QUANTIFYING NO NET LOSS OF PRODUCTIVITY OF FISH HABITATS

A net change equation is derived for assessing no net loss of producti vity of fish habitat (NNL). NNL is the guiding principle of the Canadi an policy for the management of fish habitat. The equation provides a middle ground between the extremes of no conservation and no developme nt. Projects affecting fish habitat are accountable for the productive capacity in loss areas and the difference between current and future productivities in modified areas. The equation implies quantitative co nservation targets overall and loss-offsetting equivalencies in modifi ed habitat areas. Generalization of the net change equation to heterog eneous habitats is illustrated with a development in a coastal wetland on the Great Lakes. The net change framework has implications for lin kages between suitable habitat supply and fish population dynamics. Ar ea fish habitat management plans envisioned in the policy and site-lev el net change assessments are connected. Quantitative ways are propose d for simultaneous assessment of NNL and ''harmful alteration, disrupt ion, or destruction'' of fish habitat, as required in the Canadian Fis heries Act. Defensible methods for applying the net change equation ar e superior to earlier nonquantitative approaches. Lf the available sci ence is insufficient, the precautionary principle is recommended. Futu re development steps for the quantitative net change framework are sug gested.