When shellfish grounds or franchises located within the limits of the towns of West Haven, New Haven, Milford and Westport, and northerly of the state jurisdiction line, have been surveyed, and a map of the same made and accepted by the Commissioner of Agriculture according to law, said commissioner shall have and exercise all the powers and duties with reference to the grounds designated thereby which he has with reference to the grounds south of the state jurisdiction line; and any copies of such books, records and maps which were used in connection with such survey shall be kept on file in the office of the commissioner; provided the selectmen of the town of Westport shall have exclusive jurisdiction over, and power to designate, shellfish grounds in the waters, in said town, of all creeks and estuaries tributary to Compo Mill Pond in said town, and the selectmen of the town of Milford shall have exclusive jurisdiction over, and power to designate or lease, shellfish grounds in the waters, in said town, of the Indian River, Gulf Pond and that portion of the Milford Harbor located northerly of the breakwater. The map of such grounds in the town of Milford shall be published with the annual report of the Commissioner of Agriculture. Taxes and rentals on grounds in the towns of West Haven and Westport and in the city of New Haven and on franchises in the town of Milford designated on such maps shall be paid to the treasurer of the town or city.