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


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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.
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Glass eels (Anguilla anguilla) imprint the magnetic
direction of tidal currents from their juvenile
Alessandro Cresci 1,2*, Caroline M. Durif2, Claire B. Paris1, Steven D. Shema3, Anne Berit Skiftesvik2&
Howard I. Browman2
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 pig-
mented. 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
owing 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 ows. This mechanism could help them to maintain their position in an
estuary and to migrate upstream. OPEN
1Department of Ocean Sciences, Rosenstiel School of Marine & Atmospheric Science, 4600 Rickenbacker, Causeway, FL 33149-1098, USA. 2Institute of
Marine Research, Austevoll Research Station, Sauganeset 16, N-5392 Storebø, Norway. 3Grótti ehf., Grundarstíg 4, 101 Reykjavík, Iceland.
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The European eel (Anguilla anguilla) is a migratory species
that crosses the Atlantic Ocean twice during its life (Fig. 1).
After hatching in the Sargasso Sea1, eel leptocephali larvae
move with the gulf stream more than 5000 km until they reach
the continental slope of Europe2,3. There, they metamorphose
into the post-larval transparent glass eel4. At this stage, glass eels
migrate across the continental shelf to the coast2,5. After reaching
the coast, glass eels enter estuaries, where some of them continue
their migration upstream into freshwater6. The eels that enter
freshwater spend most of their lifetime (525 years) there,
growing rst into the adult yellow eel stage, and then into silver
eels2. Silver eels then navigate back to the Sargasso Sea where they
spawn and die1,7,8.
The European eel is a commercially important species that is
critically endangered [International Union for Conservation of
Nature (IUCN)]: eel populations have declined precipitously
since the 1980s911. Much research on the conservation and
management of eels has been undertaken12,13, driven to some
extent by the requirement for member states of the European
Union to develop management plans for the recovery of eel
populations. The arrival of the early-life stages to estuaries
(recruitment), is an important phase of their migration, and the
number of recruiting glass eels have been consistently declining
over the past decades10,14. Thus, a better understanding of the
dynamics of this step of the migration, including deeper knowl-
edge of the orientation mechanisms involved, is needed.
Glass eels use multiple spatial and sensory cues for orienta-
tion1517, which could hypothetically be imprinted and used years
later during their return journey to the spawning areas. It is
possible that eels imprint spatial information from the
environment at several steps during their migration, such as at
the time of hatching or during the journey to the European coast.
Imprinting is associated with a broad variety of processes in
animals, including food and habitat preference, host selection in
parasitic animals, and homing1820. Imprinting is a fast-learning
process that typically occurs during a specic life history
phase18,19,21. Imprinting of spatial cues, such as olfactory cues in
salmon22, occurs in several aquatic animals. Animals can also
imprint information from the magnetic eld of the Earth. Aquatic
species such as pacic salmon (Oncorhynchus nerka)23 and sea
turtles (Caretta caretta)20 imprint specic features of the Earths
magnetic eld and use this to orient during migration. The
European eel is a long distance migrator that also uses magnetic
elds to orient during migration24,25. However, whether
imprinting of magnetic cues occurs, either at the larval or glass eel
stage (or both), remains unknown.
Glass eels recruit at tidal estuaries along the European coast,
where they are exposed to the alternation of ebbing and ooding
tidal currents. In aquatic environments, sh display an uncon-
ditioned response to water currents (rheotaxis), which can be
positive (the sh swims into the current) or negative (the sh
swims in the same direction as the current)26,27. Rheotaxis is a
major component of sh orientation in tidal estuaries in which
currents can be fast and visibility low27. In such situations, sh
use rheotaxis for both upstream migration and upstream-oriented
station holding behavior to minimize energy expenditure in
owing water28. Glass eels display both of these rheotactic
behaviors when they recruit to estuaries, showing rhythmic pat-
terns of positive or negative rheotaxis synchronized to the tidal
phase29. This tidal-dependent orientation is important during
Brackish water
Brackish water
Glass eel
(testing stage)
Yellow eel
(non-mature adult)
Silver eel
(migratory adult)
Fig. 1 Life history of the European eel (Anguilla anguilla). Eels hatch as leptocephalus larvae in the Sargasso Sea. As larvae, they drift across the Atlantic
Ocean to the continental slope of Europe, where they metamorphose into post-larval, transparent glass eels. The glass eels migrate across the continental
shelf and eventually reach the brackish water of estuaries. After metamorphosing into pigmented juveniles, called elvers, they start the ascent into
freshwater, where they will grow into adult yellow eels. After some years, yellow eels undergo another metamorphosis into silver eels, which migrate for
thousands of kilometers to the Sargasso Sea where they spawn and die. Eels used in this study were at the stage of glass eel (red font), and the
Hypothetical Period of Imprinting (H.P.I.) is highlighted by a dashed blue polygon. Artwork credit A. Cresci
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migration, as glass eels exploit tidal ows to enter brackish and
freshwater using selective tidal stream transport (STST)3033. This
constitutes a deeply rooted behavior in many species of sh and
invertebrates inhabiting tidal estuaries34.
In order to orient with respect to water ow, sh rely on
multiple sensory cues, including visual, vestibular, and tactile35,36.
Rheotaxis in sh is also inuenced by changes in the magnetic
eld at intensities as low as the Earths37,38, suggesting that
magnetic elds could be one of the reference cues that sh use to
orient in the presence of owing water. Glass eels exhibit rheo-
taxis in the presence of tidal currents and sense magnetic cues:
our previous work showed that glass eels use the magnetic eld
for orientation using a magnetic compass mechanism, switching
magnetic direction according to an endogenous tidal rhythm in
the absence of a current16. Specically, eels oriented to the
magnetic south with the ebb tide and to the north with the ood
tide16. While these results show that glass eels use a magnetic
eld-based compass mechanism, the stimuli that cause glass eels
to swim toward specic magnetic directions at this stage of the
migration are unknown.
We tested the hypothesis that the magnetic orientation direc-
tion of glass eels (i.e., the orientation direction relative to the
direction of the magnetic eld) is imprinted from the tidal cur-
rents at the estuaries where they recruit. To test this hypothesis,
222 glass eels were collected at stream estuaries owing toward
different cardinal directions (north, southeast, south, and north-
west). The magnetic orientation of glass eels was observed in a
magnetic laboratory facility, using an electric coil system that
modied the direction of the magnetic eld, while depriving the
glass eels of any other external cues that they could use for
orientation. We show that glass eels orient toward the magnetic
direction of the prevailing tidal current occurring at their estuary.
