This book is actually not about otters; Big Otter is an Indian chief, and the story details the adventures of fur traders as they establish a wilderness outpost in the harsh Canadian wilderness. (Amazon)
Robert Michael Ballantyne (24 April 1825 – 8 February 1894) was a Scottish author of juvenile fiction who wrote more than 100 books. He was also an accomplished artist, and exhibited some of his water-colours at the Royal Scottish Academy. (Wikipedia)