scholarly journals Tracking the marine migration routes of South Pacific silver eels

2020 ◽  
Vol 646 ◽  
pp. 1-12
Author(s):  
YLK Chang ◽  
G Dall’Olmo ◽  
R Schabetsberger
Keyword(s):  
Migration Routes ◽  
Spawning Area ◽  
Spawning Areas ◽  
Silver Eels ◽  
Diel Vertical Migrations ◽  
Equatorial Current ◽  
Southern Branch ◽  
Subtropical Underwater ◽  
Counter Current ◽  
Northern Branch

It is still a mystery how catadromous eels find their way through the seemingly featureless open ocean to their spawning areas. Three catadromous Pacific eels (2 Anguilla marmorata, 1 A. megastoma) from the Archipelago of Vanuatu were tagged with pop-up satellite archival transmitters, and their migration tracks towards their presumed spawning area approximately 870 km northeast of the point of release were reconstructed in order to evaluate their movements in relation to oceanographic conditions. We used the timing of diel vertical migrations to derive the eels’ positions. The 2 A. marmorata exhibited steep-angled turns resulting in a zig-zag migration path along the east-west axis, while the A. megastoma took a relatively straight course towards the presumed spawning area. They migrated with a speed over ground of 21-23 km d-1. In this region, the eastward flow of the South Equatorial Counter Current (SECC, ~5°-10°S) separates the westward flowing South Equatorial Current (SEC; ~0°-5°S and 10°-18°S) into 2 branches. During shallower nighttime migration depths around 150 m, eels crossed a variable flow field through the southern branch of the westward SEC with westward propagating mesoscale eddies and the eastward SECC, but stayed south of the stronger northern branch of the SEC, possibly increasing retention time of larvae within this area. The eels headed towards a tongue of high-salinity Subtropical Underwater (STUW). The eels did not move beyond a salinity front of 35.9-36.0 at a depth of 100-200 m, which may have provided cues for orientation towards the spawning area.

Challenges for Diadromous Fishes in a Dynamic Global Environment

2009 ◽  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Sargasso Sea ◽  
Atmospheric Conditions ◽  
Feeding Success ◽  
The North ◽  
Spawning Areas ◽  
Silver Eels ◽  
Ocean Conditions

<em>Abstract</em>.-Declines in recruitment of temperate anguillid eels have occurred in the past 30 years in many areas of their species ranges. The cumulative effects of anthropogenic changes to their freshwater growth habitats are likely contributors to reductions in population sizes, but changes in ocean-atmospheric conditions in the ocean also appear to be contributing to the declines. This paper reviews how changes in the ocean may contribute to recruitment declines by affecting the spawning location of silver eels, larval feeding success, or the transport of their leptocephalus larvae by ocean currents. Recruitment of European eels <em>Anguilla anguillla </em>has shown correlations with the North Atlantic Oscillation and specific changes in ocean conditions in the Sargasso Sea where spawning and development occurs. The American eel <em>A. rostrata </em>spawns in an area that overlaps with the European eel and so could also be affected by these types of changes. Recruitment of Japanese eels <em>A. japonica </em>appears to be correlated to the El Niño Southern Oscillation index and latitudinal changes in salinity fronts in the western North Pacific. The general spawning and recruitment patterns of the temperate Australasian shortfin eels <em>A. australis </em>and New Zealand longfin eels <em>A. dieffenbachii </em>in the western South Pacific are similar to those of the northern temperate anguillids and also may be affected by El Niño-related factors. The changes in ocean conditions associated with atmospheric forcing or a warming of the ocean could alter the biological characteristics of the surface layer where leptocephali feed, due to changes in productivity or community structure, in addition to having possible effects on larval transport and location of the spawning areas by silver eels. Changes in ocean-atmospheric conditions could result in lower feeding success and survival of leptocephali, or increased retention in offshore areas due to changes in the location of spawning areas, resulting in reductions in recruitment.

scholarly journals The October 20, 2006 Manyas (ML=5.2) and October 24, 2006 Gemlik (ML=5.2) earthquakes in the Marmara region (NW Turkey): ground motion characteristics