This is interpreted as evidence that glass eels form and retain a
magnetic memory of tidal ows.
Tests in the magnetic laboratory. The magnetic orientation
behavior of glass eels was observed following the methods
described in our previous work (see the Methods section)16.In
brief, a circular transparent chamber (Drifting In Situ Chamber,
DISC; Supplementary Fig. 1b)39 was submerged in a circular
black tank in a magnetic laboratory (MagLab; https://shlarvae.
org/facilities/magnetoreception-test-facility/) located in Austevoll,
Norway (60.1175 N, 5.2118 E; Supplementary Fig. 1). The
MagLab is equipped with a triaxial electric coil system that
allowed us to manipulate the magnetic eld to which glass eels
were exposed in the experimental tank.
Glass eels were collected at four stream estuaries located
around the Austevoll archipelago (Fig. 2), before they migrated
into freshwater. The tidal estuaries were selected according to
their geographical features, as we searched for estuaries owing
toward different cardinal directions. Glass eels were collected at
Vasseide (60.1122 N and 5.2298 E, owing to the north),
Torvesund (60.0294 N, 5.3016 E, owing to the southeast),
Vinnesvåg (60.0088 N, 5.2583 E, owing to the south), and
Stolmen (60.0082 N and 5.0788 E, owing to the northwest)
(Fig. 2). Upstream of these tidal areas (for example, in Torvesund,
where the stream changes direction), there was no action of the
tides and only pigmented elvers were present. The data set used in
this study is composed of the orientation data of 222 glass eels.
These include the re-analysis of the orientation data from our
previous work of 49 glass eels tested in the MagLab in 2015 (eels
coming from Vasseide)16, and 173 glass eels newly collected from
Vinnesvåg, Torvesund, and Stolmen (S, SE, and NW oriented
estuaries; Table 1).
Glass eels were individually exposed to different congurations
of the magnetic eld: the magnetic north in the laboratory was
rotated toward one of the four cardinal points of the Earths
magnetic eld, and each eel was exposed to only one of the four
magnetic conditions used in this study (Supplementary Fig. 2).
The orientation of each glass eel was then assessed with respect to
the rotated magnetic north in the laboratory (Supplementary
Fig. 2).
Each eel was tested in the magnetic lab between the peaks of
high and low tide, during one of the rising/lowering tides (ebb/
ood) occurring along the Austevoll archipelago. The magnetic
orientation direction of each eel was then analyzed with respect to
the magnetic direction of the tidal current occurring contempor-
aneously at the eels recruitment estuary. Thus, in our reference
system, we considered the magnetic direction of the tidal ow
with respect to the Earths magnetic eld) as 0°. Finally, we
computed the angular difference between the magnetic orienta-
tion direction of each eel and the magnetic direction of the
tidal ow.
Magnetic orientation. The overall proportion of glass eels
showing a preferred magnetic orientation direction was 70% (155
out of 222). This proportion, however, changed depending on the
estuary, but it was always >50% (Table 2). Glass eels signicantly
oriented to the magnetic direction of the prevailing tidal ow that
was occurring at their recruitment estuaries during the tests.
Their average magnetic orientation direction was 359° (N =155,
Rayleighsp=0.0018, r=0.2; Fig. 3), and it matched the mag-
netic direction of the incoming tidal ow (0°, Fig. 3).
Glass eels use their magnetic compass to memorize the magnetic
direction of the currents at the estuaries where they recruit. This
is evidence that these sh are capable of forming and retaining a
magnetic memory of the direction of water currents, and to use it
to orient in moving water during migration.
Satellite tracks of loggerhead sea turtles (Caretta caretta) and
fur seals (Callorhinus ursinus) indicate that they detect the
downstream direction of currents in open waters, implying the
use of magnetic cues40,41. It was also hypothesized that elasmo-
branchs, that navigate by detecting electromagnetic elds42, could
sense the direction of oceanic currents through the electricity
produced by the friction of water moving over the sea bottom43.
When visual reference points were present, the interaction
between the magnetic sense and orientation to water ows was
observed in shoaling zebrash (Danio rerio), which change their
orientation in owing water according to the direction of the
magnetic eld37.
The results described in this study add evidence that eels detect
and form a memory of the magnetic direction of currents, sup-
porting the possibility that these shand possibly othershave
the sensory capacity to integrate magnetic and rheotactic infor-
mation and use them for orientation. Analogous results involving
learning of magnetic cues were reported at a later stage in the life
cycle of the eel: silver eels displaced between different locations
learned the compass direction of their displacement24. In that
study, orientation was dependent on temperature, demonstrating
their ability to modulate their response to the magnetic eld
according to other environmental signals.
The magnetic memory of the ows at the recruitment estuaries
described in this study might represent a specic case of
imprinting. In its original denition21, imprinting describes a
learning process that occurs in a restricted, sensitive time of the
life of an animal, and that this memory is stable and retained over
time. Considering the glass eels, it is possible that they imprint the
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10 km
0 2E4E6E8E
5E 5.5E
5.078 5.079 5.257 5.258 5.259 5.260
5.300 5.301 5.302 5.303
North Sea
North Sea
Geographical orientation of the estuary
5.229 5.230 5.231
Flood tide Ebb tide
02040 m
02040 m
02040 m02040 m
50 km
Fig. 2 Estuaries where glass eels (Anguilla anguilla) were collected and the direction of tidal currents. Maps show Norway (upper left) and the Austevoll
archipelago. Red points show the location of the estuaries. Blue arrows and blue cardinal points show the magnetic direction toward which the estuaries
ow; arrows start from the freshwater side, and point toward the seawater side. The satellite images show the aerial view of each one of the four estuaries.
