Fishing with Rod Discussion Forum
Fishing in British Columbia => General Discussion => Topic started by: fisher man on February 04, 2012, 09:25:44 PM
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If i'm a hatchery fish that survives and spawns do my fishlings become wild and is that the objective of the enhanchment projects. if so is it working as in are we getting more wild in the rivers ie; vedder
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I'm no scientist but i'll give it my best shot.
Short form answer: yes and yes.
The progeny from the hatchery parents will be "wild" per se - as what defines wild fish is the presence of an adipose fin, which hatcheries clip off to make identifying them easier for anglers. But since the parents were hatchery, the new generation of "wild" fish aren't true "wild's" in my opinion.
The second part of your questions is a little more complicated....
The objective of enhancement programs is to "enhance". They provide retention opportunities for anglers while inflating the size of the run. Fish raised in a hatchery have a better chance of survival. Some might argue this. But they are fed until a certain size which allows them to hit the ground running so to speak. On the other hand, their wild cousins...out of say 100 5 will survive, but the hatchery brethren will have 20 out of 100 survive (just for illustrative purposes). So fewer wilds go out to sea than hatcheries, who by proxy have a
better chance of surviving to adult stage and returning...whatever happens to them in the ocean is unknown...but more hatchery fish will come back simply because of numbers. I think the hatcheries also give a healthy "cushion" to the wild stocks as hatcheries will be caught more often due simply to their larger returning numbers, therefore giving the wilds better chances to escape and spawn...less chance of hooking a wild and therefore these guys don't become pincushions - hence the "leave after bonking" rule.
Is it working? Yes and no. Are we getting "more" wild fish in the rivers? Well, it depends on what you consider wild :D Personally I feel that no true "wild genes" exist, as hatcheries use artificial selection to pair up two wild mates, whereas they would have chosen the healthiest and strongest partner in the wild. Some will also say that hatchery fish are inbred - on the chilliwack river I doubt this is the case, as they use wild fish only for broodstock - the chances of the pairs being from the same parents are low. But on smaller systems most fish are inbred, as the hatcheries have to make the best of what their broodstock anglers bring them and often time it will be two hatchery fish mating together if that's all they get one year...the chances of them being related are higher....In any case, we are without a doubt getting more fish returning in the river. I would think that without a hatchery, the "wilds" numbers would be way down also. This is because since more hatchery fish return, more fish are spawning in the wild, period. Despite the fact anglers take out the hatcheries for retention, even though people think "you're supposed to because it maintains the genetic integrity of the run" - there are no real wild fish. many hatcheries spawn in the wild...I think most wilds are progeny only once removed from hatchery parents. Therefore without the hatchery fish, there would be a very small run of wilds fighting the odds to return as adults.
If you want real wild fish, go to the Thompson or Skeena...oh, actually.... don't go to the Thompson ;D
Hope this helps.
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I remember reading in Dec Hogans book regarding a study by Washington Department of Fish and Wildlife scientists about survival to adulthood of wild - wild, wild - hatchery and hatchery - hatchery combinations. The study was done for Kalama River steelhead and only wild - wild combinations produced off springs surviving to adulthood in a statistically meaningful sense. A wild fish mating with a hatchery steelhead had a "zero" chance to produce an off spring which will survive to adulthood. This was based on 30 years of field research so it does makes us think about benefits of a hatchery program vs. protection of wild steelhead.
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hmm I'd be interested to look at that book, what's it called? It would be hard to look at DNA samples of the adult fish and determine the origin of their parents...and this would probably be the only way to do it as there would be no way to track a fisk from the alevin to adult stage over 4+ years
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The book is called Passion for Steelhead and written by Dec Hogan.
The study was mentioned in page 296.
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To add to what fishhunter has said, the hatchery fish are there for one purpose, to provide angling opportunities and to allow anglers to retain a fish. They are NOT there to try to rebuild the wild populations (although it is hoped the decreased pressure from anglers on the wild fish will allow more to survive). If hatchery fish spawn, they will produce offspring with less genetic diversity, so they will serve to weaken the wild population's gene pool. Anglers are encouraged to kill the harchery fish they catch. The only reason to release a hatchery fish is to allow another angler the opportunity to catch and kill it. I will release a hatchery fish in the canal, with the idea that the fish is bound to be caught again before it reaches the spawning grounds. However, if I catch one above Allison canyon, I will kill it and take it home.
