You might be referred to as a marine biologist or a marine mammalogist (a mammalogist works with mammals - and seals, of course, are mammals).
There may be a couple of routes to take if you want to specifically work with seals. If you study seals as part of a graduate and post-graduate program in university, you could work as a research scientist and research seals, populations, physiology, behaviour - this could be part of your research interests as a professor. That is a long road - and a challenging one, but if you really love it, it can be very rewarding.
You could also work with the government as a research scientist that works with seals. In Canada, the Canadian Wildlife Service has seal specialists. There may also be seal specialists who work with the Department of Fisheries and Oceans as seal populations are thought to significantly affect fish populations.
Be aware though - with seals,although there are endangered species that would lead you to a path of "conservation", in many parts of the country, the more common species are considered a harvestable commodity. You would be dealing with hunting issues and as a government biologist, you have to walk the middle line on these issues if people have the legal right to hunt a species (no matter what your personal views are).
People need to go into the field of biology with their eyes open. It isn't all about "saving the whales". A big part of working as a biologist is working with game species and hunting quotas, determining acceptable levels of mortality for particular populations.
If you want to look at salaries, find a branch of government that does what you like and search the pay grids.
Here is the career link for Environment Canada (and the Canadian Wildlife Service)
The American equivalent is the US Fish and Wildlife Service.
For a specialization like you are talking about (seals) you would need at least a Master's of Science studying that particular species group - and preferable in a conservation related area.