All income of the state game and fish department deposited by the director with the state treasurer must be credited to the state game and fish fund and the fund may be used only by the department. All money derived from the investment of the fund, special accounts, or portions of the fund may be credited to the game and fish department private land habitat and access improvement fund. The department shall spend moneys in the game and fish fund within the limits of legislative appropriations, only to the extent the balance of the fund is not reduced below fifteen million dollars, unless otherwise authorized by the legislative assembly or the budget section if the legislative assembly is not in session. Any request considered by the budget section must comply with section 54-35-02.9. Investment of up to fifteen million dollars of the balance of the game and fish fund may be made under the supervision of the state investment board and the moneys must be invested by the investing authority according to the laws relating to state investments. The department shall notify the state investment board of the amount available for investment.