Some rivers have had attempts to rebuild a wild population using fish raised in hatcheries (Living Gene Bank), but these are smolts that are captured on their way out to sea and raised in hatcheries until adults, and then spawned and their offspring are released into the original donor stream.
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To add to what fishhunter has said, the hatchery fish are there for one purpose, to provide angling opportunities and to allow anglers to retain a fish. They are NOT there to try to rebuild the wild populations (although it is hoped the decreased pressure from anglers on the wild fish will allow more to survive). If hatchery fish spawn, they will produce offspring with less genetic diversity, so they will serve to weaken the wild population's gene pool. Anglers are encouraged to kill the harchery fish they catch. The only reason to release a hatchery fish is to allow another angler the opportunity to catch and kill it. I will release a hatchery fish in the canal, with the idea that the fish is bound to be caught again before it reaches the spawning grounds. However, if I catch one above Allison canyon, I will kill it and take it home.
Some rivers have had attempts to rebuild a wild population using fish raised in hatcheries (Living Gene Bank), but these are smolts that are captured on their way out to sea and raised in hatcheries until adults, and then spawned and their offspring are released into the original donor stream.
I disagree with this statement completely. When 2 wild fish mate and produce offspring, their genetics will be the same regardless if their offspring were hatchery clipped or not. I believe that the hatchery on the Chilliwack-Vedder uses wild stock for its hatchery production so although the pairing would not necessarily be the same as in the wild, the overall genetics will be. Raising a fish in a hatchery does not change the genetics of the fish. The phenotype may be different due to the environment, but the DNA does not change due to a hatchery environment. Two hatchery fish making it back to mate and produce the next generation have proven that they have what it takes and natural selection will make their offspring phenotypically the same as offspring of wild fish.
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Thanks guys for replying. it helps out alot. I used to think that hatchery fish were used to produce more hatchery offspring. Luckily i met a nice fellow (tuber) on the river and we talked as he explianed to me how they use wild fish to take up to the hatchery. So in my mind the only difference is a clipped fin? When that fish survives and comes back to spawn, and those offspring don't have clipped fins (then they are wild). Are we not restocking wild fish?
So my guestion now is how are they genetically altered other than being raised in a friendlier environment.
Cheers
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Interesting article:
http://www.msnbc.msn.com/id/45743468/ns/technology_and_science-science/#.Ty7NppiidLq
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Fish are never genetically altered per se... what people mean is that on some systems where there is minimal spawning habitat - like the cap - the fish are pretty much 95% hatchery, so there is no diversity as the hatchery staff breed the fish year in year out and choose which ones to breed. This is done so many times that often they breed two fish from the same parents, as the hatchery releases have a better chance of returning back in adult stage thus increasing the chances that brothers and sisters make it back to the fish fence and theoretically that is done to their progeny over and over until the whole run are basically genetically identical...
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Raising them in a hatchery doesn't alter them, but just think...from a younger age the fish are taught to feed on the surface, as that is where their food is (pellets) this is bad because the little fish will think this behavior is okay and hence become vulnerable to predators when they are released
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Fish hunter your last post is an interesting thought, so how much does this behavior decrease survival chances do you think.
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I disagree with this statement completely. When 2 wild fish mate and produce offspring, their genetics will be the same regardless if their offspring were hatchery clipped or not. I believe that the hatchery on the Chilliwack-Vedder uses wild stock for its hatchery production so although the pairing would not necessarily be the same as in the wild, the overall genetics will be. Raising a fish in a hatchery does not change the genetics of the fish. The phenotype may be different due to the environment, but the DNA does not change due to a hatchery environment. Two hatchery fish making it back to mate and produce the next generation have proven that they have what it takes and natural selection will make their offspring phenotypically the same as offspring of wild fish.
