Addressing the impact of mercury estuarine contamination in the European eel (Anguilla anguilla L., 1758) – An early diagnosis in glass eel stage based on erythrocytic nuclear morphology

2018 ◽  
Vol 127 ◽  
pp. 733-742 ◽  
Author(s):  
D. Castro ◽  
C.L. Mieiro ◽  
J.P. Coelho ◽  
S. Guilherme ◽  
A. Marques ◽  
...  
Keyword(s):  
Early Diagnosis ◽  
Anguilla Anguilla ◽  
Nuclear Morphology ◽  
European Eel ◽  
Glass Eel ◽  
The Impact

Challenges to quantifying glass eel abundance from large and dynamic estuaries

2017 ◽  
Vol 75 (2) ◽  
pp. 727-737 ◽  
Author(s):  
Sarah Walmsley ◽  
Julie Bremner ◽  
Alan Walker ◽  
Jon Barry ◽  
David Maxwell
Keyword(s):  
Large Scale ◽  
Anguilla Anguilla ◽  
Commercial Fishing ◽  
European Eel ◽  
Estuarine System ◽  
Glass Eel ◽  
The North ◽  
Adequate Sampling ◽  
South Shore ◽  
Glass Eels

Abstract European eel Anguilla anguilla recruitment into the rivers of the northeastern Atlantic has declined substantially since the 1980s. Monitoring of recruiting juveniles, or glass eels, is usually undertaken in small estuaries and rivers. Sampling of large-scale estuaries is rare, due to the size of the sampling area and the resources needed to provide adequate sampling levels. Here we describe surveys for glass eels in the UK’s largest estuarine system, the Severn Estuary/Bristol Channel. We sampled across a 20 km-wide stretch of the estuary in 2012 and 2013, using a small-meshed net deployed from a commercial fishing trawler, and the surveys yielded over 2500 glass eels. Eels were more abundant in the surface layer (0–1.4 m depth) than at depth (down to 8.4 m depth), were more abundant close to the south shore than along the north shore or middle of the estuary, and were more abundant in lower salinity water. Numbers were higher in the second year than in the first and eels were more abundant in February than April. The difficulties and logistics of sampling in such a large estuary are discussed, along with the level of resources required to provide robust estimates of glass eel abundance.

scholarly journals Rethinking swimming performance tests for bottom-dwelling fish: the case of European glass eel (Anguilla anguilla)

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
P. Vezza ◽  
F. Libardoni ◽  
C. Manes ◽  
T. Tsuzaki ◽  
W. Bertoldi ◽  
...  
Keyword(s):  
Water Temperature ◽  
Swimming Performance ◽  
Life Stage ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Fish Swimming ◽  
Glass Eel ◽  
Swimming Time ◽  
Swimming Mode ◽  
Active Swimming

Abstract Systematic experiments on European eel (Anguilla anguilla) in their juvenile, early life stage (glass eel), were conducted to provide new insights on the fish swimming performance and propose a framework of analysis to design swimming-performance experiments for bottom-dwelling fish. In particular, we coupled experimental and computational fluid dynamics techniques to: (i) accommodate glass eel burst-and-coast swimming mode and estimate the active swimming time (tac), not considering coast and drift periods, (ii) estimate near-bottom velocities (Ub) experienced by the fish, rather than using bulk averages (U), (iii) investigate water temperature (T) influence on swimming ability, and (iv) identify a functional relation between Ub, tac and T. Results showed that burst-and-coast swimming mode was increasingly adopted by glass eel, especially when U was higher than 0.3 ms-1. Using U rather than Ub led to an overestimation of the fish swimming performance from 18 to 32%, on average. Under the range of temperatures analyzed (from 8 to 18 °C), tac was strongly influenced and positively related to T. As a final result, we propose a general formula to link near-bottom velocity, water temperature and active swimming time which can be useful in ecological engineering applications and reads as $${\rm{U}}_{\rm{b}}=0.174\cdot \left({{\rm{t}}_{\rm{ac}}}^{-0.36}\cdot {\rm{T}}^{0.77}\right)$$ U b = 0.174 · t ac - 0.36 · T 0.77 .

scholarly journals A mechanical approach to understanding the impact of the nematode Anguillicoloides crassus on the European eel swimbladder

