Information about the name Qualtrough can be found @
1. http://www.qualtrough.org/name.htm
2. http://www.qualtrough.org/name2.htm
3. http://www.qualtrough.org/name3.htm
#3 is from Frances Coakley's site www.manxnotebook.com from which I am sure you will find more information on this name and the anglicised form Wat(t)erson as well as other Manx surnames.
Elizabeth