As for catching crawfish I used to use a fishing pole and tie bacon to the line and the crawdads would grab the bacon and not let go.
Crawdad traps can be purchased at Bi-mart for a resonable price and are easy to use.
As to the legallity of keeping them I am unsure of the ODFW regs, but know that I can not purchase ANY of the crawfish that are kept in the tropical fish trade here in Oregon as it is illegal to own them (probably due to the fact that they wouldn't die if they got into our native waters); I also can not have Mystery or Apple snails in my aquariums, and many of the amphibious newts and other amphibians are not legal to be kept here in Oregon. There are also a few fish that can't be imported into Oregon (Pirana, walking catfish, Paccu, and others).
As to breaking the rules and selling wild caught game without permits I am one who is greatly opposed to this practice and the perpetrator of said criminal action usually gets charged with poaching along with the other violations they may or may not have commited.
for a list of prohibited and permitted specie go here:
http://www.dfw.state.or.us/OARs/56.pdf
Dave
