Area of Occupancy (AO) is a frequently used indicator to assess and inform designation of conservation status to wildlife species by the International Union for Conservation of Nature (IUCN). The applicability of the current grid-based AO measurement on freshwater organisms has been questioned due to the restricted dimensionality of freshwater habitats. I investigated the extent to which AO influenced conservation status for freshwater taxa at a national level in Canada. I then used distribution data of 20 imperiled freshwater fish species of southwestern Ontario to (1) demonstrate biases produced by grid-based AO and (2) develop a biologically relevant AO index. My results showed grid-based AOs were sensitive to spatial scale, grid cell positioning, and number of records, and were subject to inconsistent decision making. Use of the biologically relevant AO changed conservation status for four freshwater fish species and may have important implications on the subsequent conservation practices.

Area of Occupancy (AO) is a frequently used indicator to assess and inform designation of conservation status to wildlife species by the International Union for Conservation of Nature (IUCN). The applicability of the current grid-based AO measurement on freshwater organisms has been questioned due to the restricted dimensionality of freshwater habitats. I investigated the extent to which AO influenced conservation status for freshwater taxa at a national level in Canada. I then used distribution data of 20 imperiled freshwater fish species of southwestern Ontario to (1) demonstrate biases produced by grid-based AO and (2) develop a biologically relevant AO index. My results showed grid-based AOs were sensitive to spatial scale, grid cell positioning, and number of records, and were subject to inconsistent decision making. Use of the biologically relevant AO changed conservation status for four freshwater fish species and may have important implications on the subsequent conservation practices.