Temperature moderates eDNA–biomass relationships in northern pike

Abstract

Support for eDNA as a quantitative monitoring tool is growing worldwide. Despite advances, there are still uncertainties regarding the representability of the eDNA signal over varying spatiotemporal scales, the influence of abiotic forcing, and phenological changes affecting the behavior of the study organism, particularly in open environments. To assess the spatiotemporal variability and predictive power of quantitative eDNA analysis, we applied species-specific real-time quantitative PCR on water filtrates during two visits to 22 coastal bays in the Baltic Sea. Within bays, we collected water along four transects across each bay and compared the pooled eDNA concentration to temporally matched catches from standardized angling targeting the northern pike (Esox lucius), a species for which reliable monitoring data is lacking.We found the variability in eDNA concentrations between transects to be moderate (21%) but still considerably lower than across bays and visits (52%), suggesting small-scale spatial differences are of less importance during spring when pike spawn.Standardized angling catches, bay area, and water temperature together explained 48% of the variance in eDNA concentrations. DNA concentrations decreased with the increasing bay area, likely indicating a dilution effect. Notably, the relationship between eDNA and standardized catches was positive but varied with temperature and the eDNA-abundance relationship was only significant at higher temperatures, which also coincided with a higher proportion of spawning/spent fish. We conclude that temperature is a key moderating factor driving changes in pike behavior and spring DNA-dynamics. We recommend that future surveys focus on larger spatiotemporal scales during times when the influence of changing temperatures is minimized.

Tide impacts the dispersion of eDNA from nearshore net pens in a dynamic high‐latitude marine environment

“…Beyond this basic pattern, characteristics of each experiment influence the actual dispersal distance, DNA concentration, and presence of eDNA at depth. Fish biomass or abundance interacts with multiple environmental variables (Lacoursière‐Roussel, Rosabal, & Bernatchez, 2016; Ogonowski et al., 2023) that generally differ among studies and almost certainly impact eDNA fate and transport. For example, eDNA degradation in the Sea of Japan (21.4°C) exceeded the exponential decay predicted by tank experiments with temperatures in a comparable range (18.7 ± 1°C to 22.0 ± 1°C) (Murakami et al., 2019).…”

“…Similarly, a study of eDNA from four Atlantic salmon farms, raising adult fish, detected eDNA farther than 5 km from the nearest farm—consistent with the substantially larger biomass among the Atlantic salmon farms (Shea et al., 2022). More broadly, the relationship between biomass/abundance and eDNA concentration has been correlated with trawl catches (Kasmi et al., 2023; Maes et al., 2023; Salter et al., 2019), acoustic data (Shelton et al., 2022), beach seines (Shelton et al., 2019), and angling catches (Ogonowski et al., 2023). These studies generally identify a positive relationship between biomass and DNA concentration, presumably due to increased DNA shed by more individuals.…”