive 'non-biters' to carry-on their genetics. Some research suggests that the answer to both questions is 'yes'. From a layman's perspective, this is a compelling answer and one I think worthy of more study.
Another Guest |
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Posts: 32886
Location: Rhinelander, Wisconsin | 'One point seems to be that allowing the removal of the genes of fast-growing aggressive fish (through angler harvest) will eventually lead to a population of fish whose genetics make them less inclined to aggressively bite. This theory is supported by research done on other fish.'
Do the research on an actual waterbody applied to esox and I'd be inclined to look more seriously at trying to apply ithere. The idea is not well supported in practice, obviously, or fishing would stink in waters where this should be happening. Is the 'fast growing' fish going to reach harvest size as any faster than a slow growing fish if the limit is 48" and the water is capable of putting out big fish? Maybe not...fast growth in some Muskies in the North is from what I have read through the first few years within any strain, and long term different stains seem to hit a reasonable equilibrium on potential.
If indeed fast growing fish are susceptible to this syndrome, we may not want introduction or restocking of those fish; is that not also a valid argument based on the above premise?
I don't know of any example to look to, do you? Bass, walleye, pike, crappies, etc...seems like if people CPR them they get big and bite as readily as anywhere even after a waterbody has been hit pretty hard by harvest of the larger fish. I watch that cycle here in the Oneida county area repeat over and over on panfish waters and even some muskie waters.
Any stocking blows the whole idea out of the water.
'To me, the most important questions in play here are whether: 1) clipping-off the largest individuals in a musky population (via harvest) will adversely impact the genetics of the overall population over time'
I'd ask how that would effect the genetics over time. This was also a concept introduced to indicate the new 54" requested limit on Bay of Green Bay is a BAD idea...how could this concept push both ways?
When this was floated as a concept a couple years back I spoke with a few folks in the know and was assured that it's not a big issue in the world of Muskie management for many reasons. I did talk to a few folks who supported the possibility that the concept could apply to populations heavily fished and totally reliant upon NR, as in commercial fishing in salt water.
We are not talking about harvesting the 'aggressive segment' of an entire year class as they reach legal size as the premise suggests, are we? Additionally, if a muskie is that 'aggressive' that segment of the population might have been caught multiple times, perhaps kicking in the angler related mortality concern before the fish even reaches trophy class.
Maybe the 'easy, stupid' fish SHOULD be culled out, playing totally off the wall devil's advocate here.
As to the clipping off of the top muskies; would not a specimen at the largest available in that waterbody have passed on it's 'genetics' as many as 15 times or more? When that fish was only 40" it was busy then, too. Not to encourage the removal of any large Muskie, but at what point has that fish contributed to the overall diversity in the population enough to make it's mark?
What is a 'non aggressive non biter', and if that indeed exists in the esocids, would that not be a GOOD thing? As a group we deisre muskies larger...seeing as the only way a muskie can get big is to get old, and avoiding capture is a sure way to increase the odds...why would that be bad? Are we figuring that we will cease to catch them altogether, or fishing will become too tough?
IS that behavior a result of a genetic trait?
Do waves on the water make the wind blow? |
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Posts: 8780
| Steve, it seems to me, based on little more than common sense, that a non agressive, non biting genetic trait would be unfavorable in any predatory species, most notably the apex predator in the ecosystem.
If they are non-agressive in their feeding habits, I would expect them to be non-agressive in their mating habits, and less likely overall to A. survive, and B. reproduce.
If angling pressure and harvest did contribute to the genetic makeup by removing a significant number of the more agressive fish, what would happen??
I would think that a few things would occur:
1. Fewer agressive predators would lead to better recruitment of prey species, which in turn would mean more abundant food for the remaining less agressive muskies now in the system.
2. Those well fed fish, being less agressive than previous generations, would probably be caught by anglers with a lesser frequency. (or by a different manner, topic for another discussion) Presumably they would live longer, and with the increase in available forage no longer being eaten by the agressive fish, they'd be bigger, and heavier.
