Researchers can identify individual humpback whales by the patterns on the underside of their flukes. I matched photos and helped to manage the database of sighting records for the 5200 animals in the North Atlantic Humpback Catalog. I obtained this position at Allied Whale because I had attended College of the Atlantic and was in the right place at the right time. Getting a biology degree can be a start in a career in marine mammalogy. But you should be prepared for a lot of hard work before you can get a secure job doing work with marine mammals.
Many people begin by volunteering on research projects or at aquaria.
There are some great resources on Careers in Marine Science on the web. I would encourage you to check some of these out. Look at the WhaleNet web site index for the link to these sites. Good luck in the pursuit of your career.