1. Foraging specialisms, movement and migration ecology of the European eel Anguilla anguilla
James Barry
University of Glasgow
Introduction
In the last 30 years, the European eel (Anguilla anguilla) has shown a 90% decrease in the number of juvenile fish found in European waters.
The vast geographical distribution and the two trans-Atlantic migrations the species makes to mature and reproduce means finding the reasons underpinning this decline have remained elusive.
The European Commission has made it a requirement that member states develop plans for the freshwater management of this species.
This project aims to investigate inland population dynamics through sampling of eels from sites throughout the study area, with particular interest on trophic morphology, migrations and habitat use in study sites.
Identify effective conservation measures to aid the restoration of European eel populations
European eel life cycle
Glass eel
(4-7cm), enter our estuaries from March-June.
Elver
(7-30cm), migrate into our river and lakes in search of suitable habitat.
Yellow eel
(>30cm), this is the feeding stage. Resident eels begin to condition themselves in preparation for their spawning migration.
Silver eel
(>30cm), leave our rivers and lakes in late Autumn and begin their spawning migration estimated at 6000km in the direction of the Sargasso Sea.
Eel larvae
travel 6000km from spawning grounds, travelling on ocean currents en route to European waterways.
Study Snapshot
Study Snapshot
Study Snapshot
Broad-headed
Trophic Morphology: Comparison of broad and narrow head yellow eel specimens (both 48cm)
Narrow-headed
Ecomorphology of the European eel: Heading in the right direction?
We are investigating the importance of understanding life history variations and the effect of the observed phenotypic variation in head shape has on growth and lipid reserves in a range of continental habitats. Broad-headed individuals were observed to grow faster however lay down lipid at a slower rate in comparison to narrow-headed individuals.
Foraging specialisms influence space use and movement patterns of European eel
We assessed summer home range size, temporal change in spatial behaviour and activity patterns of broad headed and narrow headed morph types. Eel activity was strongly dependent on light conditions. Lunar phase period also influenced eel movement within the lake. These results provide valuable insights into the spatio-temporal distribution of eels in a lake system, demonstrating that individuality in foraging behaviour has direct influence on spatial patterns.
Significant loss of tagged individuals was observed in the sea lough, with only 26% of the tagged individuals successfully detected at the outermost end of the ALS array. This indicates high levels of mortality during sea lough migration. This has important implications for eel management plans. FW= freshwater, TW=Transitional water, SL=Sea lough
Freshwater and coastal migration patterns of silver stage eels
Summary
Using the applied methods outlined will help answer questions related to the habitat use and trophic ecology of European eels within the study area.
The relationship between phenotype and ecology suggests that efforts towards conservation may require the assessment of morphological variation within the population and its proximate causes, especially if the observed phenotype differentiation influences life history while resident in continental waters
Understanding the movement and habitat use of a threatened species is vital to implementing effective conservation strategies.
Evidence gained from this project will be used to set meaningful targets and highlight appropriate management options to aid achieving EU targets for sustainable eel stocks.