If you are planning a career in (any kind of) scientific research, I think that the best way to approach your education is from a "pyramid" perspective. First, you should build a broad, strong foundation, then as you move up you will get more specific (narrower). You likely will pursue an advanced degree (PhD) if you truly wish to make studying marine mammals your profession.

For undergraduate work, I suggest focusing on two things - a very solid base in biological sciences (does not have to be a specialized type of biology) and getting some real research experience. This can be through working with faculty at your university or through summer internships, or both. I also encourage you to consider a year studying abroad. Because you already have some idea about what you want to do, you might then select your undergraduate school to be one where there are opportunities to work in that specific area. However, try to keep an open mind and explore other areas as well early on - you might get "hooked" on something totally unexpected! Even "marine mammals" is pretty broad -- this might be some specific aspect of "behavior" (group relationships? migration? reproduction?) or ecology (position in food web?) or even a large scale policy or economic study of marine mammals.

Once you decide on a more specific area of study, then you can select your graduate school program based on that.So essentially, just pick a good school for biology and one in which there are going to be research opps for undergrads. Most schools that have a marine lab associated with them can give you a solid undergraduate degree in marine biology, and then you can be more selective about graduate schools based on your specific interest. And remember, no matter what school you go to, you will get out of it what you put into it. There are lots of opportunities, but you generally have to seek them out and be willing to go the extra distance in terms of getting that research experience.
Hope this helps - and best of luck to you!

I have a different suggestion about your major.More and more biologists are working with molecules now, even marine biologists.We're asking questions about the DNA sequences of different animals and their proteins and cells. I recommend that you major and minor in:
1. Marine Biology or Zoology AND
2. Biochemistry or Molecular Biology or Cell Biology.
Another idea is that you have only your college years to learn about history and literature and a big variety of subjects, so you might want to have a science major of some sort and no minor. That would give you the freedom to take more courses outside of science. It depends on how interested you are in non-science areas or whether you're happy to take lots of science courses.

In any case, I recommend that you look seriously at science courses that are more difficult than zoology or marine biology. I wanted to be a biochemist when I went to college, but I was advised to major in chemistry. I'm really glad I did, but I wish I knew more math,especially calculus. I have a PhD. If you don't want to get such a high degree, you might want to make different decisions about your college education.

Check out New College in Sarasota, Florida. I knew some of the first graduates from this new college, long ago. It was a great little college when it started, and I expect it is still quite good