scholarly journals Growth potential can affect timing of maturity in a long-lived semelparous fish

2018 ◽  
Vol 14 (7) ◽  
pp. 20180269 ◽  
Author(s):  
Kazuki Yokouchi ◽  
Françoise Daverat ◽  
Michael J. Miller ◽  
Nobuto Fukuda ◽  
Ryusuke Sudo ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
Growth Conditions ◽  
Growth Potential ◽  
Individual Growth ◽  
Growth Trajectories ◽  
Female Size ◽  
European Eel ◽  
Growth And Survival ◽  
Silver Eels ◽  
Reproduction Cost

Many diadromous fishes such as salmon and eels that move between freshwater and the ocean have evolved semelparous reproductive strategies, but both groups display considerable plasticity in characteristics. Factors such as population density and growth, predation risk or reproduction cost have been found to influence timing of maturation. We investigated the relationship between female size at maturity and individual growth trajectories of the long-lived semelparous European eel, Anguilla anguilla . A Bayesian model was applied to 338 individual growth trajectories of maturing migration-stage female silver eels from France, Ireland, the Netherlands and Hungary. The results clearly showed that when growth rates declined, the onset of maturation was triggered, and the eels left their growth habitats and migrated to the spawning area. Therefore, female eels tended to attain larger body size when the growth conditions were good enough to risk spending extra time in their growth habitats. This flexible maturation strategy is likely related to the ability to use diverse habitats with widely ranging growth and survival potentials in the catadromous life-history across its wide species range.

scholarly journals Is the continental life of the European eel Anguilla anguilla affected by the parasitic invader Anguillicoloides crassus ?

2013 ◽  
Vol 280 (1754) ◽  
pp. 20122916 ◽  
Author(s):  
François Lefebvre ◽  
Géraldine Fazio ◽  
Béatrice Mounaix ◽  
Alain J. Crivelli
Keyword(s):  
Reproductive Potential ◽  
Adaptive Immune Response ◽  
Anguilla Anguilla ◽  
Individual Variability ◽  
Growth Potential ◽  
Size Increase ◽  
European Eel ◽  
History Of ◽  
Internal Marker ◽  
Anguillicoloides Crassus

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus , high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (+11% and +41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host–parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected—via trophic parasite transmission—during their continental life.

Eels at the Edge: Science, Status, and Conservation Concerns

2009 ◽  
Keyword(s):  
Warning System ◽  
Anguilla Anguilla ◽  
Hydropower Station ◽  
European Eel ◽  
Mortality Factors ◽  
River Meuse ◽  
Silver Eels ◽  
Hydropower Stations ◽  
Integrated Study ◽  
Migration Event

<em>Abstract.—</em>To evaluate mortality factors and potential mitigative measures during downstream passage of silver European eel Anguilla anguilla in the River Meuse, an integrated study was performed consisting of: 1) telemetric experiments where the descent of 150 transpondered eels was tracked at 14 detection stations; 2) monitoring daily commercial catches; 3) testing a system to predict migration events from activity of captive eels in riverside tanks (the Migromat system); and 4) measuring turbine mortality by netting eels at turbine outlets. Migromat systems installed at two hydropower stations predicted 41 migration events. Most warnings (58.5%) were false positives, but Migromat failed to predict only one migration event. Mortality of eels passing through a turbine at the Linne Hydropower station was 24%. However, part of the downstream migrating population bypassed the turbines by descending over adjacent weirs. Descending eels moved primarily in brief pulses that were associated with increasing discharge and especially during the first half of the night. Thirty-seven percent of transpondered eels released at Ohé en Laak reached the sea. Because both fisheries mortality (estimated at 22–26% by fishing recoveries) and hydropower mortality (estimated at 16–26%) were considerable, a reduction in fisheries harvest and implementation of turbine management by application of the Migromat warning system would substantially increase escapement of silver eels from the River Meuse.