I realize that not everybody feels this way, but I'd rather catch one big heavy slow old fish than two young agressive not-so big and heavy fish. |
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Posts: 32886
Location: Rhinelander, Wisconsin | First, a fish caught is not necessarily a fish feeding. I was waiting for that one...perhaps these mythical muskies are more apt to react to abnormal stimulus and it has nothing to do with feeding habits at all.
Or is it that fact that these mythical muskies are supposed to be 'growing faster' than the same year class of the same gene pool of the same population in the same lake for a reason not yet explained and therefore need more food so that translates into more strikes on lures...would it not be as logical to think that these fish would be more opportunistic and be fed up more often on what the water offer as prey, offering LESS of an actual 'feeding' contact with us and our presentations?
Second, would a fish less aggressive yet obviously successful at feeding be less aggressive at spawning/reproducing successfully and in good numbers, growing old and large in our mythical trophy potential water as muskie research suggests? Would an aggressive fish somehow be MORE successful? How, is there dating involved?
Your last point is exactly part of what I was trying to say, Addict.
There's gotta be a wave around outside today somewhere, that wind is really blowing. |
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Posts: 8780
| Well, Steve...
Don't ask me about muskie courtship and dating, I'm still trying to figure that out for my own species!
If they are more agressive by nature, you could expect them to burn more energy, therefore requiring more caloric intake. But I'm not sure how you could tie that to growth rates.
As for this agressive trait as it relates to spawning: Males compete for the chance to pass on their genetic material, correct? So if that holds true, than the more agressive males might be expected to "win" that opportunity. Or would it be the bigger males?
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Posts: 32886
Location: Rhinelander, Wisconsin | Either way, in this model the males would not be a likely target for harvest. |
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Posts: 8780
| Among muskie anglers, what little harvest occurs is usually limited to the top tier fish, right? So as you said earlier, they have had ample chance to spawn. I suppose in the areas with low size limits and unusually high rates of harvest there would be a trend towards the agressive fish being removed from the gene pool. But would it be significant to alter the genetic makeup of the whole population? That I doubt. In fact, based on what I've read, genetic variation is but a tiny piece of the muskie pie in terms of size and growth potential, and much more significant influences prevail when assessing the size structure of a particular population of muskies.
It's looking to me like the conclusions drawn in this article really are insignificant when it comes to managing muskie fisheries.
You have fun watching us navigate our way through your carefully placed road cones don't you, Steve? It's like watching rats run through a maze for the piece of cheese -- you COULD just give 'em the cheese, but what's the fun in that, right?  |
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Posts: 384
Location: Eagle River, Alaska | Interesting discussion which has moved a ways from the original question….did anyone actually look at this study….. its basic premise is based on unfounded assumption. This is one studies’ opinion and I'm not sure how you correlate "netting" fish with actually catching the fish angling.....to my knowledge this whole study would fall apart by not being able to supply any supporting data for this basic premise. These idiots….uh, researchers…netted the stocked fish in lakes and equated the number netted with more aggressive behaviour….does this make anyone besides me scratch their head and say….huh?? Additionally you would really have to look at what fish were stocked....there are so many strains of trout...some which are more active in shallower water and some which hang deeper....doesn't necessarily have anything to do with their foraging habits or ultimate growth potential. There have been many studies done of European brown trout where there are at least 3 different strains in the same lake, each being reproductively isolated....and all of the big browns are fish which live longer, hang deep and become purely piscivorous. By doing so their double their lifespan and get many times larger than the others in the same lake....they are commonly referred to as "ferox" trout. Way too many variables to accept their conclusion with how the experiment stated it was done.
As far as comparing any of this behaviour to anything it would certainly be a stretch to equate “aggressive feeding” with aggressive mating……I know a lot of guys that eat aggressively but don’t do so well with the ladies. Steve is right about the ability to catch fish not necessarily mean they are feeding….I live in the land of fish, salmon, who enter freshwater, their stomachs contract so they can't really eat and yet they hit eggs, lures, flies, etc..
