It's probably due to the new USCG AAWPP. Don't you love govt acronyms Assumed Average Weight Per Person. The USCG realized that their old weight per passenger didn't apply to todays plus size passenger so they upped the weight. More weight per passenger means the vessel can carry less passengers in some cases. Some vessels need to get new stability certificates.
Weight has become a critical issue on certain boats
http://www.uscg.mil/hq/cg5/cg5212/docs/secg12142010.pdf
(2) Weight compensation. One method to
demonstrate compliance with the new AAWPP requirement
is to reduce the cargo weight carried by an amount equal
to the difference in permitted weight of passengers and
crew associated with the new and old AAWPPs. This is only
available to vessels carrying either deck or vehicular cargo
in addition to passengers.
(3) Direct verification. Every time a vessel is loaded,
the owner or operator ensures that the weight of persons
loaded on the vessel does not exceed the total permitted
weight. The way this may be verified, such as weighing all
persons as they board,