On the application of models of European eel (Anguilla anguilla) production and escapement to the development of Eel Management Plans: the River Severn

2007 ◽  
Vol 64 (7) ◽  
pp. 1472-1482 ◽  
Author(s):  
M. W. Aprahamian ◽  
A. M. Walker ◽  
B. Williams ◽  
A. Bark ◽  
B. Knights
Keyword(s):  
Reference Conditions ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Silver Eel ◽  
Management Scenarios ◽  
Test Management ◽  
Management Measures ◽  
Silver Eels ◽  
Management Plans ◽  
The Uk

Abstract Aprahamian, M. W., Walker, A. M., Williams, B., Bark, A., and Knights, B. 2007. On the application of models of European eel (Anguilla anguilla) production and escapement to the development of Eel Management Plans: the River Severn. – ICES Journal of Marine Science, 64: 1472–1482. The European eel stock has declined significantly since the 1980s, and the Eel Recovery Plan of the European Commission requires Member States to develop river basin Eel Management Plans (EMPs) that will achieve an escapement of silver eels that equals or exceeds 40% of the escapement biomass that would be produced in the absence of human activities. However, because silver eel escapement is not quantified within the UK, a modelling approach is required to estimate potential and actual escapement, and to assess the likely effects of management measures. We focus on two approaches developed in the UK, the Reference Condition Model (RCM) and the Scenario-based Model for Eel Populations (SMEP), and illustrate how such approaches can be used in EMPs using selected data from the River Severn. The RCM results indicate that the yellow eel population in the River Severn basin may be just 30–40% of the potential density indicated by reference conditions derived from a selection of rivers between the late 1970s and the early 1980s. The challenges of applying a model designed to be as realistic of eel production as possible, and the limited data on natural eel habitat and eel production in the Severn, preclude a SMEP analysis similar to that of the RCM, but simulations based on a simplified basin description and eel survey data from the early 1980s illustrate the potential of this model to assess compliance and test management scenarios.

A size and age-structured model of the European eel (Anguilla anguilla L.)

1995 ◽  
Vol 52 (7) ◽  
pp. 1351-1367 ◽  
Author(s):  
G. A. De Leo ◽  
M. Gatto
Keyword(s):  
Sexual Maturation ◽  
Anguilla Anguilla ◽  
Population Data ◽  
Individual Growth ◽  
European Eel ◽  
Demographic Model ◽  
High Plasticity ◽  
Crucial Information ◽  
Age Structured ◽  
Age Structured Model

The life cycle of the European eel (Anguilla anguilla) presents several distinctive features, such as high plasticity in body growth, marked sexual dimorphism, sex ratio strongly skewed in favor of females and sexual maturation largely dependent upon the size of individuals. A demographic model incorporating all these characteristics is derived on the basis of a multiple classification of individuals by age and size, and variability in individual growth is explicitly included. Existing theory for size-structured stocks is extended to include the dependence of sexual maturation on size, while natural mortality is age specific. Using 1989 population data from Comacchio lagoons (Italy), we estimate mortality and metamorphosis rate and abundance in each age- and size-class for both yellow and silver eels, crucial information for the management of the Comacchio fishery. The use of a nonparametric technique (bootstrapping) yields not only the moments, but also the distributions of these estimates. Validation of the model is performed on the data collected in 1990. The approach adopted is very flexible and different assumptions about survival, sexual maturation, and net selectivity can be easily incorporated in the model.

scholarly journals European eel (Anguilla anguilla): prediction of spawner escapement from continental population parameters

2000 ◽  
Vol 57 (8) ◽  
pp. 1627-1635 ◽  
Author(s):  
Eric Feunteun ◽  
Anthony Acou ◽  
Pascal Laffaille ◽  
Antoine Legault
Keyword(s):  
Population Structure ◽  
Environmental Factors ◽  
Anguilla Anguilla ◽  
Downstream Migration ◽  
The Other ◽  
European Eel ◽  
Population Parameters ◽  
Sedentary Population ◽  
Continental Population ◽  
Silver Eels