2020 ◽  
Vol 223 (17) ◽  
pp. jeb219808
Author(s):  
Helen A. L. Currie ◽  
Nicholas Flores Martin ◽  
Gerardo Espindola Garcia ◽  
Frances M. Davis ◽  
Paul S. Kemp
Keyword(s):  
Mechanical Damage ◽  
Severe Infection ◽  
Anguilla Anguilla ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
European Eel ◽  
Sargasso Sea ◽  
Mechanical Integrity ◽  
The Impact ◽  
Anguillicoloides Crassus

ABSTRACTOne of the most detrimental factors in the drastic decline of the critically endangered European eel (Anguilla anguilla) was the inadvertent introduction of the invasive nematode Anguillicoloides crassus. Infection primarily affects the swimbladder, a gas-filled organ that enables the eel to control its depth in the water. A reduction in swimbladder function may be fatal for eel undergoing their spawning migration to the Sargasso Sea, a journey of over 5000 km. Although the physiological damage caused by this invasive parasite is well studied through the use of quantifiable gross pathological indices, providing a good measure of the swimbladder health status, they cannot separate the role of mechanical and morphological damage. Our study examined the appropriateness of three commonly used indices as a measure of mechanical damage by performing uniaxial tensile tests on swimbladder specimens obtained from an infected eel population. When the test results were compared with the gross pathological indices it was found that thickness correlated most strongly with mechanical damage, both confirming and, more importantly, explaining the counterintuitive findings of earlier work. In a damaged swimbladder, the immune response leads to a trade-off; increasing wall thickness raises the pressure required for organ rupture but decreases strength. The results indicate that for moderate infection the mechanical integrity of the swimbladder can be maintained. For severe infection, however, a reduction in mechanical integrity may reach a tipping point, thereby affecting the successful completion of their oceanic migration.

scholarly journals Modelling the recruitment of European eel (Anguilla anguilla) throughout its European range

2017 ◽  
Vol 75 (2) ◽  
pp. 541-552 ◽  
Author(s):  
Virginie Bornarel ◽  
Patrick Lambert ◽  
Cédric Briand ◽  
Carlos Antunes ◽  
Claude Belpaire ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Anguilla Anguilla ◽  
Distribution Area ◽  
European Eel ◽  
Estimation Model ◽  
Glass Eel ◽  
The North ◽  
The Status ◽  
The North Sea ◽  
Sea Area

Abstract European eel (Anguilla anguilla) recruitment has been declining at least since the early 1980s at the scale of its distribution area. Since the population is panmictic, its stock assessment should be carried out on a range-wide basis. However, assessing the overall stock during the continental phase remains difficult given its widespread distribution among heterogeneous and separate river catchments. Hence, it is currently considered by the International Council for the Exploration of the Sea (ICES) more feasible to use glass eel recruitment data to assess the status of the overall population. In this study, we used Glass Eel Recruitment Estimation Model (GEREM) to estimate annual recruitment (i) at the river catchment level, a scale for which data are available, (ii) at an intermediate scale (6 European regions), and (iii) at a larger scale (Europe). This study provides an estimate of the glass eel recruitment trend through a single index, which gathers all recruitment time-series available at the European scale. Results confirmed an overall recruitment decline to dramatically low levels in 2009 (3.5% of the 1960–1979 recruitment average) and highlighted a more pronounced decline in the North Sea area compared to elsewhere in Europe.

scholarly journals Problems and perspectives of artificial reproduction and conservation of the european eel (Anguilla anguilla (Linnaeus, 1758)) (a review)

2021 ◽  
pp. 34-44
Author(s):  
V. Bekh ◽  
◽  
I. Kononenko ◽  
R. Kononenko ◽  
◽  
...  
Keyword(s):  
Large Scale ◽  
Technological Development ◽  
Natural Populations ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
Artificial Reproduction ◽  
Promising Area ◽  
Stable Source ◽  
The Impact

