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| Shrinking at Sea: Harvesting drives evolution toward smaller fishes
Ben Harder
Fish are becoming smaller and growing more slowly in response to pressures introduced by fishing, scientists say. That shift, which new data suggest is hard to undo, creates populations of fish that are poor at reproducing and inefficient at bulking up.
Commercial fishing is generating a "Darwinian debt," in the form of less valuable fishes, that could take generations to pay off, says Ulf Dieckmann of the International Institute for Applied Systems Analysis in Laxenburg, Austria.
People have long noted a downward trend in the average size of fish of many species. That's not surprising. Small fish are more likely than large ones to slither from nets. Also, laws intended to protect juveniles often require that fish smaller than a certain size be returned to the sea.
Fast-growing fish therefore get "penalized" evolutionarily because they quickly become large enough to get caught, says David O. Conover of the State University of New York at Stony Brook. In recent years, he and other marine scientists have shown that fishing can induce inherited changes that cut the average growth rate, maturing time, and size in fish from generation to generation.
In six aquarium tanks, Conover grew successive generations of Atlantic silversides. To mimic commercial fishing in two of the tanks, he periodically removed the largest fish. With each generation, the fish in those tanks grew more slowly.
Conover observed an opposite growth trend in tanks from which he took the smallest fish, and he saw no change in growth rates in tanks subjected to random harvesting.
Small, slow-growing fish burn most of the calories they consume and generate little edible tissue. Relative to larger fish, they also produce smaller, more vulnerable eggs and less-hardy offspring, Conover found.
In his newest work, Conover simulated a halt in fishing to see whether wild stocks might recover their former growth patterns. Preliminary data from two lab-grown generations suggest that such recovery is slower than the initial fishing-induced changes, he says.
This implies that fish populations that have historically been overharvested could face lingering effects, even after fisheries scale back their harvests, says Mikko Heino of the Institute of Marine Research in Bergen, Norway.
In separate research, Dieckmann and Heino compared data collected as far back as 1932 and recent statistics on size and growth in wild stocks of Atlantic cod, herring, and other fish. All the examined species show a shift toward earlier maturation and smaller adult size, the researchers report.
Conover suggests one tactic to counteract such trends: Require that fleets throw back the largest fish as well as the smallest ones, thereby preserving fast-growing fish in any population.
Both studies were presented on Feb. 18 at the annual meeting of the American Association for the Advancement of Science in Washington, D.C. | |
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Posts: 906
Location: Warroad, Mn | Interesting!
Wonder how much of this applies to fresh water fish? Probably more than what we think!
Doug Johnson
Edited by dougj 3/16/2005 6:10 PM
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| Seems to me, harvesting wouldn't be as significant of a factor in shaping the growth patterns of musky since the release rate is >90%.
However, I've often wondered whether fishing pressure alone (not necessarily harvest) might impact the growth and body shape of muskies. I've seen studies that suggest certain animals (mammals) under the near constant 'stress' of being hunted tend to reflect this in their body condition. They are not as robust as animals protected from predation. Could this be with muskies?
In musky fishing, we often hear generalizations that "weed fish" are thinner and "rock fish" or "suspenders" are fatter. While forage that tend to inhabit these areas probably explains these general body conditions (e.g., perch vs. ciscoes), I've wondered if the difference might also have something to do with the intensity of fishing pressure exerted on the fish in these areas. That is, fish in that inhabit shallow weedbeds, being more accessible and easily found by anglers, might experience more fishing pressure and thus show a poorer body condition?
Just a thought.
BrianF. | |
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Posts: 714
Location: Rhinelander, WI | This is interesting stuff, of special interest I think is this sentence.
“This implies that fish populations that have historically been overharvested could face lingering effects, even after fisheries scale back their harvests, says Mikko Heino of the Institute of Marine Research in Bergen, Norway.”
Catch and release has really only been around the last 20 years with a real take off in the last 10. However the majority of fish that are kept are still the biggest fish in the system.
With a low density fish like the musky is it possible that this type of artificial evolution may be even more effective.
Could this be why the Wisconsin fish are smaller on average. The Minn. fisherie is new and grew up in the age of C&R the Canadian fisheries are much larger and fished by fewer so there isn’t as big a chance for this type of effect.
Definitely interesting stuff.
Nail A Pig!
