A Question About The Black Bass Season

[Tim Smith]

Tim, hybridization is part of the problem, but I don't think it's a huge part. If it were, you'd catch a lot more obvious hybrids. In the stretches where spotted bass are in the process of taking over or have taken over, I'll catch about two hybrids for every 50 or so bass of both species that I catch.

Maybe the spots are more aggresive and get the best spawning areas, leaving the smallmouth in more vulnerable areas where the spawn fails or young are quickly picked off as they hatch.

That could be part of it, Justin, but if the spots are all runts, how are they displacing the larger smallmouth?

Al, I know this is a topic close to your heart, so I'd be anxious to hear any insights you may have. I don't see anything conclusive out there about how this kind of displacement plays out, but there are multiple scenarios where hybridization can impact a population without showing up in the fishery.

Remember, that's a cross of 2 species and with a genetic code that's not adapted to anything anywhere. Crazy mixed-up kids don't generally fare well in the world. Simply by feeding over-agressively hybrids could easily be wiped out by small predators before they ever reached 2 inches in length(even under ideal circumstances only 2 offspring would make it in a stable population anyway).

There is pretty good evidence that hybridization has wiped out smallmouth during spot invasions in the Southeast. There was much less hybrization where the 2 species co-occurred naturally.

Here's a couple of papers that studied this issue.

Hybridization between introduced spotted bass and smallmouth bass in reservoirs

Author(s): Pierce, Patrick C.; Van Den Avyle, Michael J.

Source: Transactions of the American Fisheries Society Volume: 126 Issue: 6 Pages: 939-947 Published: Nov., 1997

Abstract: Introductions of black basses Micropterus spp. beyond their native ranges have led to hybridization within the genus. In the southeastern USA, the potential for hybridization appears high because species introductions have been common in reservoirs. We determined the extent of hybridization between smallmouth bass M. dolomieu and spotted bass M. punctulatus in reservoirs in which introductions of either species into the native range of the other species had occurred. Three allozyme loci were used to distinguish the two species and their hybrids. Significant hybridization occurred in two of three reservoirs where introductions had been reported. In Lake Chatuge, Georgia-North Carolina, where the Alabama subspecies of spotted bass M. p. henshalli was introduced, 77 of 276 fish had hybrid genotypes, and only 2 fish had genotypes of the native smallmouth bass. In Thurlow Reservoir, Alabama, where smallmouth bass were introduced and Alabama spotted bass were native, 3 of 17 fish had hybrid genotypes. Only 1 fish with a possible hybrid genotype was identified in two reservoirs containing native smallmouth bass and northern spotted bass M. p. punctulatus.

Cytonuclear introgressive swamping and species turnover of bass after an introduction

Author(s): Avise, J. C.; Pierce, P. C.; Van Den Avyle, M. J.; Smith, M. H.; Nelson, W. S.; Asmussen, M. A.

Source: Journal of Heredity Volume: 88 Issue: 1 Pages: 14-20 Published: 1997

Abstract: Species-specific RFLP markers from mitochondrial DNA (mtDNA) were identified and employed in conjunction with previously reported data for nuclear allozyme markers to examine the genetic consequences of an artificial introduction of spotted bass (Micropterus punctulatus) into a north Georgia reservoir originally occupied by native smallmouth bass (M. dolomieui). The cytonuclear genetic data indicate that within 10-15 years following the unauthorized introduction, a reversal in these species' abundances has occurred and that more than 99% of the population sample analyzed here consists of spotted bass or products of interspecific hybridization. This demographic shift, perhaps ecologically or environmentally mediated, has been accompanied by introgressive swamping; more than 95% of the remaining smallmouth bass nuclear and cytoplasmic alleles are present in individuals of hybrid ancestry. Dilocus cytonuclear disequilibria were significantly different from zero, with patterns indicative of an excess of homospecific genetic combinations (relative to expectations from single-locus allelic frequencies) and a disproportionate contribution of smallmouth bass mothers to the hybrid gene pool. Results document dramatic genetic and demographic changes following the human-mediated introduction of a nonnative species.

