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. 2023 Feb 27;13(2):e9800.
doi: 10.1002/ece3.9800. eCollection 2023 Feb.

Integrating environmental DNA monitoring to inform eel (Anguilla anguilla) status in freshwaters at their easternmost range-A case study in Cyprus

Nathan P Griffiths  1   2 , Rosalind M Wright  3 , Bernd Hänfling  2 , Jonathan D Bolland  1 , Katerina Drakou  4 , Graham S Sellers  1 , Stamatis Zogaris  5 , Iakovos Tziortzis  6 , Gerald Dörflinger  6 , Marlen I Vasquez  4
Affiliations

Integrating environmental DNA monitoring to inform eel (Anguilla anguilla) status in freshwaters at their easternmost range-A case study in Cyprus

Nathan P Griffiths et al. Ecol Evol. .

Abstract

Despite significant population declines and targeted European Union regulations aimed at Anguilla anguilla conservation, little attention has been given to their status at their easternmost range. This study applies wide-scale integrated monitoring to uncover the present-day eel distribution in Cyprus' inland freshwaters. These are subject to increasing pressures from water supply requirements and dam construction, as seen throughout the Mediterranean. We applied environmental DNA metabarcoding of water samples to determine A. anguilla distribution in key freshwater catchments. In addition, we present this alongside 10 years of electrofishing/netting data. Refuge traps were also deployed to establish the timing of glass eel recruitment. These outputs are used together, alongside knowledge of the overall fish community and barriers to connectivity, to provide eel conservation and policy insights. This study confirm the presence of A. anguilla in Cyprus' inland freshwaters, with recruitment occurring in March. Eel distribution is restricted to lower elevation areas, and is negatively associated with distance from coast and barriers to connectivity. Many barriers to connectivity are identified, though eels were detected in two reservoirs upstream of dams. The overall fish community varies between freshwater habitat types. Eels are much more widespread in Cyprus than previously thought, yet mostly restricted to lowland intermittent systems. These findings make a case to reconsider the requirement for eel management plans. Environmental DNA-based data collected in 2020 indicate that "present-day" eel distribution is representative of 10-year survey trends. Suggesting that inland freshwaters may act as an unrealized refuge at A. anguilla's easternmost range. Conservation efforts in Mediterranean freshwaters should focus on improving connectivity, therefore enabling eels to access inland perennial refugia. Thus, mitigating the impact of climate change and the growing number of fragmented artificially intermittent river systems.

Keywords: Mediterranean; catadromous; connectivity; dams; distribution; eDNA; eel management plans; intermittent; island; policy.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
The distribution of data points across Cyprus, including the 130 eDNA sampling points in 2020 (black triangle) and the 299 fish survey points from 2009–2019 (grey dot). Areas of higher elevation are shaded in blue.
FIGURE 2
FIGURE 2
The relative abundance (% Reads) for each species detected, grouped into 5 freshwater habitat types. (a) The breakdown of eDNA survey sites within each habitat type. Note, that no fish DNA was detected at site KO. (b) Percentage reads merged by habitat type.
FIGURE 3
FIGURE 3
(a) The number of Anguilla anguilla individuals captured each survey year, and (b) the size classes of A. anguilla captured. Note, that no fish surveys were carried out from 2013–2015, and no eels were captured in 2009–2010 surveys.
FIGURE 4
FIGURE 4
Heatmaps from fish surveys using Kernel Density Estimation, weighted by (a) eel catch and (b) species richness respectively.
FIGURE 5
FIGURE 5
The distribution of Anguilla anguilla based on (a) eDNA surveys, (b) electrofishing/netting, and (c) combined positive detections.
FIGURE 6
FIGURE 6
Scatter plots (top) including the Spearman's rank correlation outputs, and smooth curves (loess) to visualise Anguilla anguilla associations. Including a correlation matrix to visualise all eDNA based (bottom left) and catch based (bottom right) associations, blank values indicate no significance (p = >.05).
FIGURE 7
FIGURE 7
The distribution of artificial instream barriers in Cyprus, based on data from the AMBER Consortium (2020).
See this image and copyright information in PMC

References

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