Unnatural Selection causing fish to get smaller

[MoCarp]

good points... perhaps more detailed studies on the biodiversity of benthic critters would be in order?

most great fishing seems to have a diverse aquatic populations, less diversity are never as good

I think people moving dirt and erosion in general caused the gravel to find its way into our creeks, deforestation in the past of the Ozarks washed tonnage of gravel into the streams, I still think we are still paying the price for that, wintering holes on many streams are less deep,....food for though at least

[Al Agnew]

I've been doing some thinking on all this...supposedly, healthy forest cover means less erosion of gravel into the streams.  Makes sense...the tree roots stabilize the ground.  We know that before the huge logging boom in the Ozarks starting in the lat 1800s and continuing until the 1930s or so, there was a lot less gravel in the streams.  Early descriptions mention that much of the bottom of the streams described was solid bedrock.  Once the trees were removed and the land was often burned to "keep down the ticks" and keep the brush down so that there was more grazing, the streams filled up with gravel.  But now, there is a lot more land within national forests and much of the original forests have grown back into nice second growth, maturing forest.  So, theoretically there should be a lot less gravel entering the streams.  But we've all seen creeks that have filled in with gravel a LOT in the last few decades.  Why?

Well, I have an idea.  The original forests, pre-logging, were described as being big, widely spaced trees with GRASS growing around and underneath them.  Savannahs.  Or barrens, as some of the settlers called them.  Was it really the GRASS that was holding the gravel?  Now, look at almost any forest in the Ozarks.  Smaller, closely spaced trees, so closely spaced that grass almost never grows on the forest floor.  Maybe tree roots aren't enough to hold gravel.  Maybe the second growth forest actually allows a lot more erosion of gravel than the original forests.  Maybe that's why the gravel erosion that started with the extensive logging is simply continuing with second growth forest that shades out anything else that could hold the gravel.

The amount of gravel entering the streams is amazing, but since it happens in floods, you don't notice the actual influx of gravel, you just notice when it fills in pools.  But I know the volume is huge, due to a single instance I saw years ago.  On middle Big River, a storm settled and dumped 12 inches of rain over a very small area, with almost NO rain upstream.  So the river never rose upstream.  Yet all the ravines and small creeks entering the river in that small area were gushing in water...and gravel (and rocks as big as basketballs).  The river wasn't high enough, especially on the upstream part of that section, to take all the gravel that was coming in and spread it around, so it remained as huge deltas of gravel at the mouths of every hollow and creek.  A hollow that was ordinarily completely dry and not even very big, a couple miles long,(and completely forested) had a delta the size of the average garage at the mouth, spreading halfway across the river.

So maybe, even though we're doing things right in many cases, we're still paying for doing things wrong in the past.  When you couple that with the undeniable land clearing that goes on in many watersheds, and the gravel that's already in a lot of the smaller tributaries that is still washing into the larger streams with every flood, the streams are still filling in, a process that started long ago and has never really ceased. 

[Al Agnew]

5 hours ago, tjm said:

I'm not sure that the gravel infill either helps or harms over the long term, it has been happening a long long time, that's part of the karst geology as I understand it; most of the gravel is sucked into the streams from hilltop sink holes, isn't it? There are sink holes where there were none fifty years ago and more numerous holes where they were back when, do the hundreds of earth tremors that we experience each year have something to do with this?  I own about a quarter mile of limestone bluff and the leaching of minerals/formation of stalactites etc. is visually obvious over time, how does this chemically affect the streams? 

When I look at a creek and see no mounds of mussel shells, no hellgrammites , no numbers of crayfish I don't expect to see numbers of large fish and I don't believe catch and release will improve the food base. I suspect that over a long period the catch and release and the size limits won't make a real difference. 

During the last sixty, or perhaps the last thirty, years (or maybe this is a thousand year trend) there has been some change in the water chemistry that is harming the life forms? Frogs, there are more in my yard and field than on the creek and I've not heard a bull frog in decades. So is it unnatural that selection that predators are adapting to a less bountiful prey base?

Not much of the gravel comes from sinkholes.  See my thoughts above.  And chemical composition of the water coming from karst topography doesn't change much, either.  The karst in this case just means that there is a LOT of gravel within the matrix limestone (actually dolomite), and the dolomite is eroded and dissolved away, leaving the gravel on the surface.  Acid rain dissolves the dolomite quicker, though, and there's no denying that rain is generally more acid now, thanks to man-made pollutants and CO2 levels in the atmosphere rising.  But I don't think it's happening on a time scale quickly enough to make a huge difference in the amount of gravel coming in.

