Is a masters degree necessary?

I have just graduated with a degree in marine science, and I decided to take a year out to try find how much employment there is out there for graduates, but it seems to be impossible to find a job in relation to conservation or marine science. I am contemplating furthering my career prospects with a masters, but with �3500 tuition fees, I'm unsure if it would be a good direction. I would really appreciate any advice from those who already completed a masters to let me know if its worth it.