There is no easy way in. All marine mammal related jobs are typically extremely competitive and poorly paid. On the plus side, Marine parks are typically not too picky about what sort of degrees their trainers have, some of, for example, SeaWorld trainers have degrees in journalism and business, others only got one after starting to work there. SeaWorld state they prefer a degree in psychology.As it's a competitive field though, a degree might look good on the CV.
In the words of a former trainer:
"Few trainers possess specialized skills or educational training such as might accompany an undergraduate or graduate degree in the sciences. Reality is that a job as a killer whale trainer requires mostly the same skills as other theme park workers–the ability to look good and be well-spoken in front of a crowd."
You should also be aware that many trainers work second jobs and working conditions are often poor as they know you can be easily replaced by lots of candidates. Most you can expect after 5 years experience is about $18 per hour.
Similarly to a job working with wild marine mammals, you are unlikely to walk straight onto a job, there are literally hundreds of people who want to work in this field, you'll need a lot of- usually unpaid- work experience.
The sort of experience they usually look for as far as I'm aware is anything to do with training animals, particularly large animals, handling livestock for instance. There are a few places that also offer training internships on quite a frequent basis as for example Miami Seaquarium but their standard of animal welfare is so appalling it's really not worth considering in my opinion, no doubt may parks will consider it valuable experience though.
Disney's Epcot offer internships as well;
Mote Marine Lab is a well respected research institution and also have some internships were you work with their unreleasable dolphins:
Internship Ops - Animal Care, Training & R&category=Education
Most places will also require you to be a strong swimmer and a confident public speaker so if you can take up some extracurricular activities that underline those abilities, it would probably be advisable to do that.
Something you might want to consider though before following up on the trainer career plan is the stuff that SeaWorld and company don't tell you.
Training has nothing to do with animal welfare, conservation or education.
Or that many of their animals die prematurely and are in bad health despite the 'excellent veterinary care' they claim they have:
Or how many of their trainers get injured by the animals they are working with (about 50?or that a lot of dolphins in captivity get highly aggressive due to the stress that they are under and that incidents like the one with Tilikum are not really accidental or that exceptional- and it's not just orcas either:
Or that there is little more to the fabled 'bond' between dolphin trainers and dolphins than the fish supply provided by the trainer, this is an extract from a book by a trainer who was involved in releasing dolphins back into the wild about the dolphins behaviour after the trainers stopped directly supplying them with fish:
"Early on Echo and Misha would spend some time playing with people. Michelle didn't want to frustrate them by cutting of their interactions with humans abruptly, so occasionally she would sit in a small inflatable boat and let the boys come by to be rubbed. They seemed to like it at first . Then they started to get snippy about it, sometimes even slapping their tails on the water and making it perfectly clear "i don't need these rubs."
once after a feeding session, when the fish were gone, michelle gave Echo the 'retrieve' sign, thinking he might bring back a ring that was floating in the water. He left and returned with a fish in his mouth. he shook it and ate it in fron of her- as if to say, "i don't need your fish, either."
(Dolphin Chronicles by Carol J. Howard, good read I recommend it)
When former trainer John Jett was asked: Sea World and other marine parks have done an effective job glamorizing the life of a killer whale trainer. There are literally thousands of young people that would do just about anything to get the job of a trainer. Do you have any specific message to those young folks out there that want to swim with Shamu?
He replied: Low pay and hazardous working conditions should be sufficient to dissuade anyone but the most ignorant among us.