"It is the bulwark against starvation." According to the statement, what is the writer referring to?

In context, "the bulwark against starvation" is the ownership of a boat.... a way to provide for one's family.

Kino and Juana came slowly down to the beach and to Kino's canoe, which was the one thing of value he owned in the world. It was very old. Kino's grandfather had brought it from Nayarit, and he had given it to Kino's father, and so it had come to Kino. It was at once property and source of food, for a man with a boat can guarantee a woman that she will eat something. It is the bulwark against starvation.