The short answer is ‘yes’. The long answer is much more interesting and covers the ins and outs of eel sex, how smoked eel led to a revolution in eel consumption, and the most significant wildlife crime on the planet…
Despite being critically endangered, if you know what to look for you can buy eel that could even have a net benefit on the overall eel population.
There is a lot of expert knowledge contained within this post, so I have tried to make it understandable for anyone who doesn’t specialise in eel management and is just trying to eat responsibly. With that in mind, we’ll start with the basics:
Why am I writing this and what are my source?
The European eel’s status as critically endangered, as discovered by Chefs Sarit Packer and Itamar Srulovich of Honey & Co recently when creating a smoked fish and celeriac brunch dish: They lamented the lack of clear information on sustainable food, so I decided to investigate.
I started by speaking to eel fisher, Terry Smith from Smith’s Smokery in Lincolnshire, who very kindly filled me in on the extraordinary life of eels, but as with so many things, once you start learning, you realise how much you still don’t know.
Our conversation led me on to do some of my own desk research, where I came across eel feed expert Joost Blom in a recent article on The Fish Site. Joost was incredibly helpful and introduced me to several other eel experts, who in turn introduced me to others.
The experts involved
The people who contributed to this post are:
- Terry Smith, eel fisherman from Smith’s Smokery
- Dr. Joost Blom, eel feed expert from BioMar
- Dr. Arjan Palstra, eel reproduction scientist from Wageningen University and Research
- Andrew Kerr, chairman of the Sustainable Eel Group
- Dr. Willem Dekker, marine biologist and director of science at the Sustainable Eel Group
- Norbert Jeronimus, secretary of the Eel Stewardship Fund
- David Bunt, director of conservation operations at the Sustainable Eel Group
- Florian Stein, director of scientific operations at the Sustainable Eel Group
A divine sign?
My housemates have been getting the daily lowdown on eels for at least a few weeks now, so when I returned to my parents’ house in Hampshire for the weekend, it appeared like some kind of divine message that the first thing I saw on arriving was….an eel!
It was most unusually basking in the sunlight (they’re nocturnal) in the small stream outside our kitchen. I wish I’d been able to take a photograph, but taking a picture of something brown against something brown with the reflection of sunlight on the water was never going to work.
What types of eel are there?
There are many different types of eel, but the three we typically eat are the American eel, the European eel and the Japanese eel, otherwise known as ‘Unagi’. Of these, the American and Japanese eel are endangered, while the European eel is critically endangered according to the IUCN.
The fact that we continue to fish eel has led to concern over the sustainability of their population. For this post I am only going to focus on the European eel. These are quite different from the more fabled Conger eels and Moray eels that live and breed only in the sea.
You might hear people talk about glass eels, yellow eels and silver eels, but you would be wrong to assume that these are different types of eels. Instead they refer to different stages in the eel life-cycle.
Birth and larvae
Eels start life as larvae in the Sargasso Sea, a sea bounded not by land, but by four different sea currents; the Gulf Stream, the North Atlantic Current, the Canary Current and the North Atlantic Equatorial Current, also known as the North Atlantic Gyre. It’s positioned to the north east of the Caribbean and the Gulf of Mexico.
As larvae, European eels rely on the North Atlantic currents to complete their migration drifting towards Europe over probably 20 months.
Aside from being the birth-place of both the European and American eel, the currents are also known for supposedly trapped ships covered in weed for centuries. This is most likely because there is often very little wind to propel sailing vessels and the weed tricked sailors into thinking they were closer to land than they were.
Writing for The Royal Geographical Society in 1925, Captain C.C. Dixon:
“Who could know whether this weed got thicker and thicker till there was no turning back? Its changing tints and shadows as daylight faded and at the approach of dawn needed but little help from the imagination to be wrought into fearsome monsters that inhabited its depth and whose very appearance would steal away one’s sanity.”
The Sail Magazine presents an interesting modern account of travelling to ‘the weirdest sea on Earth‘ where the water is warmer, saltier and startlingly clear compared to the surrounding Atlantic.
By the time they reach the European coasts, they are already becoming Glass Eels. This is a transparent larval state in which they continue their migration up estuaries to freshwater streams and rivers.
Glass eels, called ‘Angulas’ in Spain and ‘Civelles’ or ‘Pibales’ in France, are considered a regional delicacy in the Spanish Basque country. The young eel are caught in their droves in the Severn Estuary as well as off the coasts of Morocco, Spain and France.