Numbers of game fish may not change much with changes in the food base in the Ozarks.  It simply doesn't take many adult smallmouth, for instance, to produce enough young to keep the numbers up.  But growth rates and top end size probably suffers greatly from reduced forage base.

My home stream, upper Big River, is a prime example.  The lead mine tailings that have been in the river for many years smothers the natural gravel and cobble bottom, filling in the spaces between rocks that hold a lot of benthic organisms, including crayfish.  Crayfish are far less abundant in the mine waste sections, hellgramites and other larger aquatic insects are practically non-existent, there are few if any sculpins, not a lot of madtoms.  Any critter that spends the day hidden down in the gravel and rocks is far rarer on Big River than the typical Ozark streams.  Yet the mine waste sections have plenty of bass, as many as any other stream with similar size and habitat.  But they are usually long, lean fish with bigger heads and tails than those on the Meramec, for instance.  They still have a lot to eat, because the minnow population is still high, but maybe it isn't as easy to catch minnows, even though some minnows have a greater nutritional value than crayfish.

[MoCarp]

good points... grass savannah almost park like situation with shortleaf pines prob was much better keeping gravel out of the streams, anyone thats trekked down a steep ozark hillside can tell you the gravel is right under the surface, ...It might be doable to dredge gravel out of historical deep holes even on small creeks and the gravel could be sold to offset costs

 I know 30 foot freight boats moved around the spring river around carthage before the dams when in, not a chance that could happen today, shoal creek downstream from grand falls is considerably shallower than was in my youth in the 70's ( hard to believe is was over 40 years ago)

[Al Agnew]

Nope, it's been studied and investigated by scientists in many different places, and pretty much proven that anytime you dig gravel out of a river channel, the adverse effects outweigh any good effects.  It simply isn't as simple as scooping out a bunch of gravel and making a deep pool.  I've done a lot of investigating myself, reading the literature on it and looking at the effects of gravel mining that I'm familiar with.  Digging gravel out of a stream channel further destabilizes the banks AND gravel bottom upstream, and more gravel just washes into the pool that's been dug, while the banks upstream start eroding.  The gravel bottom downstream also destabilizes, moving more gravel into the next deep pool.  This happens also when you dig on a gravel bar.  A natural gravel bar, even one without much vegetation on it, is reasonably stable.  But digging around in it loosens the gravel and makes it move, and I've seen this happen...the next deep pool downstream fills in with gravel moving off the loosened bar with the next flood.  Add in the huge disruption while digging is going on--siltation downstream, removing all cover from the dug-out area, tearing up the banks with the machinery and removing trees.

And you'd have to do it over and over again.  I've mentioned this elsewhere, but there was once two huge gravel dredged pools on lower Black River that I fished for walleye.  The upper one was more than a mile long, four or five times the width of the normal river channel, and 20-50 feet deep.  The lower was a bit less than a mile long, about twice the normal channel wide, and 15-35 feet deep.  There was just a riffle between them.  The lower one was the older of the two.  Keep in mind that lower Black River is controlled by Clearwater Dam and seldom floods much.

Dredging had stopped on the upper, newer pool by the late 1960s.  By the mid-1970s the upper one was starting to fill in a bit.  By the 1980s the upper half was getting pretty much filled in.  By the 1990s, the upper half of the upper pool was totally filled in and there was just a normal river channel winding through the gravel bars covered in small willows and sycamores.  By the 2000s that upper pool was 3/4th filled in.  Now, there is virtually nothing left of the upper pool except a little deepish backwater just above the riffle at its lower end and a big clean gravel bar just upstream.  And now the upper half of the lower pool is almost filled in.  That is a LOT of gravel moving in a river that seldom floods at all.

[tjm]

I have one of the many dry waterways on my place, lots of run off after 6"+ rain of course, but dry looking most all the time; thing is there is water moving under the gravel on most of these ditches and streams all the time. There is some substrate that holds water from going deeper into the earth and it moves the gravel ever so slightly all the time, I know a branch that flows at both ends and has a half mile of dry gravel between. Creeks I'm familiar with seem to all be underlayed with stone with the gravel over it; often the gravel is almost floating on water that moves through it. In effect the gravel flows.  Digging/dredging accelerates the flow, as an example, a neighbor excavated a 1/4 mile of the dry ditch and straightened it some what many years ago; over the next several months my portion of the ditch became noticeably deeper even with no rains that caused runoff. I saw a mining operation set in one spot for about 40 years that never ran short of new gravel. I'm sure it would still be there if the divorce had not ended in selling off the equipment and land. Dams tend to stabilize the stream of gravel above them,   I think, by stopping or slowing the flow of gravel as well as by slowing the runoff during floods. 