The scenario is not when two wild fish (and by this we should mean truly "wild" fish, but what is that really any way) spawn, but when two hatchery raised fish (fish that are raised by human selection, not natural selection) spawn. Fish that spawn in the wild, compete with each other for spawning habitat and a mate. The biggest and baddest of the fish get the best redds and the best mate. The weaker fish are forced to take less ideal redds (lower chance of their eggs successfully surviving to hatch), or perhaps don't mate at all and their genes are naturally selected out of the pool. However, if a pair of wild fish are taken for brood stock and spawned, there is the possibility of a fish that, if left to spawn naturally, may not have been successful for a variety of reasons (smaller, not aggressive enough, etc), being given the opportunity to pass on those inferior genes to offspring who, because they are raised in the hatchery, are given a better chance to survive to smolt stage than if left naturally in the river environment. When these possibly genetically inferior fish are released, natural selection will of course, select out the weakest of those offspring and only the fittest will return, and if they are left to spawn, they will pass those genes (those still possibly inferior genes) to their own offspring, especially if they are spawning with one of their own siblings (which is likely as the hatchery fish are more numerous and therefore stand a statistically better chance of returning to spawn). The next generation of fish (still genetically inferior to the wild population) could, if they survive, then match up and spawn with a wild fish and mix those genes (weakening the wild fish's genes or strengthening the hatchery fish's genes, depending on if you are a cup is half full kind of guy). What is worse, is that the offspring of the hatchery produced pair is then taken as a "wild" fish and used to create another generation of hatchery fish. Now, while in a river like the Vedder with a large gene pool of wild fish to draw on, the genetic dilution would be low, you can see that this spawning of the hatchery raised fish could still potentially weaken the wild fish's gene pool.
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In a river with a sustainable run of 2000 wild fish, the approximately 2000 fish returning the following year would be offspring from the some 600-800 pairs that spawned successfully (were not caught by anglers, bears, otters, etc., and were not out competed by other spawners). In a hatchery enhanced river, the 2,000 returning hatchery fish would be the offspring of a few dozen brood pairs, representing a loss of genetic diversity.
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i was involved in hatchey steelhead programs for many years......its simple , take away the enhancement and they stop returning.
a good example would be the brunette and kanaka creek in the early 90's had upwards 300-400 fish....cut the program in the late 90's and 3 years later you get 6 fish back.
it just shows the hatchery band-aid is not the solution.
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i was involved in hatchey steelhead programs for many years......its simple , take away the enhancement and they stop returning.
a good example would be the brunette and kanaka creek in the early 90's had upwards 300-400 fish....cut the program in the late 90's and 3 years later you get 6 fish back.
it just shows the hatchery band-aid is not the solution.
Jim, seriously? 400 fish in the Brunette and Kanaka Creek in the early 90’s??
Who did these enumerations?
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we collected alot of that info for Peter C.
http://www.bccf.com/steelhead/r2-focus5.htm#kan (http://www.bccf.com/steelhead/r2-focus5.htm#kan)
http://www.bccf.com/steelhead/r2-focus3.htm#brun (http://www.bccf.com/steelhead/r2-focus3.htm#brun)
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The pages at the links only show the results of the steelhead harvest analysis which is based on the mail-out questionnaire to anglers. The analysis does not provide estimates of run size, only estimates of angler effort and catch. The analysis is biased for various reasons that I'm not able to explain. There are a couple of papers that discuss the issues.
I think the analysis is able to illustrate trends in effort and catch but the actual numbers are not reliable. There is nothing preventing Average Steelheaderperson from fudging (or perhaps slightly exaggerating ;)) their submission in whatever way they want.
The only enumeration attempts on Kanaka that I am aware of (through prov govt files) are a couple of fairly recent snorkel swims that counted a couple of fish.
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Thanks for that link. Wow, 13% smolt to adult survivals in the B ... wonder when that last happened ??? Whatever, and sadly, it was the best science of the day.
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The pages at the links only show the results of the steelhead harvest analysis which is based on the mail-out questionnaire to anglers. The analysis does not provide estimates of run size, only estimates of angler effort and catch. The analysis is biased for various reasons that I'm not able to explain. There are a couple of papers that discuss the issues.
I think the analysis is able to illustrate trends in effort and catch but the actual numbers are not reliable. There is nothing preventing Average Steelheaderperson from fudging (or perhaps slightly exaggerating ;)) their submission in whatever way they want.
The only enumeration attempts on Kanaka that I am aware of (through prov govt files) are a couple of fairly recent snorkel swims that counted a couple of fish.
i still have some of the old log books to show the ammount of fish that was there pre/hatch and hatch and post hatch.....heck you could go there now and see how many there are.
in the early 90's it was not uncommon to catch 5-6 fish on a morning after a rain.
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Thanks for that link. Wow, 13% smolt to adult survivals in the B ... wonder when that last happened ??? Whatever, and sadly, it was the best science of the day.
The figures for adult capacities listed for all streams on the GGBSHRP site are based on 13% marine survival which may have been the case a decade or more ago when the figures were drawn up. I think the trend over the last few years has been something like 3 or 4% marine survival for streams in the Greater Georgia Basin.
