Factors affecting the diet and abundance of northern populations of Rio Grande sucker (Catostomus plebeius)

We surveyed streams within a broad portion of the northern range of Rio Gra nde sucker (Catostomus plebeius) to assess factors associated with the spec ies' diet and abundance. We also examined potential interplay between habit at, food availability, and dietary overlap with the nonnative white sucker (Catostomus commersoni). Rio Grande sucker and white sucker primarily consu med periphyton, resulting in high diet overlap. Amount of fine sediment in streams was negatively related to abundance (catch per effort) and conditio n of Rio Grande sucker. Condition of Rio Grande sucker was negatively relat ed to white sucker catch per effort, and abundance of Rio Grande sucker was significantly lower in streams with white sucker. We suggest that the high degree of diet overlap between the two sucker species may be ecologically important.