The Biology of the eel – an extraordinary life history
European eel is a catadromous fish species, long lived (on average
males 8-11 years, females 12-18 years in northern Europe but
significantly shorter in the Mediterranean and North Africa) and the
life cycle involves several metamorphic changes before the final adult
spawning migration to the Sargasso Sea. Reproduction:, whilst still to
be observed in the wild (indeed neither spawning adults nor eggs have
ever been seen), is a singular event. The life cycle has still not been
resolved and consequently critical and determining factors remain
unproven. However this is not a reason to abandon efforts to find easy
and low cost solutions to some of the more obvious problems.
Eels often dominate the fish fauna in lower rivers and estuaries, where it represents a considerable component of the aquatic ecosystem, and constitutes a major part of the diet of many other fish and semi-aquatic predators such as otters, cormorants and herons. There is also a coastal population that is largely unrecognised and undetermined.
Glass eels arrive along the coastal waters in winter in southern Europe to late spring in most northern regions.
Present status of eel stocks
The recruitment of glass eels compared with the 1980’s has been stated by ICES to be 1% of former levels. Specific structures for the management of eel stocks have been developed at an international level (EU Council Regulation EC No 1100/2007; CITES, 2007), establishing measures for the recovery of the stock of the European Eel, protection and sustainable exploitation.
Our experience in the UK would suggest a recruitment figure of between 10%-15% of former levels. Local and regional environmental conditions have a marked impact on capture results. However, it would appear that the decline in recruitment has occurred over the whole distribution area. The causes for the decline are not understood but are believed to be multi-factorial and include loss of migratory pathways, habitat, and climatic changes. Many other hypotheses such as exploitation, pollution and various pathogens have been proposed but the reality is that these things are not quantifiable. Catch data would indicate that glass eel recruitment from the 1980s to the present time was lowest in 2008-9 with an increase for 2010-11 and a significant one in 2013-2014. Anecdotal evidence would indicate that there have been other historical lows and highs. We are fortunate that the Severn Estuary is one of the major glass eels fisheries in Europe still viewed to have a surplus supply of glass eels. To date there has not been a similar decline in adult eels. An extensive review of 54 data sets (including 31 time series) for various stocks in NW Europe (dating from the 1970s onwards) was provided to WGEEL in 2007 and again in 2008 (Knights & Bonhommeau). but has not been considered (Analyses indicate that 61% of the data sets showed no significant temporal changes, 35% showed significant declines and 4% showed significant increases. Comparable trends in 31 of these data sets comprising continuous time series were 52, 42 and 6% respectively. Combined time series showed a peak in 1982 but stock levels appeared to have been as low in the 1970s as in the 1980s. On the River Severn studies suggest that the population is similar to those of 1980’s and that there is no direct link between volume of Glass Eel arrival recruitment and adult stock.
Eels are cultured to a significant degree in Europe but unlike the other major cultured species, the juvenile stock is still obtained by capture from the wild and there is no closed cycle of production as exists for the fully domesticated fish species.
Developing a Europe Wide Sustainable Fishery
For many decades we have been at the leading edge of Glass Eel Fishery management and innovation have pioneered many techniques to make our industry more complete and effective. We recognise that sustainability is the key not only for the future of the glass eels fishery and the future of the European aquaculture industry (until it is possible to reproduce the eel in captivity). It is therefore not surprising that we have been directing our resources and energies to promoting a sustainable fishery since 2006. Carrying on as before, with the various European fishery and environmental practices can only lead to further eel loss and ultimately end the livelihoods of all those engaged in this historic European industry. We have been working over the last five years to introduce and support effective, immediate and concerted action to introduce change. Initially we reviewed our own practices at UK Glass Eels, compared them with others and then tested them against a yardstick for sustainable fishery management. Initially under the Marine Stewardship Council and subsequently we have reviewed our operation and practices using Professor Callum Roberts “straight forward and common sense reforms” for the worlds fisheries. These were modified under the direction of Dr Gascoigne from MacAllistair Elliot. There has, in the last few years been further development of the sustainable fishing practice under the guidance of the Sustainable Eel Group.