‘Elver’ refers to a stage between glass eel and yellow eel – effectively a mini eel. At this stage, only weeks after arriving in freshwater, the formerly transparent Glass Eels darken. On the Severn, the term Elver applies to both Glass Eel and Pigmented Elver, but Elvers are typically eaten less because they become gritty.
As the eel grows, it develops a brownish-yellow colour, hence the term ‘Yellow Eel’. After 5-20 years, the eel will start sexual maturation. You can tell their maturity from their silver flanks and white belly.
The term ‘Silver Eel’ refers to an eel about to start sexual maturation and ready to return to the Sargasso Sea to spawn.
Difficulties of assessing the population size
It is worth noting that accurately assessing population size is more difficult for particular species like eels than for large mammals like rhinos or pandas. When it comes to eels, there are many factors that contribute to this.
They are difficult to spot in the wild, are nocturnal animals that live underwater, and swim at great depths while in the ocean. The way that eels migrate to breed, and that their offspring return – drifting to Europe as larvae – means that measuring the stability of local populations, such as the one Terry fishes in Lincolnshire, is not effective.
Young eels don’t return to the same place where their parents came from. Indeed their parents could have come from very different locations since all eels return to the Sargasso Sea to breed and appear to die there. The IUCN have done their best to gain as accurate an understanding of the international population of European eels using data from fisheries and scientific surveys.
A worrying trend
The overall numbers of eels are not particularly low. Terry gave me a sense of this when describing the Glass Eel fishing in France: The country accounts for 75% of all Glass Eel catches in Europe, but during the season (roughly November-April) it declares catches of 50 tonnes of Glass Eels, and, with approximately 4,000 Glass Eels to a kilo, that’s about 150-200 million Glass Eels coming from the wild.
Rather than the overall numbers, it is the speed of decline in population that has contributed to the European eel’s categorisation as critically endangered.
While it is clear that the eel population needs careful management, it seems unlikely that they are close to extinction in the wild, especially given the eel industry’s interest in maintaining the population and the measures already put in place to help them recover.
Trade bans aren’t necessarily the answer
Importantly, the classification of critically endangered doesn’t necessarily mean that trade is prohibited. CITES (the Convention on International Trade in Endangered Species of Wild Flora and Fauna) places European eel on Appendix II of their monitored species lists, which means that trade is allowed if authorities are satisfied with measures taken to prevent detrimental effect of the trade to the survival of the species.
Indeed, the IUCN has recently warned strongly against trade bans on endangered species, explaining that sustainable trade is frequently a much more effective means of species recovery than a total ban. According to the organisation, trade bans often encourage illegal trade and remove incentives to protect populations. The example, in the article above, the IUCN’s discusses Selfridges’ ban of exotic leather goods from endangered crocodiles and snakes.
Why is the European eel population in decline?
There is no denying that the eel population has suffered a major loss as a result of human actions, but it’s not all what you might think. Dr Willem Dekker recently published a scientific paper that looks at the human impact on eel population over the last century.
It started as early as 1865
While overall catch figures point towards a more recent decline since around the 1980s, the actual decline in eel population started much earlier. As early as 1865 there were reports in France that “the eels that feed us have almost disappeared from our small waters”. This prompted the development of a national restocking programme between 1840 and 1879 to repopulate upriver marshes and streams.
The same decline was noted in Germany in 1881: “In a short time, eel fishing will have to be restricted if the eel is not to be completely out‐fished in our waters.” And by 1884 it was known that migration barriers were largely at fault. A scientist called Benecke advocated eel ladders for the region around Königsberg (now Kaliningrad, Russia) noting that eel migration had suffered as a result of water mills and other barriers.
Unfortunately despite this nascent concern for the eel population, a number of factors came into play towards the end of the 1800s and the early 1900s that put much greater pressure on the already declining population.
Eel, which had been appreciated primarily for its nutritional value rather than its taste, had always been a cheap staple food eaten by Europe’s poor. London’s Eel Pie & Mash Houses were a prime example from the early 1900s.
However, in the late 1800s a new process for hot-smoking eel appears to have been developed in the Netherlands. The earliest record we have of it comes from a Frenchman, Sauvage, who describes the process taking place in a Dutch village in 1881.
