Australia have faculty with actual experience on marine mammals. My best recommendation is that you explore universities with vet schools that have faculty with research record on marine mammals. Usually you can find in their web pages the list of faculty, their especialties, and list of publications. Varies widely from conutry to contry and from institution to institution. I guess you mean to apply to enter in vet school.
Vet schools are like graduate, medical or law schools.
You go there only after completing your undergraduate education. The years you spend in vet school will depend upon the school itself, since requirements also vary. Again, it depends upon the school and the way the have designed the curriculum. Again, you shoud contact them directly, but there is a great difference between being a veterinarian and an animal trainer. To be a veterinarian you have to go to vet school.