Feeding Ecology of Co-Occurring Early Life Stage Suckers in a Regulated River

Authors: Casey Pennock, Michael Farrington, Keith Gido

Year: 2018

Abstract

Survival of early life stage fish is affected by multiple factors including environmental conditions, biotic interactions, and starvation. Low survival of early life stage Razorback Sucker, Xyrauchen texanus, in the San Juan River, NM & UT is thought to cause a recruitment bottleneck. Conversely, two other native sucker species, Flannelmouth Sucker, Catostomus latipinnis, and Bluehead Sucker, C. discolobus, recruit to adulthood successfully. To explore a potential factor leading to this discrepancy among species survival, we used museum specimens collected from the San Juan River in 2007 to investigate diets of co-occurring early life-stage (< 30 mm SL) Bluehead, Flannelmouth, and Razorback Sucker. We evaluated both the diversity of diet (number of diet categories) and frequency of occurrence of different diet items. Bluehead and Flannelmouth Sucker did not differ in diet diversity, but on average had 40% and 42%, respectively, more diverse diet compared to Razorback Sucker. Discriminant function analysis (DFA) correctly classified species by frequency of occurrence of diet items 65% of the time, and accuracy varied among species. A low frequency of occurrence of most diet items in Razorback Sucker drove most of the variation (76%) explained by DFA. Razorback Sucker might be less efficient foragers compared to Bluehead and Flannelmouth Sucker. The lack of some diet items (i.e., sand, adult diptera) from Razorback Sucker diets suggests more constrained diet and potential habitat differences compared to other sucker species. Findings from this study shed light on differences in feeding ecology among species that have potential to influence success of early life stages through resource use or predation mechanisms.