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Studies on the reproductive biology of the European Eel in the central Sargasso Sea
Project
Project code: TI-FI-08-PID1609
Contract period: 01.02.2011
- 31.12.2020
Purpose of research: Inventory & Assessment
The European eel is endangered. There are still large gaps in our knowledge about its reproductive biology. A better understanding of the processes in the spawning area is necessary to develop a better basis for the protection and sustainable management of the species. The life cycle of the eel is complex and essentially characterized by long migrations both in the ocean and in inland and coastal waters. The recruitment of glass eels has declined throughout the distribution area for more than three decades and the yellow and silver eel stocks have also decreased. Since about 15 years, the International Council for the Exploration of the Sea has stated that the eel stock is 'outside safe biological limits'. The clarification of the causes of the population decline is crucial for successful establishment of protective measures. However, this will only be possible if the complex life cycle is known and understood. However, there are still large gaps in our knowledge on the oceanic life stages and on the processes in the spawning area. Therefore, we study distribution and abundance of early developmental stages of the European eel in the central Sargasso Sea and we try to better localize the spawning area. By establishing a time series, the investigations will allow conclusions about the long-term effects of changing hydrographic conditions but also about the effects of management measures on distribution, abundance and survival of eel larvae in the Sargasso Sea. So far, glass eel recruitment at the European coast is the only measure for eel recruitment. However, from these data it cannot be deduced whether a) predominantly continental factors and hence reduced numbers of spawners are responsible for the decline in the eel population, or whether b) mortality of larvae during the two to three-year oceanic migration from the spawning area to the coasts has changed due to climatic factors. For this reason, surveys in the spawning area are essential. In addition, the abundance and distribution of leptocephalus larvae of other species is examined to obtain information on possible variation of the larvae community in the Sargasso Sea. The investigations in the spawning area of the eel contribute to a better understanding of the biology of the early larval stages. E. g., gut content studies on early-stage leptocephalus larvae could provide very valuable insights into food composition of the early developmental stages, which may also be highly relevant for the artificial reproduction of eel. The feeding of the youngest eel larvae so far is the core problem in the controlled breeding. Therefore, eel aquaculture is so far exclusively based on wild caught glass eels. In the central Sargasso Sea (approximately in a range of about 70°W to 49°W and 24°N to 31°N) we investigate distribution and abundance of early developmental stages of the European eel (Anguilla anguilla). The studies allow us conclusions about the long-term effects of changing hydrographic conditions on distribution, abundance and survival of eel larvae in the Sargasso Sea. In the medium term, the data series will provide necessary information for a successful management of this endangered species. In addition, we study the abundance and distribution of leptocephalus larvae of other species to obtain information on the possible variation of the larval community in the Sargasso Sea. Together with the oceanographic data collected, the investigations of the ichthyoplankton with Isaac-Kidd Mid-Water Trawl (IKMT) will be used to better localize the spawning area of the eel and to characterize the relevant abiotic factors in the spawning area. The research in the Sargasso Sea was and will be conducted in cooperation with national and international partners.
Section overview
Subjects
- Marine fisheries
