My understanding of Dungeness crab biology is that the males mature several years prior to reach legal size. The minimum size limit is important in that female crabs tend not breed with males that are smaller than they are. While females tend to grow slower than the males as we all have seen here in Puget Sound some do reach 6 inches (sometimes larger) or so to assure that there are males larger enough to breed with those females there is a need for the larger minimum size.

Crabs have complicated and at times vulnerable behaviors between the time the eggs/larvae are released by the females until the young
"crabs" reach maturity. Having enough "breeders" is only part of the equation to having a strong population. The crab larvae and newly settled juveniles survival is strong influenced by a wide range of water quality and other factors which naturally result in variable year classes. Just like the survival factors align in recent years to produce exceptionally strong populations those same factors can align to produce weaker populations. As much as we all would like to see record abundances of our salmon and crabs to be the norm the harsh biologically reality is that is not in the cards. In recent years we have seen environmental conditions in the sound/ocean that have affected the survival of salmon, recruitment of central Puget Sound ling cod, etc. can we be surprised that crab also might be impacted?

There are indications that changing marine conditions associated with climate change (acidification of the ocean) in the next decades may lead to significant reductions (as much as 70%) of critters like Dungeness crabs.

Curt