I suppose with hatchery augmentation and 13% or higher marine survival, a few hundred fish in Kanaka and Brunette could have happened.
Oh, for those glory days of the mid-late 80's again ... sigh.
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The figures for adult capacities listed for all streams on the GGBSHRP site are based on 13% marine survival which may have been the case a decade or more ago when the figures were drawn up. I think the trend over the last few years has been something like 3 or 4% marine survival for streams in the Greater Georgia Basin.
I suppose with hatchery augmentation and 13% or higher marine survival, a few hundred fish in Kanaka and Brunette could have happened.
Oh, for those glory days of the mid-late 80's again ... sigh.
yeah totally, I saw that and laughed. 13 percent is gold! for some species on some systems which I know of, less than 1% is the norm even with hatchery aug :(
But hey - THESE are the new good old days, so conserve your catches and enjoy!
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Fish hunter your last post is an interesting thought, so how much does this behavior decrease survival chances do you think.
Honestly, your guess is as good as mine...
Don't get me wrong, fish feed on the surface regardless - even truly wild adults, but hatcheries encourage this behaviour during every feeding event... surface-dwelling is positively reinforced by pellet feeding :/ I sometimes wonder with the hatchery only rivers if each year it takes more fish to bring back the same number of adults as the year prior because of this...but we will never know exactly, as the ocean stage remains such a mystery as to what goes on out there...
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i was involved in hatchey steelhead programs for many years......its simple , take away the enhancement and they stop returning.
a good example would be the brunette and kanaka creek in the early 90's had upwards 300-400 fish....cut the program in the late 90's and 3 years later you get 6 fish back.
it just shows the hatchery band-aid is not the solution.
And the government always promised us that if the fish returning fell below 20 then we would get a return in funding to start with steelhead again. Well the steelhead counts are now below 6 in the Kanaka creek and still no funding. I guess this will be another stream where steelhead are gone. On a side note the cutthroat have faired a little better.
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Yes they can become wild. Wild self sustaining populations of rainbow trout and steelhead have been established from hatchery plants in many parts of the world.
However there is evidence that hatchery fish are not as genetically able to reporduce as wild fish:
http://www.sciencedaily.com/releases/2009/...90610091224.htm
http://rsbl.royalsocietypublishing.org/con...1.full.pdf+html
which suggests such interactions can be a negative thing.
I'd be careful about the loss of steelhead in a river like Burnette creek as the stream has very poor habitat. Steelhead were extripated from the river in the middle of the 20th century. Water quality is not great and there isn't much spawning gravel. Hatchery plants can't re-jeuvinate such a stream Kanaka doesn't have great habitat either.
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lol, thanks guys, i was just wondering if a if hatchery had offspring that it would be a wild. oops didn't know the sensitivity!.
Thanks Sandman and Fishunter your earlier replies were perfect, lets not blame who or who, it is what it is, safe to say a river with a hatchery is hard to tell if the wild are
"true" or "hatchery wild", but without the hatchery there probably would be no fish
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but without the hatchery there probably would be no fish
I'm all for wild fish, but amen to that in most LML flows.
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I think people need to exercise a little care when talking about wild vs hatchery and also about genetics, particularly when most of us are not 'experts'
Each steelhead will be genetically unique from each other though steelhead within a given river system likely have more genetic similarities than from another system.
Is a steelhead, the offspring of 2 hatchery fish that spawned in the river wild? Yes it is.
Has the interaction between hatchery fish that spawn in the river and wild fish changed the genetic character of the steelhead population of a river like the Chilliwack. Possibly.
There is good evidence from the US that this has taken place. But that's largely in rivers with a long (over 50 years) history of heavy hatchery augumentation where the wild and hatchery fish were also mixed in the hatchery and the wild fish had no protection from harvest and were basically fished to near extinction leaving mostly surplus hatchery fish to utilize the available spawning gravel.
This is completely different from how hatchery enhancement of steelhead has been managed in BC from the get go. There is not much evidence if any the fish in the Chilliwack have been genetically much affected by the hatchery program. There is also no evidence the Chilliwack needs that hatchery to sustain any of it's native wild salmonids. It just needs appropriate management.
Perhaps hatchery fish has changed the genetics of the wild fish but does anyone think the genetics weren't altered over decades of merely angling for them before the hatchery?
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Perhaps hatchery fish has changed the genetics of the wild fish but does anyone think the genetics weren't altered over decades of merely angling for them before the hatchery?