HYBRIDIZATION BETWEEN SMALLMOUTH BASS, MICROPTERUS-DOLOMIEU, AND SPOTTED BASS, M-PUNCTULATUS, IN THE MISSOURI RIVER SYSTEM, MISSOURI

Author(s): KOPPELMAN JB

Source: COPEIA Issue: 1 Pages: 204-210 Published: FEB 1 1994

Times Cited: 13 References: 17 Citation Map

Abstract: Micropterus dolomieu, M. punctulatus, and hybrids between the two species were examined electrophoretically to provide identification and to determine the extent of introgression. Micropterus punctulatus has invaded Moniteau Creek and South Moreau Creek, two tributaries of the Missouri River system in central Missouri, in the past 50 years. Samples of the two species from nonhybridizing populations were also examined to establish diagnostic loci. Allozyme patterns revealed a high hybrid proportion in population samples from the two study streams. Only one F-1 hybrid was identified, indicating that limited interspecific hybridization events are occurring. Most hybrids were diagnosed as backcrosses with the most abundant pure species in each stream, verifying that introgression has occurred. Environmental factors have likely contributed to the higher rate of hybridization in these streams than in other streams where the two species occur. Electrophoresis of allozymes proved a suitable technique for detecting introgressive hybridization under these circumstances.

It's likely that effects of hybridization play out differently in different environments. I've fished streams where spots and smallmouth seemed to be in equillibrium, where long term data suggests smallmouth have displaced spots, and where spots seem to have taken over. What exactly happened/is happening in Missouri? You'll need more data to know for sure. And you'll need a controlled scientific experiment to know if removing the catch limit will help.

[Al Agnew]

Interesting stuff, Tim.

The possibility that strikes me as seeming to be likely is that, as you said, the hybridization is occurring very regularly but the young of the year hybrids are not surviving. I could see a scenario where a lot of male spotted bass are herding female smallmouth to their nests and spawning with them, thus removing those females' eggs from the future smallmouth population, but the hybrids produced don't survive well. So spotted bass spawning with other spotted bass produce lots of young, male spots spawning with female smallies don't produce much, but fewer female smallmouth are spawning with male smallmouth, thus producing fewer smallmouth young.

While I don't expect the streams most affected to ever get back to the way they were, it seems that on the lower Meramec at least, and perhaps the middle portion of Big River, the population ratios have reached some kind of equilibrium, and in some areas smallmouth have actually gotten a little more common in the last few years. However, I have to wonder how many of the seemingly pure smallmouth actually have spotted bass genes that could perhaps reduce their growth rate and potential top end size.

I've written this before, but even on streams where spotted bass are native, changes in conditions in some cases seem to have made spots more common. Specifically, the streams above the big reservoirs seem to have more spotted bass than they did before the reservoirs were built. The reservoirs are excellent spotted bass habitat, and spotted bass are big upstream migrators, so there seems to be a constant influx of spots out of the reservoirs and up into the streams above. The James River, Kings River, War Eagle Creek, Bryant Creek all seem to have more spots than the habitat says they should compared to similar streams not connected to the big reservoirs. On the other hand, the upper North Fork has very few, probably because it's too cold.

The other reservoir effect is on lower Black River, which once had a dominant smallmouth population all the way down to fairly near Poplar Bluff. But the construction of Clearwater Dam, a flood control dam that releases water from the reservoir surface, made the lower river warmer and more murky, thus favoring spots.

However, in recent years, in both the lower Black and the St. Francis there seem to be more smallmouth than there was a couple decades ago. The St. Francis is the oddest situation. In most undammed streams where spots are native, the smallmouths dominate in the faster, cooler, clearer upper portions and spots get more common in the lower ends where it's slower and murkier. But the St. Francis isn't like this. It has spots throughout. In the upper end up around Farmington, spots are common and smallmouths very rare. Then the river goes through a series of shut-ins with rapids, and in those areas and below smallmouths have always been present. Below the shut-ins area smallies were present but until 20 years or so ago weren't all that common and were outnumbered by spots. Now, the smallies seem to have really increased in population over most of the river. Interestingly, largemouths are also very common over the entire St. Francis, much more common than they are in most Ozark streams. If you want to fish a river in Eastern Missouri where you never know what kind of bass the next one that hits will be, go fish the St. Francis.

[Smalliebigs]

Interesting stuff, Tim.

