The development of environmental DNA (eDNA) techniques for the detection and monitoring of the critically endangered European eel, Anguilla anguilla

Weldon, Laura

Abstract

The European eel Anguilla anguilla, is currently classified as critically endangered (IUCN Red List). In the UK the eel population is estimated at less than 5% of numbers observed in the 1980s and this trend is reflected throughout its European freshwater habitat range. The EU Eel regulation (EC 1100/2007) established measures for the recovery of A. anguilla, to be implemented through eel management plans, but a lack of baseline data has restricted the ability to assess habitat improvement strategies. Traditional eel survey methods such fyke net surveys and electrofishing are reliable but require technical skill, are invasive, selective and in very low eel populations have the potential to underestimate total numbers. Environmental DNA (eDNA) techniques are potentially powerful tools for ecological monitoring in aquatic environments. This thesis describes the development and steps toward validation of a single species eDNA method for the detection and quantification of A. anguilla eDNA using surface water samples. The new method was assessed in the field and compared to a standardised fyke net monitoring survey in Irish freshwater lakes. The recovery of eels using fyke nets at five freshwater lakes was compared with the intensity of eDNA recovered from surface water samples at the same locations. Water samples were analysed for A. anguilla eDNA before and after fyke net fishing for 24 hours and compared with the recovery of eDNA from shore side sampling. The data suggests that eDNA methods are more sensitive at detecting eels and the quantities of eDNA recovered in 1L surface water samples were comparable with simple categories of high, medium and low eel populations. The methods were applied to a range of lentic freshwater habitats and different survey strategies were assessed. These confirmed that the eDNA method was robust and that physicochemical environmental variations in the habitats surveyed had a minimal impact on the survey results. The shedding and decay of A. anguilla eDNA was assessed using eels in an aquarium setting. The data confirmed the rapid decline of detectable eDNA and found little differences in the decay of two different sized A. anguilla eDNA fragments over 24 hours. Yet when the ratio of large to small fragments was compared there was a significant positive change suggesting that decay of one fragment is occurring at a faster rate. These insights and developments offer a timely and robust eDNA method to enhance monitoring and surveillance that will support the recovery of critically endangered Anguilla anguilla.

• Thesis Type: Thesis
• Deposit Date: Mar 29, 2022
• Publicly Available Date: May 5, 2023
• Public URL: https://uwe-repository.worktribe.com/output/9259727
• Additional Information: The dataset for this thesis can be accessed at: http://researchdata.uwe.ac.uk/571/
• Award Date: May 5, 2023