Purpose. Rearing of the European eel (Anguilla anguilla) is a promising area of aquaculture, the development of which in Ukraine and the world is constrained by several factors. Spawning, egg incubation, lack of a stable source of supply of fish seeds – these and other problems, as well as the importance of such studies form a basis for finding approaches for their solution and conducting new large-scale studies. This area attracts attention of scientists, there are certain results and achievements; however, they are still not enough to solve the problems of artificial reproduction of the European eel. Findings. The authors revised, analysed and systematized literature sources focused on the study of the European eel. As a result, it was possible to identify the main achievements and shortcomings in this area, which are promising for further study. In addition, we identified some obstacles faced by scientists and analysed available methods for their solving. Practical value. This review can be used to stimulate new studies and technological development towards industrial cultivation of eel in Ukraine, which will allow reducing the impact on natural populations of this species and stabilize its number in the natural environment. In addition, the authors of the article intend to draw attention of scientists and manufacturers to the perspectives and problems of growing and studying the European eel. Key words: European eel, glass eel, leptocephali, migration, Sargasso Sea, cultivation, fish seeds.

scholarly journals Cause or consequence? Exploring the role of phenotypic plasticity and genetic polymorphism in the emergence of phenotypic spatial patterns of the European eel

2017 ◽  
Vol 74 (7) ◽  
pp. 987-999 ◽  
Author(s):  
Maria Mateo ◽  
Patrick Lambert ◽  
Stéphane Tetard ◽  
Martin Castonguay ◽  
Bruno Ernande ◽  
...  
Keyword(s):  
Life History ◽  
Phenotypic Plasticity ◽  
Habitat Selection ◽  
Life History Traits ◽  
Environmental Variability ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Anthropogenic Pressures ◽  
The Impact

The European eel (Anguilla anguilla), and generally, temperate eels, are relevant species for studying adaptive mechanisms to environmental variability because of their large distribution areas and their limited capacity of local adaptation. In this context, GenEveel, an individual-based optimization model, was developed to explore the role of adaptive phenotypic plasticity and genetic-dependent habitat selection, in the emergence of observed spatial life-history traits patterns for eels. Results suggest that an interaction of genetically and environmentally controlled growth may be the basis for genotype-dependent habitat selection, whereas plasticity plays a role in changes in life-history traits and demographic attributes. Therefore, this suggests that those mechanisms are responses to address environmental heterogeneity. Moreover, this brings new elements to explain the different life strategies of males and females. A sensitivity analysis showed that the parameters associated with the optimization of fitness and growth genotype were crucial in reproducing the spatial life-history patterns. Finally, it raises the question of the impact of anthropogenic pressures that can cause direct mortalities but also modify demographic traits and act as a selection pressure.

scholarly journals An Evaluation of Restocking Practice and Demographic Stock Assessment Methods for Cryptic Juvenile European Eel in Upland Rivers

2020 ◽  
Vol 12 (3) ◽  
pp. 1124 ◽  
Author(s):  
Billy Nzau Matondo ◽  
Jean-Philippe Benitez ◽  
Arnaud Dierckx ◽  
Xavier Rollin ◽  
Michaël Ovidio
Keyword(s):  
Stock Assessment ◽  
Release Site ◽  
Anguilla Anguilla ◽  
Assessment Method ◽  
Assessment Methods ◽  
European Eel ◽  
Mark Recapture ◽  
Glass Eel ◽  
The North ◽  
The North Sea

Restocking of the critically endangered European eel Anguilla anguilla is widespread, but it is rarely scientifically evaluated. Methods used to assess its associated performance by estimating the survival rate and implement restocking for maximum recruitment in rivers have not yet been investigated. Based on two glass eel restocking events using a single release site/point and multiple sites per river performed in upland rivers (>340 km from the North Sea), the recruitment success of stocked eels was scientifically evaluated during a 3-year study using multiple capture-mark-recapture methods and mobile telemetry. We compared the observed data with the data estimated from the Telemetry, De Lury and Jolly-Seber stock assessment methods. For recruitment data, Telemetry was very close to Jolly-Seber, an appropriate stock assessment method for open populations. Using the best model of Jolly-Seber, survival probability was higher (>95%) in both restocking practices, but recruitment yields were higher and densities of stocked eels were lower in multiple sites compared to a single site. Our results suggest that Telemetry can help to rapidly assess cryptic juvenile eel stocks with good accuracy under a limited number of capture-mark-recapture sessions. Artificial dispersal of glass eels on several productive habitats/sites per river appears to be the better-suited practice for restocking.

scholarly journals Saving the European Eel: How Morphological Research Can Help in Effective Conservation Management

2020 ◽  
Vol 60 (2) ◽  
pp. 467-475
Author(s):  
Jens De Meyer ◽  
Pieterjan Verhelst ◽  
Dominique Adriaens
Keyword(s):  
Environmental Changes ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Silver Eel ◽  
Critically Endangered Species ◽  
Morphological Studies ◽  
Management Measures ◽  
Migration Barriers ◽  
And Behavior ◽  
The Impact

