Conservation biology of the European eel (Anguilla anguilla) on a hydropower-regulated Irish river

• Main Author: MacNamara, Ruairi
• Other Authors: McCarthy, Thomas K.
• Format: Thesis
• Language: unknown
• Published: 2012
• Subjects: Silver eel; Anguilla anguilla; Downstream migration; Hydropower; Zoology; Natural Sciences; Weir
• Online Access: http://hdl.handle.net/10379/3108; https://doi.org/10.13025/16254

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 ...