Vital population statistics of the exploited eel stock on the Swedish west coast

Abstract

The population dynamics and exploitation of the yellow eel ( Anguilla anguilla (L.)) stock on the Swedish west coast were studied. In contrast to a generally observed reduction in the recruitment of glass eels in Europe, including in Swedish waters, there was no indication of a decline in the total eel fishery yields along the Swedish west coast. Long-term records of daily catches as well as by test fishing results also shown that this stability in eel fishery yields has not been maintained by an increase in fishery effort, as the catch-per-unit-efforts in the past 20 years have been more or less unchanged. These findings implied that the number of recruits to the fishery has been rather stable, possibly indicating that density-dependent factors at the elver and yellow eel stages may moderate variations in glass eel recruitment. Total instantaneous rate of mortality was estimated from records on eel length distribution in the professional fyke-net fishery. The estimated total mortality rate in an isolated archipelago population on the west coast was chosen as an approximation of the instantaneous rate of natural mortality and net emigration in the west coast eel stock. The differences between these two estimates could, thus be regarded as the mortality that occurred due to fishing. It was found that the eel fishery was very intense and most fish were caught in small sizes, resulting in a low escapement rate of maturing fish.