Exploring the Consequences of Nest Association Among Freshwater Cyprinds in a Multiple Working Hypotheses Framework

Although nest association among Nocomis chubs and other cyprinids is common throughout North America, the nature of the relationship and its beneficial mechanisms remain unclear. We explored these mechanisms using a multiple working hypotheses framework on fish assemblage data from 25 reaches on three tributaries to the New River, VA. We compared multiple linear regression models predicting reproductive success (age-0 CPUE) of chubs and associates based on model weights (w_i) calculated from model AICc. For age-0 chubs, models represented hypotheses emphasizing the additive effects of 1) adult CPUE, 2) nest abundance, and 3) egg dilution by associates (causing decreased egg predation). For age-0 associates, models represented hypotheses emphasizing 1) adult associate CPUE, 2) gravel substrate availability, 3) nest abundance, 4) parental care from chubs, and 5) egg dilution by chubs. The hypothesis that chubs benefit from egg dilution was overwhelmingly supported (w_i=0.99). The best supported hypotheses for age-0 associate CPUE included nest abundance (w_i=0.46) and adult associate CPUE (w_i=0.44). The importance of gravel availability, parental care, and egg dilution were negligible (w_i<0.02). Because chubs and associates benefit from the association, we consider this relationship to be mutualistic. Positive interactions should be considered when designing conservation plans for imperiled nest associates.