Mike
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Posts: 1937
Location: Black Creek, WI | What I find interesting is how "angling pressure" and "Harvest" seem to be so closely related in some anglers perceptions. Is the "stress" of Catch and Release as significant as the certain death of angler harvest?
I can understand how HARVEST impacts the demographics related to fish density/distribution within a population, but unless the "stress" from C&R leads to premature death (a form of harvest?) I just don't see the connection.
If "stress" slows the growth rates or even jeopardizes the overall "health" of the fish.... what impact does this have on the overall demographics of the fish population? Wouldn't it eventually reach an equilibrium? Perhaps it may take longer for a fish to reach "trophy" size, but if they are never "harvested" they should still reach their fullest potential.... only it may take longer?
Thus, my biggest interest is understanding how "stress" could potentially reduce the maximum growth potential (mature adult size) for a predator. We all know that once a fish is harvested... it stops growing (the foundation for C&R). But, will two genetically identical fish (sisters?) reach different maximum sizes if one is caught and released 4 times a year and the other is never captured during their entire life cycle? If the fish that is C&R'd repeatedly has poorer health and growth due to the "stress", how can we better manage it? Stop fishing altogether?
Which is more important of an issue RIGHT NOW for musky management? Restricted/controlled harvest or restricted/controlled STRESS? As angling pressure continues to increase, is it possible that one day the amount of angling pressure a given fishery recieves will be managed??? Geez, I hope not.... but its something to consider.
jlong | |
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Posts: 1438
| Mike
That's exactly my point on the "demands" or the one sided viewpoint of the WMRP. I'm not saying that what they are trying to get accomplished right now is "bad". I don't know yet. I don't think anyone doe's. While the end result of growing larger fish is something that we all want, I find it real hard to believe that the sole avenue to that goal is the stocking of a different strain of fish.
I believe that there are a ton of factors that influence the growth of muskies. And, until they have a plan in place to address most of those factors the stocking of a different strain may not help the current fishery. What happens when all these self-proclaimed experts from the WMRP are dead and gone and because of the practices that they insist are for the good of the fishery are found to be detrimental? I think there's an overall picture that needs to be addressed before changes are made.
When will we look at outside influences like pollution, fishing pressure, spearing, water use issues, degenerative genetic practices (the ones like this post addresses) and find a way to do something about it. I think that what needs to happen is that all the people involved in this issue need to look at the well being of the fishery as a whole instead of what personally affects their own little world. The resort owners need to stop worrying about "little Johnny", the Indians need to stop worrying about spearing, the legislators need to stop worrying about how an issue affects their run for re-election, businesses need to stop worrying about the bottom line.
See that's why I don't think that you'll ever see things done the "right way". You'll never ever get all these people to agree to the single solution. Along the way there may be a bright spot and one change may help a little here or a little there, but, I don't think you'll ever see an end result like everyone envisions.
My 2 cents.
Scott
Edited by theedz155 3/30/2005 8:00 AM
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Posts: 32884
Location: Rhinelander, Wisconsin | The theory that harvest of the large fish causes 'accelerated evolution' in salt water commercially harvested fish is 'interesting'.
I don't think stress has anything to do with this issue unless that stress leads to the fish dying.
I spoke last week to a biologist who manages the waters with perhaps the highest harvest rate on Muskies in the country. The fish there still follow the exact same parameters of growth/mean maximum size/average maximum size, etc. they always have. He feels that any additional CPR rulings will just damage the fishery long term because the density of the fish there, currently at 3.5 fish per acre, and will not increase the quality of the top end or average muskie in that water. As I have said, details...
Assume that the total catchable population of muskies in a lake in Vilas county at 800 acres is 1 adult fish per acre making it a a class A water. If the average population consists of many year classes, which would be good form what I've read, an assumption or 'guess' I have heard is that approximately 10% of the older adult population reaches 'trophy' size. If those fish are from, say 3 of 6 successful year class adults in that lake, the largest fish in there might number at about a dozen, give or take. If 3 are speared and 3 are harvested and 2 die of natural causes per season from the two oldest year classes, and the next year class experiences equal harvest rates, then we can expect that the number of truly big fish will, over time, suffer. Am I figuring wrong here? | |
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| Steve,
please define trophy size. According to the Wisconsin DNR and their literature many people consider a trophy muskie to be 34".
