I just heard about 3 boys adrift in the pacific in an aluminium canoe for three weeks.
With only rainwater and a seagul to drink and eat for three weeks, they survived.
Would they have been more likely to survive with more seagulls to eat?
Surprisingly no. The greatest danger in a situation like this is dehydration. Protein in meat needs lots of water to digest, so in fact protein contributes to dehydration, as do many foods in fact. Therefore, unless you have water with you, through your food to the fish.