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.

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.

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.

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.

The Saguenay Fjord: A Third Factor in the Toxic Chemical Contamination of the St. Lawrence River Estuary

1990 ◽  
Vol 25 (1) ◽  
pp. 1-14
Author(s):  
R.J. Allan
Keyword(s):  
Toxic Metals ◽  
River Estuary ◽  
Organic Chemical ◽  
Organic Chemicals ◽  
Chemical Contamination ◽  
Lawrence Estuary ◽  
The Past ◽  
Saguenay Fjord ◽  
St Lawrence Estuary ◽  
St Lawrence River

Abstract The Saguenay Fjord enters the north shore of the St. Lawrence River estuary. The St. Lawrence River is one source of a variety of toxic metals and organic chemicals to its estuary. Some of these chemicals are transported by the river from its source in Lake Ontario and others are added along its course. However, the second major source of water inflow to the St. Lawrence Estuary is the Saguenay Fjord, which is by no means free of contamination. This paper overviews the types of toxic metals and organic chemical contamination and sources in the fjord proper and upstream in its drainage basin. The principal contaminants recorded in bottom sediments are polyaromatic hydrocarbons and mercury. An extensive forest products industry may also be a source of toxic chlorinated organic chemicals. The combined (peak) inputs of these chemicals to the Saguenay Fjord system was in the past and may have continued for many years, even decades. The relationship between the type of contaminants introduced in the past to the St. Lawrence estuary by the St. Lawrence River and the Saguenay Fjord may have implications concerning contamination of the beluga whale population which is located most frequently in the estuary near the fjord inflow.

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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