I'll work with the analysis here. But at the end of the day I'll still wonder why these details are not necessary in lakes where they stock fish that grow big - Minnesota. (The details were perceived to be the problem when MN stocked fish that did not grow big.)
Bob | |
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Posts: 32884
Location: Rhinelander, Wisconsin | Bob,
I did define trophy size. You know what I mean. Maybe the alalysis wasn't necessary, but it is right there in the Minnesota work linked here, to age 6.
Minnesota has not had the spearing pressure we have here, nowhere near. This started here in the early 80's on hundreds of lakes, and it has an effect. To pretend that effect isn't important to the future of this fishery, especially considering the announced cuts in the stocking program, is not realistic.
Detail's what they are, but important none the less. Harvest of the largest fish in Minnesota WILL increase as pressure increases, and the big fish are available to a larger cross section of anglers who are not well versed in CPR or are seeking a trophy, it is very likely recruitment will decrease over time, and there WILL be an effect unless those big fish are protected.
By the way, Howie Meyer last night quoted his overall AVEREAGE fish from his guiding last year. Take a look at the chat, that stat is interesting. | |
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| Steve,
still not sure what size you mean...will look, but it would help if you just type it.
I have to dispute the 10% number. I checked 6 muskie population with large fish (6 is all I have) and each of them showed over half of the females were over 48 inches and I'd assume the other half were younger and on their way there. Since the females were approx 35% of the population - I feel 10% off. Since harvest is directed at primarily females is that the reason why females are less than 50%??? Not sure it matters...
Anyway also checked a couple Wisconsin lakes and approx 1% were over 48".
Don't think the stats will work.
Harvest is an issue. Spearing is an issue. I don't disagree. To say harvest is not and has not been an issue in Minnesota is not a valid statement, please do not repeat it. many of their lakes have seen the same harvest ours have since the early 1900s.
When we have no spearing and 90 inch size limits on Mud Callahan, the females will still be 27 inces at age 15. Spearing and harvets is not an issue there GENETICS is the issue.
Bob | |
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| Steve,
Howie sounds like a great guy and an Outstanding Guide. His numbers are fantastic! It shows that the fish can and do grow big in many waters in spite of harvest,spearing, small lakes and fishing pressure. Funny all those factors don't affect Howie. I'm not saying they can't grow big here (I'm saying they can) - I believe we can have many more big fish if we use fish that can all grow big. I'd like to investigate the stocking records of lakes Howie is fishing...but won't ask for those details without booking a guide day with him.
How can you have a 44 inch average if only 10% of the fish grow that big?
I think they can all get that big - males and females if we plant the right fish. They do on many waters I fish.
Bob
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| Theedz155 (Scott) says: I find it real hard to believe that the sole avenue to that goal is the stocking of a different strain of fish.
From MDNR Investigational Report 418.
"As a result of the findings in this study,MDNR fisheries managers have discontinued propagating Shoepack strain, and inplemeted a culture program using the Mississippi strain muskellunge. The superior growth characteristics of the Mississippi strain should provide the trophy fishery most anglers prefer. In addition, the differences observed between the two Minnesota strains provide evidence of the potential problems associated with stocking programs using fish of unknown genetic qualities. Although both are native to Minnesota, each has its own unique characteristics well adapted to a local environment."
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Were the MDNR biologists wrong here? They simply changed strains for stocking and it worked. They also suggest that there are potential problems using fish of unknown genetic qualities.
Unknown genetic qualities = fish from WI brood lakes maybe?
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Posts: 1438
| I don't know that they are wrong. As of now things look good. 100 years from now when a group like yours gets together and looks at the data collected between now and then, they might say different. That's my point.
Check your quote. I saw several words that peaked my interest. This is only a partial quote "...Mississippi strain should provide the trophy fishery..." Key word should. There's also "...the differences observed between the two Minnesota strains provide evidence of the potential problems associated with stocking programs using fish of unknown genetic qualities..." Key words provide evidence.
"Should" does not mean "will". And, "provide evidence" does not mean "proves beyond a doubt".
MDNR has been stocking these strains for what??? Maybe 20 years?? In another thread, your group has referenced errors in the Wisconsin program back as far as the 1800's if I remember correctly. So, another 100 years from now we'll see if the MDNR is still stocking as they are today, or if there are changes made adapting to the changing environment, pressures or political climate. As well, lets call into play all the advancements that I expect will be made in genetic and environmental engineering in the next 100 years and we'll use that as well to see if the decision made "back in the 1990's" was still correct.
