Home About Us Sustainability Life Cycle Fishing News Contact Us

Anguilla anguilla

IUCN “To Be or Not To Be” critically endangered?

Our organisations objective is to promote the sustainable management of the eel by working with both the aquaculture industry and with the EU Commission to implement the national and river basin eel recovery plans. . There are some major misconceptions about the declines in recruitment in the European eel since the 1980s, with erroneous statements being made such as “stocks have shown unprecedented falls throughout Europe by 99%'”and” the species is near to extinction”’ and” it is being destroyed by pollution parasites and viral infections infections”.  It us very import that a balanced perception of the issues involved reaches the public domain if inappropriate management actions are to be avoided.


Dr Brian Knights MSc, PhD, CBiol, FIBiol, CEnv, FIFM

Ref: Freyhof, J. & Kottelat, M. 2008. Anguilla anguilla. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. http://www.iucnredlist.org/details/60344



There are important errors, omissions and contradictions in this document that severely weaken the case made that the European eel is ‘critically endangered’.

A. lack of consideration of data available for stocks in NW Europe

B. incorrect assumption that a reconstructed time series of commercial FAO landings since the 1960s is a direct proxy for all European-N African stocks.

C. lack of consideration of pre-1980 data, leading to assumptions that recruitment and stock are at ‘historic lows’

D. lack of consideration of recent and historical regime shifts, indicative of major wide-scale shifts in ocean-climate and biology.

E. over-estimation that average age-at-maturity throughout the European eel’s range is ~20 years and that declines and ‘recovery’ take many decades

F. incorrect assumption that there is a clear relationship between measures of stocks and recruitment

G. lack of consideration of similar changes in recruitment in the American and Japanese eel and probable causes – and that the American eel has formally been judged as not endangered

H. lack of consideration of evidence that (natural) oceanic factors are of major importance – and that eels have survived major oceanic and continental environmental changes over millions of years



Taxonomic Notes:

1. Even from natural stocks. This statement is meaningless.


2. The species has undergone a sharp decline in both recruitment and yield and stock Analyses of 54 stock data sets from NW Europe post-1970 show that only 35% have declined significantly (Knights & Bonhommeau, 2008). Time series (N = 31) indicate that stock levels were relatively low in the early-1970s but increased to peaks in the early-1980s in N Atlantic and North Sea sites, such that current stock levels appear similar to those in the early-1970s. Of stock data sets showing a significant decline, the majority (74%) only cover the period of decline that followed the peaks in the early-1980s.

3. An historical time series for the Skagerrak (Norway) shows similar recent changes but also that stocks were as low or lower in the 1920s as in recent years (Durif et al., 2008)

4. Recruitment of glass eels has declined since 1980 and since 2000 is at an historical low at just 1-5% of the pre-1980 levels. Recruitment has declined from peak levels around 1980 but the term at an historical low needs qualifying because 21 time series stretching as far back as the early-1900s show that recruitment has fluctuated widely over decadal time scales (Knights & Bonhommeau, 2008). Recruitment showed relatively large peaks in the early-1980s and in previous decades, but was relatively low in the 1970s and, very probably, in the early 1900s.

5. and since 2000 [recruitment] is at an historical low at just 1-5% of the pre-1980 levels. Glass eel recruitment has declined since peak levels in the early-1980s to ~1% in North Sea sites and by ~10% in N Atlantic sites

6. Yield and stock abundance has declined since the 1960s. This statement is based on the assumption that reconstructed FAO landings are a proxy for stocks. However, there is no specific evidence for a range-wide decline in stocks over this time scale, except in Baltic Sea sites concurrent with declines in recruitment, largely of juvenile yellow eels (Knights & Bonhommeau, 2008).

7. As the recruitment rate is so low the population is continuing to decline as older eels disappear from the stock. Relationships between recruitment and stocks are too unclear to make such a definitive statement for the whole species.