Based on the assumption that larger fish are killed at a higher rate, it's conceivable that angling could eventually remove the genes for large size from a population resulting in a lower average size :(
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Oops ... the above would only apply to a wild kill fishery so our great, great, great grandchildren probably have nothing to worry about ;)
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It would depend entirely on how you define "wild" and "hatchery" fish. The way I see it, "wild" fish are those fish where natural selection has occurred in every pairing in their genetic lineage to give an entirely wild genome, resulting in a very genetically-fit fish. That said, personal definitions of what is wild and what is hatchery aren't terribly important in the grand scheme of things and probably are best left to arguments on semantics.
Now for the Genetic 101 answer... Hatcheries reduce genetic fitness of steelhead offspring as sexual selection is removed from the reproductive process. The short explanation here is that hatcheries allow less-genetically fish fish the same chance at reproducing as more genetically-fit fish. The process hatchery process doesn't allow for natural selection to weed out the fish that, for whatever reason, are unable to find or hold on to a mate for long enough to pass on their genes.
I'm not aware of any documented instances where hatchery programmes have benefitted wild populations, or where hatchery fish have been able to recolonize a self-sustaining population that can exist without the help of a hatchery programme. Hatcheries do try to preserve genetic diversity by pairing one male with one female, that way if one set of genes is a dud, it only affects the offspring of a single pairing. Hatcheries do allow fish populations to exist in numbers where habitat is unavailable to support such numbers in the wild.
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I think people need to exercise a little care when talking about wild vs hatchery and also about genetics, particularly when most of us are not 'experts'.
Sorry Ralph, I forgot to post my bibliography. Absolon would be very upset with me too. I believe the second article below is the one you posted a link to (but yours did not seem to work when I clicked to check).
Hitoshi Araki, et. al. (2009, June 10). "Carry-over effect of captive breeding reduces reproductive fitness of wild-born descendants in the wild," Biology Letters, Retreived on February 6, 2012 from rsbl.royalsocietypublishing.org
Oregon State University (2009, June 10). "Hatchery Fish May Hurt Efforts To Sustain Wild Salmon Runs." ScienceDaily. Retrieved February 6, 2012, from http://www.sciencedaily.com /releases/2009/06/090610091224.htm
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Sorry Ralph, I forgot to post my bibliography.
I think you mean your C-V. Go ahead I can make 30 seconds available. :D
Sorry not trying insult anyone's background but just to caution about taking idle speculation as facts. How readily the findings of a few studies down south transfer to BC is hard to gauge.
believe the second article below is the one you posted a link to (but yours did not seem to work when I clicked to check).
Hitoshi Araki, et. al. (2009, June 10). "Carry-over effect of captive breeding reduces reproductive fitness of wild-born descendants in the wild," Biology Letters, Retreived on February 6, 2012 from rsbl.royalsocietypublishing.org
the link:
believe the second article below is the one you posted a link to (but yours did not seem to work when I clicked to check).
http://rsbl.royalsocietypublishing.org/content/5/5/621.full.pdf+html
opens a pdf ... works when I just did it. Not sure why it doesn't work for you or on this site
Last note: who defines wild by genetics? Wild is a qualitative description.
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I think you mean your C-V. Go ahead I can make 30 seconds available. :D
No, I meant bibliography...it was the list of articles that followed. Since I am not an "expert" myself (I am an environmental historian, not a biologist or geneticist), I get my information from other experts. 30 seconds? Sorry... I always have trouble getting my CV down to 2 pages. ;)
http://rsbl.royalsocietypublishing.org/content/5/5/621.full.pdf+html
opens a pdf ... works when I just did it. Not sure why it doesn't work for you or on this site
That one did work, I too am not sure while the other did not (the Science Daily one).
Last note: who defines wild by genetics? Wild is a qualitative description.
I don't know...but let me know when you find her ;D.
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Based on the assumption that larger fish are killed at a higher rate, it's conceivable that angling could eventually remove the genes for large size from a population resulting in a lower average size :(
there is this part and though there's been no kill on wild fish for 30 years or so kill was substantial before that. Those genes are gone. People use to think that only a % of fish were 'takers'. Catching a fish also changes it's before. It may effect reproductive efficiency. Some released fish die. I have known anglers who were quite insistent that a released fish was no longer a 'wild' fish.
