Mark Brian mentions the sadness in Jim Wallace's eyes in I Heard the Owl Call My Name. What are the Indians sad about?

Mark Brian is a young vicar who's been sent by his bishop to live among the Kwakiutl Indians in the village of Kingcome and patrol neighboring villages by boat. A member of the Kwakiutl named Jim Wallace, who is about the same age as Mark, goes with him on his patrols and helms the boat until Mark passes his licensing exam. When Mark first meets Jim, he senses deep sadness behind the pride in his eyes. This is something he notices quite a lot among the Kwakiutl.
Initially, Mark doesn't quite understand the cause of this sadness. But gradually, he comes to realize that the village is dying, and with it, the old customs and language that have sustained it for so many years. Many of the young people have left the village to seek better lives for themselves in white society. No wonder, then, that there's such an overhanging air of sadness about the place.