International eel symposium, 2003 - Quebec August 11, 2003
Oral Presentation

Long Term Changes in Recruitment, Population Dynamics and Status of European Eel in a River and Lagoon System in Southern England

Bark, A.W.* Department of Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Waterloo,London, SE1 9NN
Dunn, S. Department of Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Waterloo,London, SE1 9NN
Knights, B. Applied Ecology Research Group, University of Westminster, 115 Cavendish Street, London. W1M 8JS.
Williams, B. Department of Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Waterloo,London, SE1 9NN
Williams, E. Department of Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Waterloo,London, SE1 9NN
Winter, E. Department of Life Sciences, Franklin-Wilkins Building, 150 Stamford Street, Waterloo,London, SE1 9NN

Presenter email address: tony.bark AT kcl.ac.uk

Abstract Text: The Piddle and Frome are linked rivers in southern England which drain to the sea via the large coastal lagoon of Poole Harbour. They are amongst the very few UK river systems for which there is reliable quantitative data on eel stocks dating back to the 1970s and 1980s. Data on current stock status was collected from 1999 onwards.In both rivers, there appears to have been a major decline in eel population density since the 1970s/80s, but a relatively small decline in biomass. The male:female ratio of yellow eels in one Frome tributary was 3.7:1 in 1982/3 compared with 0.43:1 in 2000. The male:female ratio of migrating silver eels in the Piddle was 2.8:1 in 1976/7 compared with 0.07:1 in 1999-2002. There is also some evidence of an increased proportion of female eels in the harbour. Very few small (<150 mm) eels are now found in either river. There have thus been major changes in eel population structure within the system. This suggests that the carrying capacity of Poole Harbour is sufficient to support a high proportion of the currently reduced recruitment, thus lessening competitive pressure to migrate up river. This hypothesis is now being tested.