8. FAO global catch landings, which cannot be directly linked to population due to stocking and harvest effort (though scientific evidence supports this decline)… The statement underlined conflicts with the assumption that reconstructed FAO landings are a reliable proxy for stocks. Furthermore, scientific evidence in the form of actual data for stocks post-1970 does not match the declines in landings (Knights & Bonhommeau, 2008).

9. The recent decline in recruitment will translate into a future decline in adult stock, at least for the coming two decades (ICES 2006). This statement is not well supported by evidence from recruitment-stock relationships (Knights & Bonhommeau, 2008).

10. Noting the longevity of this species, and the extremely depleted state, restoration of the stock is expected to take several generations (Astrom and Dekker 2007), from 60 to >200 years depending on the protection level. These conclusions are not based on actual stock-recruitment or recruitment-stock data. Stock-recruitment relationships are unclear and evidence shows that recruitment and stocks vary widely over much shorter time scales (Knights & Bonhommeau, 2008). This conflicts with the assumption that Temporary increases (10-15 years) in abundance following the implementation of protective measures thus do not guarantee ultimate recovery, if not severely protecting the stock (Dekker pers. comm.).

11. Although a reliable population decline in mature individuals is not known, This statement conflicts with the definitive claims made elsewhere for ‘stock’ declines – and evidence is now available re. trends in populations of yellow and silver eels (see above)

12. It is inferred that there has been a decline of over 80% in the past three generations (60 years) based on the massive decline in recruitment (>95% in 24 years) and also supported by the decline (in) catch landings of 76% between 1968 and 2005. See criticisms above of these inferences and generalisations. Stocks have declined by ~35% from a peak in the early 1960s in Baltic Sea sites but to have been relatively stable since the mid-1970s (Knights & Bonhommeau, 2008). The Baltic is towards the edge of the range of the European eel and factors such as a lack of major inflows of sea water from the North Sea in recent decades may be associated with low recruitment.

13. re. three generations (60 years) – this is again based on the assumption of a long average generation time of ~20 years, whereas in NW Europe, males mature and emigrate at an average of ~7 years and females at ~11 years - and at younger ages from warmer Mediterranean habitats (e.g. see Tesch, 2003).

Range Description:

14. Stocked in most inland waters. This is far too broad a generalization.

15. Large parts of the population remain at sea (northwestern Atlantic and Mediterranean). Very probably true, and if so this counteracts the emphases in the citation on factors affecting the freshwater component of stocks.


16. Glass eels: since the early 1980's, a steady and almost continent wide decline of 90% has been observed in the recruitment of glass [juveline] eels (Dekker 2003), and according to ICES and FAO (2006) recruitment reached an historical low in 2001 of 1 to 2% of the pre-1980 level, it has not improved since and is an indication that the reproduction is seriously impaired and that the stock is severely depleted. See previous comments on ‘% declines’ and ‘the stock is severely depleted’.

17. Yellow/silver eels: ICES and FAO (2006) states that even though there is no analytical assessment of the state of [continental] European eel stock, all available information indicates that the stock is at a historical minimum in most of the distribution area and continues to decline. The statement underlined is incorrect, data and analytical assessments were presented to the Working Group on Eel in 2007 and 2008 by Knights & Bonhommeau.

18. all available information indicates that the stock is at a historical minimum in most of the distribution area and continues to decline. Incorrect, stock time series have shown wide fluctuations over decadal time scales and were relatively low in the early-1970s and in the early 1900s.

19. From However, even though catch effort…to the last line in the ‘Population’ section – this appears to say that landings data are not very reliable but goes on to discuss changes in fishery yields. The relevance of these points in the ‘Population’ section is unclear.

20. This is supported by the possibly only long-term scientific data [from Lake Ijsselmeer in the Netherlands] where there has been a gradual decline since 1960 (Dekker 2004a). The IJsselmeer is an unusual fishery, being an enclosed and heavily-exploited water body off the southern North Sea where recruitment would be expected be relatively low and where access for glass eels is difficult.

