
Part of it comes from women tend to gravitate towards more nurturing roles, such as marine bio or environmental science as a whole. While men tend to be more interested in engineering or technical portions. It's also a degree that heavily accepts women and there's less of a pressure to excel over men to prove yourself. It's similar in a general bio degree as well. Not saying that's it's right or wrong, but that's just my interpretation of why.
I had a very unfortunate wake-up call to this in my senior year at undergrad. I had a professor that would hire female students to do gruntwork in his lab saying they MIGHT be credited if they do a good enough job. Then hed fire them immediately after they finished the work and take the credit. He was extremely sexist and blamed modern societys problems on women having rights (i wish i was kidding). And the worst part is, hes nowhere NEAR alone in this practice.