I go to the Univ of Hawaii at Hilo for Marine Science. Its a BA program that is quite biologically intensive, but also covers other things (phys oceanography, chem oceanography). Most universities won't offer a marine bio degree, but instead offer a bio degree with a marine emphasis, which varies from a really good program, to crap.
Try to go to a school on a coast, a lot of marine bio schools are land locked, which leads to getting no field experience, which is crucial for a job.
Coastal Carolina has a good program, Univ of Hawaii at Hilo is a nice small school for Marine Science. As for marine mammals I would say its not good to limit yourself to something that specific, cause then your stuck with it, even if you did a marine bio or science degree you could still do a thesis with mammals, take mostly mammal classes, but still not narrow your scope.