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Quebec Bulletin
December 2015-January 2016/Volume 18/Number 6

The American Eel, a Species at Risk

American Eel
© Claude Nozères
American eel.

The American eel has been identified as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). This designation was made following a review of the status of the species in 2012. In 2006, COSEWIC assessed the species as Special Concern. The redesignation by COSEWIC points to a deterioration in its status despite a drop in the mortality rate attributable to commercial harvesting.

The eel is a fascinating species. It probably occupies the widest variety of aquatic habitats of all fish. It has a very broad range in the Atlantic, stretching from Venezuela all the way to Greenland and Iceland. Its range includes all freshwater bodies, estuaries and coastal marine waters accessible via the Atlantic Ocean. In Canada, it can be found in the Great Lakes and up to the middle of the Labrador coast.

Between 1996 and 2010, a 65% decline in the number of eels close to maturity was noted in the Lake Ontario–St. Lawrence River system. In some parts of Ontario, the decline exceeded 90% in two generations. Substantial declines were also observed in some parts of the Maritimes.

The American eel faces a number of threats, such as obstacles in freshwater preventing its upstream migration, mortality due to hydroelectric power plant turbines, fisheries, contaminants, swim bladder parasites, climate change and changes in ocean conditions.

The American eel is of great cultural and historical significance, particularly for many Aboriginal groups and communities. Fisheries and Oceans Canada is currently exploring the possibility of listing the American eel under the Species at Risk Act. The purpose of the Act is to prevent the disappearance of wildlife species, provide for their recovery and ensure the conservation of biological diversity. If it is listed as a threatened species, automatic prohibitions will come into effect and no person will be permitted to kill, harm, harass, capture, take, possess, collect, buy, sell or trade American eel. A recovery strategy will be developed to determine the measures to be implemented to mitigate the known threats associated with human activity. The critical habitat of the American eel will also be protected following its designation.

For more information or to share your comments, go to the Species at Risk Public Registry. Please submit your comments by March 18, 2016.

Marthe Bérubé
Ecosystem Management

An Eel's Journey to the Sargasso Sea

DFO M. Castonguay
Eels range in length from 40 to 120 cm and weigh anywhere from 0.5 to 3 kg. Female eels in the St. Lawrence are the largest in the species' entire range (up to 120 cm) and can live more than 20 years. Photo credit: Mélanie Béguer-Pon, Dalhousie University.

How do eels travel from their river to the southwestern Sargasso Sea? This is quite a long way to travel, 2,400 km to be exact, for a fish that, once it arrives, will reproduce, and then die. A team of university and government researchers, to which Fisheries and Oceans Canada is party, managed to solve the mystery using satellite tags.

The team of researchers fitted eels with satellite tags that continuously record water temperature, depth and light. These tags are programmed to detach after some time, floating to the surface where they begin to send their data to the Argos satellites in orbit.

With the data it collected, the team was able to trace the eels' migration routes. Five of the tagged eels managed to make it out to the open sea, beyond the continental shelf, in the Laurentian Fan area, more than 500 km off Cabot Strait. One of the eels veered due south and migrated to the northern boundary of the spawning site over a distance of 2,400 km.

The researchers identified two distinct migratory phases. During the first phase on the continental shelf and slope, the eels migrate vertically on a daily basis between depths of 50 m at night and about 240 m during the day. Once they are off the continental slope, their vertical migration pattern changes; they migrate northeast along the slope and then southeast, in the open sea, to the Laurentian Fan. One eel suddenly changed its route (second phase) and migrated due south, while making significant daily vertical migrations (140 m at night and 600 m during the day). It crossed the Gulf Stream 29 days after being released and reached the northern boundary of the spawning site at 30° N latitude, 45 days post‑release.

Considering the speed and the directed migration of this eel, it seems likely that eels use the Earth's magnetic field for guidance. It has long been known that eels can detect the Earth's magnetic field and use it to guide them. This work has shed some light on this mysterious migration.

Note: Fisheries and Oceans Canada researcher Martin Castonguay is part of the research team that tagged the eels with satellite tags.

At the beginning of the 20th century, a Danish scientist discovered that the southwestern Sargasso Sea, more than 500 km south of Bermuda, was the only location where small larvae of the American eel and European eel (two distinct species) could be found.

Therefore, we have indirectly known about this eel spawning site for a long time. However, no adult American eels were ever found in the open sea or at the spawning site. Furthermore, scientists had no idea of the migration routes and guidance mechanisms of these fish, which embark on one of the most spectacular migrations of the animal kingdom.

Martin Castonguay

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