This paper describes the assessment of silver European eel (Anguilla anguilla) escapement based on a "sedentary" population fraction analysis in a 60-km2 watershed of northern Brittany (France). Downstream migration fluxes were monitored using eel traps and related to environmental factors. Intensive electrofishing and fyke-net fishing were conducted to assess eel biomass, densities, and population structure. A total of 564 eels, including 81 silver eels, were PIT tagged. In 1996, 616 eels were caught in the catchment including 68 silver eels (11%). During the following downstream migration period, 12 of the PIT-tagged silver eels, among a total of 678, were recaptured in the downstream traps. Seven were recaptured in the catchment in 1997. It was shown that (i) only about 20% of the silver eels present in the catchment emigrated during the following year, (ii) 12% stayed in the catchment including two (3.4%) that recovered yellow eel characteristics, and (iii) the other eels either died or settled in the catchment but were not recaptured. It was also estimated that 2% (650 eels) of the population (34 000 eels) among 3000 silver eels considered "emigration candidates" emigrated each year,.

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.

PRESSOR ACTIVITY IN EXTRACTS OF THE CORPUSCLES OF STANNIUS FROM THE EUROPEAN EEL (ANGUILLA ANGUILLA L.)

1966 ◽  
Vol 34 (3) ◽  
pp. 393-408 ◽  
Author(s):  
I. CHESTER JONES ◽  
I. W. HENDERSON ◽  
D. K. O. CHAN ◽  
J. C. RANKIN ◽  
W. MOSLEY ◽  
...  
Keyword(s):  
Intravenous Injection ◽  
Renin Angiotensin System ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Silver Eel ◽  
Renin Substrate ◽  
Angiotensin System ◽  
Corpuscles Of Stannius ◽  
Silver Eels ◽  
Pressor Activity

SUMMARY Extracts of corpuscles of Stannius from the silver eel have been shown to contain a substance with a powerful pressor action on intravenous injection into the rat. This material resembles mammalian renin in being non-diffusible through cellophane, heat-labile, and destroyed by acidification to pH 2. The effect in the rat differs, however, from that produced by mammalian renin in being more prolonged, and frequently biphasic. Pressor activity has also been demonstrated in extracts of kidneys from freshwater silver eels. Incubation of kidney extract with mammalian renin-substrate produced an angiotensin-like pressor substance. Both renal and corpuscular extracts had a prolonged pressor effect on intravenous injection into the eel. The identities of these pressor materials have not been finally established. Removal of the corpuscles of Stannius from freshwater silver eels was followed by a drop in blood pressure to levels normally found in eels adapted to seawater. The possible existence, in the eel, of a renin-angiotensin system analogous to that existing in mammals is discussed.

scholarly journals Stocking is essential to meet the silver eel escapement target in a river system with currently low natural recruitment

2015 ◽  
Vol 73 (1) ◽  
pp. 91-100 ◽  
Author(s):  
Uwe Brämick ◽  
Erik Fladung ◽  
Janek Simon
Keyword(s):  
Anguilla Anguilla ◽  
River System ◽  
European Eel ◽  
Net Benefit ◽  
Silver Eel ◽  
Natural Habitats ◽  
Silver Eels ◽  
Management Plans ◽  
Approaches To Study ◽  
Study Population

Abstract Under the European Eel Regulation EG 1100/2007, Member States exhibiting natural habitats for the European eel (Anguilla anguilla) on their territory are obliged to prepare Eel Management Plans (EMP) containing appropriate measures to safeguard the escapement of a river system specific silver eel target biomass. Stocking is one management option to reach this target. We used various methodical approaches to study population parameters in a large lowland river under the application of a multi-annual intense stocking programme. The approaches were used to further enhance modelling of stock dynamics and silver eel escapement, in particular. Parameterizing the German Eel Model III (GEM III) with values and functions obtained for recruitment, growth, and mortality resulted in an annual escapement estimate of roughly 32 000–64 000 silver eels from 2010 to 2012. Escapement estimates based on a mark-recapture study conducted in parallel revealed somewhat lower values (11 000–25 000) for the same years. In view of the small number of natural recruits, such values are only contingent if stocking had a profound effect on silver eel production. Results from modelling annual silver eel escapement values indicate that escapement targets set in the EMP for this tributary cannot be reached without stocking. This constellation is likely to apply to other Eel Management Units with low current natural immigration values as well, and might be considered a key dilemma in eel management in such catchments due to the current confusion whether translocation of recruits yields a net benefit to the panmictic stock of the European eel.

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