|Scientific Name:||Anguilla anguilla|
|Species Authority:||(Linnaeus, 1758)|
Muraena anguilla Linnaeus, 1758
Other Anguilla species have occasionally been stocked in Europe, but none have established a self-sustaining population. Pure A. rostrata (American Eel) have been recorded, likely due to stocking attempts, but are relatively rare (Böetius 1976). DNA analysis is the best tool to distinguish between European Eels and other species, and A. rostrata have fewer vertebrae than A. anguilla (102-112, usually 106-108, vs. 111-119, usually 114-116). Hybrids are known to have been found in Iceland where pure A. rostrata and A. anguilla also exist (Albert et al. 2006).
|Red List Category & Criteria:||Critically Endangered A2bd+4bd ver 3.1|
|Assessor(s):||Jacoby, D. & Gollock, M.|
|Reviewer(s):||Beaulaton, L., Belpaire, C., Dekker, W., Diaz, E., Durif, C., Freyhof, J., Knights, B., Turnock, S. & Wickström, H.|
|Contributor(s):||Ahn, H., Bennett, L., Casselman, J., Crook, V., DeLucia, M., Kaifu, k., Kottelat, M., Kurwie, T., Sasal, P., Silfvergrip, A., Uchida, K. & Walker, M|
Anguilla anguilla exhibits facultative catadromy, has multiple life stages, and is semelparous and panmictic; these life history traits made application of the IUCN Red List criteria more challenging. Anguillids are often referred to as ‘freshwater eels’, however, it is known that they can exhibit inter-habitat migration and that a proportion may stay in estuaries, lagoons and coastal waters, rarely, if ever, entering freshwater: this element of the population is particularly poorly understood.
Ideally, the IUCN Red List criteria would be applied to mature eels at their spawning grounds, and in the absence of such data, the criteria would be applied to silver eels starting their spawning migration (in the case of European Eels, leaving ‘continental’ waters), as these represent the maximum estimate of spawning stock biomass, but data sets for this are very rare. The majority of available data relates to glass eels and yellow eels but the relationships between recruitment, yellow eel populations, silver eel escapement, and spawner stock biomass are poorly understood. As such, the IUCN Red List criteria have to be applied to an amalgamation of multiple life stages, which may not exactly mirror the mature spawning stock but can be used as the current best estimate. Finally, the European Eel is a panmictic species, i.e. they come from one spawning stock. Taken literally, this assumes equal importance of the continental populations, and as such escapement from a specific river/country/region is not equivalent to the subsequent recruitment as this relies on the spawning stock as a whole, irrespective of escapement location. However, there are hypotheses that certain regions may have greater importance for the spawning stock, e.g. males primarily escaping from North Africa (Kettle et al. 2011), and as data are only available from certain parts of the species' range - data are particularly sparse for Mediterranean and North African populations - it is important that conservation initiatives and management actions are adjusted as new data become available.
In relation to A. anguilla, only a very small amount of data are available for silver eels, and while this is not geographically representative of the stock as a whole, a cursory analysis of this alone indicates that the mean decline in silver eel escapement is estimated to be 50-60% over the period of three generations (45 years), just placing them in the Endangered category. There is a similar dearth and uneven geographical spread in the data that relates to yellow eels; however, taking these limitations into account, analysis indicates that there has been a slightly greater decline in this life stage compared to silver eels. Compounding these declines in escapement of maturing eels, according to the available data, there has been substantial declines (90-95%) in recruitment of the European Eel across wide areas of its geographic range during the period of the last 45 years (or three generations) due to a range of threats facing freshwater eels at multiple life history stages. Recruitment has fluctuated during the last century. However, the analysis carried out as part of the IUCN Red List assessment mirrors the WGEEL recruitment index (five year average) which, despite increases in recruitment during the last few years, is currently at its lowest historical level of 1-10% the recruitment of the 1980s, (ICES WGEEL 2013). Further, there is concern that due to the period of time eels spend feeding and growing, prior to silvering and migrating to spawn, that silver eels may continue to decline, even if recruitment is showing recovery.
