Changes in Abundance of Anguillid Leptocephali in the Sargasso Sea

The decrease in recruitment of European eel Anguilla anguilla in recent decades has led to a series of action plans, culminating in the European Council Regulation No 1100/2007 that is only targeting an increase in the number of silver eels to escape from European inland waters to the sea. Such a focus implicitely supports two hypotheses: the increase of continental mortality regarded as the major driver for the decline of the stock and also a spawner-recruitment relationship for European eel. Both hypotheses are yet unproven and do not account for recent literature pointing at the influence of atmospherically driven oceanic condition variation as a contributor to declines and fluctuations in glass eel recruitment. To test whether the relative abundance in European eel leptocephali significantly changed compared to collections in 1983 and 1985, two sampling surveys for anguillid leptocephali were conducted in 2011 and 2014 in the central Sargasso Sea. The sampling design based on Isaacs-Kidd Midwater Trawl (IKMT) catches deployed in the style of double oblique tows in the upper 300 m was chosen to directly compare to collections made in the same way in previous surveys of the spawning area in 1983 and 1985.