Attracting Common Carp to a bait site with food reveals strong positive relationships between fish density, feeding activity, environmental DNA, and sex pheromone release that could be used in invasive fish management

Abstract

Measurement of environmental DNA (eDNA) is becoming a common technique to survey for rare and invasive fish due to its sensitivity and specificity. However, its utility is limited by an incomplete understanding of factors governing its sources and fates. Failure to detect eDNA is especially difficult to interpret so surveillance techniques often collect large numbers of samples across broad regions. If, however, fish could be reliably attracted to a single location where their eDNA could be easily measured that would be useful. We conducted a proof‐of‐concept study of this idea using invasive Common Carp. We monitored the distribution of radio‐tagged Carp and their eDNA across a 67 ha lake focusing at the bait site while a pheromone (Prostaglandin F2α; PGF 2α) was also measured to determine their reproductive condition. Prior to baiting, Carp were patchily distributed and while eDNA was occasionally detectable, it was patchy and only loosely associated with moderately dense groups of fish. Further, neither Carp, nor their eDNA were consistently measurable at the bait site and surrounding region, and the pheromone was not measurable at all. However, once baiting commenced, Carp started visiting the bait site and feeding, especially at night, where eDNA levels increased 500‐fold as fish densities doubled and PGF 2α became detectable. Fish presence, eDNA and pheromone concentrations peaked at night after 6 days, strongly suggesting feeding activity was the main driver. While the presence of eDNA precisely coincided with this aggregation, levels had dropped dramatically within 5 m. PGF 2α levels dropped less rapidly and demonstrated the presence of live mature fish. We suggest that food could be used to train fish to come to locations where they otherwise are too scarce to be reliably measured, increasing their eDNA release, making them measurable, and their reproductive condition also discernable by measuring pheromones.

Comparing the efficiency of open and enclosed filtration systems in environmental DNA quantification for fish and jellyfish

“…The activity variation of organisms may also influence the seasonal fluctuation of eDNA. eDNA emission increases by feeding [12,73] and reproduction [24,74,75], and is dependent on the lifestyle of the target species [69]. In the present study, the detection rate of eDNA was different between fish species having different lifestyles (e.g., Fig 2).…”

Environmental DNA analysis as a non‐invasive quantitative tool for reproductive migration of a threatened endemic fish in rivers

“…Further studies are required to understand the quantitative effect and mechanisms of eDNA flow in lotic water (Seymour et al, 2018); however, our findings would support the use of quantitative eDNA analysis in lotic environments. In contrast, the use of eDNA for the quantification in the lake was not validated in this study, because the depth gradient makes counting fish by eye difficult and also because unpredictable water currents and eDNA diffusion may have made the eDNA analysis inaccurate, as stated above (Dunker et al, 2016;Eichmiller et al, 2014;Ghosal et al, 2018).…”

“…In addition, the regression analysis showed a higher probability of visual detection in the river than in the lake by one order in eDNA concentration. Since the depth gradient makes visual detection difficult in the lake, and unpredictable water current and eDNA diffusion may have made eDNA analysis inaccurate in the lake (Dunker et al, ; Eichmiller, Bajer, & Sorensen, ; Ghosal, Eichmiller, Witthuhn, & Sorensen, ), this difference is not surprising. Researchers should pay attention to the unreliability of conventional data as well as to that of eDNA data (Chambert et al, ).…”

Standards for Methods Utilizing Environmental DNA for Detection of Fish Species

“…When the water has low turbidity, number of samples is small, and portable pump has enough power to process samples, we recommend on-site filtration [36,49]. When sampling turbid water or the sample number is large, water samples should be transported back to the laboratory in a sterile bottle for filtration [50,51]. Additionally, we recommend water sample transport under dark conditions because ultraviolet (UV) light is damaging to DNA.…”