Again, I am not saying what your group is suggesting is the wrong direction to be going. As I stated before, I don't know that. I refuse to blindly follow someone, whom I don't know, and jump on their bandwagon without "showing me the money". Exactly what is your background besides a love of Muskies and the intention to improve the fishery. I've heard Mr. Ramsell's name before but what exact training, schooling or experience does he have??? Or anyone else in your group for that matter???
Are any of you genetic or biomedical engineers??? Do any of you have a degree in data management, data interpretation, data collection or some type of statistical collection and interpretation??? Are any of you current or prior WDNR employees with any type of training or experience in fisheries biology or wildlife management???
Are you starting to get what I'm saying here? I'm not against growing larger fish in Wisconsin. But, at what cost will this come. Can you tell me positively that down the road the decision to do so will have been the right one?
I don't like the "because we said so" attitude that I seem to be getting from the posts I've seen.
And I'm not disputing what MDNR has done so far has turned out good. But, that doesn't mean that it will work here. Do I hope it does?? Yes. Might it work here?? Maybe. Is it a guarantee?? No.
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Posts: 32884
Location: Rhinelander, Wisconsin | I said:
'Minnesota has not had the spearing pressure we have here, nowhere near. This started here in the early 80's on hundreds of lakes, and it has an effect. To pretend that effect isn't important to the future of this fishery, especially considering the announced cuts in the stocking program, is not realistic.
Detail's what they are, but important none the less. Harvest of the largest fish in Minnesota WILL increase as pressure increases, and the big fish are available to a larger cross section of anglers who are not well versed in CPR or are seeking a trophy, it is very likely recruitment will decrease over time, and there WILL be an effect unless those big fish are protected.'
I think you didn't read my post carefully, and assumed I said something else.
I've been to the landings on and off since 1984, and watched the boats come in during April. I've seen the fish up close and personal, and I can guarantee that the harvest from spearing here on most of our lakes would NOT be real healthy for many of the Minnesota lakes, either. We're talking spearing as many in the winter as 30 or more on a 1000 acre lake by ONE darkhouse, and those fish are not counted as part of the TAC.
And you are right, it IS funny that the effects that you've been posting about don't seem to effect Howie's average. Mine either. He fishes areas that are not pressured in the waters he fishes, in other words, he's a bit of a specialist. I would say I do the same. Would my fish be larger in Minnesota? On an average? Probably, yes. Would they all be 48" or larger? No.
To define what I mean by 'trophy' size, that would be the upper end of the anticipated maximum length of any fish in the population. I personally think a trophy is what the angler holds as such. The accepted standard for better or worse today is over 50".
Out of 3000 fish stocked in Waconia for the study, only 152 were expected to survive to age six, and that's with no angling pressure. Of those, there is a formula that accounts that .320 annual mortality rate for fish 5 to 13. What percentage, by this study's data, of the fish that reach 6 years of age (maturity) will reach the maximum age AND maximum size?
The last paragraph of that paper was discussing the Shoepac and MS strain, not the Wisconsin strains, as I read it.
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| Steve,
not sure if it's you or me, but you confuse me lately....I still like the concept, but we need to start over. I'm glad you are on vacation, hope you get to do some fishing. Get your mind straight, I'll be here when you get back.
Theedz,
I hope both Wisconsin and Minnesota aren't doing the same things 100 years from now that they are doing today. The MN DNR freely admits that 20 years from now people are going to be saying - "Holy cow look what these crazy guy's in Minnesota did. How are we going to fix that. " I hope it doesn't take even 10 years to find things they can be doing better in Minnesota.
The whole point is doing the best thing using all knowledge available every day. It's clear to me Wisconsin was stuck in a rut, I'm betting we pissed the Wisconsin DNR off big time, and they come back with a vengeance - Muskie world beware. I know right now, they'd like nothing more than to prove us wrong by growing 60 lb Wisconsin strain fish - I hope they do and I catch it!
There are some interesting concepts we need to discuss - are the M/C strain that rarely exceeds 30 inches that small because of 30 inch size limits? Interesting that their growth stops right at the sizelimit isn't it? Fact is no one knows - not me or any fisheries biologist, all we know is they don't grow when we put them in lakes with more forage or restrict harvest - why? It's the fish! The DNR was so fascinated with these fish that did not grow (I am too) that I think they forgot to lkook at the other side of the equation.