There is a suite of threats that have been implicated in causing the decline in European Eel recruitment and stocks: barriers to migration – including damage by hydropower turbines; poor body condition; climate change and/or changes in oceanic currents; disease and parasites (particularly Anguillicola crassus); exploitation and trade of glass, yellow and silver eels; changing hydrology; habitat loss; pollutants; and predation. The impact of these threats individually or synergistically, are likely regionally specific; however, more broadly, climate and ocean currents have been suggested to play an important role in the survival and transport of the leptocephalus larvae and recruitment of glass eels to coastal, brackish and freshwater habitat. Further research is required to fully understand the complexities of this particular aspect of the eel's life history but there are conflicting opinions as to the degree, if any, which oceanic factors contribute to broad fluctuations in eel numbers.
Eel Management Plans (EMPs) have been developed in European countries since 2007 as a stipulation of the EU Council Regulation No 1100/2007 relating to the recovery of the European Eel. Currently, more than 50% of the 81 EMP progress reports across Europe are failing to meet their target silver eel biomass escapement of 40% in accordance with the regulation, indicating that more work is required (WKEPEMP 2013). Further, international regulation was enforced for this species in 2007 when CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) listed A. anguilla on Appendix II (this came into force in March 2009). Since this time, exports outside of Europe have been banned due to concern over the decline in recruitment and stocks, however, trade continues within the EU and from non-EU countries within its range to other non-EU countries.
A number of management measures are being implemented in line with EMPs, for example easing of barriers. The influence of these measures, however, will take time to determine as they have only very recently been implemented and very much focus on the freshwater component of the eel's life-history. Arguably the most widely practised measure is restocking; however, there remains a great deal of debate as to whether this benefits eel spawning stocks and thus enhanced future recruitment. Measures that apply to silver eels, such as fisheries management, and/or trap and transport programmes, can theoretically have an almost immediate effect on the potential spawning stock, although when carried out in isolation, their benefit is significantly reduced.
As stated above, the relationship between life-stages is poorly understood, but it was generally agreed that it is very likely that the low recruitment will ultimately translate, though not linearly, to reduced future escapement for, at best, one generation length (15 years). Further, low recruitment has been proposed to be indicative of low historical breeding stock due to the relatively short time period (~2 years) between spawning and subsequent glass eel abundance. As such it was deemed appropriate to assign A. anguilla a Critically Endangered listing under current observations and future projected reductions of mature individuals (A2bd+4bd).
While this status is unchanged from the previous assessment, it is important to highlight that the process of this designation was very different in that it was carried out as part of an anguillid specific workshop, and that new data were incorporated – for example the generation length was reduced. There was general agreement that the situation had improved, albeit slightly, for this species both as far as recruitment and implementation of management measures was concerned. As such it is imperative to highlight that this listing is borderline, and that if the recently observed increase in recruitment continues, management actions relating to anthropogenic threats prove effective, and/or there are positive effects of natural influences on the various life stages of this species, a listing of Endangered would be achievable. Further, a drive to fill data gaps – particular in relation to the southern range of this species – would allow an even more robust assessment, and we strongly recommend an update of the status in five years.
Assessment of this species was carried out during a workshop held at the Zoological Society of London from July 1st-5th, 2013.
Anguilla anguilla has been shown to be distributed from North Cape in Northern Norway, southwards along the coast of Europe, all coasts of the Mediterranean and on the North African Coast (Schmidt 1909, Dekker 2003). It very rarely enters the White and Barents seas, but it has been recorded eastward to the Pechora River in northwest Russia. The species occurs in low abundance in the Black Sea where it migrates east to the Kuban drainage (occasional individuals reach the Volga drainage through canals), in northern Scandinavia and eastern Europe. A report by the ICES Study Group on Anguillid Eels in Saline Waters (SGAESAW) indicates that eel populations typically contain a mix of freshwater residents, saline water residents, and inter‐habitat migrants (ICES/SGAESAW 2009). It also widely occurs in most inland waters of Europe (e.g. lakes). It is thought that the continental distribution of the European Eel is over an area of approximately 90,000 km² in Europe and parts of North Africa (Moriarty and Dekker 1997), with a substantially larger range if their marine distribution is considered. For example, in England and Wales, there are thought to be a total of 2,694 km² of transitional waters, which account for approximately 68% of the potential eel producing habitat across all 11 River Basin Districts (Defra 2010).