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there is this part and though there's been no kill on wild fish for 30 years or so kill was substantial before that. Those genes are gone. People use to think that only a % of fish were 'takers'. Catching a fish also changes it's before. It may effect reproductive efficiency. Some released fish die. I have known anglers who were quite insistent that a released fish was no longer a 'wild' fish.
good points in this discussion.
Would it also be fair to say that where hatchery raised stock is released, that stock then competes with "wildstock" for both food and space? therefore it is reasonable to equate that the hatchery stock will affect the wild stock in an negative manner, especially so, if there is a point where overcrowding ( for want of a better word) takes place, the "wildstock" over time may show signs of both behavioral and physical change ie: more/less aggressive and probably a smaller size .
Are hatchery stock more inclined to hang around than wild stock and or breed with local rainbows?
Again through time and mating cycles this would have to make a difference to a genetic makeup. I think Gentics are directly linked to the evolution of that stock, it will adapt to change or die.
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It would depend entirely on how you define "wild" and "hatchery" fish. The way I see it, "wild" fish are those fish where natural selection has occurred in every pairing in their genetic lineage to give an entirely wild genome, resulting in a very genetically-fit fish. That said, personal definitions of what is wild and what is hatchery aren't terribly important in the grand scheme of things and probably are best left to arguments on semantics.
Now for the Genetic 101 answer... Hatcheries reduce genetic fitness of steelhead offspring as sexual selection is removed from the reproductive process. The short explanation here is that hatcheries allow less-genetically fish fish the same chance at reproducing as more genetically-fit fish. The process hatchery process doesn't allow for natural selection to weed out the fish that, for whatever reason, are unable to find or hold on to a mate for long enough to pass on their genes.
I'm not aware of any documented instances where hatchery programmes have benefitted wild populations, or where hatchery fish have been able to recolonize a self-sustaining population that can exist without the help of a hatchery programme. Hatcheries do try to preserve genetic diversity by pairing one male with one female, that way if one set of genes is a dud, it only affects the offspring of a single pairing. Hatcheries do allow fish populations to exist in numbers where habitat is unavailable to support such numbers in the wild.
You just described most the rivers in North America
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It would depend entirely on how you define "wild" and "hatchery" fish. The way I see it, "wild" fish are those fish where natural selection has occurred in every pairing in their genetic lineage to give an entirely wild genome, resulting in a very genetically-fit fish. That said, personal definitions of what is wild and what is hatchery aren't terribly important in the grand scheme of things and probably are best left to arguments on semantics.
Now for the Genetic 101 answer... Hatcheries reduce genetic fitness of steelhead offspring as sexual selection is removed from the reproductive process. The short explanation here is that hatcheries allow less-genetically fish fish the same chance at reproducing as more genetically-fit fish. The process hatchery process doesn't allow for natural selection to weed out the fish that, for whatever reason, are unable to find or hold on to a mate for long enough to pass on their genes.
I'm not aware of any documented instances where hatchery programmes have benefitted wild populations, or where hatchery fish have been able to recolonize a self-sustaining population that can exist without the help of a hatchery programme. Hatcheries do try to preserve genetic diversity by pairing one male with one female, that way if one set of genes is a dud, it only affects the offspring of a single pairing. Hatcheries do allow fish populations to exist in numbers where habitat is unavailable to support such numbers in the wild.
You just described most the rivers in North America
I didn't phrase that well. Let me rephrase: hatcheries allow larger numbers than can be supported with available habitat in the wild. There are two sides to that coin obviously; more fish means more availability to user groups, but at the same time more hatchery fish has a negative impact on wild fish. I value wild fish a lot.
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good points in this discussion.
Would it also be fair to say that where hatchery raised stock is released, that stock then competes with "wildstock" for both food and space? therefore it is reasonable to equate that the hatchery stock will affect the wild stock in an negative manner, especially so, if there is a point where overcrowding ( for want of a better word) takes place, the "wildstock" over time may show signs of both behavioral and physical change ie: more/less aggressive and probably a smaller size .
Are hatchery stock more inclined to hang around than wild stock and or breed with local rainbows?
Again through time and mating cycles this would have to make a difference to a genetic makeup. I think Gentics are directly linked to the evolution of that stock, it will adapt to change or die.
oops , but here anyway
http://icesjms.oxfordjournals.org/content/56/4/459.full.pdf
edit to add:
http://fwspubs.org/doi/pdf/10.3996/092010-JFWM-032
and another
http://www.sciencedaily.com/articles/f/fish_farming.htm