One other thing that Larry keeps pointing out to me is that the Michigan DNR has been managing the "great Lakes" and "Northern strain" as separate fish for longer than the Minnesota DNR or anyone else. I always thought they were "goofy" but it turns out they were ahead of their time. There are so many different angles we looked at over the last few months, hopefully we'll be able to share them all at some point. Honestly, people who say we have a simplistic view couldn't be further from the truth - we left no stone uncovered.
Bob | |
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Posts: 1438
| Bob
Thanks for the reply and I can agree with you on at least one thing. That we need to do the best thing for the fishery with the knowledge available today. Now, what that best thing is will have to be determined. At this point in time, until I see more information leading me one way or the other, I'll continue to sit on the fence.
It's great that we can come together in a place like this with differing viewpoints and, if nothing else, at least see what each others thoughts are.
Thanks again for the civil responses and the open dialouge.
Scott | |
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| In a scientific double whammy, researchers report that fishing pressure is causing fish to evolve to smaller sizes, just as new studies show that larger fish are critical to sustaining populations. In species such as Pacific rockfish, the big, old females not only produce exponentially more eggs than younger, smaller females, but their hearty larvae have a far greater chance of survival. Keeping these big fish in the water increases the chances of strong population numbers in the next generation which is paramount to the recovery of overfished stocks.
Representing three fisheries science sessions from the American Association for the Advancement of Science (AAAS) meeting, Steve Berkeley of UC Santa Cruz, Larry Crowder of Duke University, Andy Rosenberg of the University of New Hampshire and a member of the U.S. Commission on Ocean Policy, and Jeremy Jackson of Scripps Institution of Oceanography highlight the latest advances in genetics, biology, and evolutionary science that point to new strategies for maintaining fisheries.
As a former leader in the National Marine Fisheries Service, Andy Rosenberg has faced the difficult realities of implementing new fisheries policies. "Over the last ten years the management struggle has been to begin to bring massive overexploitation under control, and that struggle has had some success but rebuilding fish-stocks is another matter," says Rosenberg.
Old Fish Never Retire
Fishing disproportionately removes older fish - which are larger and more highly prized. In fact, management often seeks to shift fishing pressure to these older fish in an effort to let younger, fast growing fish reach spawning age.
Researchers have long known that older fish produce exponentially more larvae. A 50 cm Boccacio rockfish, for example, will produce nearly 200,000 larvae, while an 80 cm fish will produce ten times that - nearly 2 million. These larvae are released into harsh ocean conditions without parental care. For fish, spawning is like entering the lottery, and the older, larger fish have many more lottery tickets. "For northern cod, only one in a million make it to age three," says Jeff Hutchings of Dalhousie University. Similarly, for many species of Pacific rockfish, only a tiny fraction of mothers about one in a thousand - succeed in contributing to the next generation of fish, according to Daniel Gomez-Uchida of Oregon State University.
But scientists only recently discovered that the larvae of old fish also have better odds of survival. Berkeley started investigating this advantage after observing Pacific rockfish spawning patterns. He noticed that older females spawned early in the season. And when he looked at the next generation of fish, there were years when most of them had birthdates corresponding with these early spawning events. He wondered whether it was just the timing of release that mattered, or whether the older mothers were somehow giving their offspring a leg-up in life.
"I was astounded when I got the results," says Berkeley. "I suspected some difference, but not the overwhelming difference that we saw survival rates were nearly three times higher, and growth rates were 3.5 times faster for larvae from older mothers."
Berkeley's team discovered that older mothers produce larvae with a larger oil globule, a sack lunch packed by mom that the baby fish relies on if faced with starvation. Early spawning can also give the larvae a boost when it coincides with peaks in zooplankton. By removing the big, old fish, we lose the benefits of their fecundity and superior larvae, and we also shorten the spawning season all of which reduce the chances of a robust cohort of recruits the next year.
"Without the oldest females," says Larry Crowder of Duke University, "populations lose their best hope for the success of future generations - the resiliency that can compensate for overfishing."
"Rockfish can live to be 100 years old," says Berkeley. "People understand that you can cut down a 100 year old tree in five minutes, but that it takes 100 years to grow a new one. Old fish are the same way, they accumulate over decades, even centuries, and in a flash they're gone we can remove them much faster than they can rebuild."
