Fish diversity is tightly connected to the quality of aquatic habitats in any river or stream. To assess whether aquatic habitats are supporting desireable fish communities, we compared the species present in an area to the species that the Arizona Game and Fish Department has identified as desirable or undesirable. The diversity of native fishes is most frequently used to assess quality of in-water habitat, but stocked fishes in the Rio Grande are important for recreation and have become an established part of the ecosystem. Therefore, both native fish diversity AND all fish diversity, including both native and non-native fishes, were calculated.
How is it scored?
Diversity scores for native fishes were calculated using a Simpson's Diversity Index. The index was calculated using the equation below, then converted to a 0-100% scale.
Simpson’s Diversity Index Equation
Index=1-(Σni(ni-1) / N(N-1))
where:
ni= The number of organisms that belong to species i
N= The total number of organisms