An observation on the erosion of the hills causing the gravel in the creek, My hill gravel is all sharp and is mostly chert of some sort and all most creek gravel is well rounded soft rock. I have never found a sea shell fossil in any of the hill rock, but, see many "scallop" fossils in the ditch rocks.  All the dry ditches hereabouts are several feet deeper than they were even 30 years ago. The one at my house is no wider than it was 50 years ago but is at least 4' deeper than it was then.

These bottoms are also loaded with 'sharp gravel' to the extent that some fields would look like solid gravel after being plowed, back in the days when they still farmed it.

[tjm]

Good news is that yesterday I saw a large crawdad, maybe 9" wing span. First in a long time.

[Al Agnew]

28 minutes ago, tjm said:

I have one of the many dry waterways on my place, lots of run off after 6"+ rain of course, but dry looking most all the time; thing is there is water moving under the gravel on most of these ditches and streams all the time. There is some substrate that holds water from going deeper into the earth and it moves the gravel ever so slightly all the time, I know a branch that flows at both ends and has a half mile of dry gravel between. Creeks I'm familiar with seem to all be underlayed with stone with the gravel over it; often the gravel is almost floating on water that moves through it. In effect the gravel flows.  Digging/dredging accelerates the flow, as an example, a neighbor excavated a 1/4 mile of the dry ditch and straightened it some what many years ago; over the next several months my portion of the ditch became noticeably deeper even with no rains that caused runoff. I saw a mining operation set in one spot for about 40 years that never ran short of new gravel. I'm sure it would still be there if the divorce had not ended in selling off the equipment and land. Dams tend to stabilize the stream of gravel above them,   I think, by stopping or slowing the flow of gravel as well as by slowing the runoff during floods. 

An observation on the erosion of the hills causing the gravel in the creek, My hill gravel is all sharp and is mostly chert of some sort and all most creek gravel is well rounded soft rock. I have never found a sea shell fossil in any of the hill rock, but, see many "scallop" fossils in the ditch rocks.  All the dry ditches hereabouts are several feet deeper than they were even 30 years ago. The one at my house is no wider than it was 50 years ago but is at least 4' deeper than it was then.

These bottoms are also loaded with 'sharp gravel' to the extent that some fields would look like solid gravel after being plowed, back in the days when they still farmed it.

Interesting...most of the gravel on bars in all the Ozark streams I spend time on is chert, or in the case of parts of Big River and the Meramec, among others, a mixture of chert and quartz druse.  A small percentage of it is limestone or dolomite, and sandstone, and on Big River gravel bars there is the occasional piece of volcanic rock that got washed down from the headwaters in the St. Francois Mountains.  You're right that chert gravel washing off the hills is usually sharp-edged, but even though it's a very hard rock, it gets worn smoother pretty quickly once in the river and being tumbled downstream by high water.  The drusy quartz, which is bits and pieces of the "sugar rock" that is common on the hillsides in certain geologic formations, is slower to get worn smooth--it stays rough for a long time in the stream.

I think there would be less environmental impact from dredging in the dry creek beds, if it was done right.  Doing it right means starting at the downstream end and working upstream as necessary, and most importantly, NOT digging deeply in the bed but mainly just skimming gravel a few feet deep.  What you've seen with your creek getting "deeper" with higher banks, is exactly what happens on any stream, wet or dry, when the gravel is dug too deeply downstream from a given point, and to a lesser extent if it's dug upstream from a given point as well.  Imagine the creek bed as a smooth, gentle slope going downstream.  Now dig a deep hole in the middle of that smooth slope, and the creek "wants" to smooth out the slope again.  So it takes gravel from upstream to fill in the slope, at the same time that it digs out gravel downstream to also bring that bottom to match the bottom in the hole.

[tjm]

Stacking marbles.

I don't know much about rocks and was unaware that chert slivers could be rounded quickly by tumbling. Have no idea what druse is. So maybe all this gravel is chert  and or druse. A lot of it is very light in the hand though with a generally pinkish color. I had associated it with iron, because it looks rusted sometimes, good bit of it looks somewhat like pictures of pumice with holes,or cavities.

The grandson found what he called a geode in my ditch, softer grey/pink somewhat rounded til he broke it and the inside looked like what I've heard called mozarkite.