Although most crab species are harvested responsibly with pots or traps that create a minimum of bycatch and environmental damage, more than 90-percent of the king crabs sold in the U.S. are imported from Russia, where fisheries are poorly maintained. King crabs from Alaska are preferable, but these crabs are still recovering from years of overfishing. The king crab takes four to seven years to reach full maturity, which is relatively slow and has made for a difficult recovery. Although the Alaskan fisheries are well maintained, it is not known exactly how plentiful the Alaskan king crab population is. When it comes to crab, the best choices are Dungeness crab, found in the Pacific from California to Alaska; the Canadian snow crab; and the stone crab, which usually comes from Florida. Blue crabs mature quickly and thus are another potentially sustainable species, although their populations have recently been in decline due to shrimp boats in the Gulf of Mexico, which take in juvenile crabs as bycatch. There is also a health advisory for blue crabs, related to PCBs and mercury levels, so consumers are advised to limit themselves to one meal per month.