The reason for the bluegill population explosion, Dr. Bennett explains, is that largemouths are not solely piscivorous, as biologists thought, but omnivorous. Only half their diet is made up of fish. Thus the bluegills were able to increase rapidly, and as they did they not only ravaged the small bass coming off nests as fry but also competed successfully with them for such food as crayfish and other crustaceans (Daphnia, Chydorus, Bosmina, Diaptomus and Cyclops), nymphs (damselflies and dragonflies) and frogs. "As the bluegills go up, the bass go down," Dr. Bennett says. He is now able to control the bluegill population by drawing the water level of the lake down 15 feet in the fall. As the water recedes, the bass dive for the bottom, but the numerous small bluegills seek cover on higher ground and are ultimately left abandoned on the shore. "When there are no natural predators, man must take their place," Dr. Bennett says.
Unless a pond owner is absolutely wild over fishing for bluegills, Dr. Bennett cautions against stocking bluegills with largemouths. The bass will do well enough on their own, though they are unlikely to grow to lunker size. For that, forage fish are necessary, and for this, Dr. Bennett recommends lake chubsuckers. He prefers them over other species of fish because they do not stir up the bottom, they feed on aquatic organisms the bass usually ignore, and they produce large numbers of young at the time small bass are coming off the nests. On no account, Dr. Bennett says, should any carp or goldfish be released in bass waters. Both are highly reproductive; in point of fact, goldfish may spawn within 36 hours after stocking. Moreover, both goldfish and carp root up the bottom for food. This makes the water turbid, and silt can prevent bass eggs from hatching. The turbidity also makes it difficult for mature bass to eat since they feed by sight.
As a result of Dr. Bennett's research, the state of Illinois has done away with closed seasons on largemouths. "I think the closed season is the silliest law ever concocted," he says. "We presume that by closing the season we're going to have a lot of bass, and that isn't true at all. The whole thing revolves around the fact that it isn't the fishermen who control the number of bass, but the other fish populations. We know from our experience at Ridge Lake that any time the bluegill population rises above 2,000 fish per acre, they're going to start depressing the bass. It's a mistake to close the season, impose a creel limit and a minimum length, and wait for the bass to build up to a big population. The bass never do on this basis.
"There's only one reason for a creel limit on bass that I can think of, and that is because some fishermen are successful and others are not. Our studies show that 10% of the fishermen—and it's consistently the same 10%—catch 80% of the bass, and the remaining 90% catch only 20%. A creel limit stops those 10% from making hogs of themselves. There wouldn't be any danger to the fish, but it would be a waste of fish. In the old days, fishermen used to catch 100 to 200 bass apiece in a day on the Illinois River. They caught so many that they just dumped them on garbage heaps.
"Legal length? What's the basis for legal length? So the bass can reach maturity and spawn. But what difference does it make, if one pair of bass is capable of repopulating a lake like this with its own spawn? We know that Ridge Lake won't support more than 2,000 bass of assorted sizes, from four inches to nine pounds. Now suppose that in some way you could take 1,900 of those bass out of here and leave only 100. And we'll assume that half of those 100 are females. Well, we know from counting eggs and checking broods of young that one of those big females is capable of producing 10,000 young. We know that this lake won't support more than 2,000 bass, and yet this one bass can produce five times that. Why impose a length limit so that each bass can reach sexual maturity? Nobody is going to catch 1,900 of the 2,000 bass here. Nobody's going to catch near that many. In our most successful seasons here, fishermen have been able to catch only 60% of the available bass, about 50% of the total poundage. And that 50%—and we think probably more—can be replaced in one season. When bass are taken out, they leave available the food they would have eaten, so the bass that are not caught are capable of growing much more rapidly.
"Fish have indeterminate growth. When you buy a pup, you can say that within a year he will reach mature size, and after that he won't be any larger in bone structure, whether you feed him well or poorly. But a fish keeps growing throughout its life, depending on the amount of food it can swallow and digest. It doesn't grow an inch this year and an inch next year. A fingerling bass in this part of the country can, with good food, get up to 11 inches in one summer. If it has poor feeding, it may be only two and a half inches long at the end of the summer. We've seen bass nine years old and only nine inches long. The only thing that grows are the eyes. Why the eyes grow, I don't know. They're oversized in a stunted fish.
"The danger in the average lake or pond is too many fish rather than too few. The idea is sometimes hard to sell to fishermen. But the fact is, overpopulated ponds often seem to contain no fish. The exceptional fishing found in a naturally primitive environment—before man comes in, settles down and spoils it—is the result of predation and growth. Predators prevent any one species offish from becoming overabundant, because they're continually being thinned out. Those that survive grow rapidly.
"In evolution, fishes represent a very old group. They've been around millions of years. As they evolved, predators came along and evolved with them. As new forms of predators evolved, such as fish-eating birds, reptiles, amphibians and mammals, the fish evolved to compensate for this, probably by laying more eggs. So over the years, relatively high predation and relatively high production of young became the norm. The welfare of the fish population actually depended on this high predation. If there were not this high predation in primitive areas, the fish would overpopulate the natural environment.
"Here is a good example. When I was out at McCook, Nebraska, we used to take trips to the primitive northern part of the state to fish and hunt. We located a lake, five miles long and about a mile wide, that was filled with thousands of bullheads. They were whoppers, for bullheads. Most of them went to a pound, a pound and a half. We'd go in with hip boots and use worms, and the limiting factor as to how fast you could catch them was how fast you could put a worm on. They were all big. You'd catch so many that you'd get to the point where you could hardly drag your stringer out of the lake. Now, bullheads are notorious for overpopulating and stunting. So it was very unusual to have such consistently large ones.
"One year we got the idea of going duck hunting up there. So we drove all night and arrived just before daybreak. We really thought we were going to have some good shooting, but we never used a shell. We saw no ducks, only the fish-eating, fish-tasting American mergansers. They're rough. You can't eat them. So we had to move to another lake to get mallards. Now a rancher there told us those mergansers came through that bullhead lake, spring and fall, regularly. They'd stay a couple of weeks, and obviously they were culling the small bullheads, thus leaving the big ones for us to catch.