Origins and movements of invasive piscivores determined from otolith isotopic markers.

摘要

I examined the utility of the strontium isotope (87Sr/ 86Sr) ratio in fish otoliths to determine the origins and movements of invasive piscivores in the Upper Colorado River Basin (UCRB). My goal was to determine if invasive piscivores entered riverine habitat of endangered fishes in the UCRB by escaping from reservoirs, and if so, determine their likely origins. Fishes were collected from 14 reservoirs and rivers directly downstream. My objectives were to examine the distinctiveness of 87Sr/86Sr ratios from fishes in different reservoirs, and temporal stability and interspecies variability of 87Sr/ 86Sr ratios of fishes within reservoirs. Variance components analysis and model selection using an information theoretic approach were used to rank relative importance of reservoir location, species and year on 87Sr/ 86Sr ratios. My results showed that in most cases 87Sr/ 86Sr ratios were unique across reservoirs, overlapped among species in a given reservoir, and were temporally stable across years. I was able to identify the likely reservoir of origin of river-caught fish, and I was able to determine, in some cases, the year of escapement. Overall, my results demonstrate the utility of 87Sr/86Sr ratios for tracking fish movement and origin in river-reservoir systems and provide important insights into processes that affect escapement risk such as dam operations, weather conditions, fish behavior and fish physiology. Analysis of stable isotopes hydrogen (delta2H), carbon (delta 13C), and oxygen (delta18O) were performed on a sub-set of otoliths from the 87Sr/86Sr ratio analysis to determine if additional markers aid in discriminating between groups, particularly when 87Sr/86Sr ratios are similar among different locations. A canonical discriminant function analysis was used to visually differentiate different locations using natural isotopes. These results showed that delta13C and delta18O provide very useful separation among different groups, particularly when in conjunction with 87Sr/86Sr ratios.