Long-Term Changes in Recruitment, Population Dynamics, and Status of the European Eel in Two English River Systems

摘要

Long-term changes in eel stock status are examined in two catchments in England. The River Severn supports the UK's major glass eel fishery. The Rivers Piddle and Frome and Poole Harbour form a linked river/tidal lagoon system supporting yellow and silver eel fisheries. Eel population density and structure in lower Severn tributaries appear unchanged since the early 1980s, as does eel distribution in the upper catchment. It is concluded that, despite a decline in glass eel numbers and increased fishing pressure in the 1990s, recruitment continues to be sufficient to fill local carrying capacity. In contrast, in the Piddle and Frome, population density has declined sharply since the 1970s, and there has been a major change in sex ratios from male tofemale domination. Although currently high, female silver eel escapement is likely to decline sharply over the next few years from the Piddle and possibly the Frome. It is postulated that the productive tidal lagoon acts as a sink for declining glass eelrecruits so that fewer elvers and yellow eels are entering the rivers. Fishing pressure on harbor stocks is unqualified but potentially high. Management options and priorities for the two catchments are discussed.