scholarly journals Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Alessandro Cresci ◽  
Caroline M. Durif ◽  
Claire B. Paris ◽  
Steven D. Shema ◽  
Anne Berit Skiftesvik ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
Magnetic Compass ◽  
European Eel ◽  
Sargasso Sea ◽  
North African ◽  
Compass Direction ◽  
Tidal Flows ◽  
Glass Eels ◽  
Cardinal Directions ◽  
Magnetic North

Abstract The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic compass for orientation, but whether their magnetic direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic compass direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic compass to memorize the magnetic direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.

scholarly journals The relationship between the moon cycle and the orientation of glass eels ( Anguilla anguilla ) at sea

2019 ◽  
Vol 6 (10) ◽  
pp. 190812 ◽  
Author(s):  
Alessandro Cresci ◽  
Caroline M. Durif ◽  
Claire B. Paris ◽  
Cameron R. S. Thompson ◽  
Steven Shema ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
Lunar Cycle ◽  
Global Scale ◽  
European Eel ◽  
Sargasso Sea ◽  
The Moon ◽  
Detection Mechanism ◽  
Freshwater Habitats ◽  
Glass Eels ◽  
Open Question

Links between the lunar cycle and the life cycle (migration patterns, locomotor activity, pulses in recruitment) of the European eel ( Anguilla anguilla ) are well documented. In this study, we hypothesized that the orientation of glass eels at sea is related to the lunar cycle. The European eel hatches in the Sargasso Sea and migrates across the Atlantic Ocean towards Europe. Upon reaching the continental shelf, the larvae metamorphose into glass eels and migrate up the estuaries, where some individuals colonize freshwater habitats. How glass eels navigate pelagic waters is still an open question. We tested the orientation of 203 glass eels in a transparent circular arena that was drifting in situ during the daytime, in the coastal Norwegian North Sea, during different lunar phases. The glass eels swimming at sea oriented towards the azimuth of the moon at new moon, when the moon rose above the horizon and was invisible but not during the other moon phases. These results suggest that glass eels could use the moon position for orientation at sea and that the detection mechanism involved is not visual. We hypothesize a possible detection mechanism based on global-scale lunar disturbances in electrical fields and discuss the implications of lunar-related orientation for the recruitment of glass eels to estuaries. This behaviour could help glass eels to reach the European coasts during their marine migration.

scholarly journals Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels

2010 ◽  
Vol 277 (1700) ◽  
pp. 3593-3599 ◽  
Author(s):  
Peter Munk ◽  
Michael M. Hansen ◽  
Gregory E. Maes ◽  
Torkel G. Nielsen ◽  
Martin Castonguay ◽  
...  
Keyword(s):  
Life Cycle ◽  
Life Histories ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea ◽  
American Eel ◽  
Wide Range ◽  
Frontal Processes ◽  
Glass Eels ◽  
Atlantic Eels

Anguillid freshwater eels show remarkable life histories. In the Atlantic, the European eel ( Anguilla anguilla ) and American eel ( Anguilla rostrata ) undertake extensive migrations to spawn in the oceanic Sargasso Sea, and subsequently the offspring drift to foraging areas in Europe and North America, first as leaf-like leptocephali larvae that later metamorphose into glass eels. Since recruitment of European and American glass eels has declined drastically during past decades, there is a strong demand for further understanding of the early, oceanic phase of their life cycle. Consequently, during a field expedition to the eel spawning sites in the Sargasso Sea, we carried out a wide range of dedicated bio-physical studies across areas of eel larval distribution. Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical–biological linkages in the life-cycle completion of Atlantic eels.

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 Gelatinous plankton is important in the diet of European eel (Anguilla anguilla) larvae in the Sargasso Sea

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
Daniel J. Ayala ◽  
Peter Munk ◽  
Regitze B. C. Lundgreen ◽  
Sachia J. Traving ◽  
Cornelia Jaspers ◽  
...  
Keyword(s):  
Anguilla Anguilla ◽  
European Eel ◽  
Sargasso Sea

scholarly journals Age, growth, and condition of European eel (Anguilla anguilla) from six lakes in the River Havel system (Germany)

2007 ◽  
Vol 64 (7) ◽  
pp. 1414-1422 ◽  
Author(s):  
Janek Simon
Keyword(s):  
Growth Rate ◽  
Condition Factor ◽  
Energy Content ◽  
Anguilla Anguilla ◽  
European Eel ◽  
Annual Increment ◽  
Otolith Increments ◽  
Gross Energy ◽  
Glass Eels ◽  
Mean Annual Increment

