Family history of Paul Johansen

My father, Paul Johansen was born March 26. 1881 on the Island of Erlandit in the area of Heroy. I would like to find out more about his parents and grandparents. I was not able to discover anything about the island of Erlandit, but I visited there by boat in about 1997. The island was the property of the Johansen family at that time, but nothing is there now. When he came to the United States they changed the name to Anderson, which was his Mother's maiden name. Paul had brothers named George, Haldor, and Edward. I think Paul immigrated to the US in 1900. I would appreciate any information that someone may know about the family name, origin, or the island of Erlandit.