The link below contains the salient information regarding travel to Cuba by US citizens:

http://travel.state.gov/travel/cis_p.../cis_1097.html

My Cliffs Notes would read as follows:

It is possible, but inherently complicated, to arrange legal travel to Cuba in order to solely fish recreationally. Many Americans travel clandestinely from Mexico or Canada under the assumption that, if caught, the penalties will be minimal, or not prosecuted at all by the current administration. Caveat emptor.