Abstract The European eel (Anguilla anguilla) is a critically endangered species, whose recruitment stocks have declined to nearly 1% compared to the late 70s. An amalgam of factors is responsible for this, among them migration barriers, pollution, habitat loss, parasite infection, and overfishing. A lot of recent studies focus on aspects that can increase the mature silver eel escapement rate, such as identifying migration barriers and developing passageways or addressing the impact of pollution on the eel’s health. However, little attention is given to the eel’s morphology in function of management measures. Worryingly, less than 50% of the currently installed management plans reach their goals, strongly indicating that more information is needed about the eel’s ecology and behavior. Functional morphological studies provide insights on how species perform behaviors crucial for survival, such as feeding and locomotion, but also in how environmental changes can affect or limit such behaviors. Consequently, functional morphology represents an important biotic component that should be taken into account when making conservation decisions. Hence, here, we provide an overview of studies on the eel’s morphology that do not only demonstrate its relation with ecology and behavior, but also provide information for developing and installing proper and more specific management measures.

scholarly journals Just go with the flow? Route selection and mortality during downstream migration of silver eels in relation to river discharge

2007 ◽  
Vol 64 (7) ◽  
pp. 1437-1443 ◽  
Author(s):  
Henrice M. Jansen ◽  
Hendrik V. Winter ◽  
Maarten C. M. Bruijs ◽  
Harry J. G. Polman
Keyword(s):  
River Discharge ◽  
Radio Telemetry ◽  
Anguilla Anguilla ◽  
Downstream Migration ◽  
European Eel ◽  
Route Selection ◽  
Migration Routes ◽  
Silver Eel ◽  
Silver Eels ◽  
The Impact

Abstract Jansen, H. M., Winter, H. V., Bruijs, M. C. M., and Polman, H. J. G. 2007. Just go with the flow? Route selection and mortality during downstream migration of silver eels in relation to river discharge. – ICES Journal of Marine Science, 64: 1437–1443. The European eel (Anguilla anguilla) has been in steep decline for several decades. Fisheries and hydropower-induced mortality presumably play an important role during the downstream migration of silver eels, and downstream-migrating silver eels must make various navigation and route-selection decisions to reach the sea. We examined the influence of river discharge on route selection of silver eels. To quantify the impact of hydropower and fisheries on silver eel mortality, radio-telemetry experiments were performed in the River Meuse in 2002 and 2004, surgically implanting 300 silver eels with Nedap-transponders. Route selection and passage behaviour near detection stations was assessed. Silver eels were distributed over the alternative migration routes in the river in proportion to the discharge until the silver eels reached the entrance to the turbines. The eels altered their behaviour when approaching the turbines of hydropower plants and showed stationary and recurrent behaviour. We discuss the consequences of this on route selection and mortality rates caused by hydropower facilities and fisheries.

On the distribution of the European eel (Anguilla anguilla) and its fisheries

2003 ◽  
Vol 60 (7) ◽  
pp. 787-799 ◽  
Author(s):  
Willem Dekker
Keyword(s):  
Meta Analysis ◽  
Anguilla Anguilla ◽  
Western Mediterranean ◽  
Qualitative Description ◽  
Suitable Habitat ◽  
European Eel ◽  
Silver Eel ◽  
Southern Limit ◽  
Glass Eel ◽  
The North

For the distribution of the European eel (Anguilla anguilla), only Schmidt (1909) has conducted substantial investigations, yielding a qualitative description (Atlantic and Mediterranean coasts of Europe and Northern Africa). In this article, a meta-analysis of reported fishing yields is presented, showing a major concentration of glass eel yield in the Bay of Biscay (and possibly farther south) and of yellow and (or) silver eel yield in the western Mediterranean. Fisheries target the glass eel stage at highest stock density and shift to the silver eel stage at low density. Because there is no suitable habitat in the Sahara, the southern limit is, contrary to Schmidt's belief, primarily determined by continental conditions. From the centre of the distribution to the north, a long and slow decline in density occurs. The mismatch between northern temperatures and the species' preference, in combination with the very low abundance, indicates that the European eel is best seen as a warm-water species, like most other eel species (Anguilla spp.), showing a considerable northern diaspora.

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