Whale Rider is yet another book that has been taken by the screen industry, and morphed into a movie. Yet, there is little that can be complained about. While the book itself is powerful, the changes made to create a movie from the story bring it to life, making it a story of power and a happily ever after for those who watch it. Everything comes out right, and everyone learns a powerful lesson.
While many would argue that all movies should stay loyal to the text they are inspired by, many are just that, only inspired. The story stays enough the same that people recognize the link, but the story being told is different. In those cases, it does not seem logical or reasonable for the movie to strictly follow the book. In many cases (such as Jurassic Park) it does not make sense, as the book has scenes and moments that either cannot be portrayed cinematically, or that draw from the primary plot, and damage the story. Movies are limited in both time, and in their ability to accurately portray everything that a book can get across, and the same is true in reverse. Where a movie portrays emotion, a book might share each character's innermost thoughts, which is hard to do on a large screen. So it becomes necessary to change the story enough that it will be successful cinematically, but also still follow the story.