Evolution in Our Lifetimes
Having fewer and smaller fish may not bother the average consumer just yet, but creates a "Darwinian debt" for future generations. Researchers say that the evolutionary effect of fishing has been a blind spot for managers overlooked, downplayed, ignored because of the complexity, or just not on the radar screen. "The truly worrisome aspect is that repairing evolutionary damage is vastly more difficult than causing it," says Ulf Dieckmann. "The debt we build up is increasing at a sky-high interest rate."
While many think of evolution as a slow, historical process, research by Jeff Hutchings (Dalhousie University), David Conover (Stony Brook University), Mikko Heino (Institute of Marine Research in Norway), Ulf Dieckmann (International Institute for Applied Systems Analysis in Austria) and others shows that by taking out the big fish, we are actually driving selection for smaller fish that mature earlier. Studies show fishing pressures can significantly change the genetic composition of fish populations in as little as 20 to 50 years.
"We see it in the models, in the lab, and in the real world ? smaller fish and fewer of them," says Heino, a co-organizer of one of the AAAS fisheries sessions. "Since these changes are genetic," adds Hutchings, "they are not readily reversible we'll be stuck with them for a long time. No one wants that fishermen or conservationists."
Scientists now have evidence that the age of sexual maturation in several populations of cod has been reduced by a quarter, and for plaice (a type of flatfish) nearly a third. "These examples are probably just the tip of the iceberg," says Heino. "We've detected fisheries-induced evolution in almost every species we've studied."
"Resource managers and decision-makers need to be aware that fishing can cause genetic changes - changes to characteristics that are vitally important to the continuity of the population," says Hutchings.
Overfishing Can Reach A Point of No Return
Cod off the coast of Newfoundland - once one of the largest populations in the world has suffered a 99% decline since the 1960s. Hutchings latest work shows that the changes in size and age at maturity caused by just 30-50 years of fishing have reduced the chance of cod's recovery by 25-30%. Hutching's findings confirm the importance of keeping old fish in the sea and may explain the failure of closures to bring about a rebound in the cod population.
Researchers suspect that this evolutionary change is happening with other stocks too. "We have this belief, that we can knock down fish populations to exceedingly low levels and they can bounce back rapidly," says Hutchings. "Not to say that it can't happen. But little or no recovery appears to be the general pattern. Unfortunately, it appears to be the exception that drives policy."
Genetic and ecological studies led by Ralph Larson of San Francisco State University point to an additional problem with current management. Larson's work shows that simply keeping enough spawners in the sea isn't enough to prevent populations from crashing ? first you need the big fish, but you also need big fish throughout their geographic range. Each year only a subset of rockfish spawn successfully, and it's impossible to predict where these "winners" will be from year to year. "If we want to have more consistent levels of replenishment from year to year rather than a boom and bust cycle we have to protect spawners throughout their range," he says.
Solutions
While the scientists acknowledge that there is no quick and easy way to integrate the true complexity of fish population dynamics into management, they all point to the need to preserve large, old fish and maintain the balance of age classes in the population.
"If the new studies are widely applicable to other species, then it isn't a question of doing a better job, it is a question of doing a different job. The old management tools will not work to protect age structure or genetic diversity, or prevent local depletions we'll have to use new tools to achieve new objectives," says Berkeley.
Crowder calls for new strategies that address cumulative impacts on fish populations and protect entire segments of struggling populations. "We have to move toward true ecosystem based management," he explains. "Commercial and recreational fishing have reduced top predators to a remnant of their former abundances, but pollution and nutrients from the land also drive fish, crabs, and shrimp to suboptimal habitat, making it even harder for these populations to recover it's in fact a triple whammy."
One approach consistent with ecosystem-based management is ocean zoning. "Some areas might be totally protected, some closed seasonally, some open to commercial fishing, some only open for recreational fishing and so on," says Berkeley. "As far as protecting age structure and maintaining big old fish, I can't come up with anything better than a marine reserve-type approach where you protect a segment of the population from fishing. There may be other approaches that would work, but I think we know enough to get a good start on a network of marine reserves."
