I combined the Hill etal paper above with another I found..
http://nlc1.nlc.state.ne.us/epubs/U1500/T004-2008.pdf
which is a MS thesis from Nebraska. He sampled 2 NE lakes.

Plus a paper from Ball State on Yellow Perch from Lake Michigan.
http://cms.bsu.edu/-/media/WWW/DepartmentalContent/Biology/pdfs/GapeLimitationYEP.pdf



First LMB is the Hill paper. Next 6 lines are the NE MS thesis, and then the last two YP are the BSU work.

FYI, the sample size for the HSB was 168 fish, so a nice population from two lakes.
I'm struggling to believe the YP data though it was 284 fish. They have a very narrow mouth for body length. But I can see no other way to interpret their paper. As I am sending BSU tuition money for my daughter, I may well call one of the authors and inquire.

But, I'm pleased to find some reasonable census measurements for gape!