This had the effect of making eel much more palatable and elevating it from a poor-man’s staple to nobleman’s delicacy. Now eel could be eaten by rich and poor alike and Dutchman, Christiaan Saur, from Amsterdam wasted no time in developing this new luxury marketing, taking 148 out of 233 smoked eel ads in 1895 for his Dutch smoked eel.
Around the same time, improvements in transport systems (postal services, steamers and railways) meant eel could be transported on ice as far as from Lithuania to Paris, and people much further inland were able to develop a taste for it.
The development of commercial fisheries
The decline in upriver eel population and the sudden increase in demand for eel, required a significant change in the way eels were fished and the technology was there to facilitate that. Fishing gear was scaling up and such quick technological progress was being made that several international exhibitions were organised on the subject around the late 1800s, including the “Internationale Fischerei‐Ausstellung zu Berlin 1880”.
The fykenets used along the Baltic coasts grew in size from 22-29m in the 1870s to 150-600m by the 1960s and larger thereafter. New eel habitats were identified in larger bodies of waters such as lakes, coastal lagoons and estuaries. These had been largely unexploited until this point and most likely would have contained primarily silver eels starting their migration back to the Sargasso Sea to breed.
The combination of fresh habitats, larger-scale fishing gear and increased demand led to a surge in eels caught completely unsustainably.
In 1933 Röhler, general secretary of the all-German fisheries society, compared the catch volumes of traditional fisheries at water mills and fixed eel traps to the ‘new fisheries’ of his time. Where the traditional fisheries produced less than 250 tonnes/year, the ‘new fisheries’ produced more than 5,000 tonnes/year.
He concluded that; “during the last decades there has been a considerable intensification of the eel economy.” Unfortunately, the fact that such large volumes were being caught seemed to encourage fishers of the time, rather than raise alarm bells.
In 1910, while discussing options to develop eel fishery further, Walter, a nobleman and landowner, describes “an increasing depletion of the inland waters of eels” in Germany as if this is is merely a nuisance that requires finding alternatives.
Demand from Asia put pressure on Glass Eels
Eel fishing continued to develop into the 20th century with eel imports to Germany reaching 20,000 tonnes/year before the Second World War broke out. This was probably close to the total European eel catch and has only been repeated once since in 1968.
This over-fishing of mature eels in the early-to-mid 1900s was then compounded by the development of aquaculture in the 1980s, which required stocking with Glass Eels coming from the Sargasso Sea. Unprecedented demand from Asia to stock their own eel farms as the population of Japanese eel diminished, fuelled the development of aquaculture in Europe and encouraged direct trade of Glass Eels to Asia.
The FAO remarked on their current data set that the European eel is more abundant in the Uono River in Japan than the Japanese eel, and that in 2000 a migrating European silver eel was captured in the East China Sea.
Quite what happens to their migratory patterns if they have to start off in Japan or China, I’m not sure! That’s certainly a route I wouldn’t want to navigate. I would hope they follow the Japanese eels, but whether they can cross-breed isn’t clear. Given that European eels don’t eat on their migration to the Sargasso Sea, it is quite possible that they wouldn’t survive the extended journey from Asia, even if they could navigate it.
Increasing migration barriers are significant
Simultaneously the numbers of migration barriers, which were already recognised as causing problems in the 1880s, have increased dramatically.
Recently, the World Fish Migration Foundation’s project AMBER counted 1.3 million barriers in the rivers of Europe. Many waterways are literally covered with water pumps that are used to shift the water for agriculture and other human uses. Most of these pumps have no fish-friendly engineering.
In addition, Europe’s 25,000 hydro power plants do a very efficient job of mincing up the returning silver eels. This is a tragedy in itself, but if you consider that a large female typically carries 1-3 million eggs, its death has a staggeringly disproportionate impact on the overall eel population.
Climatic changes and pollution, which are often cited for species decline, are also contributing factors, but relative to the impact of increasing migration barriers, more effective fisheries, and continued demand from Asia, they don’t seem to play a major role.
The main factors in terms of climate change, are changes to oceanic currents the eels rely upon, changes in water temperature, pollution through PCBs and heavy metals, and apparently even cocaine in the River Thames!
So, can you get sustainable eel? And farmed v wild?
We’re nearly there! The answer you’ve been waiting for. I bet you didn’t think it would take this long to get there or that there was so much to learn about eels along the way. I certainly didn’t! But, there is one more surprise waiting for you before we look at the sustainable practices in place today and it is worth looking at it in detail.