21. All European catches have decreased, possibly because the eel fishery was developed over this period. In Norway the catches seem to be stable. (ICES 2002). The meaning and relevance of both of these statements in relation to ‘Population’ is obscure.

22. As the recruitment rate is so low and declining the population is continuing to decline as older eels dissapear from the stock. See previous criticism of such statements


23. Estuarine, brackish and marine habitats aren’t mentioned(see 14 above)

Habitat & Ecology:

24. Glass-eels are observed in autumn on Portuguese coasts, in winter in North Sea and in spring. But appear all year round in some Mediterranean sites, e.g. in S France

25. The generation length of the species ranges from 2 to > 50 years, with a typical mean of 20 (Dekker pers comm.). Females are twice the size and age of males). Inaccurate estimate of typical mean generation time (see above) and of female v. male size and age differences.


26. The North Atlantic Oscillation (NAO) may have reduced larval survival and/or growth rate (Castonguay et al. 1994). The NAO itself cannot have any effects, it is only an index of atmospheric pressure difference in the N Atlantic region which can be related to climatic factors, such as temperature, winds and precipitation. There is increasing evidence that these factors can have major effects on recruitment (Knights, 2003; Freidland et al., 2007; Bonhommeau et al., 2008a,b; Kettle et al., 2008a; Knights & Bonhommeau, 2008).

27. However, Dekker (2004b) shows that the NAO index correlation is strong for growth rate but weak for glass eel numbers (in 2000 the NAO index returned to normal but recruitment still declined) and Climate change may have an impact upon the breeding grounds (Sargasso Sea). Relationships with the NAO have indeed weakened in recent years, but significant negative correlations between recruitment and temperature and primary productivity in the Sargasso Sea have been demonstrated by Bonhommeau et al., 2008a,b). Significant negative correlations have also been demonstrated between recruitment and longer-term increases in the Northern Hemisphere Temperature index by Knights and Bonhommeau (2008)

Major Threat(s):

28. Overfishing for glass eels (mainly in France, Spain, Portugal and UK) and downstream migrating eels (silver eels) across Europe (Dekker pers comm.) and the current fishery is not sustainable. There is no specific evidence for recruitment or spawner overfishing to the extent of endangering the species throughout its range. Glass eel fisheries are only viable in areas where recruitment is very high (because of proximity to the N Atlantic migration pathways) and it appears that numbers surviving are probably sufficient to meet the carrying capacity of local rivers, such as the R. Severn, England (Bark et al., 2007).

29. As a general point, there is no direct proof that any specific anthropogenic or natural factor has impacted on recruitment and stocks to the extent of endangering the survival of the species throughout its range. Causes of changes in recruitment and stocks can thus only be predicted from looking for significant spatio-temporal correlations with suspected ‘Major Threat(s)’. No such correlations have been determined for anthropogenic factors, but they have been for changes in oceanic factors over short and long time scales, as discussed above.

30. Further support for the importance of oceanic factors comes from the correlations and regime shifts in recruitment and oceanic change over similar spatio-temporal scales in all three N Hemisphere eel species, A. anguilla, A. rostrata and A. japonica (Bonhommeau et al. 2008a,b; Miller et al., 2009).

31. It should also be noted that the European and other eels have not been exterminated by extreme environmental changes occurring over millions of years, e.g. due to tectonic events and ice ages (e.g. see Kettle et al., 2008b).

32. Classical (freshwater) fish stock-recruitment relationships may not be shown by anguillids. They are periodic strategists characterized by relatively large and highly fecund marine spawners, producing very large numbers of small eggs to compensate for potentially very high levels of natural mortality, due to stochastic environmental changes, during a prolonged marine planktonic larval stage (King and McFarlane, 2003; Winemiller, 2005).

33. Further support for the importance of oceanic factors to recruitment in N Atlantic eels come from the sensitivity analysis of Beak International (2001).