Sky-blue and yellow arrows show the magnetic direction of the tidal currents at each of the estuaries (E =ebb current, F =ood current)
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rhythm of the tide and the magnetic direction of ows during a
specic, possibly sensitive period, when they rst enter the
estuary, which constitutes a life history transition from seawater
to freshwater physiology. Previous studies on salmon smolts show
that imprinting can occur in such transition periods associated
with surges in plasma thyroxine44. Furthermore, otolith analyses
revealed that the time that glass eels spend at the estuaries could
be very long as some never enter freshwater6. Thus, this memory
could be retained and used for a signicant portion of the life of a
glass eel, before the elver stage. However, it is also possible that
these results may represent a phenomenon of continuous ongoing
learning, and that this magnetic memory of ows could remain
exible over time. For example, eels might adjust their magnetic
heading to varying hydrodynamic conditions at the estuary, or
further upstream, where the magnetic direction of the current
could change. These are interesting scenarios that we intend to
address in future work. Furthermore, the estuaries selected in this
study are quite rectilinear systems, but it is possible that highly
curvilinear estuaries are harder for glass eels to navigate and
future work should investigate whether this affects recruitment to
such sites.
In movement ecology, the concept of imprinting has been
mostly associated with the return of animals to natal areas
(homing). Among aquatic species, the most studied case is that of
salmon. As smolts, salmon record the specic combination of
odors from their natal stream, which they will use as adults to
guide their spawning migration upstream22,45. In addition to
olfactory cues, there is evidence that salmon imprint magnetic
information when they make rst contact with seawater, which
they use later in life to nd the coastal area where their natal
estuary is located23. Similarly, sea turtles imprint the geomagnetic
eld associated with their natal beach, which they use years later
to return and nest20. In the case of the eel, the magnetic
imprinting observed in glass eels has a different importance for
their migration. Glass eels learned the magnetic direction of
currents at their recruitment estuary. This estuary will be the
same as that which they encounter years later during the descent
from the stream to start their oceanic spawning migration as
adult silver eels. Whether eels keep a magnetic memory of their
estuary through adulthood, and whether this constitutes a refer-
ence to start the marine phase of the spawning migration in the
right direction, is unknown. For example, it is possible that adult
eels recognize the direction of the alternating tidal ows experi-
enced as glass eels when they descend the estuary, and that this
constitutes a trigger to undertake the last physiological and
behavioral changes at the start of their long marine migration.
However, this hypothesis needs to be tested in future work.
The use of the magnetic sense to imprint the direction of
currents at estuaries could also help glass eels at this earlier phase
of their migration. During their estuarine residency, glass eels
undergo physiological and morphological changes, developing
pigmentation, developing jaws and teeth, and adapting to fresh-
water2. Thus, glass eels need to maximize the energetic efciency
of their swimming behavior at the estuary, both to keep their
position and to migrate upstream46. In environments such as
streams, rivers, or estuaries, sh orient with respect to the current
by using visual and tactile cues (such as the bottom)35,47. Our
results show that glass eels also use their magnetic sense as a
reference to orient against the direction of the ow. This could
help them in several ways, such as keeping the right compass
course when visual reference points are lost or obscured (turbid
water in rivers or muddy streams), or when there is no physical
contact with the substrate. This would be of great importance
especially for glass eels recruiting to large, long tidal estuaries
such as the Gironde in France, where the effect of the tidal ows
extends for kilometers. Moreover, in such large estuaries the
water is turbid, and temperature and salinity are subjected to high
variability. Thus, the use of the magnetic compass system
described in this study would have obvious advantages in such
environments, providing a xed reference for orientation.
Table 1 The estuaries where the glass eels (A. anguilla)were
collected are listed
Estuary Orientation of the
nDates of the tests
Vasseide N491622 April 2015
Vinnesvåg S36916 May 2016
Torvesund SE 24 1316 May 2016
Stolmen NW 113 28 April18
June 2017
Orientation of the estuary is the cardinal direction toward which each of the estuaries ows. n
number of glass eels tested in the magnetic laboratory listed by stream of provenience. The
dates of the tests are also indicated
Table 2 Proportion of glass eels (A. anguilla) showing a
signicant magnetic orientation direction
Estuary nOrienting
glass eels
Proportion of
orienting eels
Vasseide 49 35 71%
Vinnesvåg 36 20 56%
Torvesund 24 15 62%
Stolmen 113 85 75%
Total 222 155 70%
n: the number of glass eels tested in the magnetic laboratory listed by stream of provenance.
The Table shows the number of glass eels displaying signicant orientation and the proportion
of eels that oriented
Fig. 3 Magnetic orientation of glass eels (Anguilla anguilla) with respect to
the magnetic direction of the tidal ows. In the circular plot, the outer gray
circle represents the x-axis. The angle between the magnetic orientation of
each glass eel that signicantly oriented (Rayleighsp< 0.05 on individual
tracks) and the direction of the tidal ow (top of the plot) is shown as a
navy-blue data point (N =155). The bottom of the plot represents the
downstream direction of the ow. Signicant (Rayleighsp< 0.05) collective
orientation toward the upstream magnetic direction of the tidal ow is
shown as a black arrow pointing toward the top of the plot. The direction of
the arrow point toward the mean orientation direction of the glass eels.
Dashed gray lines show the 95% condence interval around the mean
direction of the eels. For clarity, the data are displayed binned by 5°
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Although glass eels oriented along the magnetic direction of
tidal currents at their recruitment estuaries, there was unac-
counted for interindividual variability (Rayleighsr=0.2). Var-
iation in orientation response is dependent on the internal state
(or behavioral traits) of the animals, which signicantly con-
tribute to their decision to move48. The internal state (often
classied as proactive and reactive, or migratory and non-
migratory phenotypes) plays an important role in the magnetic
sense of sh, up to the point that it can make the difference
between responding or not responding to magnetic stimuli38.
European eels display signicant differences among individuals
concerning their tendency to migrate. Experiments using ume
tanks showed that glass eels (A. anguilla), elvers, and yellow eels
display different tendencies to migrate and can be separated into
migrants that actively move upstream or downstream and non-
migrant that do not show a particular tendency to migrate46,49.It
is possible that those glass eels not showing any preferred mag-
netic orientation direction have a nonmigrant phenotype. Future
work should repeat these experiments on magnetic imprinting
after dividing the glass eels according to their motivation to
migrate and dividing migrating glass eels into upstream vs.
downstream migrants. This could be accomplished using an
experimental setup similar to that used by Bureau Du Colombier
et al., with a ume tank connected to upstream and downstream
Glass eels learn the features of the environments that they
encounter during migration. Future work should investigate
whether migrating silver eels that are translocated at the glass eel
stage have more difculty in nding their way toward the sea
compared with nontranslocated ones. If they do, then the results
of this study would be relevant to management plans that include
the restocking of glass eels in freshwater where the population is
most depleted46.
