Trout Unlimited developed the Conservation Success Index (CSI) to quantify and map the conservation status of native coldwater fishes in order to make better conservation decisions. The index has succeeded admirably in that respect.
For the angler, the index conflates some information which is highly relevant to finding fish (e.g. population density, which is essentially a measure of how many fish you’ll find in a stream when you find it) with many other measures that are much less relevant. As trout anglers and citizens of the planet we care, for example, about future security of a trout population, but when it comes to casting a line, only the population density is immediately relevant.
If you dig deeply on the TU website, you discover that they publish a great deal of the information used to calculate the various indexes, including population density. In the case of Greenback and Rio Grande Cutthroats, it also includes measures of fish/mile of the streams in each basin.
In the download system you’ll find this “enhanced” TU CSI basin data for the 3 native cutthroat variants within the State of Colorado. Note coverage extends into Wyoming, Utah, and New Mexico. In addition to the conventional index, we’ve added the relevant information from the detailed reports to improve its value as a trout-finding tool. Shading is based on Population Density which is provided on a scale of 0-5. 0 means pop density information was not available, while higher numbers indicate higher density. All of these basins hold native trout, including the 0 basins. We eliminated the basins in which native trout are deemed “extirpated”.
Data provided by Trout Unlimited’s Conservation Success Index.