34. Given the general similarities between the biology and recent population changes in European and American eels (see above), consideration should have been given to the fact that A. rostrata has been assessed as ‘of Special Concern’ by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2006) but the species has not been listed ‘at risk’ under the Canadian Species At Risk Act. Also, following a review by the United States Fish and Wildlife Service (USFWS 2007), A. rostrata is not listed as such in the USA under the Endangered Species Act (1973). The main conclusions were that ‘On the basis of the best available scientific and commercial information, we conclude that the American eel is not likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range and is not in danger of extinction throughout all or a significant portion of its range.’ The ruling also stated ‘Although the interactions are not completely understood, the success of early eel life stages and subsequent recruitment to fresh water is dependant on oceanic conditions, which are subject to natural variation (but) oceanic conditions are within normal variations (and) the American eel is evolutionarily adapted to oceanic variations’


Beak International (2001). The Decline of American Eel (Anguilla rostrata) in the Lake Ontario/St. Lawrence River Ecosystem: A Modeling Approach to Identification of Data Gaps and Research Priorities. White Paper Prepared for the Lake Ontario Committee of the Great Lakes Fishery Commission. Beak International Inc. Brampton, Ontario, Canada, 70 pp.

Bonhommeau, S., Chassot, E. and Rivot, E. (2008a). Fluctuations in European eel (Anguilla anguilla) recruitment resulting from environmental changes in the Sargasso Sea. Fisheries Oceanography 17, 32–44.

Bonhommeau, S, Chassot, E., Planque, B., Rivot, E, Knap, A.H. and Le Pape, O. (2008b). Impact of climate on eel populations of the Northern Hemisphere. Marine Ecology Progress Series 373: 71-80.

Durif C.M.F., Knutsen J.A., Johannessen T., Vøllestad L.A. (2008) Analysis of European eel (Anguilla anguilla) time-series from Norway. Report No. nr.8/2008, Institute of Marine Research, Storebø, Norway, 23pp.

Friedland, K.D., Miller, M.J. & Knights, B. (2006). Ocean-climate change, regime shifts and possible impacts on the recruitment of the European eel, Anguilla anguilla. ICES Journal of Marine Science 64:519-530.

Kettle, A. J., Bakker, D. C.E. and Haines, K. (2008a). Impact of the North Atlantic Oscillation on the trans-Atlantic migrations of the European eel (Anguilla anguilla). Journal of Geophysical Research doi:10.1029/2007JG000589. 113:GO3004.

Kettle, A.J., Heinrich, D. Barrett, J.H., Benecke, N. And Locker, A. (2008b). Past distributions of the European freshwater eel from archaeological and palaeontological evidence. Quaternary Science Reviews 27:1309-1334.

King, J.R & McFarlane, G.A. (2003. Marine life history strategies: application to fishery management. Fisheries Management and Ecology 10:249-264.

Knights, B. (2003). A review of the possible impacts of long-term oceanic and climate changes and fishing mortality on recruitment of anguillid eels of the Northern Hemisphere. The Science of the Total Environment 310:217-244.

Knights, B. & Bonhommeau, S. (2008) Status and trends in European eel (Anguilla anguilla L.) stocks, recruitment and landings in north west Europe. Manuscript and data presented to WGEEL 2007 (Draft 1) and 2008.

Miller, M.J., Kimura, S., Friedland, K.D., Knights, B., Kim, H., Jellyman, D.J & Tsukamoto, K. (2008). Review of ocean-atmospheric factors in the Atlantic and Pacific oceans influencing spawning and recruitment of anguillid eels. Challenges for Diadromous Fishes in a Dynamic Global Environment. American Fisheries Society, Bethesda, MA, USA. In press.

Winemiller, K.O. (2005). Life history strategies, population regulation, and implications for fisheries management. Canadian Journal of Fisheries and. Aquatic Sciences. 62: 872–885.