I respect your opinion, Eric. But my assertion is neither unfounded nor baseless; in an earlier post I outlined my objections in more detail; I didn't do so here initially out of a desire to not specify the study I'm referring to. I want to make friends in this business; but I won't bite my tongue if I feel pond owners and anglers are being misled. I did go into depth above on one of my objections, and I think it would be very difficult to counter my argument above: the size structure of a significant food source of a fish has been proven to affect the growth of the fish, and yet inexplicably the study notes that plankton size was reduced, but then claims it shouldn't have an effect. The author who cites this study as evidence that gizzard shad don't affect bluegill size also claims bluegill don't eat plankton, and claims to have proven this in research he did for his master's; but his statement directly contradicts what has been accepted as scientific fact by fisheries biologists and anglers across the country for many years; and, not one bit of substantive proof was given in the study corroborating this claim - it was simply stated by the author that he had observed that bluegill eat mainly invertebrates in well-fertilized ponds, without in any way stating how he observed the bluegill feeding. As I noted in my post a couple months ago on this subject, there is no mention of how he came to this conclusion - did he scuba-dive in the pond and videotape bluegill of all sizes feeding for days or weeks, and in that process observe that they only ate invertebrates? Invertebrates on average are pretty small, so he would have to be pretty close to the bluegill while they were eating to determine this conclusively; further, he would have to record a large number of bluegill of all sizes over an extended period of time. A well-fertilized pond has a visibility of 18" or less, so it would be quite difficult even to get close enough to a wild feeding bluegill to see him, much less get him lighted well enough to videotape; and it would be an extraordinary feat indeed to capture one of the invertebrates on video in such conditions; it would be completely impossible to do so with plankton, meaning if a bluegill ate a plankton, he certainly wouldn't be able to see it, much less document it. As I suggested before, did he examine the contents of several bluegill stomachs and upon not finding any microscopic plankton conclude the bluegill had not eaten any? I think it would be very difficult to prove that bluegill don't eat plankton; it would be one thing if it had not already been accepted as scientific fact that bluegill DO eat plankton, when he made his claim; but he simply made the claim with no substantiation whatsoever. When you make a claim that one hundred percent contradicts accepted science on the topic and then don't give empirical evidence backing your claim, and give no mention beyond that of your methods by which you arrived at your claim, that's bad science.
Getting back to the study that the author cites as proving gizzard shad have "no effect" on bluegill size, and don't compete with bluegill: the study consisted of one lake. I think it's pretty safe to say that any objective scientist from the field of fisheries science or any other science would look at a conclusion based on an experiment with only one subject, and quickly conclude that the study was not a thorough study, and therefore not valid. And then there's the study itself: the researchers chose a lake that already had gizzard shad. They applied rotenone to kill the shad, then observed the bluegill and bass populations. A few years later the gizzard shad had recovered to their pre-rotenone levels, and based on the data they observed while the shad were rebounding the researchers concluded that gizzard shad do not affect bluegill populations. That's about as sloppy as science can get.
1) Partial elimination is not remotely the same as complete elimination of shad. The fact that the shad were able to rebound to prominence within a few years of poisoning shows that obviously several shad remained in the lake, and had good success relatively quickly in spawning. I'm going to go out on a limb here and assume that the largemouth present in the lake did not suddenly agree to stop eating any gizzard shad they could fit into their mouths during the time of the study, which means the shad were quickly able to spawn successfully despite pressure on them and their offspring from the bass (and catfish, and crappie, all of which are present in the lake) in the lake, which means there's a very good likelihood that there was not a significant period of time when the lake was largely free of the influence of shad on its population dynamics. Unless the shad tried several times unsuccessfully in the first two or three years to spawn, and then suddenly had a successful spawn, which is extremely unlikely, the shad that remained in the lake were spawning successfully and adding to the lake the bass's preferred forage in fusiform prey, always preferred over cuneiform prey such as bluegill, within a few months (maximum) of when the study began. This alone makes it at best not good science, and at worst irresponsible research. Who would give credence to a study entitled, "The Effects of Gizzard Shad Just Getting on Their Way Back to Prominence in a Lake?" Yet that's exactly what this was. And no one has questioned it. Look at how quickly carp rebounded in the lake of a PB regular on the forum who just rotenoned a couple months ago with the intent to kill every fish in the lake, especially the carp. They had to do a second kill within a very short time period of the first.