Abstract Simon, J. 2007. Age, growth, and condition of European eel (Anguilla anguilla) from six lakes in the River Havel system (Germany). – ICES Journal of Marine Science, 64: 1414–1422. A total of 199 female yellow European eels (Anguilla anguilla), 21.6–66.2 cm long and 3–14 years old, was collected by electro-fishing from six lakes in the River Havel system (Germany) in spring 2001. The condition and the growth rate, estimated by otolith increments, varied between eels within single lakes and between lakes. Fulton's condition factor ranged from 0.10 to 0.24 and the gross energy content varied between 4.3 and 15.3 MJ kg−1. There were no significant differences in mean condition factor (0.16–0.18) or gross energy content (6.5–9.3 MJ kg−1) between lakes. Fastest growth was in Lake Blankensee (mean 5.3 cm year−1), and the slowest in Lake Sacrow (mean 4.0 cm year−1). For all lakes combined, the overall mean annual increment was estimated to be 4.5 cm year−1. The biggest annual increment on the otoliths was generally laid down during the first and second years in fresh water, when the growth rate was 6.1–8.5 cm year−1. Then, in the subsequent 12 years, the annual increment remained almost constant or decreased slightly (with lake-dependent values of between 1.6 and 6.8 cm year−1). In the River Havel system, the time between stocking of the lakes with glass eels and the recapture of eels at 45 cm body length was 7–10 years. The physiologically possible maximum length (L∞ values) of eels lay in the range 50–130 cm. In comparison with previous investigations (between the 1950s and the 1970s), the only difference observed was a trend towards slower growth.

scholarly journals Bacterial and parasitic factors diagnosed in eel farmed in Poland in the years 2010-2014

2016 ◽  
Vol 72 (10) ◽  
pp. 647-651
Author(s):  
Elżbieta Terech-Majewska ◽  
Alicja Bernad ◽  
Stanisław Robak ◽  
Joanna Pajdak ◽  
Patrycja Schulz ◽  
...  
Keyword(s):  
Health Assessment ◽  
Anguilla Anguilla ◽  
Good Health ◽  
European Eel ◽  
Test Results ◽  
Aeromonas Sobria ◽  
Controlled Conditions ◽  
Etiologic Agents ◽  
Controlled Rearing ◽  
Glass Eels

European eel Anguilla anguilla L. is a fish species highly valued in European fisheries, currently reared under controlled conditions (Aquatic Recirculation System - RAS). In order to protect the health of fish, regular check-ups are carried out in specialized veterinary laboratories. Health hazards are recognized on the basis of clinical, pathological, microbiological, and parasitological surveys. The aim of the study was to analyze the results of health assessment of eels reared under controlled conditions, which was performed in the Diagnostics Laboratory of Fish and Crayfish Diseases, Department of Veterinary Hygiene, Voivodeship Veterinary Inspectorate in Olsztyn, in the period from 2010 to 2014. The results are presented according to the etiologic agents, divided into bacterial and parasitic diseases. In this period, 73 samples (100%) were examined, including 5 samples (6.85%) from glass eels and 68 (93.15%) from elvers. Microorganisms isolated from the collected material were mainly conditionally pathogenic, such as Pseudomonas fluorescens, Aeromonas hydrophila, Shewanella putrefaciens, Aeromonas sobria, Flavobacterium spp., and Chryseobacterium indologenes. The parasitological examination revealed infection with Trichodina spp., Ichthyophtirius multiphilliis, and Pseudodactylogyrus spp. The most frequently diagnosed were gill monogeneans, detected in 34 cases (75.55% of all positive parasitological test results). In 21 cases (61.8%) the infestation manifested itself as a disease. The remaining 13 cases were asymptomatic carriers (38.2%). The analysis shows that the main problem in the controlled rearing of eel are parasitic infestations, which may be endemic and pose a constant threat. Systematic monitoring and preventive measures are necessary throughout the rearing and fattening of fry to maintain a good health status of eels.

Do Leptocephali of the European Eel Swim to Reach Continental Waters? Status of the Question

1998 ◽  
Vol 78 (1) ◽  
pp. 285-306 ◽  
Author(s):  
J.D. McCleave ◽  
P.J. Brickley ◽  
K.M. O'Brien ◽  
D.A. Kistner ◽  
M.W. Wong ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Anguilla Anguilla ◽  
Late Winter ◽  
European Eel ◽  
Sargasso Sea ◽  
North East ◽  
Nutritional Mode ◽  
Mid Atlantic Ridge ◽  
One Year ◽  
European Coast

We examined recent arguments that leptocephali of the European eel,Anguilla anguilla, swim in an oriented manner, rather than drift, to reach the continental shelf of Europe and the Mediterranean Sea. There is a cline of increasing body length of leptocephali from south to north and from west to east from the Mid-Atlantic Ridge (30°W) to the continental shelf, which could represent migration from south-west to north-east, transport eastward at all latitudes, or increased growth rate with latitude. Evidence that this cline is a trend in age of arriving glass eels along the European coast, and that the duration of migration is less than one year, is weak. Ages reported in the literature for specimens from Morocco to The Netherlands were based on the unvalidated assumption that rings in otoliths were deposited daily. The assumption is unwarranted because of low metabolic rate and uncertainty of nutritional mode of leptocephali. If the assumption were accepted, calculated hatching dates of eels arriving at the European coast imply year-round spawning. Lengths of leptocephali in the Sargasso Sea at various times imply that eels spawn only in late winter and spring. Leptocephali contain tiny amounts of muscle, especially aerobic muscle for sustained swimming. They probably have insufficient capability to swim across the Atlantic in the less than 1–2 y reported by others.

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.

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