For several decades prior to an EU-wide ban on export in 2010, A. anguilla was also exported to Asia for seed stock in eel farms (Ringuet et al. 2002). This species may well have been introduced in some parts of Asia (through escape or release from farms), however these are not thought to contribute to the population and therefore areas of introduction have been excluded in the range information. Anguilla anguilla are thought to spawn in the Sargasso Sea in the West Central Atlantic between late winter and early spring, before eggs hatch and leptocephalus larvae migrate back across the Atlantic to begin the continental phase of their life history (Schmidt 1912, Aarestrup et al. 2009).
Native:Albania; Algeria; Austria; Belarus; Belgium; Bosnia and Herzegovina; Bulgaria; Croatia; Cyprus; Czech Republic; Denmark; Egypt; Estonia; Faroe Islands; Finland; France; Georgia; Germany; Gibraltar; Greece; Guernsey; Iceland; Ireland; Isle of Man; Israel; Italy; Jersey; Latvia; Lebanon; Libya; Lithuania; Luxembourg; Macedonia, the former Yugoslav Republic of; Malta; Mauritania; Moldova; Monaco; Montenegro; Morocco; Netherlands; Norway; Poland; Portugal; Romania; Russian Federation; Serbia (Serbia); Slovakia; Slovenia; Spain; Sweden; Switzerland; Syrian Arab Republic; Tunisia; Turkey; Ukraine; United Kingdom
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Atlantic – western central; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
A subset of the recruitment index data in the ICES WGEEL 2012 report was used for analysis i.e., data collected as part of fisheries independent scientific monitoring or fisheries dependent data with an associated metric of effort (e.g. catch per unit effort (CPUE)). Other data were kindly provided by Dr Brian Knights, and this was included as part of the assessment process. Catch effort can be variable in fishing data, and under-reporting and, in some cases, an absence of reporting of landings is a serious problem in most European countries. Thus landings data cannot be accepted as a precise measure of stock status. However, trends in the reported catch data will, to some extent, reflect true changes in fishing yields. All the data were analysed to assess trends in recruitment, population and spawner escapement; however, it was primarily used to guide discussions that resulted in the broad agreement of the Critically Endangered listing by the assessment team, which was in turn supported by the majority of reviewers.
|Habitat and Ecology:||
|Use and Trade:||
The various life stages, ranging from glass eel to silver eel, of all Anguilla species are harvested and traded on a global scale for consumption - directly or after culture - and for stocking purposes, with current demand predominantly driven by East Asian markets, in particular Japan and mainland China. A concerning pattern of exploitation is already apparent – when one Anguilla species or population declines in abundance or new catch/trade measures come into force limiting exploitation levels, industry moves to the next in order to fulfil demand (Crook and Nakamura 2013).
The causes of the declining recruitment rates are still not fully understood (Dekker 2007), and while there are many hypotheses, the significance of any single threat, or the synergy it may have with other threats is still poorly understood. It is important to highlight, however, that management measures focusing on a single threat, in isolation of other identified pressures (listed below), are less likely to have a significant positive effects on eel numbers. The assessment process and accompanying external review indicated that a comprehensive discussion of these threats and their impacts was significantly beyond the scope of this assessment – there is a significant body of information including a great deal of contradiction in peer-reviewed and grey literature, and in expert opinion relating to these threats. Below we list (in alphabetical order) suspected threats with some (but not all) key references and a very brief synopsis of these threats – this is by no means comprehensive and does not attempt to fully dissect the wide range of views and data on these pressures. As such, a robust and comprehensive analysis of the existing data and opinion on factors linked to decline in abundance of the European Eel would be extremely timely.
The majority of conservation actions historically in place for the European eel were set up and controlled at local and national level, often with little coordination which is of particular concern in relation to trans-boundary watersheds.
|Citation:||Jacoby, D. & Gollock, M. 2014. Anguilla anguilla. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 21 September 2014.|
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