2) Even more egregious than the way the experiment was set up, is the complete lack of research into the effects the gizzard shad may have already had on the lake that would not be righted merely by removing them. Gizzard shad are known to impede bass recruitment; this study was done on a public lake, and public lakes generally have a lower density of bass per acre even without shad or any egg-eating species other than bluegill being present, simply due to high fishing pressure. It is eminently possible that Walker Lake had a low bass density before the study was ever begun; the article even states that researchers expected bass recruitment to increase, which implies bass numbers were not high at the outset of the study. This can be at least partially attributed to the presence of gizzard shad in the lake for years before the study was undertaken - and yet no action whatsoever was taken to counter the low bass numbers other than the partial removal of gizzard shad. If there were still enough gizzard shad in the lake to spawn successfully, I doubt those shad swore an oath to stop eating bass eggs for the duration of the study; and if the bass numbers were already low from the influence of the shad, then it would take far fewer shad to negatively impact the recruitment of the bass. Most importantly, though, if bass numbers had been reduced by the presence of gizzard shad for a number of years, then there's a very strong possibility that the bluegill population of the lake was overpopulated at the time of the outset of the study. If this was the case, then the study had no chance at validity because removing a portion of the bass's preferred food source would make no difference in an overpopulated bluegill population if there were already too few bass to control the bluegill even in the complete absence of gizzard shad. Here are a few pictures of bass recently caught from Lake Walker:
http://www.outdooralabama.com/Fishing/freshwater/where/lakes/walker/angler/The lake recognizes trophy bass caught by anglers - with a ten-pound minimum. Based on that and these pictures, and the authors of the study's remarks about expecting bass recruitment to increase when shad were reduced, I feel pretty safe in concluding that this lake is decidedly low-density with its bass population. Which means less predation on the bluegill, and seeing as how the lake is only 163 acres, it's highly possible that the bluegill are overpopulated. The fishing information listed for the lake states that the bass fishing is good year-round; nothing positive is said about the bluegill fishing, which would lead one to conclude that the bluegill are probably small, and probably were small before the study began, meaning they were probably overpopulated. Bluegill when overpopulated drastically reduce bass recruitment; so it is very sloppy science indeed to expect that suddenly removing a portion of one species that reduces bass recruitment will result in better bass recruitment if another species that just as severely reduces bass recruitment when overpopulated, is at an overpopulated state.
If the bluegill were already overpopulated when the shad were reduced, the bluegill would not suddenly increase in numbers because they were already at a level at which their food source did not meet their numbers. They would not suddenly increase in size because they were overpopulated and removing the shad would do nothing to alleviate the low numbers of bass that had led to the bluegill overpopulation in the first place, or the overpopulation and resultant food shortage.
3) Walker Lake has crappie. 163 acres is small enough that crappie are eminently capable of overpopulating it. No mention whatsoever is made in the study of the possible effects of crappie in the lake on bluegill size. If large numbers of crappie were present in the lake at the time of the study, removing gizzard shad would have no effect on the direct competition for food that the crappie present to the bluegill in the lake. It could reasonably be assumed that removal of the shad would make said competition worse, as certainly the crappie would have been feeding on gizzard shad fry and fingerlings, and when that food source was reduced they could logically be expected to eat more invertebrates etc.
4)The article in question notes that many people in the past have said that gizzard shad will take over a lake, and then states categorically that this is not true - with not a shred of substantiation, no proof of any kind, not one study, no data whatsoever. I personally have more than once read accounts of state agencies stocking tiger muskie or taking other remedial measures to reclaim a public lake because gizzard shad had taken over the lake to the point that they occupied 70% of the total biomass of the lake. So for the author of the article championing gizzard shad to claim that this doesn't happen, is not just bad science, it borders on dishonesty and misrepresentation to the reading public.
Even if none of the major, fundamental flaws I've listed above existed with the study, simply the fact it was performed on just one lake, renders the study bad science; I think any objective scientist from this field or any other would be amazed that someone claiming to be a scientist would even try to present it as a study. When taken in sum with the fact that the shad were never eliminated from the lake and were rebounding in the lake from the moment of inception of the study, I think it's pretty bad science, and that it's irresponsible to advise pond owners based on it. The author of the study is probably not a bluegill fisherman; he likes catching big bass, and he wants to grow big bass in his clients' lakes; that's completely understandable, and his company does an exceptional job of doing that. But I'm working right now with a lake that company used to manage, that according to the owner had huge bluegill in years past; five years ago threadfin and gizzard shad were stocked in the lake. The bluegill are overpopulated now and average 4", whereas they once averaged 9" or better. I've seen firsthand that it's simply not true that shad don't impact bluegill very severely in a negative way, not just in this lake but many others. I have the utmost respect and admiration for the author's company, for many reasons; I'd love to work for them but I don't have a degree in fisheries science. But just because I admire 99% of what they do, does not mean I'll bite my tongue if I feel pond owners are being misadvised and told something that's just not true.
