American Airlines is ending its codeshare and frequent flier partnership with Cape Air effective February 28, 2014.
The last date to book award travel on Cape Air is February 28, 2014, and you cannot make any changes for Cape Air segments on tickets issued.
American Airlines has allowed using miles on select Cape Air routes within Caribbean to/from San Juan and to/from St. Louis.
American Airlines announced in late 2013 (read more here) partnership with Seaborne Airlines for select routes from San Juan. Maybe that was the precursor for ending the agreement that AA has had with Cape Air?