We have been ingenious enough to figure out how to overexploit a very big ocean. We must now be ingenious enough to figure out how to deal with the complexity and regain our lost resources. | |
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Posts: 32884
Location: Rhinelander, Wisconsin | The premise that harvest of the lagest fish in any population at very large percentages drives down the upper mean weight and length and causes accelerated evolutionary trends in some populations may or may not apply to alot of the Muskie water I fish, but I doubt it. Given the intense pressure on the larger fish in Northern Wisconsin from spearing and angling combined, and the relatively low density of old fish at the upper end of that year class's potential, suggests that the possibility is there if this idea applies to our fishery, but that's a stretch.
As Minnesota matures as a Muskie vacation destination, and the anglers show up (they already have) and the pressure increases(It already has), this syndrome might apply to that water very soon, but only in the fact that the top tier fish will be subject...not necessarily a done deal, but subject...to harvest. Since many of the waters there have only experienced this for what amounts to a relatively short period of time all things considered, it simply occured to me this might be something to watch over there.
The other observations were to indicate how few individual fish from each the original year classes from natural reproduction or stocking make it to the age necessary to reach 50" or more. | |
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| From the Guest reply above...
"Studies show fishing pressures can significantly change the genetic composition of fish populations in as little as 20 to 50 years."
Hmmm...would not suprise me if this was true for muskies as well. I've pondered that anecdotally in watching how mostly thick fish in newly discovered waters became mostly thin fish as pressure increased over the years.
While not suggesting that the genetic change concept does, in fact, apply to muskies, intuitively there is little to prevent folks from making such a leap. Only good, controlled, unbiased studies on muskies will tell us one way or the other if there is applicability to our favorite fish.
As a musky angler interested in catching more and bigger fish, the concept of angling pressure has been THE most significant issue on my mind this off-season. I just don't think we have broken the code on this yet, and that is what so intriguing to me. Heck, even very experienced musky anglers still disagree on whether fish get conditioned to pressure. Seems to me there are many things we still don't understand about this fish and how they are effected by the mere act of angling or the resulting mortality - whether intentional (harvest) or unintentional (delayed mortality).
Do I suggest putting an end to musky fishing as JLong implies? That is silly. I love fishing - and live for fishing - as much as anyone here. I simply want to learn how to be more successful while fishing in waters with heavy angling pressure in the hopes of someday averaging, say, 3 or 5 fish per outing vs. one or none per outing.
Perhaps this isn't possible on heavily pressure waters. Admittedly, I don't know how yet. However, my guess is that long term success like that which I think is possible won't be done with a conventional musky angling philosophy and approach. An approach that is a bit outside the box might get us there, and that is where my interest lies.
BrianF.
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Posts: 2752
Location: Mauston, Wisconsin | I don't believe it, i.e., that harvest genetically affects the size- harvest targets specific year classes. F. ex. If th year classes are all + 34 inch fish and the freaking size limit is 34" the majority of fish removed are the +34" class fish. The smaller fish are still carrying the same genetic's - 20 year-50 years for genetic mutation to smaller fish seems absurd.
Here's a test- watch ice fisherman fishing for bluegills or crappies- from what I have observed (antedotal evidence) they go through a selective culling process as the season progresses, until at the end of the season they only are catching a majority of dink's. Why?- My answer! They are being piggish and removing graduated smaller fish as the season progresses, i.e. I need to take home my limit mentality! Magically the majority of the smaller year class that survives becomes next season's early season big fish. The key to big muskies is management of the harvest- Wisconsin hasn't done that very well for a whole slew of reasons, including pressure from resort's and meat eater's. Of course some waters need harvest to control populations.
Wisconsin needs to let the biologist's manage the resource, not the politician's or the resorts, or the meat eater's or the CPR folks like you & me. It seems so insane that we pay these highly qualified folks to manage the resources and then they are handcuffed by political agenda's. License increase? Heck yes as long as the revenue expenditures are dedicated and controlled by the biologist's for the best interest of the resource.
BTW: I think there are also merit's to stocking fish that have shown ability to grow! Are we stocking to preserve the genetic purity of the species? or to enhance the fishery? It makes a big difference in the response to this question.
Al
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Posts: 1438
| "Wisconsin needs to let the biologist's manage the resource, not the politician's or the resorts, or the meat eater's or the CPR folks like you & me. It seems so insane that we pay these highly qualified folks to manage the resources and then they are handcuffed by political agenda's."
Amen Al!!
Scott
Edited by theedz155 4/2/2005 5:55 AM
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Harvesting drives evolution toward smaller fishes