The Thacher & Straitsmouth Islands Association (TSIA) was established in 1981 by the Thacher Straitsmouth Islands Town Committee (TSITC) as a non-profit group dedicated to raising funds for the restoration and on-going maintenance of Thacher and Straitsmouth Islands. On Thacher Island, the Town of Rockport owns the southern end of the Island and manages it via the TSITC and TSIA. The northern end is owned by U.S. Fish and Wildlife Service (U.S.F&WS) and is managed by the Town under an agreement with U.S.F&WS. On Straitsmouth Island, the Town of Rockport owns the northern end of the island and manages it via the TSITC and TSIA. The southern end is owned by Mass Audubon Society (MAS) and is managed by the Town under an agreement with MAS.