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.

Why Is Recruitment of the American Eel, Anguilla rostrata, Declining in the St. Lawrence River and Gulf?

1994 ◽  
Vol 51 (2) ◽  
pp. 479-488 ◽  
Author(s):  
M. Castonguay ◽  
P. V. Hodson ◽  
C. M. Couillard ◽  
M. J. Eckersley ◽  
J.-D. Dutil ◽  
...  
Keyword(s):  
Anguilla Rostrata ◽  
Commercial Fishing ◽  
Hydroelectric Dams ◽  
Chemical Contamination ◽  
The Past ◽  
Silver Eels ◽  
High Prevalence ◽  
American Eels ◽  
Reference Stock ◽  
St Lawrence River

We critically review four potential causes of a drastic decline in juvenile American eels, Anguilla rostrata, recruiting to Lake Ontario (81-fold decline from 1985 to 1992) and in juvenile eel densities in tributaries to the Gulf of St. Lawrence. Silver eels from the St. Lawrence River were much more contaminated and had a high prevalence of deformities and lesions than a reference stock although they were on average less contaminated in 1990 than in 1982 (1.12 versus 4.54 μgg−1 for PCB; 0.025 versus 0.07 μg∙g−1 for mirex). Lethal toxicity from chemical contamination has been known to occur in St. Lawrence River eels for the past 25–30 yr. Major habitat modifications in the St. Lawrence took place in the 1950's (St. Lawrence Seaway and hydroelectric dams), about 30 yr before recruitment started declining; this long delay argues against these perturbations being primary causes of the decline. There is little evidence that commercial fishing and oceanographic changes caused the decline. Overall, we conclude that we do not know what caused the pronounced recruitment decline. We propose research avenues and hypotheses that may advance understanding and emphasize that because of panmixia, the recruitment decline could be species wide.

Challenges for Diadromous Fishes in a Dynamic Global Environment

2009 ◽  
Keyword(s):  
Average Rate ◽  
Underlying Mechanism ◽  
Local Circulation ◽  
Vertical Movements ◽  
Swimming Depth ◽  
Open Sea ◽  
Silver Eels ◽  
Vertical Distributions ◽  
The Baltic ◽  
American Eels

<em>Abstract</em>.-The horizontal and vertical movements of 20 silver American eels <em>Anguilla rostrata </em>migrating through a macrotidal estuary and bay were tracked with hydroacoustic telemetry. Eels initiated their seaward migrations around or shortly after sunset, mostly migrated at night, exhibited no bias for migration on ebb versus flood tides, and swam both with and against tidal currents with little preference for depth. Profiles of eel vertical distributions during transit through the estuary, the bay, and the tidal passages that connected the bay to the open sea differed and differed from analogous profiles for silver European eels <em>A. anguilla </em>transiting the Baltic Sea where tidal forcing is negligible. The underlying mechanism(s) associated with their direction of net displacement appears to be innate, although local circulation features may influence transit speeds and exit routes to the open sea. Our results in combination with published information for both the silver American and the European eel suggest that the horizontal migration speed for both species is relatively invariant, around 0.5 body lengths per second. The rate of ascent/descent of eels exhibiting a change in swimming depth of greater than 5 m could not be estimated with precision from the available records of eel swimming depths. The observed average rate of 0.11 m/s was, however, within the relatively narrow range of the average vertical swimming speeds (0.11-0.18 m/s) reported in the literature for silver eels executing vertical dives.

Correlations between pathological changes and chemical contamination in American eels, Anguilla rostrata, from the St. Lawrence River

1997 ◽  
Vol 54 (8) ◽  
pp. 1916-1927 ◽  
Author(s):  
C M Couillard ◽  
P V Hodson ◽  
M Castonguay
Keyword(s):  
Anguilla Rostrata ◽  
Chemical Contamination ◽  
Pathological Changes ◽  
Preneoplastic Lesions ◽  
Biomarkers Of Exposure ◽  
Reproductive Impairment ◽  
Migratory Season ◽  
American Eels ◽  
The Relationship ◽  
St Lawrence River

American eel (Anguilla rostrata) from the St. Lawrence River are heavily contaminated with chemicals that may be associated with increased incidence of diseases and reproductive impairment. The relationship between tissue mirex concentration and body mass was used to separate eels into two groups: the proportion of eels migrating from contaminated areas (Lake Ontario and upper St. Lawrence River) increased as the migration season progressed. Vertebral malformations and basophilic foci in the liver (preneoplastic lesions) were more frequent at the end of the migratory season, when the eels were more heavily contaminated with organochlorine compounds. In contrast, mesenteric nematodes were more common in the first week of the season, when eels were less contaminated. Diameters and percentages of different stages of oocytes, and density and surface area of pigmented macrophage aggregates in the spleen, did not vary among weeks. While basophilic foci are specific biomarkers of exposure to environmental contaminants, vertebral malformations may be caused by a variety of other anthropogenic or natural factors.\b Further studies are needed to confirm the observed associations between chemical contamination and pathological changes.

