Your operative term is "can." Physiologically you are probably correct. But two serious concerns come to mind: (1) the impact on survival performance, and (2) why would you plan on that?

I have personally fasted for some time (two weeks on one occasion) to see the effects and benefits. After the first few days there are some benefits in terms of mental alertness and positive feelings. After that it's downhill! At least for me after 10 - 12 days things began to look grim. Muscular weakness, confusion over simple tasks, etc. The gurus who do this are in situations with minimum demands on physical and mental resources. Survival, IMO, would be a much different story. Things you would want to be able to do, like maintain fire and gather water, could become dangerously difficult. Which brings me to the second point: why plan for this?
You mentioned in your post several reasons to plan for food gathering - even if only an edible plants card (which I always recommend). Building confidence by planning, learning and practicing (PRACTICE!) food gathering makes it feasible to mentally endure a long term isolation waiting for rescue. The protein may not be the biggest benefit of a 4 oz. fish! <img src="/images/graemlins/smirk.gif" alt="" />