The fractal geometry of the European eel stock

The European eel Anguilla anguilla L. is found in most European waters. This widespread species is usually exploited by small-scale companies fishing in localized areas. This implies a contrast of scales. This study analysed data on recruitment, stock, and fisheries to determine how they vary geographically. Coherence between 17 data series on glass eel recruitment is analysed by multivariate techniques. It is shown that the majority of these series exhibit a mutually correlated downward trend since 1980; two of the three stations in Ireland, one in the UK and one in Scandinavia show aberrant trends. The geographical distribution of the continental stock is exemplified by a variogram of the length of eel in the Netherlands. It is found that at a distance of only 10 km a large variance component is found, that can not be explained by mere distance. Apparently, the continental stock is fragmented by the fragmentation of the inland waters themselves. The geographical distribution of the continental fisheries is exemplified in an analysis of the dispersion of Dutch fishing licence holders over the country. It is shown that the licence holders are highly over-dispersed, except for the companies fishing on lake IJsselmeer. It is concluded that the distribution pattern of the European eel is characterized by great uniformity in the recruitment stage over the majority of the continent. In the growing stages, the stock (and fisheries) exist in extremely small, fragmented units. It is argued that this dual distribution characteristic necessitates large-scale, continent-wide management, while assessment of the fragmented continental stock and centralized management of the scattered fisheries is not practicable.