The experimental ten-sunfish limit is also in effect on Pools 5 and 5a. I fish 6 and 8 during the winter, and I do believe the size of the bluegills on Lawrence Lake (Pool 8)has gone up since the tighter limit went into effect.
The Lake Winona bluegill study done by the DNR found that in fertile waters with ample food and habitat for bluegills, the key to improving the size structure of populations facing heavy fishing pressure lies in limiting the harvest of large male bluegills. I lived in Winona for seven years, and as anyone familiar with the lake knows, it is over-run by stunted bluegills, a situation the DNR has been trying to fix for twenty years. What they found was that when male bluegills begin spawning, all their energy goes into spawning and they stop growing. In a balanced bluegill population, large males rule the spawning beds, and stop smaller males from spawning. This allows those smaller males to keep growing. Remove too many of the large males, and smaller males begin spawning, and stop growing. This begins a vicious cycle, as anglers often respond by keeping those smaller males as the best available, thus allowing still-smaller males to spawn…the end result is Lake Winona. As I recall, the cycle is difficult to break, once the overall average size of spawning males has diminished to a certain point.
This finding does not apply to all bluegill populations, but it did indicate that limiting the harvest of large bluegills in very good bluegill habitat could improve the average size of the bluegill in those waters. Building on that, a minimum size limit does not seem to be the answer in those situations where over-harvest is reducing the number of large male bluegill. Tighter limits on bluegill regardless of size may be more fruitful on Mississippi backwaters, based on the Lake Winona study. For the record, I release all my bluegills that are larger than 8″ flat for just this reason.
On the subject of Iowa bluegills limits (none on inland waters), the prevailing belief down here is that the more sunfish you harvest, the better. When you point out that the panfishing is superior in Wisconsin or Minnesota where there are some limits in place, the response from the IDNR and public alike is that Iowa-lakes/ponds/reservoirs-have-small-panfish-because-Minnesota-and-Wisconsin-have-more-lakes-and-better-water-quality-and-there-is-no-point-to-limits-in-Iowa-because-the-bluegill-need-to-be-fished-heavily-otherwise-they-will-overrun-the-lake/pond/reservoir-and-you-will-have-nothing-but-small-panfish.
This is true on some of the larger artificial lakes like Macbride, whose bluegills rival Lake Winona’s for puniness. While Macbride and Lake Winona are seemingly similar, with nearly the same surface acreage and average depth, the bluegill in Macbride are stunted due to lack of suitable forage owing to the scarcity of weedgrowth in Macbride, a situation made worse by competition with shad for the small invertebrates (which need weed growth to thrive) that both species eat. Tighter limits on bluegills on Macbride and reservoirs like it would do nothing to improve the size of bluegills in it, according to the IDNR fisheries biologists I spoke with about the problem.
I am skeptical that this is true for the small ponds down here, though. I have found the best panfishing in southern Iowa to be on private ponds with little or no fishing pressure, while otherwise identical public ponds have noticeably smaller bluegills. When you point this out, you are told that Iowa-lakes/ponds/reservoirs-have-small-panfish-because-Minnesota-and-Wisconsin-have-more-lakes-and-better-water-quality-and-there-is-no-point-to-limits-in-Iowa-because-the-bluegill-and-crappie-need-to-be-fished-heavily-otherwise-they-will-overrun-the-lake/pond/reservoir-and-you-will-have-nothing-but-small-panfish. I am probably moving back to Minnesota next fall, so I won’t have to argue the point for too much longer.