What variables most impact invasive crayfish distribution in the San Juan River?

The objective of our research was to quantify spatiotemporal variation in Virile Crayfish density in the San Juan River along an 89 river kilometer reach between Shiprock, New Mexico and Montezuma Creek, Utah. Within this reach we focused our sampling on secondary channel and island backwater habitats, as they are crucial nursery habitats for imperiled native fishes. We seined 50 m sites within 20 backwater habitats four times from July through September 2021, for a total of 80 sites. All captured individuals were counted and measured, then returned to their capture habitat. We collected a total of 457 Virile Crayfish at 40/80 sites. We found that nonnative Virile Crayfish attain higher densities in secondary channel backwaters than in island backwaters, possibly due to the lower velocity of secondary channel backwaters compared with island backwaters. The higher densities of Virile Crayfish could result in competition with and predation on the imperiled fishes that prefer these habitats as nursery areas. For these reasons, further study concerning how nonnative Virile Crayfish are impacting native fishes in the San Juan River is warranted.