This study couldn’t stand on its own period. Additionally I might add that actual maximum size would not necessarily have anything to do with feeding habits and fast burners generally die earlier than others.
Brian
Edited by DocEsox 2/27/2008 11:15 PM
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Posts: 32886
Location: Rhinelander, Wisconsin | And PLEASE, hijackers, this theory isn't about which fish; comparatively between watersheds, water bodies, strains, etc., is better or worse genetically to reach a certain size. The premise is about 'degradation' of big fish potential WITHIN a fish population in a selected body of water or limited area due to harvest of the top tier fish WITHIN THAT PARTICULAR population, causing a selection to less aggressive fish that grow slower.
I just don't see how it could apply to Muskies, but that's me! I actually considered the topic in 2005 when it was first discussed here, but after discussing the concept with fisheries folks who manage Muskies, have come away with the opinion that in a 95% cpr situation and no commercial harvest it flat don't wash.
Doc, thanks sir for the info on the trout over there, interesting stuff which get the largest and why.
This ain't an open door for the WMRT crew to begin the diatribe again, wrong subject matter. That's what started the entire crapstorm a few years back, by then unannounced WMRT folks hijacking a near identical thread.
Memories....
http://muskie.outdoorsfirst.com/board/forums/thread-view.asp?tid=19...
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Posts: 154
Location: Appleton, WI | My point for posting this was to see what type of debate this started. As Steve stated, I could see this being used both ways. A couple of major flaws, this assumes you have a genetically different population with specific traits to that population, while true in trout, definitely not been proven in muskies. Second, as pointed out I am not sure how netting would equate to angling pressure. Sure drop some gill nets down and you can take a large percentage of the population, not very realistic to angling pressure. Their conclusion of rapidly removing these genes from the population is very weak. This study was posted on Yahoo in the science section, so I am sure it got lots of looks. |
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Posts: 32886
Location: Rhinelander, Wisconsin | Thanks for the article and link Chaser, interesting stuff for those of us whacko enough to be seriously interested in this sort of thing! |
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Posts: 714
Location: Rhinelander, WI | I’ll muddy this water up a little bit.
The following is an exchange I had with Doctor Erik Williams, Research Fishery Biologist with the Center for Coastal Fisheries and Habitat Research, during my massive information search during the Pelican Lake planning stages.
This was related to differential selection which is similar to what this thread is talking about.
Take it for what it’s worth, but his opinions are pretty interesting. Not a musky guy and not real familiar with the Wisconsin fishing history, but he offered his ideas on the subject.
Notice the value he places on “Population Decline” it’s greater than differential selections.
Also he points out the concern about a high limit causing an increase in pressure. I think what he discussed in that paragraph could be exactly the concern many are having with the current situation on Green Bay.
Anyway I hope you enjoy, the link to his article is in the email I sent him.
Nail A Pig!
Mike
>>Mr. Williams,
>>
>>I hope I am not bothering you but I had some questions on your Manuscript titled "Effects of fishing growth traits: a simulation analysis", I found the article on a Google search for information on the effects of fishing on growth structure. Your article showed up at the following link:
>>
http://www.findarticles.com/p/articles/mi_m0FDG/is_2_103/ai_n148395...
>>
>>
>>Specifically my interest in is Muskellunge. I am just a layman when it comes to fisheries biology, but I am becoming more familiar every day. I am involved because I am helping a group of local fishermen and lake association members in their attempt to get the minimum size limit on musky changed from the Wisconsin state minimum of 34" to a minimum of 50"
>>
>>There is a huge debate going on right now in the State of Wisconsin on the state of the musky fishery, and what has happened in the last 100 years of exploitation. Many of the same questions are being asked about the Walleye population.
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>>I read your article and found it extremely interesting, my biggest question for you is can your simulation analysis be applied to a inland fish like the Muskellunge?
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>>I also found the report "Sustaining Fisheries Yields Over Evolutionary Time Scales" where they studied Menidia, I pointed that report out to a local State Fisheries Manager and he told me to be very carful because that study was done on a fish with an extremely short generational time scale. And it may not apply to Musky.
