One century of eel growth: changes and implications

Abstract

– A cooperative effort gathered a large European length‐at‐age data set (N = 45,759, Lat. 36S–61N Long. 10W–27E) for Anguilla anguilla, covering one century. To assess the effect of global warming during the last century and habitat effects on growth, a model was fitted on the data representing the conditions met at the distribution area scale. Two GLMs were designed to predict eel log(GR): one model was fitted to the whole data and the other was fitted to the female data subset. A model selection procedure was applied to select the best predictors among sex, age class, five temperature parameters and six habitat parameters (depth, salinity and four variables related to the position in the catchment). The yearly sum of temperatures above 13 °C (TempSUP13), the relative distance within the catchment, sex, age class, salinity class and depth class were finally selected. The best model predicted eel log(GR) with a 64.46% accuracy for the whole data and 66.91% for the female eel data. Growth rate (GR) was greater in habitats close to the sea and in deep habitats. TempSUP13 variable had one of the greatest predictive powers in the model, showing that global warming had affected eel growth during the last century.

Synergistic patterns of threat and the challenges facing global anguillid eel conservation

“…As defined by IUCN, generation length is intended to reflect the turnover rate of breeding individuals in the population (IUCN, 2012b) and in semelparous species like freshwater eels that breed only once, the generation length will equal the average life span. For all anguillid species, however, latitudinal variation and sexual dimorphism significantly affects average generation length because of differences in temperature, distance from spawning ground to maturing habitat and other biological and environmental influences (Holmgren et al, 1997;Feunteun et al, 2003;Cairns et al, 2009;Daverat et al, 2012, see also Table 1). The American eel (Anguilla rostrata), for example, has a broad range of generation lengths across its vast distribution from a mean (range) of 17.5 yrs (5-43) in the St Lawrence River system, Canada, to 5.6 yrs (1-16) across the Southern Atlantic coastal states of South Carolina, Georgia, Florida, Louisiana and Texas (Casselman, 2003).…”

A user-friendly tool to assess management plans for European eel fishery and conservation

“…Sex ratio is assumed to shift in favour of males as eel density increases (Lambert and Rochard, 2007). Body growth is described by a von Bertalanffy curve (Meli a et al, 2006a(Meli a et al, , 2006bAndrello et al, 2011) with gender-specific parameters depending upon the geographical location: in fact, in colder waters eels grow more slowly but become larger than in warmer waters (Daverat et al, 2012). Inter-individual variation in body growth is accounted for through an assignment-at-birth approach (Kirkpatrik, 1984).…”

“…Scrimgeour and Oxley, 2001;Halide et al, 2009;Worrapimphong et al, 2010;Gao and Hailu, 2012). In particular, for the European eel, recruitment-settlement, body growth, natural and fishing mortality, sexual differentiation and maturation are all non-linear functions of age, body size and/or population density and are affected also by environmental variables such as salinity, temperature and productivity of the water body (Edeline et al, 2005;Daverat et al, 2012). Consequently, the ultimate response to conservation measures depends upon the interaction between demographics processes and environmental drivers.…”

EvEel (evolutionary ecology-based model for eel): a model to explore the role of phenotypic plasticity as an adaptive response of three temperate eels to spatially structured environments

“…Growth rate in the salted and brackish downstream parts of catchments is significantly higher than in the upper parts of the catchments (Helfman et al 1984;Melià et al 2006b;Daverat et al 2012). A lower mortality in the upper parts of river catchments is sometimes assumed to balance the associated lower growth.…”