biologically informed length class break points

[afredston]

Right now, the breakpoints between the three size classes in the model are determined as:

Small juvenile / large juvenile: halfway between smallest size caught, and length at maturity
Large juvenile / adult: length at maturity (mean of Lm for two sexes, if different)

The large juv / adult breakpoint is biologically informed and the small juv / large juv is not. May be worth considering what the meaningful differences between the latter groups, and if we can find a more biologically informed break point.