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>>I figured I would try to go to the source so to speak on this issue and directly ask you. Your study seemed to be much broader.
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>>In Wisconsin people have been fishing musky for over 100 years, some time early on they place a length limit of 30 inches on the fish, later it was raised to 32 and in the early 80's it was changed to the current state wide minimum of 34 inches. There are some lake with 40" minimums and a few with 45 and 50" limits. Information varies but I think the common age of maturity is around 5 years for Wisconsin Musky and the average length is between 30 and 35 inches at 5 year. A 50" fish can be between 15 and 20 years old. They are a very low density fish in this area with population goals of around .5 fish/acre.
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>>I don't know if this is enough info for you to answer my questions, but I figured I would give it a shot. I would like to be able to reference your report in a list of reasons why a 50" size limit would be beneficial to the Musky population on some lake.
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>>In Wisconsin the power to make fishery management decision has been give to the people and any rule changes proposed by the WDNR have to be approved by a yearly hearing where these issues are voted on by the public. So it is very political, doesn't make since to me, but it's the way it is.
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>>One more question, is your simulation one that is interactive. Can you input data for individual fish species from different areas of the county and run them through the simulation. If that is the case I am pretty sure I could get some Musky Clubs to try and fund a project that would specifically study musky with your simulation.
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>>Thank you very much for your time.
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>>Mike Roberts
>Mike,
>
>I am not sure if I can answer your question directly, but I can discuss
>some issues from my paper that have implications for fisheries management.
>
>My paper focused on selection differentials, which is one part of the
>equation for determining potential genetic effects of size selection on
>a population. The missing part is the heritability of growth and this
>can vary by species and remains largely unknown. What my paper revealed
>were some factors that can increase selection differentials. One factor
>which showed to be important is the amount of fishing activity and the
>duration of that fishing activity. Heavy fishing pressure in a short
>amount of time will cause increased selection differentials.
>
>Therefore (this may not be the answer you are looking for) an increase
>from 34" to 50" may actually concentrate fishing pressure on the bigger
>fish. An individual angler may decide to fish longer to catch a
>"keeper" compared to when the regulation is only 34". The longer
>duration of fishing time means more pressure and this could increase the
>potential for selection differentials. I don't think my paper alone
>will support the idea of going from 34" to 50" minimum size limit.
>
>However, the more important concern is usually the size of the spawning
>biomass of the population. If the musky population seems to be in
>decline or overfished and they do not mature until the same size as the
>minimum size regulation, then a bump up to 50" could definitely increase
>the spawning biomass in the population, leading to a higher population
>size. As was stated in the paper, usually population decline is of
>greater importance than selection differentials.
>
>My paper did suggest that a good strategy for management is to use slot
>limits, which would protect many of the biggest fish. The idea of slot
>limits is becoming more appealing in the fisheries biology community
>because there seems to be good evidence that the bigger older females
>produce young that have a higher chance of survival compared to younger,
>smaller females. A slot limit might be worth considering.
>
>Here's my opinion (and it's just that). From your description, if I
>were looking at this fishery, I would be concerned that the minimum size
>limit is too close to the size at maturity. Usually you want to allow
>fish the opportunity to spawn 2 3 times before they get hit by fishing.
>A size limit corresponding to the size at age 7 may be more appropriate.
>
>I couldn't agree with you more about the politics in fisheries
>management not making sense. I deal with it on a much larger scale.
>
>Good luck,
>
> Erik
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Posts: 154
Location: Appleton, WI | Mike I would agree with what Dr Williams has to say. I think his model is directed at fisheries where the fish are harvested. You up the size limit which then removes the females that produce the best egg masses. In that type of scenario I would also agree that slots make sense. Ideally in a muskie population you would like to keep the big females around until there egg mass production begins to decline and then remove them from the population. Obviously something that would be very hard to figure out. Green Bay has lots of unanswered questions at this time and while I do agree with increasing the limits there, I think we need lots more information. I sure would like to see some documented spawning success up there. Great info from Dr Williams. |
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