2015 ◽  
Vol 57 (6) ◽  
Author(s):  
Esref Yalcinkaya
Keyword(s):  
Surface Waves ◽  
Ground Motion ◽  
Empirical Relation ◽  
General Character ◽  
Marmara Region ◽  
Resonance Frequencies ◽  
Nw Turkey ◽  
Southern Branch ◽  
Motion Characteristics ◽  
Northern Branch

<p>In this study, we analyze the ground motion characteristics of October 20, 2006 Manyas (M<sub>L</sub>=5.2) and October 24, 2006 Gemlik (M<sub>L</sub>=5.2) earthquakes. Both earthquakes occurred on the southern branch of the North Anatolian Fault Zone in Marmara region, which has a lower seismic hazard relative to the northern branch. The two events are the largest earthquakes on the southern branch recorded by a modern and vast seismological network; therefore their records are valuable to evaluate seismic risk of the region and the understanding of physics of wave propagation. The analysis show that the attenuation of PGAs is very similar for two earthquakes, but they are not represented by the empirical relation obtained for earthquakes occurred on the northern branch. The waveforms of the Gemlik earthquake recorded by BYTNet array indicate an EW rupture orientation with right-lateral slip which fits to the general character of the southern branch. Ground motions at the stations located within basin are strongly influenced by the presence of locally induced surface waves resulting in lengthening of significant shaking duration with respect to a nearby ridge site. Surface wave characteristics are very similar for the Manyas and Gemlik earthquakes, but variations are observed on components which may be related to 3D basin geometry. Resonance frequencies of the surface waves generated within basin are very close to the 1D site resonances at the stations obtained from H/V ratios of S waves. The resonance frequency is about 0.2 Hz within the large Bursa Plain, whereas it increases to about 0.9 Hz within the smaller Gemlik Plain.</p>

scholarly journals Marine Reservoir Variation in the Bismarck Region: An Evaluation of Spatial and Temporal Change in ΔR and R Over the Last 3000 Years

Radiocarbon ◽  
2012 ◽  
Vol 54 (1) ◽  
pp. 45-58 ◽  
Author(s):  
Fiona Petchey ◽  
Sean Ulm
Keyword(s):  
Large Scale ◽  
Current System ◽  
Climatic Conditions ◽  
Ocean Eddies ◽  
North Equatorial Counter Current ◽  
Equatorial Current ◽  
Oceanographic Data ◽  
Counter Current ◽  
New Britain ◽  
Ekman Upwelling

Interactions between islands, ocean currents, and winds cause large-scale eddies and upwelling in the lee of islands that can result in spatial variation in the marine radiocarbon reservoir. For waters around New Ireland and the Bismarck Sea, ΔR values ranging from 365 to −320 14C yr have been reported (Kirch 2001; Petchey et al. 2004). Petchey et al. (2004) proposed that some of this variation was caused by seasonal reversals in the South Equatorial Current and North Equatorial Counter Current system, combined with Ekman upwelling from the Equator. McGregor et al. (2008) suggested additional complexity within this region caused by a change in the reservoir value over time in response to changing climatic conditions. We present a series of 14 new and extant published ΔR and R values on historic shells, combined with 8 values from archaeological terrestrial/marine pairs and U-Th dated coral, that support observations of localized variability caused by a complex interplay between seasonal currents, riverine input, and ocean eddies. On the basis of these values and oceanographic data, we divide the Bismarck Sea surface marine 14C reservoir into 6 tentative subregions. In particular, our results support significant variation within channels at the southwest and southeast ends of New Britain and towards the equatorial boundary of the sea. Our results indicate that within the Bismarck Sea geographical variation appears to be more extreme than temporal over the last 3000 yr.

