Patterns of silver eel (<i>Anguilla anguilla</i> L.) sex ratio in a catchment

Laffaille, Pascal; Acou, Anthony; Guillouët, Jérôme; Mounaix, Béatrice; Legault, Antoine

doi:10.1111/j.1600-0633.2006.00195.x

Cited by 31 publications

(29 citation statements)

References 32 publications

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“…1997). In the French river Frémur, Laffaille et al. (2006) observed over a nine year study (1996–2004) a gradual shift of silver eel sex ratio from male to female.…”

Section: Discussionmentioning

confidence: 99%

Decreasing eel stocks: survival of the fattest?

Belpaire

Goemans

Geeraerts

et al. 2009

Ecology of Freshwater Fish

114

120

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– Since the 1980s, the European eel Anguilla anguilla stock is in steep decline. Lipid reserves are essential to cover energetic requirements for silver eel migration and reproduction. Two large and independent data sets from Belgium and The Netherlands show an average one‐third decrease in fat contents of yellow eels over the past 15 years. Also Le Cren’s relative condition factor decreased. On the basis of the somatic energy reserves, reproductive potential of eels from various latitudes over Europe was estimated, assuming fat levels in yellow eel are indicative of those in silver eels. Only large individuals, females as well as males, with high lipid content seem to be able to contribute to the spawning stock. The decrease in fat content in yellow eels may be a key element in the stock decline and raises serious concerns about the chances of the stock to recover.

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“…1997). In the French river Frémur, Laffaille et al. (2006) observed over a nine year study (1996–2004) a gradual shift of silver eel sex ratio from male to female.…”

Section: Discussionmentioning

confidence: 99%

Decreasing eel stocks: survival of the fattest?

Belpaire

Goemans

Geeraerts

et al. 2009

Ecology of Freshwater Fish

114

120

View full text Add to dashboard Cite

show abstract

“…(2001) reported that the sex ratio of migrating silver American eels in the five rivers varied from 2% to 51% females. But, Laffaille et al. (2006) showed a gradual shift in the silver eel sex ratio from a dominance of males to females according to the changes in the numbers of silver‐phase European eels in the same river over a 9‐year period.…”

Section: Discussionmentioning

confidence: 99%

Variation in the demographic characteristics of yellow‐phase Japanese eels in different habitats of the Hamana Lake system, Japan

Yokouchi

Aoyama

Oka³

et al. 2008

Ecology of Freshwater Fish

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– Yellow‐phase Japanese eels (Anguilla japonica) were investigated in the Hamana Lake system, Japan, from 2003 to 2004 to understand how their demographic attributes vary within the lake system. A total of 779 yellow eels were collected during sampling in two inlet rivers and two brackish/saltwater lakes within the lake system. Female eels predominated, constituting 84% of the 75 sex‐determined eels in the river, and 50% of the 151 sex‐determined eels in the lakes. Total lengths (TL) of all eels examined ranged from 54.2 to 715.0 mm (mean = 320.4 ± 145.4 SD). In the inlet river, the TL of eels showed a significant positive relation with the distance from the river mouth. The estimated relative abundances of eels ranged from 0 to 1.8 eels·m−2 effort (mean: 0.3 ± 0.41) in the river and was negatively correlated with the distance from the river mouth. This suggested that larger eels might tend to be distributed at lower abundances in upstream reaches of the river. Mean age of yellow eels determined by their otolith annuli was younger in the lake (N = 117, 3.3 ± 1.4 years) than in the river (N = 214, 4.3 ± 1.7 years). Growth rate was higher in the lake than in the river at age 1–2 years (131.9 and 104.4 mm·year−1, respectively). The results of this study suggest that, although Japanese eels can adapt to various types of environments, significant differences can occur in population structures and growth patterns among habitats.

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“…Thus, the distribution of different size classes on both large and small scales reflects various mechanisms depending on eel size. Finally, 300 mm corresponds to the size from which silvering may occur in males (Dekker et al, 1998;Feunteun et al, 2000;Laffaille et al, 2006). Above this size, individuals may leave freshwater and head for the Sargasso Sea, and so the distribution patterns of > 300 mm eels that we observe may be biased, and the relationships between the factors we are tracking and eel distribution substantially distorted.…”

Section: Differences In the Nature Of Information According To Sizementioning

confidence: 97%

Assessing the freshwater distribution of yellow eel

Lasne

Laffaille

2008

Knowl. Managt. Aquatic Ecosyst.

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In the global context of the decline in wild species, modeling the distribution of populations is a crucial aspect of ecological management. This can be a major challenge, especially for species, such as the European eel, that have complex life cycles, exhibit cryptic behavior, or migrate over long distances. A review of the literature suggests that eel size data could be used to assess and analyze freshwater distribution of eel. We argue that analyses based on small yellow eels (≤ 300 mm) along the longitudinal course of rivers could provide a valuable tool for population monitoring. We propose a standardized catchment recruitment index and a colonization index based on the probability of occurrence (presence/absence data) using logistic models for different size classes. The model developed here provides a convenient guide for assessing yellow eel stages in freshwater areas, and should have concrete applications for management of the species. RÉSUMÉ Évaluation de la distribution des anguilles jaunes en eau douceDans le contexte actuel de déclin des espèces, la modélisation de la distribution des populations est une étape importante pour la gestion de la biodiversité. Cependant, cette modélisation peut s'avérer difficile, particulièrement pour les espèces qui, comme l'anguille européenne, possèdent des cycles de vie complexes, ont un mode de vie cryptique ou effectuent de grandes migrations. Un examen de la littérature suggère que la taille des anguilles peut être utilisée comme critère pour évaluer et analyser la distribution des anguille en eau douce. Nous suggérons que l'examen des patrons de distribution des petites anguilles (≤ 300 mm) le long des réseaux hydrographiques peut fournir des informations précieuses pour le suivi des populations. Nous proposons un indice standardisé de recrutement et de colonisation des bassins versants sur la

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Patterns of silver eel (Anguilla anguilla L.) sex ratio in a catchment

Cited by 31 publications

References 32 publications

Decreasing eel stocks: survival of the fattest?

Decreasing eel stocks: survival of the fattest?

Variation in the demographic characteristics of yellow‐phase Japanese eels in different habitats of the Hamana Lake system, Japan

Assessing the freshwater distribution of yellow eel

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