Variation of life traits of glass eels of Anguilla anguilla (L.) during the colonization of Ríos Nalón and Minho estuaries (northwestern Iberian Peninsula)

Abstract

Analyses of the pigmentation stages and the size of glass eels during the arrival period to two northwestern Iberian estuaries (Ríos Nalón and Minho) and comparison of the patterns elucidated in this study with those reported for other geographical locations of the Atlantic and Mediterranean ranges showed nine pigmentation stages ranging from practically transparent to fully pigmented in the twofirst locations. Overall, stage V B was predominant but within a broad variance across rivers and seasons. Consistent with previous studies, pigmentation stages tended to increase when the season progressed whilst, for a given individual length, mass tended to be higher during the early months of arrival. Moreover, both mass and condition factor were lower in individuals of advanced stages. Whilst we found no significant differences on glass eels length among pigmentation stages, both mass and condition factor were lower in more pigmented individuals. Given that larger glass eels with better physical condition may reveal greater energy content implying improved upstream migration earlier individuals may be better migrants than latter individuals.

Glass eel (Anguilla anguilla) recruitment to the river Lis: Ingress dynamics in relation to oceanographic processes in the western Iberian margin and shelf

“…Glass eels are known to enter river basins of the European Atlantic coast throughout the year, but, even before the onset of management restrictions, fisheries only took place from October to March/April in central and northern Portugal (Domingos, ; Weber, ), northern Spain (Iglesias et al., ), and southern France (De Casamajor, Prouzet, & Lazure, ). Modeling ingress dynamics of glass eels in the river Lis also revealed strong seasonal patterns in abundance and biometry, in addition to effects related to other scales of temporal variation (daily, fortnightly and interannual).…”

“…Fishing for glass eels was banned across Portugal in 2001, with the exception of the international river Minho that is jointly managed with Spain and where a commercial fishery is still in operation with stow nets (Antunes, ; Iglesias, Lobon‐Cerviá, Costa‐Dias, & Antunes, ). As part of the eel management plan for Portugal, IPMA launched a pilot project for monitoring glass eels during 2013–2014 with the intention to replicate the sampling conditions of the 1996–1997 study in the river Lis.…”

“…Non‐linear biometric relationships were explored using the library nlme and glass eel condition was estimated as in Iglesias et al. (). Non‐parametric Wilcoxon tests were used to compare variables related to sampling effort between the two experimental fishing periods and Pearson tests were used to explore correlations among biometric variables.…”

Differential effects of behaviour, propensity to migrate and recruitment season on glass eels and elvers’ growing performance

“…Another interesting characteristic of migratory glass eels concerns the evolution of glass eel biometry according to season. Indeed, glass eels caught from September to February had higher condition factor (CF) than glass eels arriving between March and June (Desaunay & Guerault 1997;Iglesias et al 2010), this decrease in CF being associated with a decrease in lipid contents (Charlon & Blanc 1982). Interestingly, Briand et al (2003) observed that up river, autumn glass eels were more numerous than spring glass eels.…”

Primer registro de la fase juvenil de la anguila europea Anguilla anguilla en la laguna hipersalina, Mar Menor, sureste español

“…En el presente estudio no fue evaluado la actividad locomotora de los ejemplares capturados, pero tanto su longitud como su peso son similares a los descritos por otros autores en angulas de ecosistemas mediterráneos (Iglesias et al 2010). Cabe destacar que no fue capturada ninguna angula en el estadio 1 de pigmentación, probablemente debido al tiempo transcurrido desde que las angulas accedieron a la laguna hasta su captura.…”