American eels are fast disappearing from restaurant menus as stocks have declined sharply across the North Atlantic. While the reasons for the eel decline remain as mysterious as its long migrations, a recent study by a NOAA scientist and colleagues in Japan and the United Kingdom says shifts in ocean-atmosphere conditions may be a primary factor in declining reproduction and survival rates.
Although many aspects of spawning and early life history of this species are poorly understood, they are clearly adapted to grow in the low productivity waters of the Sargasso Sea south of Bermuda, NOAA biologist Kevin Friedland said. They spend up to a year or more as larvae and tend to live in the upper 100 meters (about 330 feet) of the water column, so any changes in the surface waters will have a big impact during critical stages in their development.
Friedland and colleagues have found a significant correlation between the North Atlantic Oscillation, a decadal long ocean-atmosphere circulation pattern, and long-term variations in the catches of juvenile stages of the eels, commonly called glass eels. Considered a delicacy, the harvest of glass eels remains controversial due to concerns about stocks that some say may be close to collapse. Since the 1970s, the numbers of eels reaching Europe is believed to have declined by more than 90 percent.
In a study recently published in the ICES Journal of Marine Research, the researchers reviewed data of annual catches of glass eels since 1938 at Den Oever in the Netherlands. With the exception of the war years when no data was collected, the time series correlated to broad scale measures of climate variation such as the NAO and with specific local variations such as sea surface temperature, dominant wind pattern and the nature of the mixing in the upper layers of the ocean that control productivity. Changes in these factors matched changes in recruitment.
Eels in both the Atlantic and Pacif
|Contact: Shelley Dawicki|
NOAA National Marine Fisheries Service