The development of eel aquaculture gives consumers a false sense of security. There is an understandable misconception that farmed fish is a sustainable alternative to wild fish of the same species, because it can be bred on the farm and therefore (once stocked initially) has no impact on the wild population.
While this can be true in the case of some fish like sea bass, the environmental impact of different farming methods also has to be considered, and in the case of eels it is not even true that they can be bred on the farm.
The difficulties of reproducing eels
Part of the problem here is understanding, or rather, mis-understanding eel sex: Due to a quirk in the way that eels spawn, no-one has ever seen them ‘at it’ in the wild. For a long time it remained a mystery and much conjecture was made:
According to Aristotle, eels grew spontaneously “from the entrails of the earth”. Pliny the Elder suggested that “they rub themselves against rocks, upon which the particles they thus scrape from themselves come to life”.
And by the 17th century the ideas were no less fanciful. Writer, Izaak Walton, thought that eels could be “bred of a particular dew falling in the months of May and June falling on the banks of some particular ponds or rivers…which in a few days are, by the sun’s heat, turned into eels“!
By the 19th century one of the greatest British scientists, Sir Humphry Davy declared of eels that “the problem of their generation is the most abstruse, and one of the most curious in natural history”.
We were clearly flummoxed! It wasn’t until 1922 when Danish professor Johannes Schmidt managed to trace them back to the Sargasso Sea, that we at least knew roughly where they went to breed.
It appears that nowhere, but the depths of the Sargasso Sea will do. Talk about mood lighting…perhaps for eels the temperature, pressure, lighting, salinity and seaweed all need to be exactly right. If you thought your partner was awkward, they haven’t got an inch on an eel! And bringing up baby eels is apparently even worse…
In 1984 Russian scientists did manage to get European eels to spawn, but the larvae only survived four days. The Japanese have since been able to reproduce eels in labs, but not on a commercially viable scale.
I spoke to eel reproduction scientist Dr. Arjan Palstra about the difficulties of reproducing eels:
SD: Why is it only possible to get eels to spawn in the lab rather than on the farms? What kinds of conditions do eels require to spawn?
AP: We simulate the life cycle from glass eel to spawning eel in the lab with a series of tricks including feminisation, providing the right brood stock nutrition, simulated migration and hormonal stimulation. Thus far, European eel cannot be reproduced with environmental conditioning only but we are getting better and better in providing the right natural triggers and optimal maturation protocols.
SD: Why do you think we are still unable to get the European larvae to grow into adults?
AP: Last year we were able to produce 35 different larvae batches, so we have that under reasonable control. The current protocols are, however, still not optimal, resulting in inferior gamete and larval quality. A functional diet for larvae is still lacking. We are strongly encouraging the eel research community to collaborate to force scientific breakthroughs.
SD: I understood that eels die after spawning in the wild. Is this true of both the male and the female?
AP: We suspect that but we do not know for sure. The energy spent on migration and maturation would probably not demand immediate death but capacities to somehow resume feeding and switch back from the intense sexual maturation to growth stage does not seem realistic. There are however no recordings of massive amounts of dead eel carcasses, nor a live eel population in the Sargasso, nor recordings of large eels coming back to Europe.
SD: Do eels that spawn in a lab also die after spawning or are they able to survive to spawn again later?
AP: European eel may spawn more than once with up to some weeks in between. May be similar to Japanese eels that spawn at several new moons. We have observed oocyte batches maturing at different stages, we have spawned eels twice with 2-3 weeks in between, and eels could be kept alive after stripping the gametes for a long period, even up to one year. On the other hand, we also had eels that we could strip completely empty and they were often the most successful ones. Still, hormonally induced sexual maturation in the lab may not be the best reference for ecological questions.
All farmed eel was originally wild
What this means is that there is very little difference between wild and farmed eel from a sustainability perspective. All farmed eel was originally wild and has to be restocked from the wild so any eel farm that does not release a percentage of their silver eels back to the wild is very short-sighted indeed. Many farms today also restock their natural habitat with younger eels too, so what is fished in the wild could in fact be the result of restocking from farms.
Both wild and farmed eel are subject to fishing quotas. The main difference is that sustainable eel farms are required to restock a percentage of their catch and so wild eel fishing needs to be carried out on a much smaller-scale to limit the impact it has on the eel population. The use of more traditional fishing gear such as the fixed eel traps mentioned by Röhler in 1933 and used by Terry in Lincolnshire, can help to limit catches.
