A few things to keep in mind when picking a camera for filming your fishing trips.
GoPro cameras are versatile due to the fact that there are lots of mounting accessories which allow you to strap it onto your body, press the record button and capture whatever you are looking at. If all you want to show to people is your POV, and some underwater footage, then this is the camera for you, but keep in mind that because the camera is in a waterproof case, the audio captured is very poor.
If audio is important to you, then perhaps consider a point and shoot camera. The latest models all record excellent video footage as well as capturing good audio. You can also snap good photos at the same time. Mirrorless cameras are also worth considering if you want to spend a bit more. What this lacks is the ability of being underwater, unless you buy a case specifically designed for it, but how often do people actually bother with underwater videos?
64gb is very large and can store up to around 2.5 hours of true HD video footage, but keep in mind that if the card collapses, you are losing a lot of files at once. Personally I use 32gb cards. To fill up a 64gb card, you'll need about three batteries for your GoPro Hero3+ white edition.