The possibility that strikes me as seeming to be likely is that, as you said, the hybridization is occurring very regularly but the young of the year hybrids are not surviving. I could see a scenario where a lot of male spotted bass are herding female smallmouth to their nests and spawning with them, thus removing those females' eggs from the future smallmouth population, but the hybrids produced don't survive well. So spotted bass spawning with other spotted bass produce lots of young, male spots spawning with female smallies don't produce much, but fewer female smallmouth are spawning with male smallmouth, thus producing fewer smallmouth young.

While I don't expect the streams most affected to ever get back to the way they were, it seems that on the lower Meramec at least, and perhaps the middle portion of Big River, the population ratios have reached some kind of equilibrium, and in some areas smallmouth have actually gotten a little more common in the last few years. However, I have to wonder how many of the seemingly pure smallmouth actually have spotted bass genes that could perhaps reduce their growth rate and potential top end size.

I've written this before, but even on streams where spotted bass are native, changes in conditions in some cases seem to have made spots more common. Specifically, the streams above the big reservoirs seem to have more spotted bass than they did before the reservoirs were built. The reservoirs are excellent spotted bass habitat, and spotted bass are big upstream migrators, so there seems to be a constant influx of spots out of the reservoirs and up into the streams above. The James River, Kings River, War Eagle Creek, Bryant Creek all seem to have more spots than the habitat says they should compared to similar streams not connected to the big reservoirs. On the other hand, the upper North Fork has very few, probably because it's too cold.

The other reservoir effect is on lower Black River, which once had a dominant smallmouth population all the way down to fairly near Poplar Bluff. But the construction of Clearwater Dam, a flood control dam that releases water from the reservoir surface, made the lower river warmer and more murky, thus favoring spots.

However, in recent years, in both the lower Black and the St. Francis there seem to be more smallmouth than there was a couple decades ago. The St. Francis is the oddest situation. In most undammed streams where spots are native, the smallmouths dominate in the faster, cooler, clearer upper portions and spots get more common in the lower ends where it's slower and murkier. But the St. Francis isn't like this. It has spots throughout. In the upper end up around Farmington, spots are common and smallmouths very rare. Then the river goes through a series of shut-ins with rapids, and in those areas and below smallmouths have always been present. Below the shut-ins area smallies were present but until 20 years or so ago weren't all that common and were outnumbered by spots. Now, the smallies seem to have really increased in population over most of the river. Interestingly, largemouths are also very common over the entire St. Francis, much more common than they are in most Ozark streams. If you want to fish a river in Eastern Missouri where you never know what kind of bass the next one that hits will be, go fish the St. Francis.

Al, I was about to mention that the St Francis is making a come back withe population of smallies.I noticed it in 2009 and in 2010, I'm anixous to float it this spring when the levels are right.

I have also seen a huge increase in smallies in the Salt River in the last two years......just my opinions....two positive things from me so it doesn't sound like I'm bitching all the time

[Tim Smith]

The other reservoir effect is on lower Black River, which once had a dominant smallmouth population all the way down to fairly near Poplar Bluff. But the construction of Clearwater Dam, a flood control dam that releases water from the reservoir surface, made the lower river warmer and more murky, thus favoring spots.

However, in recent years, in both the lower Black and the St. Francis there seem to be more smallmouth than there was a couple decades ago. The St. Francis is the oddest situation. In most undammed streams where spots are native, the smallmouths dominate in the faster, cooler, clearer upper portions and spots get more common in the lower ends where it's slower and murkier. But the St. Francis isn't like this. It has spots throughout. In the upper end up around Farmington, spots are common and smallmouths very rare. Then the river goes through a series of shut-ins with rapids, and in those areas and below smallmouths have always been present.

That's how it works in Central Illinois too. You usually know immediately which species you've caught just because of the habit habitat you're in.

About once a year I fish a long slow gallery of timber fall downs in Central Illinois. Until recently it used to be full of big spots, but those have gone...died of old age I assume. I also rarely see hybrids there, but they do occur.

In that system there is a long term data set there that shows smallmouth were nowhere in sight 100 years ago...but now they dominate most of the river. I have hypothesized that the river was silitier at the beginning of the 19th century due to the coal mining on the river there there and that favored the spots. Now things are better (but not perfect) and the hard substrates have opened the door for smallmouth. It's just a guess.

As is the notion the spotted bass affinity for warmth is one reason The Subject That Shall Not Be Named will affect this forum and middle American fisheries more and more in years to come.