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ranger520vx

Where are all the BIG FISH?

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Very interesting read folks....

 

LINK

 

 

Fish that lunge at lures drain gene pool

Tom Spears , Canwest News Service

Published: Tuesday, February 26, 2008

OTTAWA- Old-timers who insist that fish don't bite like they used to are right, says a new Canadian study that warns we're killing off the aggressive, fast-growing fish in lakes and oceans.

Aggressive fish chase food harder, grow faster and get caught more often. These, unfortunately, are the fish that would have the largest number of offspring if they lived.

That's likely one reason the northern cod isn't coming back faster, the University of Calgary study suggests: fishing killed off the fittest fish.

What happens is a reverse of the usual evolution. The timid, slow-growing fish lose the race for food and would normally lose the evolutionary race. But in heavily fished waters they're the ones that survive and pass on their genes. The result: a whole gene pool of slow-growing, passive, timid fish that don't lay very many eggs.

``Fast-growing fish . . . are harvested at three times the rate of the slow- growing genotypes within two replicate lake populations,'' says the study, published today in the Proceedings of the National Academy of Sciences.

Peter Biro and John R. Post of the University of Calgary studied rainbow trout in two small lakes near Merritt, B.C. The idea came from the fact, already well known, that some fish in any population are much bolder than others, Biro said in an e-mail interview from Australia. He is now a postdoctoral fellow at the University of Technology in Sydney, but did the fish research while in Calgary.

``It just made sense that those that tend to be active and bold would also be more likely to bump into and be caught by gill nets . . . Active and bold fish encounter more food, feed more and grow more, but get caught and killed more.''

That theory is what the experiment tested. The young fish tend to carry on the same personality - aggressive or timid - as their parents, he noted. This leads to a population where the aggressive fish are weeded out and replaced by shy ones. Biologists call this ``genetic selection.''

Timid fish, he said, are generally less fit for breeding. ``The problem is that such a population does not yield much to a fishery (remaining fish are harder to catch and smaller, so less profitable) and does not rebound well from overfishing because slow growers tend to be smaller at any age, possess fewer eggs, smaller eggs, and hatch smaller young that are less likely to survive.

``We think this is the reason why the (Atlantic) cod is not rebounding well after closure of the fishery,'' he said. ``The same arguments apply for (sport) angling as for commercial fishing.''

Aggressive fish grow larger, but protecting big fish doesn't help save the aggressive ones, the study found. This is ``because fast-growing fish that are still small (young) are zooming around gathering food at high rates which gets them into trouble.''

The results from both lakes were identical, lending support to the conclusions, the two scientists wrote.

Edited by ranger520vx

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Those are pretty interesting observations. I was under the belief that food supplies for fish were much more of a determining factor in a species ability to grow in size and numbers. Hmmm... this just seem to be getting more and more complicated!LOL

HH

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That doesn't disprove Darwin's theory at all. It actually supports it...

 

Defianlty an interesting study, but i think the dude made a few inferances outside the scope of the study. There is a few other points I might bering up later....but i have to get back to a lab report on Lead Availability in soils.

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That doesn't disprove Darwin's theory at all. It actually supports it...

 

Defianlty an interesting study, but i think the dude made a few inferances outside the scope of the study. There is a few other points I might bering up later....but i have to get back to a lab report on Lead Availability in soils.

 

Here is my take on it and I am not a biologist by any means. Please correct me where you see fit

 

Natural Selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.

 

So if the large, aggressive fish are getting caught at three times the rate ( and probably defintion..kept) , they are slowly decreasing the amount of offspring that can ever get that "aggressive" trait to maintain a population of large fish.

 

Central to Natural Selection theory is the concept of "fitness". Although fitness is most often as illustrated in the well-known phrase "survival of the fittest "- evolutionary theory defines fitness in terms of individual reproduction.

 

If only small, unproductive fish remain in a body of water- how does that support Darwin and the "survival of the fittest" theory? They are "fittest" in not biting lures, not in physical attributes.

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Most of what you said is correct. You understand most of the assumptions of His theory. But the "Survival of the fittest" isn't really what natureal selection is refering too...as far as our common use of language is concerned. Fitness is the average contribution of genes to the next generation. That means the better you are suited to your environment, the more you will reproduce, thus increaseing your overall fitness. (I think you understood that point)

 

Evolution isn't something that selects "better" traits from our point of view. Selection occurs on the individual and those that are "maladapted" to their environment have a lower fitness level. The agressive fish can't survive under this type of predation. So like you mentioned, the fitness of the non-agressive fish is increased. That means the non-agressive fish are now more fit the the agressive fish, because they arnt reproducing.

 

What we end up seeing is the population evolving to a place with an overall lower reproductive rate, and less agression. They have evolved to avoid the nets and lures essentially, despite the fact that their reproduction is decreased.

 

I woke up about 20 minutes ago, so let me know if I need to explain that better. Im pretty sure you understand the concept, it's just that you are judging whether or not it's for "the good of the species". Evolution doesn't have to be a positive thing all the time....especially when humans are involved in the selection. If evolution was acting on the population due to this selection , you wouldnt see a shift in the population's structure like this study is showing.

 

This is a great convo by the way....i enjoy discussions of this nature.

 

-Ramble

Edited by Ramble On

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