Stacie,
I think a similar rule is already in place. Admittedly it doesn't require that all fish caught be kept. On page 57 of the regs:
"When fishing with bait, all TROUT (except STEELHEAD) equal to or greater than the minimum size are counted as part of the daily limit whether kept or released."
Of course, I'm sure you realize as well as I do that this is virtually unenforceable as would be a law requiring that all fish be kept; unfortunately adherence depends upon the personal ethic of the individual.
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PS