Animals and maintenance. The glass eels were collected in Norway, before their
upstream freshwater migration between March and June of 2015, 2016, and 2017.
They were caught using hand nets searching under rocks and sediment at low tide.
None of the animals used in this study were pigmented (developmental stage: VVI
2), and they did not have food in the gut. Glass eels were kept in 20 -L maintenance
tanks, where they were re-acclimated to near full salinity seawater (32 ppt) after
capture. They were kept in aerated aquaria in a temperature-controlled room set to
ambient conditions similar to those of the local Langenuen fjord (ranging between
6 and 10 °C). An imals were not fed (they were at the pre-feeding stage) and were
kept in 14 h light and 10 h dark cycle (following the daylength at the study location
during the observation period). Two-thirds of the volume of each aquarium were
replaced with ltered seawater every 48 h to maintain water quality. The seawater
was provided by the ltration system at the Institute of Marine Researchs Aus-
tevoll Research Station, which collects seawater from the Langenuen fjord at a
depth of 160 m. Before the tests, glass eels were taken from the large aquaria and
placed in individual 500 -mL white plastic containers lled with seawater at the
same temperature as the aquaria and transported to the magnetic laboratory
(MagLab) in a cooler to keep the temperature stable. No permits were required by
the Norwegian authorities because no glass eels (Anguilla anguilla) were harmed
while performing the experiments, and after use, they were either returned to the
wild or killed using an approved method. Eels were collected under research catch
permit #11/11448 issued by the Norwegian Fiskeridirektorat.
Experiments and data analysis. The experiments in the laboratory followed the
same protocol as described by Cresci et al.16. The MagLab is designed to study the
magnetic orientation of aquatic animals. It is equipped with a triaxial electric coil
system (Supplementary Fig. 1c), with a design described by Merritt et al.50. The
coils are connected to a power supply (max. 3 A). A black circular berglass tank
(diameter, 1.40 m; height, 0.90 m; see Supplementary Fig. 1c) lled with seawater is
located at the center of the coils. The seawater is pumped from the sea (300 m
away). The building (see Supplementary Fig. 1a) is made of nonmagnetic material,
and is distant from any magnetic interference (163 m from the nearest electrical
disturbance and 365 m from the closest building; Supplementary Fig. 1a).
For this study, we used the DISC (Drifting In Situ Chamber, Supplementary
Fig. 1b)39 as a behavioral chamber, submerged in the circular dark tank (see
Supplementary Fig. 1c). The chamber of the DISC in which individual glass eels
swam one at a time was 40 -cm wide (diameter) and 15 cm deep. The chamber was
semi open, as the bottom was rigid and made of acrylic, while the walls were made
of transparent ne mesh, which allows water and dissolved gas exchange. The top
of the chamber was covered with opaque white plastic, which diffused light
uniformly in the chamber. Light intensity in the tank was low (0 lum/ft2from
HOBO light sensor on the bottom plate of the DISC frame).
The behavior of glass eels in the DISC was observed using a GOPRO HERO 4
camera placed on the bottom plate of the DISC acrylic frame, underneath the
chamber (Supplementary Fig. 1b, d). The DISC was equipped with an analog
compass attached to the acrylic poles of the DISC frame and placed below the
circular arena. This positioning eliminates the possibility that the compass would
be a visual reference for the eel.
The MagLab has two nested electric coil systems. We used one of them to cancel
out the horizontal component of the ambient eld. We used the second system to
create a magnetic eld of 48.8 to 50 µT, which is the same total intensity as the
ambient eld, and to rotate the magnetic north. We did not change the intensity
and inclination inside the coil compared with the ambient eld (48.8 to 50 µT and
73°, with a deviation of <1°).
We recorded each eel for 15 min, with the rst 5 min as an acclimation
period16,51. We simulated four magnetic eld conditions, with the magnetic north
rotated towards the east, south, west, or north of the geomagnetic eld (see
Supplementary Fig. 2 and Supplementary Data 1). We exposed each glass eel to
only one of the four conditions. This technique eliminated any nonmagnetic bias
that could have inuenced the orientation response of the animals. The MagLab is
a bespoke facility that was designed to study magnetic orientation in marine
organisms and to eliminate other environmental cues (water ows, odor plumes,
sunlight, or any celestial cues). The walls are constructed of aluminum and wood,
and they are insulated to protect from sound and temperature uctuation. Every
metal tting, screw and bolt, is made of nonmagnetic material (aluminum, brass, or
high-quality stainless-steel). The experimental room is completely isolated, and the
top of the facility has a roof (i.e., no celestial cues). The facility is located at the top
of a fjord, hundreds of meters from electromagnetic disturbances. To water ow in
the tank, no pumps, aerator, or ventilation systems are present. The observation
tank is supported on an autonomous concrete block, separating it from the rest of
the building and isolating it from vibrations.
All tests were conducted during daytime. The data about the tide were obtained
from the Norwegian Mapping Authority ( The direction of
ow in the estuaries was assessed in situ using an analog compass.
The orientation of glass eels was determined through the analysis of the
GOPRO images, tracking the position of the head of the eel in the circular arena
every second for 10 min. Magnetic north had a different orientation in the
laboratory during each test, and the position of the eels with respect to the
magnetic north in the laboratory was monitored using the analog compasses. The
video frames were processed using the DISCR tracking procedure, utilizing R and a
graphical user interface provided by imageJ software52,53. Using this tracking
procedure, we collected the positional data (in units of magnetic degrees) of the
glass eel with respect to the center of the chamber, which were considered as
bearings. The code utilized is available at the web page Drifting In Situ Chamber
User Software in R ( written by Jean-Olivier Irisson
(Université Pierre et Marie Curie UPMC), released under the GNU General Public
License v3.0.
We assessed the mean orientation of each individual from the bearings collected
using the video tracking analysis (Supplementary Fig. 3). The mean of 600 data
points, which represent the bearings of the eel in the chamber at each second (one
position/s over 10 min period), was considered to be the orientation of each
individual51,52. The orientation of each eel was then corrected with respect to the
rotated magnetic North induced with the coils in the laboratory (Supplementary
Fig. 3). As last step, the magnetic orientation was corrected with respect to the
magnetic direction of the prevailing current occurring at the estuary where the eel
was collected from (Supplementary Figs. 3, 4).
