Im going to say it means she is a minor character. And if thats wrong then its main character but pretty sure its B.
Salmon's need to lay many eggs because the eggs are very fragile. These eggs are not very likely to survive and hatch. Lots of eggs need to be laid to guarantee the survival of at least some of the eggs.
The answer is summarize your main points. My english teachers have been hammering this into me for like 4 years so I know this is right.