This is like three books in one.
First, is the picture story. If I were reading this with a young children or an older child who has not experience with the ocean, salmon, or life in the NW, we would study the picture, trying to pull together a story and wondering about things we see but can't explain.
Second, is the historical fiction of a girl whose family depends on salmon to support their style of life. I'd use this story when the child has outgrown the picture story. It would be particularly good for young students who are beginning to learn about ecosystems, natural history of particular animals, food chains, and other biological concepts. (But I wish the story were a little more engaging.)
And finally, there's the factual information bands at the tops and/or bottoms of the page, which are useful for anyone wanting to know more about salmon.
As I read this, it dawned on me that salmon was to the people of the NW comparable to what bison meant to the plains-dwellers. (Having spent most of my life in the central states and the NE, I know very little about salmon so I'm probably rating this differently from a rating assigned by someone native to the NW.)