Statistics and reproducibility. If the eel displayed a magnetic bearing in the
chamber of the DISC, we considered it as indicative of directionality39,52. Whether
the directionality was signicant was assessed with the Rayleighs test of uniformity
for circular data5254. An outcome was considered statistically signicant when p<
0.05 (alpha =0.05)52. This analysis was performed on 222 glass eels tested
After having assessed the orientation of each individual, the following step of
the analysis evaluated whether the eels tested in the DISC show a signicant pattern
in their orientation, or whether they go toward a common direction. To assess
collective patterns in orientation direction, we used the same statistical test, the
Rayleigh test of uniformity on all the mean individual bearings of the eels that
displayed orientation (N =155), testing whether the frequency distribution of the
directions displayed by the individuals was signicantly different from random
(95% condence interval, alpha =0.05)52. Possible effects on the results caused by
the larger sample size of the eels collected in Stolmen was assessed statistically
(analysis and results are displayed in Supplementary Fig. 5).
Reporting summary. Further information on research design is available in
the Nature Research Reporting Summary linked to this article.
6COMMUNICATIONS BIOLOGY | (20 19) 2:366 | |
Content courtesy of Springer Nature, terms of use apply. Rights reserved
Data availability
All of the data displayed in Fig. 3 are available in the Supplementary Data 2.
Received: 5 April 2019; Accepted: 17 September 2019;
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We thank Josena M. Olascoaga and Joseph E. Serafy for their help with the data analysis
and for providing insightful critical comments on the manuscript. This research was
supported by the Paris Lab at the Rosenstiel School of Marine and Atmospheric Science
of the University of Miami, and by funds awarded to H.I.B. by the Norwegian Institute of
Marine Research project Fine-scale interactions in the plankton(project # 81529) and
the Research Council of Norway (project # 234338). A.C. was supported by the U.S.
National Science Foundation NSF-OCE 1459156 to C.B.P. and by the Norwegian
Institute of Marine Research project # 81529 to H.I.B.
COMMUNICATIONS BIOLOGY | (2019) 2 :366 | | sbio 7
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Author contributions
A.C. designed the study; collected, analyzed, and interpreted the data; and wrote the
paper. C.M.F.D. designed the study; collected, analyzed, and interpreted the data; and
wrote the paper. C.B.P. designed the study; analyzed and interpreted the data; wrote the
paper; and funded the research. S.D.S. collected and analyzed the data and helped
drafting the manuscript. A.B.S. designed the study, collected and interpreted the data;
wrote the paper; and funded the research. H.I.B. designed the study; collected and
interpreted the data; wrote the paper; and funded the research.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at
Correspondence and requests for materials should be addressed to A.C.
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... Long distance migrants rely on various cues (Mouritsen, 2018). Magnetism and environmental sound are two possible factors which may affect eel orientation during migration (Cresci et al., 2019;Popper and Hawkins, 2019). It has been hypothesized that silver European eels use the Earth's geomagnetic field to navigate as they follow a specific isoline of geomagnetic intensity, imprinted during the glass eel stage (Durif et al., 2022). ...
... Further, oceanic transport is of significant importance to fish recruitment, especially for species that have an extended pelagic phase during the early life stages. After being released as eggs in the spawning region, larvae are transported by ocean currents for a wide range of distances, e.g., from less than 500 m as observed for coral reef fishes (Jones et al., 1999;Almany et al., 2007), and up to thousand kilometers, as for European eel (Anguilla anguilla) leptocephalus larvae that drift over 5000 km to European coasts from their spawning area in the Sargasso Sea (Cresci et al., 2019). To maintain fish population size, the larval transport should allow them to end up in areas suitable to their development into juvenile and adult stages. ...
Full-text available
Introduction Many hypotheses have been suggested to explain recruitment variability in fish populations. These can generally be divided into three groups, either related to: larval food limitation, predation, or transport. Transport mechanisms are central for reproduction in pelagic species and three physical processes, concentration, enrichment, and retention are commonly referred as the fundamental “ocean triads” sustaining larval survival and thus success of reproductive effort. The aim of this study is to investigate linkages between primary production and transport processes of eggs and larvae for the most important commercial fish species in the Atlantic Ocean. Methods We simulated eggs and larvae dispersion using an individualbased model and integrating information on the fish ecology of the major fish stocks. Our work included a review on spawning ground locations, spawning time, eggs and larvae duration. Simulations were performed over a 10-year time period for 113 stocks (17 species) in order to assess variability in dispersion and common trends and factors affecting transport. Results The level of primary production from initial to final position, i.e. from spawning to larval settlement, increased for some stocks (n=31), for others it declined (n=64), and for a smaller group (n=18) there was no substantial changes in level of primary production. Discussion This result implies that larval transport will not necessarily introduce larvae into areas of enhanced food availability expressed by the primary production at the site. These findings thus suggest marked differences in how physical and biological processes interact in the early life of major fish groups in the Atlantic Ocean. The results provide a further insight into fish larval drift and the potential role of primary production in emergence of spawning strategies.
... The available flood tidal flow may therefore function as a conveyer belt for upstream migrating glass eels [6]. In utilising these tidal currents, glass eels are aided by rheotactic orientation and magnetic imprinting to ascertain an upstream direction of migration [13]. Beaulaton et al. [14] demonstrated that glass eels may partially use available flood tides to migrate upstream in the Gironde estuary. ...
