The commission shall adopt regulations providing for the purchase of transferable entry permits with money in the buy-back fund for each fishery. The commission shall cease purchases of entry permits in a fishery when the number of entry permits in the fishery has been reduced to the optimum number. The commission shall terminate a buy-back assessment established for a fishery under AS 16.43.310(b) when the commission determines that the amount of revenue collected through the assessment is sufficient to purchase the number of entry permits necessary to achieve the optimum number of entry permits in the fishery and to offset the reasonable costs of the buy-back program for the fishery, including repayment of any debt the commission was authorized to incur to capitalize the buy-back fund for the fishery. The unexpended balance of appropriations made to a buy-back fund for a fishery shall lapse back into the fund from which the money was appropriated at the end of the fiscal year in which the buy-back program is terminated.