Spatial and Temporal Variations in Chemical Contamination of American Eels, Anguilla rostrata, Captured in the Estuary of the St, Lawrence River

1994 ◽  
Vol 51 (2) ◽  
pp. 464-478 ◽  
Author(s):  
P. V. Hodson ◽  
M. Castonguay ◽  
C. M. Couillard ◽  
C. Desjardins ◽  
E. Pelletier ◽  
...  
Keyword(s):  
Temporal Variations ◽  
Polynuclear Aromatic Hydrocarbons ◽  
Delphinapterus Leucas ◽  
Anguilla Rostrata ◽  
Chemical Contamination ◽  
Reference Sites ◽  
Beluga Whales ◽  
Pcb Congeners ◽  
American Eels ◽  
St Lawrence River

Levels of polychlorinated biphenyls (PCBs), mirex, and pesticides were 10–100 times higher in migratory adult American eels, Anguilla rostrata, sampled at Kamouraska, Quebec, in 1990 than in eels from an uncontaminated reference tributary; concentrations in eels within the estuary varied little among sites. In contrast, mercury levels were the same at estuarine and reference sites, suggesting natural sources or atmospheric deposition of mercury. Dioxins, furans, and polynuclear aromatic hydrocarbons were virtually absent at all sites. During the 7 wk of migration, levels of PCBs, mirex, and pesticides in eels increased, while mercury did not. Since 1982, levels of PCBs and mirex have declined by 68 and 56%, respectively, and the percentage of eels exceeding human health guidelines for PCBs and mirex was about twofold lower in 1990 than in 1982. Levels of other pesticides have also declined, except that dieldrin is unchanged since 1982. While chemical concentrations are declining, levels of specific, highly toxic PCB congeners are sufficiently high that eel consumption by beluga whales (Delphinapterus leucas) is still likely to be hazardous. The hazard to the eels themselves is unknown due to a scarcity of toxicity data, but the highest concentrations of chemicals were observed in gonads.

Swimming Depth of Adult American Eels (Anguilla rostrata) in a Saltwater Bay as Determined by Ultrasonic Tracking

1974 ◽  
Vol 31 (6) ◽  
pp. 1148-1150 ◽  
Author(s):  
A. B. Stasko ◽  
S. A. Rommel Jr.
Keyword(s):  
New Brunswick ◽  
Anguilla Rostrata ◽  
Depth Range ◽  
Pressure Sensing ◽  
Intermediate Depth ◽  
Swimming Depth ◽  
Passamaquoddy Bay ◽  
Ultrasonic Tracking ◽  
American Eels ◽  
Ultrasonic Transmitters

Pressure-sensing ultrasonic transmitters in the gut were used to determine the swimming depth of five American eels (Anguilla rostrata) in Passamaquoddy Bay, New Brunswick, in autumn. The eels made frequent dives from surface to bottom, in places diving at least 45 m deep, at vertical speeds to 76 cm/s. About one quarter of the time was spent near the surface; very little time was spent near the bottom or at any constant intermediate depth range.

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

2009 ◽  
Keyword(s):  
Water Level ◽  
Catch Rate ◽  
Catch Per Unit Effort ◽  
The Past ◽  
Silver Eels ◽  
Trap Fishery ◽  
Mean Size ◽  
Interannual Fluctuations ◽  
American Eels ◽  
St Lawrence River

<em>Abstract.—</em>Changes in abundance, seasonal occurrence, and mean size of American eels <em>Anguilla rostrata </em>in the lower St. Lawrence River during the past 50 years were examined. Catch per unit effort indices were calculated from daily catch records of eels captured in an experimental trap fishery and from the personal logbooks of a knowledgeable fisher. These two indices indicated a significant declining trend in eel catch rate by more than 50% since the early 1970s. Interannual fluctuations in catch rate were not related to variability in water level or water temperature. The timing of eel occurrence varied significantly between years and was inversely correlated to water level in August and September. It is hypothesized that eel movement is strongly determined by climatic/hydrological conditions in the previous summer. The average weight of eels has increased by 30% over the past eight years. The decline in catch rate and the increase in mean size of migratory silver eels in recent years are interpreted as the most significant symptoms of low recruitment levels and the precursory signal that the eel fishery in the lower St. Lawrence River may not be sustainable in the near future.

Distinction between American Eels (Anguilla rostrata) of Different Geographic Origins on the Basis of Their Organochlorine Contaminant Levels

1989 ◽  
Vol 46 (5) ◽  
pp. 836-843 ◽  
Author(s):  
Martin Castonguay ◽  
Jean-Denis Dutil ◽  
Claude Desjardins
Keyword(s):  
Lake Ontario ◽  
Anguilla Rostrata ◽  
Fish Tissues ◽  
Environmental Distribution ◽  
Stock Discrimination ◽  
Geographic Origins ◽  
Organochlorine Contaminants ◽  
Organochlorine Contaminant ◽  
American Eels ◽  
St Lawrence River

This study presents evidence that organochlorine contaminant levels of fish tissues represent a valuable tool for stock discrimination. Variability of concentrations of 15 organochlorine contaminants allowed a discrimination among American eels (Anguilla rostrata) of unknown (captured during the migration down the St. Lawrence River) or known geographic origins. The study also exemplifies that information regarding environmental distribution of contaminants can be gained by comparing organic contaminant levels among groups of fish. Indeed we can infer from this study that mirex contaminated sediments have extensively (at least 400 km) drifted downstream from Lake Ontario in less than 19 yr.

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