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Title Conservation biology of the European eel (Anguilla anguilla) on a hydropower-regulated Irish river
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University/Publisher National University of Ireland – Galway
Abstract The European eel (Anguilla anguilla) has a complex lifecycle, involving catadromous migration between marine spawning grounds and continental growth habitat. European eel stocks have undergone a serious population collapse, and recently introduced E.U. legislation (EC 1100/2007) specifies major conservation actions. In particular, the protection of potential spawners (i.e. silver eels) from continental waters is considered essential for stock recovery. Various aspects of silver eel migratory behaviour, population biology and conservation were examined on the hydropower-regulated River Shannon. The primary study site was at Killaloe eel fishing weir, where long-term reliable catch records are available. Ardnacrusha hydropower dam is located 18 km further downstream (near the tidal limit). Since 2000, silver eels captured at Killaloe are released below the hydropower dam as part of a 'trap and transport' conservation strategy. In 2009, Ireland's Eel Management Plan (EMP) specified that 30% of the silver eel production on River Shannon must be captured and released annually. As a result, four additional fishing sites were established in the mid/upper catchment. An estimated 228 013 silver eels, including a high proportion of females (75.9%), have been released to the lower River Shannon (2000-2010), thus avoiding the hazards associated with passage via Ardnacrusha. Analysis of silver eel migration dynamics/population structure on the river has demonstrated how multi-site capture has enabled EMP targets to be achieved (30.2% in 2009, 39.6% in 2010 and 41.9% in 2011), in addition to increasing the quantity of large female eels released. Silver eel trap and transport is ideally an interim conservation measure, pending development of non-intrusive alternatives (e.g. guidance technology, controlled spillage). To ensure effective implementation of these alternatives, accurate prediction of silver eel migration is essential. Therefore, two predictive approaches were evaluated on the lower River Shannon, by reference to silver eel catches at Killaloe: (i) the Migromat® biomonitor, which predicts migration based on the activity levels of captive eels, signalled 19.9-28.9% of the total catch, or 21.4-32.1% of migration events, during the evaluation period; (ii) alternatively, retrospective analysis of catch and environmental data (water temperature, discharge and lunar luminosity) were used to develop logistic regression models for prediction of silver eel migration. The predictive capacity of this approach varied, depending on the year (27.5-86.4% of the total catch, or 66.7-95.0% of migration events), but was generally more effective than the Migromat®. The use of behavioural guidance as a potential hydropower mitigation measure was also evaluated on the lower River Shannon. During an experiment involving an overwater light barrier at Killaloe eel weir, catch patterns were found to be significantly different between lights on and lights off periods. Eel response to the light barrier was size related, reflecting the…
Subjects/Keywords Silver eel; Anguilla anguilla; Downstream migration; Hydropower; Zoology; Natural Sciences
Contributors McCarthy, Thomas K (advisor)
Country of Publication ie
Record ID handle:10379/3108
Repository galway
Date Retrieved
Date Indexed 2020-01-06
Issued Date 2012-07-31 00:00:00

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…continental yellow and silver eel stocks of A. anguilla are also in decline (Dekker, 2000; 2003a; 2003b), and the species has recently been classified as critically endangered on the International Union for Conservation of Nature (ICUN) Red…

…EMP) for each river basin district, defined according to the Water Framework Directive. Each EMP must specify locally-implemented measures which will be taken in order to comply with a 40% escapement target of silver eel biomass which would have…

…the River Shannon and its tributaries (Quigley and O’Brien, 1996; Bielenberg, 2002), and began commercial silver eel fishing in 1937 (McCarthy et al., 2008b). In this thesis, the primary study site was at the Killaloe eel weir…

eel. 12 Chapter 1 1.7 Aims This thesis describes investigations on various aspects of the migratory behaviour, population biology and conservation of downstream migrating silver eels A. anguilla on the hydropower-regulated River Shannon, Ireland…

…programme, and to compare the River Shannon case study with international eel conservation strategies (Chapter 2); • To develop and evaluate methods of accurately predicting silver eel migration, so as to facilitate effective implementation of…

silver eel catches on the lower River Shannon; • To evaluate the guidance of silver eels using a light barrier (by reference to catch data and sonar camera observations at Killaloe eel weir) and infrasound technology (by reference to…

…x29;; • To investigate seasonal trends in silver eel population structure on the lower River Shannon, to estimate current/historical silver eel production levels for the river system above the hydropower dams, and to develop an input:output model…

…x28;based on juvenile recruitment and silver eel production) to predict future stock levels in the river system. 13 Chapter 2 Chapter 2: Case study and review of conservation strategies for downstream migrating silver eels in hydropower…

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