Some Features of Organic Phosphorus Distribution in the South-East Indian and South-West Pacific Oceans

1963 ◽  
Vol 14 (2) ◽  
pp. 119 ◽  
Author(s):  
DJ Rochford
Keyword(s):  
Organic Phosphorus ◽  
North Equatorial Current ◽  
The South ◽  
Southern Boundary ◽  
West Pacific ◽  
East Indian ◽  
South West ◽  
Equatorial Current ◽  
The Antarctic ◽  
Counter Current

Concentrations of organic phosphorus significantly different from zero (0.10-0.38 �g-atom/l) have been found at most depths in a series of stations in the south-east Indian and south-west Pacific Oceans. For three meridional sections of the central and west Pacific and east Indian Oceans mean concentrations of organic phosphorus in the 0-200 m layer were found to be maximal (0.20-0.38�g- atom/l) along the southern boundary of the South Equatorial Current, along the Equatorial Divergence, and within the boundary of the Counter Current and North Equatorial Current. South of 30�S. to about 40�S. another maximum was found which could not be associated with marked current movements. Pronounced maxima were also found in the vertical profiles of organic phosphorus. These sometimes occurred at the same depth as major hydrological core layers. The most consistent agreement in depth was found between the Antarctic intermediate salinity minimum and an intermediate depth organic phosphorus maximum around 1000 m. At 41% of stations examined these two layers were found at the same depth. At several locations the depths of the maxima in organic phosphorus varied in the same direction and at the same rate as the major hydrological layers during one year's observations.

Complex migration routes of Atlantic bluefin tuna (Thunnus thynnus) question current population structure paradigm

2010 ◽  
Vol 67 (6) ◽  
pp. 966-976 ◽  
Author(s):  
Benjamin Galuardi ◽  
François Royer ◽  
Walt Golet ◽  
John Logan ◽  
John Neilson ◽  
...  
Keyword(s):  
Site Fidelity ◽  
Bluefin Tuna ◽  
Thunnus Thynnus ◽  
Migration Routes ◽  
Western Atlantic ◽  
Spawning Period ◽  
Atlantic Bluefin Tuna ◽  
Spawning Site ◽  
Archival Tags ◽  
Spawning Areas

Movements of Atlantic bluefin tuna ( Thunnus thynnus , ABFT) from specific western Atlantic forage grounds are not well described, and the extent of their spawning areas is mainly surmised. In 2005 and 2006, we deployed 41 pop-up satellite archival tags (PSATs) on adult Atlantic bluefin tuna off the coast of Nova Scotia, Canada, and on Georges Bank. During the assumed spawning period, 56% of the tagged ABFT occupied a known spawning area, while 44% were located in distant oceanic regions. Assuming obligate annual spawning, these results are inconsistent with the notion of spawning site fidelity to the Gulf of Mexico. The ocean-wide migrations of adult ABFT tagged on a common forage ground suggest evidence of a metapopulation requiring more spatially explicit management than the current simple two-stock structure.

Tracking anguillid eels: five decades of telemetry-based research

2018 ◽  
Vol 69 (2) ◽  
pp. 199 ◽  
Author(s):  
Mélanie Béguer-Pon ◽  
Julian J. Dodson ◽  
Martin Castonguay ◽  
Don Jellyman ◽  
Kim Aarestrup ◽  
...  
Keyword(s):  
Marine Mammals ◽  
Spatial Ecology ◽  
Western Europe ◽  
Migration Routes ◽  
Future Directions ◽  
The North ◽  
Spawning Areas ◽  
North Eastern ◽  
Geographical Locations ◽  
North Eastern Part

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.

scholarly journals A Generalized Method for Estimating the Structure of the Equatorial Atlantic Cold Tongue: Application to Drifter Observations

2013 ◽  
Vol 30 (8) ◽  
pp. 1884-1895 ◽  
Author(s):  
Verena Hormann ◽  
Rick Lumpkin ◽  
Renellys C. Perez
Keyword(s):  
Complete Analysis ◽  
Cold Tongue ◽  
Equatorial Atlantic ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Large Application ◽  
Coordinate Mapping ◽  
Equatorial Current ◽  
Atlantic Cold Tongue ◽  
Northern Branch

