Using Pharyngeal Teeth and Chewing Pads to Estimate Juvenile Silver Carp Total Length in the La Grange Reach, Illinois River

Abstract

The Silver Carp Hypophthalmichthys molitrix is an invasive species in the Mississippi River basin; an understanding of their vulnerability to predation as juveniles may inform control by native predators and predator enhancement (e.g., stocking). Digestion of Silver Carp prey recovered from diets makes it difficult to determine the size-classes that are most vulnerable to predation by native fishes. The objective of this study was to determine whether the sizes of the chewing pad (CP), pharyngeal teeth (PT), and pharyngeal arch (PA)—the Silver Carp structures most often found intact in predator diets—were predictive of the TL of prey Silver Carp. During 2014 and 2015, juvenile Silver Carp (n = 136; <180 mm) were collected using 60-Hz pulsed-DC electrofishing and mini-fyke nets in the La Grange reach of the Illinois River. We extracted Silver Carp CPs (n = 136 fish) and PAs with PT intact (n = 129 fish) and measured CP length (CP_L) and width (CP_W), eight reproducible PT landmarks (PT1_L–PT4_L; PT1_W–PT4_W), and four reproducible PA landmarks (PA1–PA4) to the nearest 0.01 µm. Using simple linear regression, we found a strong predictive relationship between measurements of CP, PT, or PA and the TL of Silver Carp. The CP_L (r² = 0.94) and CP_W (r² = 0.94) had the strongest relationships with Silver Carp TL, followed by PA1 (r² = 0.89) and PT1_L (r² = 0.87). These strong relationships suggest that all three structures could be used in diet analyses to accurately estimate Silver Carp TL and thus further our understanding of predator–prey dynamics for this high-risk invasive species.

Received December 9, 2016; accepted June 29, 2017 Published online September 6, 2017

ACKNOWLEDGMENTS

We thank Boone LaHood, Ashley Stanley, Katie Mainor, Emily Szott, Cortney Cox, Allison Lenaerts, Rebekah Hahn, Charmayne Anderson, Tad Locher, and Andrew Mathis for assisting with field and laboratory work and Amber Ruskell-Lamer for creating the map of the sampled region. This project would not have been possible without access to the resources at Western Illinois University’s Kibbe Field Station (Warsaw, Illinois) and funding from the U.S. Geological Survey. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.