Full-text available
Understanding recruitment of glass eels in estuaries is crucial for the conservation of the European eel (Anguilla anguilla). However, basic knowledge on estuarine-specific glass eel migration, including in estuarine harbours, is mostly lacking. Therefore, we studied glass eel migration in the Dutch–German Ems estuary and the harbour at Delfzijl (The Netherlands) and tagged glass eels with Visual Implant Elastomer tags (VIE tags). We released 2000 tagged glass eels into the Ems estuary itself and 1000 tagged glass eels into the tidal harbour at Delfzijl. At three estuarine locations, i.e., Delfzijl–Duurswold, Termunterzijl, and Nieuwe Statenzijl, glass eel collectors were strategically placed, each location being progressively situated further upstream in the Ems estuary. Most glass eels (nuntagged = 97,089, ntagged = 74) were caught at Nieuwe Statenzijl, although this location is much further upstream. Lower numbers of glass eels (nuntagged = 1856, n tagged = 31) were caught at Delfzijl–Duurswold and Termunterzijl (nuntagged = 1192, ntagged = 7). Glass eels arrived approximately a week earlier at Nieuwe Statenzijl than at the other two locations, and the migration speed of tagged glass eels was highest at Nieuwe Statenzijl (>2 km/day) and lower (<1 km/day) at Delfzijl–Duurswold. Our study highlights that migration and the resulting potential recruitment of glass eels in estuaries and harbours may vary considerably both spatially and temporally. Further research on estuarine-specific factors that influence glass eel migration, such as the (anthropogenically altered) tidal action and flow, will provide valuable information on what influences glass eel migration in estuaries.
... Eels change pigment shortly after entering estuaries and rivers. Eels that enter fresh water will spend most of their lives before turning into young eels and adult eels (Cresci et al., 2019). The results of the cluster analysis are presented in the form of a dendrogram with Euclidean distance that describes the distance of kinship. ...
Full-text available
Indonesia is the largest exporter of eel to consumer countries such as European, America, Taiwan, Japan, South Korea, and the Middle East. Eels are catadromous fish that are in the growth phase in fresh waters and the development phase is in marine waters. Meristic measurement is done by counting the spine (vertebrates). Eel morphometric measurements include TL (Total Length), HL (Head Length), PDL (Pre-Dorsal Length), PAL (Pre-Anal Length) and ADL (Ano-Dorsal Length). The purpose of this study was to analyze the morphological, morphometric, and meristic diversity of intraspecies between populations. Based on the research, the samples identified were morphologically almost the same between the populations, this was seen from the color patterns in the form of plain black or brown and short fins. The morphometric and meristic measurements in the 3D distribution plot still appear to be clustered in one population, while in the dendrogram clade, one species is still congregated in each. The results of the interpretation of the matrix plot of the lowest diversity are the length and number of anodorsal vertebrate segments. This observation can be concluded that the TL and TV of the eel varied, while the PDL, PAL, PDV, PAV, ADV showed the intraspecies character of A. bicolor. This is because the distribution of A. bicolor eels that inhabit the waters of Java Island is widely distributed and random (panmitic).
... Changes in movement behavior, often an attraction to higher intensity MFs (Tanski et al., 2005;Scott, Harsanyi & Lyndon, 2018;Formicki et al., 2004b) or increased motor activity during a geomagnetic storm (Muraveiko, Stepanyuk & Zenzerov, 2013), have also been reported. Animals that use the Earth's MF to orient or navigate are assumed to be more vulnerable to anthropogenic MF (e.g., Phillips, 1996;Boles & Lohmann, 2003;Cresci et al., 2019;Lohmann & Lohmann, 2019), in particular long-distance migrants such as marine mammals, sea turtles and fishes (e.g., Walker et al., 1992;Lohmann, Luschi & Hays, 2008;Willis et al., 2009;Vanselow et al., 2018, Durif et al., 2022. ...
Full-text available
Submarine power cables carry electricity over long distances. Their geographic distribution, number, and areal coverage are increasing rapidly with the development of, for example, offshore wind facilities. The flow of current passing through these cables creates a magnetic field (MF) that can potentially affect marine organisms, particularly those that are magnetosensitive. The lumpfish (Cyclopterus lumpus) is a migratory species that is widely distributed in the North Atlantic Ocean and Barents Sea. It migrates between coastal spawning grounds and pelagic offshore feeding areas. We tested whether lumpfish respond to MFs of the same intensity as those emitted by high voltage direct current (HVDC) submarine power cables. Laboratory experiments were conducted by placing juvenile lumpfish in an artificial MF gradient generated by a Helmholtz coil system. The intensity of the artificial MF used (230 µT) corresponded to the field at 1 m from a high-power submarine cable. The fish were filmed for 30 min with the coil either on or off. Swimming speeds, and presence in the different parts of a raceway, were extracted from the videos and analyzed. Juvenile lumpfish activity, defined as the time that the fish spent swimming relative to stationary pauses (attached to the substrate), and the distance travelled, were unaffected by exposure to the artificial MF. The swimming speed of juvenile lumpfish was reduced (by 16%) when the coil was on indicating that the fish could either sense the MF or the induced electric field created by the movement of the fish through the magnetic field. However, it seems unlikely that a 16% decrease in swimming speed occurring within 1 m of HVDC cables would significantly affect Atlantic lumpfish migration or homing.
... Starting from the leptocephalus phase to the silver eel phase, eels continue to migrate and settle in different habitats, namely salt water, estuary and fresh water, but in the yellow eel phase, it is a fattening phase so that it is more sedentary (Arai & Chino, 2012). The distribution of eel and its abundance in an area are influenced by temperature, species origin, habits of glass eel and currents movement (Leander et al., 2012;Cresci et al., 2019), furthermore it is stated that different water and climatic conditions in each country also affect the migration behavior of eel (Gagnaire et al. 2012;Coˆte´ et al. 2013). Arribas et al. (2012) stated that the abundance of glass eel eels occurs in autumn and spring in southwest Spain. ...
Full-text available
The existence of eels in a freshwater area is influenced by various factors, one of which is the availability of habitats that are suitable for the life of eels. East Nusa Tenggara Province is an archipelago that is mentioned as one of the distribution areas for eel in Indonesia. However, the type and size of eel is strongly influenced by the distance it finds. The farther the river is from the estuary, the larger the size of the eel and the different types. As eurihaline migratory fish, eels can swim far upstream to find a suitable habitat for their life. This study aims to analyze the relationship between location distance and the size and dominance index of eel in freshwater in East Nusa Tenggara (NTT). This research was conducted from October to April. The results obtained are that the three rivers in East Nusa Tenggara province, namely the Tarus river in Kupang district, the Oetona river in Kupang city and the Kamaifui river in Alor district, managed to catch 71 eels at a fishing distance of 0.69 km to 7.86 km. from the mouth of the river. Based on the ano-dorsal analysis, two types of eel caught in the Tarus and Kamaifui rivers were identified, namely Anguilla marmorata and Anguilla nebulosa nebulosa, while in the Oetona river only A. marmorata was found. Based on the calculation of the dominance index, the most dominant species in fresh waters of NTT is A. marmorata.