The unique challenges of sustainable eel fishing
The good news is that, given our reliance on the wild population for the eel we eat, it is in the interests of the industry to ensure its survival. Having said that, there are many more and many less sustainable practices out there, so it’s important to know what you’re buying.
The nature of eel migration and breeding presents several unique challenges for sustainable practices. The fact that eels appear to die after spawning means that it is impossible to only fish mature eels that have already had the opportunity to mate, as you can with other fish such as the John Dory.
You can tell the sexual maturity of a John Dory, by its size. If it’s small enough to fit on a plate, as has, sadly, been popular in Asia recently, it hasn’t reached sexual maturity yet.
For eels, however, whatever is fished will have a direct impact on reproduction capabilities. Moreover, the eel’s general disregard for hereditary citizenship, means that producing sustainable eel requires both international collaboration and traceability on a scale not often necessary for other species.
Sustainable Eel Group setting the standard for sustainable eel fishing
The Sustainable Eel Group (SEG) was set up in 2009 to help the eel’s recovery. It is a not-for-profit organisation governed one third each by science, conservation and commercial interests. One of its strategies is the creation of the SEG standard. This is to establish international guidelines for responsible practices in eel fishing, farming and processing and to create a closed chain of custody in which clear traceability could be secured.
Like many conservation organisations across Europe, SEG also collaborates on projects to improve habitats and migration to help increase the eel population. SEG is a community member of the ISEAL Alliance, the independent global membership association for credible sustainability standards and is seeking full membership to recognise its aims, achievements and the SEG standard.
It is natural to start by trying to determine the maximum sustainable yield, as defined by the OECD (the Organisation for Economic Co-operation and Development) as “the largest long-term average catch or yield that can be taken from a stock or stock complex under prevailing ecological and environmental conditions.” This will allow the authorities to set the total allowable catch, or fishing quotas.
According to the SEG however, for a species in decline, and for one so widely distributed, poorly understood and fished at many life-stages, it is not possible to establish this until the species shows signs of recovery and can be regarded as biologically safe. Being able to determine this for the eel requires a much better understanding of their population dynamics than is currently available from existing measurement systems.
The scale of the problem can be easily understood when looking at the extent of the natural eel habitat and the variety of laws, technological resources, and cultures it covers.
To have any real meaning, quotas for eel fishing would have to be based on fully transparent, globally coordinated data and apportioned fairly across the entirety of the eel habitat. Needless to say, we are some way off achieving this, but at least we have made a start.
Dealing with illegal Glass Eel trafficking
The focus for the SEG is on securing international traceability and means of measurement. This has become particularly important since the ban on exporting Glass Eels outside the EU in 2010, since the sheer size of the Asian market and their continued demand has led to a highly profitable illegal trade.
China has 900 eel farms and they produce approximately 200,000 tonnes/year compared to Europe’s 6,000. According to the SEG and figures from Europol an estimated 350 million European eels are trafficked annually to supply Chinese eel farms. Joost Blom concludes in his interview on the Fish Site:
“One challenge that does need to be addressed is the illegal export of glass eels to China. With shortages of Japanese and American glass eels and record prices, the demand from China for glass eels is huge. Organisations in Europe earn millions by trafficking eels to Asia, and each year some of them are closed down. But with huge profits to be made it is difficult to put an end to it.
The eel industry, therefore, is a strong supporter of more transparency and full traceability in the glass eel trade. The SEG standard will prove to be very important: because of the full transparency of this standard throughout the supply chain (chain of custody), trafficking will be minimised in the future so the European eel stays where it belongs – in Europe.”
The SEG makes three suggestions to counter this trade and increase traceability:
1) Implement a European-wide electronic system that ensures full traceability of all eel trade. This would require all those in the legal supply chain from fishery to retailer to enter their catches and sales into an electronic recording system, so that all movements can be monitored and illegal movements more easily detected.
2) Genetically test all Anguilla imports into the European Union. There is evidence to show that European eels, which were trafficked from Europe and then farmed in Asia return to Europe as ready-t0-use eel products without CITES (the Convention on International Trade in Endangered Species of Wild Flora and Fauna) trade permits. This violates the European import and export ban for European eels as well as CITES restrictions. Genetically testing all eel imports would enable us to gain an understanding of how much eel imported from Asia is in origin from Europe and enforce the CITES restrictions.
