Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Abstract

– Modelling‐governing patterns of European eel (Anguilla anguilla L.) distribution of four eel size classes (<150, 150–300, 300–450 and >450 mm) in the Frémur basin (northwest France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro‐ and microscale factors, such as distance from the sea, depth and flow velocity, have the most significant influence on the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to the distance from the sea showed that densities increase weakly upstream. Another outcome was the variations in habitat preference according to the eel size, even if this species is spread over practically every type of microhabitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesise that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm.

Dispersal of yellow phase Japanese eels Anguilla japonica after recruitment in the Kojima Bay-Asahi River system, Japan

“…Based on those two studies, eels might be suggested to settle around the upper limit of tidal flow and then move into both the upper and lower reaches of the river as they grow. For freshwater, this suggestion is strongly supported by a large number of observations that reported size increases and abundance decreases of eels in the upstream direction of river systems Knights 1988, 1993;Haro and Krueger 1991;Barak and Manson 1992;Smogor et al 1995;Tzeng et al 1995;Oliveira 1997;Feunteun et al 2003;Goodwin and Angermeier 2003;Laffaille et al 2003;Moriarty 2003;Lasne and Laffaille 2008;Yokouchi et al 2008). In contrast to eels in freshwater, the movement of eels in brackish and seawater is still poorly documented.…”

Assessing the freshwater distribution of yellow eel

“…More precisely, several studies suggest that around the 300-mm size several changes occur (Michel and Oberdorff, 1995;Baisez, 2001;Feunteun et al, 2003;Laffaille et al, 2003Laffaille et al, , 2004. Firstly, elvers and small yellow eels are mainly invertivorous and live in shallow water, whereas larger eels are found in deeper water, where they feed on other fish including small eels.…”

“…Some studies use the absolute or relative density (e.g. Lobon-Cervia et al, 1995;Ibbotson et al, 2002;Laffaille et al, 2003;Imbert et al, 2008). The problem with this type of data is that the methods available do not allow reliable standardization of the data due to factors such as differing sampling efficiency in shallow versus deep habitats (Naismith and Knights, 1990;Jellyman and Graynoth, 2005).…”

Use of decision tree and artificial neural network approaches to model presence/absence of Telestes muticellus in piedmont (North‐Western Italy)

“…We chose variables according to the degree of their importance for fish fauna Mastrorillo et al, 1997;Olden and Jackson, 2001;Reyjol et al, 2001;Death, 2002, 2004;Laffaille et al, 2003;Olden et al, 2006), and according to the knowledge of experts. We chose the following set of predictive variables: (1) altitude; (2) length of the sampling area; (3) homogeneity in width of the sampled tract (classes 0-5; the larger the widths of the sections examined, the larger the value); (4) amount of human impact (classes 0-5; the larger the impact, the larger the value); (5) amount of shade (classes 0-5; the larger the shade, the larger the value); (6) shelters for fish, visually assessed as the area consisting of undercut banks, macrophyte cover and debris jams (classes 0-5; the larger the cover, the larger the value); (7) (Piedmont Region, 2006).…”