... The species spawns in the Sargasso Sea, then leptocephali larvae migrate towards the European and North African coasts for more than 5000 km [45,46], transported by the Gulf Stream [47][48][49][50]. Larvae metamorphose into unpigmented glass eels [51] able to reach continental areas [47,52] where, under stimulation by chemical attractants (pheromones, green odors, amino acids, and bile salts), magnetic and lunar orientation mechanisms, and/or salinity gradients [53][54][55][56][57][58][59][60] recruit estuarine environments, starting their upstream migration [61]. Reaching continental waters, glass eels pigment into juvenile yellow eels (elvers), developing all morphological and physiological features necessary for life in inland waters [62,63]. ...
Full-text available
Olfaction could represent a pivotal process involved in fish orientation and migration. The olfactory bulb can manage olfactive signals at the granular cell (GC) and dendritic spine levels for their synaptic plasticity properties and changing their morphology and structural stability after environmental odour cues. The GCs’ dendritic spine density and morphology were analysed across the life stages of the catadromous Anguilla anguilla. According to the head and neck morphology, spines were classified as mushroom (M), long thin (LT), stubby (S), and filopodia (F). Total spines’ density decreased from juvenile migrants to no-migrant stages, to increase again in the adult migrant stage. Mean spines’ density was comparable between glass and silver eels as an adaptation to migration. At non-migrating phases, spines’ density decreased for M and LT, while M, LT, and S density increased in silver eels. A great dendritic spine development was found in the two migratory phases, regressing in trophic phases, but that could be recreated in adults, tracing the migratory memory of the routes travelled in juvenile phases. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb as an index of synaptic plasticity involved in the modulation of olfactory stimuli. If olfaction is involved in the orientation and migration of A. anguilla and if eels possess a memory, these processes could be influenced by the modification of environmental stimuli (ocean alterations and rapid climate change) contributing to threatening this critically endangered species.
... Sidat di Perairan Pacitan, Jawa Timur (M.A. Romadhi et al.) Gambar 4. Ukuran Panjang Sampel benih ikan sidat (Glass eel) di Perairan Muara Sungai Lorok Ngadirojo Kabupaten Pacitan Gambar 5. Ukuran Panjang Ikan Sidat Muda (yellow eel) di Perairan Muara Sungai Lorok Ngadirojo Kabupaten Pacitan menghabiskan sebagian besar hidupnya (5-25 tahun) sebelum berubah menjadi ikan sidat muda dan ikan sidat dewasa(Cresci et al., 2019). Benih ikan sidat ditemukan di stasiun 1 yang berada di muara sungai dan stasiun 2 yang berjarak ± 4,8 km dari muara sungai. ...
Ikan sidat Anguilla sp. merupakan kategori ikan yang bermigrasi secara katadromous, artinya ikan sidat mengawali hidup di laut yang bermigrasi ke perairan tawar untuk tumbuh menjadi sidat dewasa dan kembali ke laut untuk melakukan pemijahan (spawning migration). Penelitian ini bertujuan untuk melakukan klasifikasi jenis dan ukuran panjang kelompok sebaran ikan Sidat di Perairan Ngadirojo, Kabupaten Pacitan. Penentuan kelompok menggunakan metode morfometrik dan jenis sampel menggunakan A/D%. Hasil menunjukkan distribusi ikan sidat yang ditemukan di Muara Sungai Lorok terdapat dua spesies, yaitu Anguilla bicolor dan Anguilla marmorata. Frekuensi ukuran panjang distribusi benih ikan sidat (glass eel) kisaran ukuran panjang total 4,8 cm hingga 7,56 cm dengan rata – rata 6,0 ± 0,9 hingga dan Sedangkan ukuran panjang distribusi sidat muda (yellow eel) kisaran ukuran panjang 37,98 cm hingga 48,0 cm dengan rata – rata 43,2 ± 3,1. Analisis uji beda mendapatkan nilai signifikansi (p= 0,00 < 0,01) maka adanya perbedaan ukuran panjang antara stasiun di aliran SungaI Lorok. Freswater eels Anguilla sp. is a category of fish that cathadromous migrate, that eel fish begin to live in the sea that migrates to fresh waters to grow into adult eels and returns to the sea to spawning migration. This study aims to classify the type and size of the length of the Eel fish distribution group in Ngadirojo Waters, Pacitan Regency. This study aims to classify the type and size of the length of the Eel fish distribution group in Ngadirojo Waters, Pacitan Regency. Group determination using morphometric methods and sample types using A/D%. The results showed that the distribution of eel fish found in the Lorok River was two species, namely Anguilla bicolor and Anguilla marmorata. The frequency of the length distribution of glass eel seeds (glass eel) ranges in total length from 4.8 cm to 7.56 cm with an average of 6.0 ± 0.9 to and. 37.98 cm to 48.0 cm with an average of 43.2 ± 3.1. The analysis of the difference test got a significance value of (p= 0,00 < 0,01), so there is a difference in length between stations in the Lorok River flow.
The spread of viral diseases in eels is suggested to severely affect the European eel (Anguilla anguilla) panmictic population. The European Commission has initiated the Eel Recovery Plan (Council Regulation No. 1100/2007) to try to return the European eel stock to more sustainable levels within that measures eel restocking. However, scientific evidence evaluating the efficacy of stocking remains scarce. In addition, knowledge about the impact and contribution of eel stocking on the distribution of infectious diseases is insufficient. In this study, we aimed to investigate virus infections in batches of eels intended for restocking. We analysed samples of glass eels from certified fisheries and farmed European eels from different aquaculture farms. All analysed eels were purchased within a North Rhine Westphalian conservation program. Via a combination of cell culture and qPCR‐based techniques, we detected infections of glass eels with the rhabdovirus Eel Virus European X and anguillid herpesvirus 1 infections in farmed eels (10–15 cm).
