There’s a growing trend these days in the scientific community toward simulated studies, where the researchers, rather than going out into the field to test their hypothesis, simply plug it into a computer and run simulations. A computer simulation, of course, has about as much relation to the actual reality of a functioning ecosystem as does a video game car chase to a real one. The video game won’t put you in the ER; the real one is a good bet to do so. A great example of this is a study we came across a few months ago in which the researchers simulated the effect of stricter bluegill length and creel limits on a southern reservoir, and found that the limits had no effect; contrast this with a 1997 study done by Melissa Drake et. al., in the field on six lakes in Minnesota, that found that bluegill in lakes with low fishing pressure grew faster and reached larger adult sizes, averaging two inches larger, than bluegill in lakes with high fishing pressure.
But the Drake study was up north, some anglers might say; it has no bearing on southern bluegill. Consider then a 1992 study by Mark Belk on Par Reservoir in South Carolina. Par Reservoir is closed to fishing, and has been since it was constructed in 1958. Largemouth bass abundance in Par is three to four times that of twenty-five other southern reservoirs that Belk studied; largemouth also average ten to thirty percent larger in Par than the other twenty-five reservoirs he studied. Par receives thermal effluent from a nuclear power plant, but Belk studied five other thermal effluent reservoirs in the south that are open to fishing, and found that the bluegill in them had the same average size as public reservoirs not associated with thermal effluent.
Belk found that bluegill in those twenty-five other reservoirs that were open to fishing seldom exceeded 7.9 inches in length. He found that bluegill in Par reached 9.5 inches by age four; the largest bluegill captured by his team in Par was 10.9 inches.
Bluegill growth slows greatly once the fish matures reproductively and begins spawning; gonadal development takes a great deal of caloric investment, which means less energy left to be allocated to growth. Male bluegill generally grow larger than females, and we now know that there are two distinct types of male bluegill in most populations, parental males that mature reproductively at large sizes and feature the large opercular tabs, the “helmet” foreheads, and the dark coloring at spawning time; and cuckolder males that mature at much smaller sizes and resemble female bluegill in appearance. Mart Gross and Eric Charnov were the first to discover this phenomenon, on Lake Opinicon in Canada in a series of studies they did there in the late 1970’s; that team found that parental males matured at seven years of age in Lake Opinicon, whereas cuckolder males matured at two years.
Back to the South: Parental males in Par matured reproductively two years later than parental males in the twenty-five other reservoirs Belk studied. Par bluegill lived longer, with the maximum age among all fish captured being nine years compared to seven for the twenty-five other reservoirs. Whereas bluegill in the other twenty-five lakes matured reproductively at one to two years of age and sizes ranging from 2.3 to 4.4 inches, they matured in Par at an average size of 8.07 inches. Male bluegill in Par matured at an average size of 10.1 inches.
Imagine fishing a public lake where the average spawning male bluegill averages over ten inches.
The lesson to be had here is that sussing something out in one’s own head, does not make it reality. This, of course, is the entire foundation of the scientific method: it’s not fact until you prove it with an actual experiment.
A few years ago I made the mistake of trying to educate anglers on a couple online fishing forums about how overharvest was ruining bluegill size structure in public waters in the South. That was before I knew about the Belk study, but I was already very familiar with the Gross one, and knew that it had been accepted as scientific fact, and furthermore that several northern states had implemented stricter bluegill regulations in response to its findings; I also knew that more than a couple of those states were already seeing improvement in the size structure of their bluegill in public waters. And yet when I cited the Gross study, and the states that had already improved their bluegill fisheries with stricter regulations, more than a couple of the other participants in the discussion on that forum summarily dismissed my facts with their purely unscientific pontification that that was up north, and southern bluegill were different, couldn’t be overfished, etc. etc. The real mechanism at hand, of course, was the fact that they didn’t want to accept that their own actions, in the form of taking coolerfuls of bluegill themselves, might be adversely impacting the lakes and rivers they fished; they didn’t want to accept responsibility for their selfish actions. So they worked it out in their heads in a way that justified them.
What does this have to do with Tennessee lake and pond management, you might ask?
I made reference in a recent post to an online community of pond enthusiasts that has circulated a very ineffective management strategy for smallmouth bass in ponds. Said strategy is one that they worked out in their heads, rather than in the field, a fact that becomes abundantly clear when one looks at the results it has yielded. These same people also regularly advise any pond owner who will listen, on the largemouth bass harvest strategy that should be utilized for growing trophy bluegill in a pond.
This strategy, like their smallmouth strategy, is one that they sussed out in the world of theory, rather than the actual reality of what happens in a pond ecosystem. They tell pond owners to harvest any largemouth over fourteen inches from their trophy-bluegill pond because those larger bass, with their larger gape, could potentially eat larger bluegill. This idea sounds great in theory to someone who has never actually managed a pond for trophy bluegill and observed firsthand what is necessary to grow bluegill to monster sizes.
None of the folks recommending this strategy have ever grown a bluegill to two pounds. We, conversely, have grown dozens to that size, and something I learned early on in my many years of managing for trophy bluegill was that there’s a world of difference between simply having a crowded largemouth population, and actually having enough largemouth to limit bluegill reproduction sufficiently to grow two-pound bluegill, or even numbers of one-pounders. So for years now I have been telling pond owners never to keep any largemouth from their trophy-bluegill pond, regardless of size, because they need every last bass they can get to have any shot at achieving their bluegill goals.
We haven’t yet touched on why bluegill in Par mature two years later on average than the twenty-five other lakes Belk studied across the southeast. Belk found that the unusually high density of largemouth, coupled with the larger average size of the largemouth, exerted so much extra predation pressure on the bluegill that they delayed spawning to larger sizes: bluegill that spawned at young ages stayed smaller and got munched, so over time the bluegill that delayed spawning repeatedly passed on their genes and became the norm in the population.