Isotopic tissue turnover and discrimination factors following a laboratory diet switch in Colorado pikeminnow (Ptychocheilus lucius)

Stable isotope ecology has made great strides in quantifying energy transfer through food webs. However, trophic inferences gleaned from field-collected data can be limited when isotopic turnover and isotopic discrimination factors (Δ13C or Δ15N) are unknown. We quantified isotopic turnover and discrimination factors using an isotopic diet switch in the endangered Colorado pikeminnow (Ptychocheilus lucius). The estimated half-life for δ13C was 62 days or a 33% increase in mass and δ15N averaged 133 days or a 52% increase in mass. Growth and metabolic processes both contributed to rates of turnover, but metabolic processes had a stronger effect in δ13C than in δ15N. Lipid-corrected δ13C values resulted in discrimination factors of Δ13C between 0.67 and 0.82 and Δ15N between 2.31 and 2.93, values similar to other fishes. These results suggest sampling fin tissue may be a useful, nonlethal tool for isotopic studies. Fins also demonstrated enrichment in 13C that was not linked to the diet switch, highlighting the importance of controls in isotopic diet switch studies to verify species- and diet-specific estimates of isotopic turnover rates.

Detecting Razorback Suckers Using Passive Integrated Transponder Tag Antennas in the Green River, Utah

In order to increase detections of razorback suckers Xyrauchen texanus tagged with passive integrated transponders in the upper Colorado River basin, we deployed two passive instream flat-plate antennas (33 × 68 cm) at a razorback sucker spawning location in the Green River, Utah, during spring of 2012 and 2013. Over the course of 29 d in 2012 and 90 d in 2013, the antennas detected 569 razorback suckers, 19 Colorado pikeminnow Ptychocheilus lucius, 16 flannelmouth suckers Catostomus latipinnis, and 1 bluehead sucker Catostomus discobolus. Despite extensive sampling via boat electrofishing (rafts and hard-bottom boats) and netting (fyke, trammel, and gill) in wetlands that occurred from the 1990s to present in the upper Colorado River basin, a large number of tagged razorback suckers and Colorado pikeminnow, including a fish released in 1996, were detected for the first time by our antennas. Our data indicate that the detectability of razorback suckers, and precision and accuracy of survival and population estimates might be increased significantly with the addition of data gathered by passive instream flat-plate antennas in the Green River.