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The European eel (Anguilla anguilla) has one of the longest migrations in the animal kingdom. It crosses the Atlantic Ocean twice during its life history, migrating between the spawning area in the Sargasso Sea and Europe, where it is widely distributed. The leptocephalus larvae drift with the Gulf Stream and other currents for more than a year and metamorphose into glass eels when they arrive on the continental shelf and move toward coastal areas. The mechanisms underlying glass eel orientation toward the coast and into freshwater systems are poorly known. However, anguillid eels, including the glass eel life stage, have a geomagnetic sense, suggesting the possibility that they use Earth's magnetic field to orient toward the coast. To test this hypothesis, we used a unique combination of laboratory tests and in situ behavioral observations conducted in a drifting circular arena. Most (98%) of the glass eels tested in the sea exhibited a preferred orientation that was related to the tidal cycle. Seventy-one percent of the same eels showed the same orientation during ebb tide when tested in the laboratory under a manipulated simulated magnetic field in the absence of any other cue. These results demonstrate that glass eels use a magnetic compass for orientation and suggest that this magnetic orientation system is linked to a circatidal rhythm.
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The spawning migration of the European eel (Anguilla anguilla L.) to the Sargasso Sea is one of the greatest animal migrations. However, the duration and route of the migration remain uncertain. Using fishery data from 20 rivers across Europe, we show that most eels begin their oceanic migration between August and December. We used electronic tagging techniques to map the oceanic migration from eels released from four regions in Europe. Of 707 eels tagged, we received 206 data sets. Many migrations ended soon after release because of predation events, but we were able to reconstruct in detail the migration routes of >80 eels. The route extended from western mainland Europe to the Azores region, more than 5000 km toward the Sargasso Sea. All eels exhibited diel vertical migrations, moving from deeper water during the day into shallower water at night. The range of migration speeds was 3 to 47 km day −1. Using data from larval surveys in the Sargasso Sea, we show that spawning likely begins in December and peaks in February. Synthesizing these results, we show that the timing of autumn escapement and the rate of migration are inconsistent with the century-long held assumption that eels spawn as a single reproductive cohort in the spring time following their escapement. Instead, we suggest that European eels adopt a mixed migratory strategy, with some individuals able to achieve a rapid migration, whereas others arrive only in time for the following spawning season. Our results have consequences for eel management.
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This symposium issue of the ICES Journal of Marine Science contains 16 contributions from the second International Eels Symposium held during the American Fisheries Society (AFS) Annual Meeting (August 2014, Québec City, Canada). This symposium followed the first International Eels Symposium held in 2003, which emphasized the international scope of the Anguilla conservation problem. This second symposium reviewed a decade of research on biology and life history, genetics and genomics, reproduction, oceanic biology, early life history, population dynamics, assessment and management, eel passage at hydroelectric facilities, stocking, and threats, focusing primarily on Atlantic anguillids. The symposium finished with a panel discussion that emphasized the need to develop inter-jurisdictional governance approaches for panmictic eels as a way to promote recovery of the various species.
How animals integrate different sensory information for orientation is a complex process involving interactions between a variety of internal and external factors. Due to this complexity, each component of a suite of factors is typically studied in isolation. Here, we examine how an internal factor (personality of fish) influences the response of zebrafish (Danio rerio) to the magnetic field, while swimming in a flow chamber. Our previous work demonstrated that the orientation to the water current (rheotaxis) of zebrafish individuals is influenced by variations of the magnetic field only when fish are part of a shoal. In this study, we evaluated the rheotactic behavior of 20 fish, grouped in shoals of “proactive” or “reactive” individuals, under magnetic fields of different directions. We found that the magnetic field influenced at which water speed rheotaxis was elicited in zebrafish with “reactive” personality, but not in those with “proactive” personality. These results suggest that fish personality influences response to or weighing of sensory inputs and provides some insight on the variation in behavioral responses to environmental stimuli in both laboratory and natural settings.
Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic spatial ecology of anguillid eels. Herein we review 105 studies published between 1972 and 2016 that used a variety of telemetry technologies to study the movements of eels in a variety of habitats. Eight anguillid species have been tracked in three main geographical locations: Western Europe, the north-eastern part of North America and Australasia. Telemetry has proven to be an effective method for determining patterns of yellow eel movements in continental waters. It has also been used extensively to investigate the migratory behaviour of maturing eels as they leave fresh water to reach the sea. Among recent findings is the observation that downstream migration in continental waters is quite discontinuous, characterised by extended stopovers. Reconstructed migration routes in the open ocean obtained from satellite tags have provided indications of spawning areas, extensive vertical migrations and initial clues about the orientation mechanisms at sea. Telemetry studies have also revealed apparent evidence of predation by marine mammals and fish at sea, suggesting a significant natural source of mortality during the eel spawning migration. Finally, we discuss some limitations of telemetry technology and future directions, as well as associated challenges, to the developing field of eel spatial ecology.
Rheotaxis, the unconditioned orienting response to water currents, is a main component of fish behaviour. Rheotaxis is achieved using multiple sensory systems, including visual and tactile cues. Rheotactic orientation in open or low-visibility waters might also benefit from the stable frame of reference provided by the geomagnetic field, but this possibility has not been explored before. Zebrafish (Danio rerio) form shoals living in freshwater systems with low visibility, show a robust positive rheotaxis, and respond to geomagnetic fields. Here, we investigated whether a static magnetic field in the Earth-strength range influenced the rheotactic threshold of zebrafish in a swimming tunnel. The direction of the horizontal component of the magnetic field relative to water flow influenced the rheotactic threshold of fish as part of a shoal, but not of fish tested alone. Results obtained after disabling the lateral line of shoaling individuals with Co2 + suggest that this organ system is involved in the observed magneto-rheotactic response. These findings constitute preliminary evidence that magnetic fields influence rheotaxis and suggest new avenues for further research.
The sensory ecology and neuroethology of the lateral line provides an overview of the role of the lateral line in natural fish behaviour. The approach is more conceptual than comprehensive, choosing representative behaviors and especially those that lend themselves to a neuroethological analysis. This approach provides a clear focus for the determination of the relevant parameters of the physical stimulus, the physical and physiological mediation of stimulus encoding, and a targeted approach as to how the central nervous system processes and transforms sensory inputs to behavioral action. Like all major sensory systems, the lateral line makes an important contribution to the sensory capabilities of fish and aquatic amphibians and contributes to a wide range of core behaviors. This overview covers the role of the lateral line in: feeding, avoidance of predators, communication, hydrodynamic imaging, and orientation to slow and turbulent flows.