From an old thread. FYI
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=60415&fpart=1It is important to note that this data is on growout ponds (aquaculture methods) not sport fish ponds. They are vastly different in purpose , methods and results.
I have copied conclusions from part of the cited study. Note that a male BG only growout pond would under these conclusions " substantially outgrow both hybrid sexes and female bluegill" and " male bluegill posses the inherent capacity to grow to food-market weights within 2 years while female bluegills and both sexes of the hybrid sunfish take longer even under the best of growing conditions " .
There is no independent disinterested scientific data that I know of that includes fecundity ( # and % male/female offspring) info on GG nor on their growth rate vs HBG (other than the one short term 12 week study) and none vs male only BG. The Hayward and Wang study on Inherent Growth Capacity and Social Costs of Bluegill and Hybrids of Bluegill and Green Sunfish: Which Fish Really Grows Faster? shows a similar conclusion as the cited study and is in the context of BG growout for food production over the 2 yr. growout time frame as opposed to 12 weeks. Please see the last sentence of the quote for the answer as best the disinterested science to this point allows one to know.
Quote below :
The conclusions of a recently completed 2-year NCRAC project on sunfish pond culture are: 1) male bluegill have the capacity to substantially outgrow both hybrid sexes and female bluegill, 2) hybrid sunfish tend to grow better in ponds because of the bluegill tendency for substantial in-pond reproduction, higher social costs, and 3) hybrid sunfish are better able to utilize natural feeds (NCRAC 2002).
In a NCRAC-funded project at the University of Missouri (UM) it has been determined that male bluegill possess the inherent capacity to grow to food-market weights within 2 years while female bluegills and both sexes of the hybrid sunfish take longer even under the best of growing conditions (NCRAC 2003). This data provide evidence that efforts to rear Lepomis species to food-market weights within the established 2-year benchmark for grow out should focus on male bluegills.
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I think your observation about overcrowding is part of the answer as it results from what are classified " social costs or social interaction costs" as a pratical matter. The studies refer to social costs as best I can describe them as the use of energy by fish in activites (other than growth) that have to do with social order like dominance and reproduction including running off cuckholders and sneekers ,nesting, mating and guarding eggs then fry. Both BG and HBG have social costs but the BG's are much higher I assume because they invest much more energy in offspring reproduction. Think about how much energy and quality growth time (spring and summer) male BG use up if they spawn and guard eggs and fry for 50 days over that period. HBG because they are 90% male don't invest as much in spawning or nest guarding and the fecundity of the few females is much less. Because BG are more successful they end up overcrowding as you noted. Thus remove the female BG from the equation and you get larger male BG which out grow HBG.
I am going back to some of the studies to see if they take into account the fact that 90% +- of the HBG are male when they use avg. lengths and weights to say HBG are bigger. Because females are smaller it may skew the growth comparison. Maybe they should calculate a BG avg. using 90% males and 10% females and compare that for growth purposes to HBG.
One factor that is not addressed here much but is in the studies is catchability and aggressive behavior by HBG. Most of the info stresses this point as the main reason for using HBG over BG but warns about the ease of fishing them out.