Pond Boss Forums Thread Like Summary - Guessing why Fla & N LMB aren't the same

Well, of course Fla LMB actually DO bite, otherwise they wouldn't get so big. But they are typically much less aggressive than Northern strain LMB. Supreme Pondmeister Bob L has recounted visiting a hatchery where N and Fla LMB reacted very differently to a forage fish dropped in their tank. The Fla bass carefully scrutinized the fish, no big hurry. The Northern bass didn't waste any time scrutinizing, wolfing it down in a sudden frenzy.

You would think that, given feeding habits, the Northern LMB would outgrow Fla. But as we all know, that's not the case. So what gives?

In a recent Eric West (IIRC) article in PB magazine, he mentioned that researchers have found that southern LMB grow faster than northern LMB. However, BG grow pretty much at the same rate, south or north. Thus, southern BG are smaller compared with mouth size of average southern LMB, & thus more vulnerable to predation. Northern BG are roughly half as vulnerable, as they more quickly outgrow typical N LMB mouth size.

And, of course, southern BG spawn more often.

So what? Well, it would seem that we may have a classic case of adaptation to local conditions. Northern LMB don't have the number of BG to eat that their southern relatives do -- one BG spawn a year is pretty typical -- plus BG tend to grow beyond what N LMB can eat pretty rapidly. Southern or Fla LMB, on the other hand, can dine on multiple spawns of BG, plus with their larger mouth size can eat BG beyond what N LMB can.

Result: Northern LMB typically need to hustle more for food. A lot more. Aggression is rewarded, hesitation punished. Southern LMB don't need to be as aggressive & take risks to feed, so they don't.

I didn't say it was a good theory, just a theory.

I will dig out the info and post.

In the meantime here is a bit to think about.

In the first year (and subsequent years also) warming spring/summer water temperatures ramp up metabolism and the need for food (feeding) and with it increased growth. An example is the information contained in Growth Rates and Temperature Selection of Bluegill, Lepomis macrochirus by Thomas L. Berttinger and John J. Magnuson in Transactions of the American Fisheries Society 108:378-382, 1979 which provides growth and temperature information for Bluegill. Interestingly maximum feeding and growth occur at different water temperatures. Bluegill feeding rates were best at 77 to 82 F and food conversion efficiencies at 83 F. High growth occurred over a broad range from 68 to 93 F (a few degrees below the upper lethal of 96 to 99 F). However, there was a difference between water temperatures at which highest growth occurred (86 to 88F) and maximum feeding (77 to 82 F).

And another one that may help

The Effect of Largemouth Bass Predation on
Overwinter Survival of Two Size-Classes of Age-0 Bluegills
DANIEL E. SHOUP*1
AND DAVID H. WAHL
Illinois Natural History Survey, Kaskaskia Biological Station,
Rural Route 1, Box 157, Sullivan, Illinois 61951, USA
Abstract.—Overwinter mortality is an important force structuring year-class strength of many fishes.
Conventional wisdom is that overwinter mortality is primarily caused by starvation; however, recent research
has demonstrated that piscivores continue to feed during winter and may also contribute to overwinter
mortality of their prey populations. We conducted experiments in ten 0.04-ha earthen ponds in central Illinois
to assess the effect of predation by largemouth bass Micropterus salmoides on survival of two size-classes
(20–30 and 40–65 mm total length [TL]) of age-0 bluegills Lepomis macrochirus. Bluegills (400 fish/sizeclass)
were stocked into each pond at the end of November. Half of the ponds also received five small
(90–124 mm TL) and four large (166–192 mm TL) largemouth bass. Survival to the end of the 113-d
experiment was higher for large bluegills than for small bluegills in all ponds. For both bluegill size-classes,
the predator-present treatment had higher mortality than the predator-free treatment. Relative to the predatorfree
treatment, mortality of bluegills in the predator-present treatment increased by 16% for the large sizeclass
and 49% for the small size-class. Mean length and relative condition (Kn) of both bluegill size-classes
increased by the end of the experiment in both treatments, suggesting that the observed mortality was not
caused by starvation. Further exploration is needed to elucidate why bluegills in the predator-free treatment
suffered overwinter mortality despite the increase in Kn during the experiment. Length and Kn of largemouth
bass increased (large size-class) or stayed the same (small size-class), suggesting that at least some of the
predators foraged during winter. Our results indicate that size-specific overwinter mortality of bluegills occurs
at the middle latitudes of the species’ range. Further, winter predation can be an important component
influencing size-specific overwinter survival and size-structured interactions between fishes.