DIED male only LMB would do the same as the spots but with no reproduction. Male LMB especially Fla LMB do not get real big. Maybe to cold for Fla's at your place. F-1 males may work. Spots and LMB will cross in the right circumstances IIRC. In your size pond seining and trapping over abundant BG or LMB should work. Do enough each year to get the balance you want.