3) Increase enforcement to ensure that eel fishery and trade is sufficiently controlled. The illegal trade of European eels to Asia is currently by number of animals (around 350 million) and perhaps also by value (estimated at £2-4bn) the most significant wildlife crime on the planet. Ensuring proper protection will likely require additional resources, but would have a major impact. In the last six months 11 people in France have been imprisoned and hopefully this will deter others.
Helping eels overcome migration barriers
In the meantime, great headway has been made with restocking programmes. The European Commission Eel Regulation requires that 60% of all glass eel catches must be restocked in waters with low eel populations and only the remaining 40% can be used for consumption mostly through the stocking of eel farms.
Whilst that is the law, it is often not properly enforced and therefore not met. The SEG Standard is awarded only whose in the supply chain can show that they meet that target. The UK is leading the way on this front. Andrew Kerr, chairman of the SEG, told me that currently only the UK regularly demonstrates 60% is achieved, while in France only one river, the Vilaine, is meeting the target with a large number of glass eels, intended for restocking, used instead for consumption or illegal trade.
Additional projects run by the Dutch and German Eel Stewardship Fund, which is largely funded by the commercial sector, help eels overcome barriers and avoid huge pumps and turbines while migrating up and down rivers.
This can involve the trap and transfer of eels in both directions, but in increasing numbers across Europe eel ladders, like the one at Windermere, are being fitted to weirs to enable elvers to make their way upstream of their own accord. Eel producers that contribute to the Eel Stewardship Fund are allowed to display the ESF logo on their packaging.
While it is clear that much of the eel trade still needs to improve its sustainability record, the SEG is providing a clear framework for responsible fisheries to demonstrate their traceability and sustainability, while putting pressure on others to follow suit.
In light of the IUCN comment on supporting sustainable practices rather than banning trade of endangered species altogether, it seems sensible to support those responsible fisheries who have gone to the trouble of supporting the recovery of the eel and and getting themselves accredited with SEG.
Indeed, as Norbert Jeronimus of the Dutch Sustainable Eel Foundation pointed out to me, if eel farms work according to the SEG standard and ESF rules, they will restock more eels into carefully chosen natural habitat, where they have the greatest chance for successful return migration, than they use for farming and can therefore have a net benefit on the overall eel population. According to Andrew Kerr of the SEG 30-50 million eels are released in this way each year.
Questioning the ban on Glass Eel exports
It may even be worthwhile questioning the efficacy of the current EU ban on glass eel exports relative to achieving greater transparency. Not only has this created a substantial illegal trade of glass eels that is difficult to monitor, but it has also shifted East Asian attention to eel habitats outside the EU, such as North Africa, where sustainability standards tend to be less well regulated.
Below is a visual representation of some of the key stats relating to the Glass Eel trade, as quoted by the SEG in their report on eel trafficking.
What I think this shows is that the demand for Glass Eels from within Europe is significantly lower than the current production and that, given the number of livelihoods that clearly depend on external trade currently, it is going to be difficult to completely prevent trade with Asia by banning it.
It is also clear that we don’t have the full cooperation of the French as the main producer of Glass Eels (75% of total production), if their annual quota for Glass Eel fishing is double that of the total demand for Glass Eels in Europe.
Traceability is clearly key to achieving sustainability for eels, so perhaps an approach that established traceability while reducing overall catch volumes/ensuring restocking without limiting trade at least initially would be more effective.
The fact that eel is classified as critically endangered does not mean that there aren’t any sources of sustainable eel and that eating eel is necessarily irresponsible. In many ways eating SEG accredited eel, especially if the fishery also funds the ESF, can have a positive impact on the recovery of European eel as a species.
And many of the most responsible fisheries are based in the UK. Your support of SEG and ESF for the sustainability of eel will help them establish greater transparency across the eel supply chain and, in the long-term, protection from international over-fishing.
Should there be a scientific breakthrough that enables eels to be bred on farms, I would hope that eel farms continue to be held to these standards. It is possible that a certain percentage of eels bred in captivity could be released to breed in an effort to speed up the recovery of the wild eel population, but there is currently no evidence to show that eels grown in captivity would know to return to the Sargasso Sea to breed.
So if you are looking to source eel sustainably, look out for the SEG and ESF logos.