Abstract A generalized method is developed to determine the position of the Atlantic northern cold tongue front across its zonal extent from satellite sea surface temperature (SST) data. Previous approaches estimated the frontal position subjectively or individually, calling for a more objective technique that is suitable for large datasets. The developed methodology is based on a median frontal SST, and associated positional uncertainties are on the order of 0.3° latitude for the period 1998–2011. Frontal characteristics are generally consistent with tropical instability waves (TIWs) and interannual variations are large. Application to drifter observations shows how the new methodology can be used to better understand circulation features near the northern cold tongue front. A drifter pair deployed on the eastern side of a passing TIW crest north of the front revealed that the trajectories of the drifters were clearly influenced by the shape of the front and they did not cross the front, but rather stayed close together about 2.5° north of the front. In a more complete analysis using all available drifters near the Atlantic northern cold tongue front, only about 12% of the trajectories crossed the front. Analyses in an along- and cross-frontal frame of reference complement isopycnal coordinate mapping, and tropical Atlantic drifter velocities averaged in frontal coordinates indicate a broadened shear zone between the northern branch of the South Equatorial Current and North Equatorial Countercurrent as well as meridional convergence near the front.

scholarly journals When did the North Anatolian fault reach southern Marmara, Turkey?

Geology ◽  
2021 ◽  
Author(s):  
Volkan Karabacak ◽  
Taylan Sançar ◽  
Gökhan Yildirim ◽  
I. Tonguç Uysal
Keyword(s):  
Shear Zones ◽  
Strike Slip ◽  
North Anatolian Fault ◽  
Plate Boundaries ◽  
Marmara Region ◽  
Plate Motions ◽  
The North ◽  
Southern Branch ◽  
Timing Of Initiation ◽  
Northern Branch

We dated syntectonic calcites on fault planes from the southern branch of the western North Anatolian fault (NAF) in northern Turkey using U-Th geochronology. We selected strike-slip faults that are kinematically related to the current regional strain field. The isotopic ages cluster around different periods during the past ~700 k.y. The most prominent cluster peak of 510.5 ± 9.5 ka (1σ) is consistent with the maximum cumulative strike-slip offset data and tectonic plate motions measured by GPS data, highlighting the fact that the present configuration of the NAF in the southern Marmara region started at ca. 500 ka or earlier. These new isotopic ages, combined with previous considerations of regional tectonics, reveal that faulting along the western NAF initiated primarily in the southern Marmara region at least a few hundred thousand years earlier than the timing suggested for the northern branch of the western NAF. This study presents an innovative approach to constrain the timing of initiation of currently active fault segments along the NAF in southern Marmara. U-Th geochronology of fault-hosted calcite thus has a wide application in determining absolute ages of fault episodes in wider shear zones along plate boundaries.

The migration of stocked, trapped and transported, and wild female American silver eels through the Gulf of St. Lawrence

2018 ◽  
Vol 75 (11) ◽  
pp. 2024-2037 ◽  
Author(s):  
Mélanie Béguer-Pon ◽  
Guy Verreault ◽  
David Stanley ◽  
Martin Castonguay ◽  
Julian J. Dodson
Keyword(s):  
Detection Efficiency ◽  
Anguilla Rostrata ◽  
Migration Speed ◽  
Hydroelectric Dams ◽  
Wild Female ◽  
Swimming Depth ◽  
Silver Eels ◽  
Diel Vertical Migrations ◽  
American Eels ◽  
St Lawrence River

The stocking of juvenile eels and trap and transport programs of large yellow (American) eels (Anguilla rostrata) were initiated in Ontario to mitigate mortalities observed at hydroelectric dams and to increase escapement from the upper St. Lawrence River and Lake Ontario (Canada). A total of 380 migrating female silver eels (stocked, trapped and transported, and wild) were tagged with acoustic transmitters between 2011 and 2014. Their migration and escapement at the exit of the Gulf of St. Lawrence, the Cabot Strait, were recorded using acoustic receivers. Escapement rates varied between 8.9% and 20.0% annually (mean = 11.4%). A high proportion of stocked eels were detected (N = 27 of 43 detected at Cabot Strait), demonstrating their ability to escape the Gulf. No differences in migration speed or crossing locations at Cabot Strait were found among the three categories. Eels crossing Cabot Strait did not display diel and tidal patterns, but their estimated swimming depth indicated diel vertical migrations. The low escapement rates observed may be related to predation events and (or) the low and variable detection efficiency of the acoustic receivers’ line.

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