Sound environmental regulation must achieve environmental objectives while maximizing economic efficiency. This paper evaluates the impact of regulation on efficiency by measuring annual productivity across regulatory regimes in two similar fisheries with differing policy expectations. Anticipation of regulatory change produced strategic behavior in one fishery, leading to depressed productivity; in the other, regulatory change was not expected, and productivity did not suffer. These results imply that fisheries regulation should take into account both firms’ policy expectations and the potentially perverse incentives that may be created by policy change.