There might be a biological reason for the slight differences in pelvic fin length based on sex.
I can see where longer pelvic fins in males might aid in fanning the milt onto eggs as the are being deposited. I can see where slightly shorter female pelvic fins would be less likely to damage or touch the eggs as they are being deposited.
I haven't caught many BG this year but a cursory look at the pelvic fin lengths in the few that I have caught also appears to be sexually differentiated as well.
Next time you are BG fishing lay the pelvic fins flat against the body, male pelvic fins should come very close to touching the anal fin, females well short of touching the anal fin. Also note whether not the belly appears to be full, empty, or somewhere in between as this will affect how close the pelvic fin comes to touching the anal fin, it's all about the difference in "the gap".
