Silvery Minnow

The Rio Grande silvery minnow (Hybognathus amarus), is an endangered species imprtant to the Rio Grande. It was once widespread throughout the river, but now occupies less than 10% of it's historic range. Efforts are being made to improve the status of this important fish species.

Senior silvery minnow, by US Army Corps of Engineers, via Flickr

How is it measured?

The Silvery Minnow score calculation was based on Catch per Unit Effort (CPUE), and was calculated for three reaches of the Rio Grande: Angostura, Isleta, and San Acacia. CPUE, calculated here using the equation below, is a common scientific method of measuring species abundance.

CPUE=100 x (total number of minnows caught/ length of stream sampled)

CPUE was converted to a report card score using a threshold that set a CPUE of 1 equal a 40% score, using the equation below.

Silvery Minnow Score=40 x CPUE.

Scores were calculated using data from 2015 to 2019, and the final score was the average of annual scores from those years. This score was only calculated for the Middle Rio Grande region.