Faced with the choice of what secondary language to learn in college, I thought about which one would be helpful within my career. A lot of Marine work can be done in the US, Australia, and South American countries. Luckily, two of those speak English natively, so I'm in good there. I actually plan on doing work in Mexico for some time, so I went with Spanish, but you probably already figured that out. However, I would suggest going beyond your University's requirements and attempt to be relatively fluent, at least be able to communicate with the guide or other biologists in the areas you plan on studying in. If you don't speak English as your primary language, but you can read enough to eke out what I'm saying, I would suggest you learn in so you can work in either the US or Australia.
Essentially, I wouldn't go with a language that cannot be easily associated with the field.
Also, Japanese or Mandarin Chinese would be good choices, but those are both countries that widely teach English to the point of fluency in grade school. Basically, if you go work in one of those countries, you'll be able to work with people that speak English. I know that sounds a bit assholish, but it is incredibly difficult for a Romanic/Germanic language to transition to a symbolic language. I know, I tried Japanese and it was brutal towards the end of the first year.
So, until next time, buenos noches, y buena suerte.
