8 May 2026

Development of a Trace Element Signature Library Across a Large Watershed for Assessing Large-Scale Fish Movement Patterns

Abstract: Using trace element or stable isotope analysis has proven to be an effective means to characterize early life history and large-scale movement patterns in fishes. Target species are assessed for analyte concentrations occurring in calcified hard structures and compared to signatures noted from associated watersheds. However, this approach assumes analyte absorption occurs in proportion to their availability, and success relies heavily on the ability to identify unique water chemistry signatures between neighboring watersheds within a defined study area. Our objective was to establish a trace element signature profile for major tributaries occurring within the Mississippi River Valley (MRV). Water samples were obtained from 49 stations and evaluated for the presence and relative concentration of Ba, Sr, Ca, Fe, and Li. Analyte concentrations (milligrams per liter) varied across the sampled stations, although Li occurred at only four stations, primarily in the upper reaches of the MRV, and provided little discriminatory use. Concentrations of Fe and Ca depicted an inverse relationship, with Ca having higher concentrations in the upper third of the MRV while Fe typically had higher concentrations in the lower third. Ratios of Ba:Ca and Sr:Ca (millimole per mole) exhibited the greatest utility for delineating river-specific or reach-specific signatures.

1 Aug 2024

Detection and Decay of Different Classes of Environmental RNA (eRNA) from Zebrafish (Danio rerio)

Purpose: This technical note contributes to the growing body of knowledge about macroscopic eukaryotic environmental RNA (eRNA) by exploring detection and decay for several different zebrafish (Danio rerio) eRNAs in a mesocosm setting. The study addressed four basic hypotheses: (1) D. rerio would deposit detectable levels of eRNA into water, (2) different classes of eRNA would be detected, (3) different eRNA sequences (for example, loci) would degrade at different rates, and (4) abiotic and biotic factors would influence rates of degradation. For the last hypothesis, we tracked eRNA concentration decay under treatments with different water temperatures and levels of microbiological activity, two factors known to significantly influence environmental DNA (eDNA) decay (Barnes et al. 2014; Lance et al. 2017; Nielsen et al. 2007; Strickler et al. 2015).