Thanks for checking in on snapping turtle trapping in Maine. It looks like you got your information from the Maine Warden Service FAQ webpage (http://www.maine.gov/ifw/warden_service/faq.html).
Aside from prohibiting the commercial take of reptiles (including snapping turtles), personal use/take is allowed and legal in Maine (exception being any species listed Endangered/Threatened). Since snapping turtles are not considered either endangered / threatened, game, or sport fish, there are no additional specific laws or rules as to harvest regulations, gear, season, etc. The gray area arises when you consider potential by-catch of fish, fur-bearers, etc. that do have rules and regs associated with them. For example, your question regarding use of a hook w/ steel leader tied to shore (i.e., fixed line) isn't covered in regard to snapping turtles but is clearly an illegal method of fishing as defined in MDIFW's Inland Fishing regulations (see the definition for "set line" on page 11 here : http://www.maine.gov/ifw/laws_rules/fishing/pdfs/Laws&Definitions.pdf).
So, while personal snapping turtle trapping is allowed/legal without specific permits, licenses, or regulations, you have to consider the anticipated methods and whether or not they could potentially take other species (by-catch) that do have laws/rules associated with them (sport fish, fur- bearers, game animals, etc.). With that in mind, here's your questions one at a time with my answers in all caps:
1. Is a fishing license required to trap snapping turtles?
NO - BUT IF YOU ANTICIPATE ACCIDENTAL TRAPPING OF FISH SPECIES IT WOULD BE A GOOD IDEA TO HAVE ONE (SAME GOES FOR IF THE TRAP CATCHES A GAME SPECIES YOU'D WANT TO HAVE A TRAPPING LICENSE AND BE OPERATING IN LEGAL SEASON, ETC.)
2. Is hook w/ steel leader, tied to shore a legal method (as used in
other states) or only box type traps?
NO - FIXED LINES VIOLATE FISHING REGS AND LIKLIHOOD OF TAKING FISH IN ADDITION TO TURTLES IS VERY HIGH
3. What types of bait are legal (raw chicken or beef liver)? Can dead bait such as minnows be used?
ALL BAIT WOULD BE LEGAL FOR SNAPPING TURTLES BUT DUE TO TAKE OF FISH YOU WOULD WANT TO BE COGNITIVE OF WHAT IS LEGAL/ALLOWED FOR THE WATER BODY YOU'RE TRAPPING/FISHING
4. How long can a trapped snapping turtle be kept before it must bedispatched?
TO MY KNOWLEDGE THERE ARE NO SPECIFIC LAWS OR RULES ADDRESSING THIS
5. Is there other information, I have not mentioned that will assist me in writing the story?
Thinking on your last question, I'd like to mention two other points regarding snapping turtle harvest. The first being that just like with large predatory fish and/or bottom feeders, snapping turtles are top level predators in many/most of the waterbodies they live in. As such it is good practice to limit consumption of snapping turtle meat (and avoid if pregnant, etc); research has shown snapping turtles carry high levels of mercury, PCB's, and other bio-accumulates. Secondly it's worth mentioning one of the reasons Maine no longer permits commercial take of snapping turtles. Snappers, like all turtles, are K-selected species that take many years to reach sexual maturity (18+ years for snappers), have very low nesting/hatching success, and thus need to live a long time in order to replace themselves. While limited personal take should allow populations to persist, a targeted commercial exploitation could quickly wipe out turtle populations for the future.
Hopefully that covered most of it Steve but again don't hesitate to follow up if I missed something. Also, I always recommend running legal interpretations on Maine Hunting/Fishing/Trapping by your local game warden cause in the end they're the ones enforcing them.
Good luck with the article and if it's not any trouble I wouldn't mind seeing a copy when it's ready.
In addition to the information provided by Jonathan's e-mail here are also a few other online resources.
Excellent Website Links:
Trapping, cleaning and eating snapping turtles:
More on Snapping turtles:
Snapping Turtle Traps:
Very Good Additional Information:
I heard this on one of the Forums and thought it was funny . . .
How To Age Snapping Turtles: Start with prodding the turtle with your little finger. If you find he can snap it off easily he is at least 3; ring finger about 5, middle finger 8, pointer finger 12, thumb over 20.