The history of Thelma Biotel goes back to the early years of the 1970s, when the Norwegian researchers Holand, Mohus, and Balchen started developing acoustic transmitters for fish, and equipment for fisheries field studies. The technology and methods were continuously developed at the independent research company, SINTEF, and the Norwegian University of Science and Technology (NTNU). It was finally commercialised under the name Thelma in 2002. In 2008 Thelma Biotel spun off as a separate company, with a sole focus on further development of wireless monitoring in the submerged environment. 

All text sourced from https://www.thelmabiotel.com/