Team:CLS CLSG UK/Description

Project Description

Project Description

Currently on the IUCN red list as critically endangered, the European Eel’s population decline has been sharp and devastating. With a population between 2-10% of what it once was merely 20 years ago, the European Eel (Anguilla Anguilla) population shows the steepest downwards trend of any freshwater fish species[1].

Eel Life Cycle

Born in the Sargasso Sea as tiny larvae, less than 10mm in length and willow shaped, these tiny organisms join the gulf stream and get dragged towards the waters of Europe. This journey can take up to two years, after which they metamorphose into glass eels[2]. They are now far more cylindrical in shape but are still transparent and only about a finger in length; they get carried inland by ocean tides and upon reaching freshwater they begin to feed and pigment.

After reaching about 8cm they become elvers and will migrate inland, looking for habitat to grow and feed. This stage is known as the yellow eel stage, and will last the majority of the eels' life; they tend to reside in marshland where they will feed and avoid predation. They have a remarkably varied diet depending on the food available to them. They have even been known to trap water in their gills and then jump onto land to eat small mammals or to move into other neighbouring waterways and lakes. After a number of years, they will undergo their final metamorphosis into a silver eel. This change will see another colour alteration, an increase in muscle mass, the shutting down of the digestive system and increase in eye size upto 10 times their original diameter[3]. This final shift in the anatomy of the Eel is in preparation for one of the most fascinating and extreme migrations in the animal kingdom. As an animal that has lived in freshwater environments for the entirety of its adult life, the European Eel then swims across the entire Atlantic (the amount of time this trip takes is unclear but it can be many months or even years)[4]. This migration has never been observed or recorded in its entirety, with tracking being very difficult. However, a recent study of eels that were satellite tracked provided more information as to the specific route of this migration and also provided strong evidence that this 5000km migration across the Atlantic does actually take place[5]. It is also thought that throughout this migration, they do not eat, relying entirely on fat stores that have been built up. Upon arriving at the Sargasso Sea they breed (the methods by which this happens is also not clear). By all accounts, after making this extreme migration and successfully mating the adult eels die.

The practises of the eel are very peculiar. Unlike other fish, such as salmon, the eel breeds in sea water and lives most of its life in the rivers. This seems illogical due to the high amount of predation in the sea comapred to the rivers. As a result, it seems counterintuitive to reproduce in the ocean while living in the river.

Reasons behind population decline

As well as this, the migratory patterns of the eels means that they are very vulnerable to population decline. Living in both the ocean and rivers, the eels are exposed and vulnerable to global as well as local issues. There are various reasons for their severe population decline, the main ones being: physical blockages to migration, overfishing, climate change and heavy pollution (including from drugs).

Migration blockages

Across Europe there are 1172 large dams or reservoirs[6]. While in recent years this number has stayed relatively stable the impact it has on the river migration of the eel is very large. The dams can prevent large numbers of eels from being free to move upstream. As well as this, hydroelectric power stations can even kill the eels if they get caught in them. Furthermore, the reduction in marshland across Europe and the United Kingdom has reduced the ability for the Eels to move between small ponds and streams. This land is often converted so that it can be used for agricultural purposes or for residential or industrial uses. In all these cases the land can no longer be used by the eel population for development and growth but it now poses a barrier for their movement.

Overfishing

Globally, the eel used to provide both a luxury and basic food source, but in recent years it has mainly been considered the latter. In an attempt to stem overfishing and increase the falling population of the European Eel, a blanket ban on export and import of eels and derived products into and out of the EU was introduced in 2010. Despite this, it is still thought that 300 million eels were illegally exported to Asia in 2018 alone[7]. The market price of the eels is thought to be around £6500/kg, making the eels the ideal target for smuggling operations due to the high price and low size[8]. Since the ban, the numbers of arrests as well as seizures has been increasing, but the level of illegal smuggling still remains very high.

Climate Change

As greenhouse gas emissions increase, the effect it is having on our world is undeniable. The increase in CO2 emissions has three main effects on the aquatic environment and thus the European Eel. The first of these is the increase in water acidity, this has been shown to decrease the ability of the eel to navigate and so impacts its migration; the second is the increase in temperature which increases the mortality rate of young eels in the ocean and so decreases the chance of large numbers finding their way into the rivers; the third is the effect that the melting ice and the increase in temperature have on ocean currents. The Glass Eel population of Europe is reliant on the gulf stream and so as climate change continues to increase the path of this particular current and its reliability changes, as such the numbers of eels arriving from the Sargasso sea decreases[9].

Pollution

The pollution in major rivers around the world is undeniable and the effects this pollution can have on the ecosystems is enormous. Ranging from drugs, like cocaine, to antibiotics, such as ampicillin, the products that we are literally flushing into our rivers can be extremely harmful and even deadly to the wildlife already there. As alluded to above, most of these chemicals enter the rivers after passing through the sewer system where they are not properly dealt with. If the prevention of the effects that these substances have on the ecosystem is a priority the most efficient way to do this is through the examination and alteration of the sewer system.

Sewer system breakdown

The sewer system is complex and varied; it often changes from location to location depending on a whole host of factors. Having studied the different structures of sewer systems in detail, we have been able to create a simplified diagram that shows the main constituents of most sewer systems at home in the United Kingdom but also abroad.[10]

References ‌

While this diagram is greatly simplified, it demonstrates the basic principles and constituent parts of wastewater treatment.

Every day large quantities of pollutants pass through the sewers of major cities and nothing is done to prevent their release into the wider environment. One of these pollutants is the drug cocaine.

London is infamous for its cocaine problem. In the capital alone more cocaine is consumed each day than Berlin, Barcelona and Amsterdam combined.

The widespread and high levels of consumption has led to the idea that every £5 note has traces of cocaine on it. While this seems nearly impossible, the concept that up to 100% of bank notes are contaminated with cocaine has been backed up by numerous studies[11]. In the body, large quantities of the cocaine is not metabolised, but instead simply excreted. As a result, the inefficiency of breakdown, combined with the high levels of intake, means that the levels of cocaine in the influent flow of the sewer system can reach over 1000ng/L[12]. While some of this is removed in the normal treatment of the sewers, concentrations as low as 20ng/L can cause massive impacts upon the European eel[12]. More specifically, cocaine has been shown by studies to cause a disease known as rhabdomyolysis, involving the hyper constriction of blood vessels and starving muscles of blood supply. This results in muscle degradation, which in turn, prevents them from migrating back to the Sargasso Sea where they breed at the end of their life cycle (as explained above).

While infrastructure development and over exploitation is being relatively managed by local governments and environmental organisations (such as the Sustainable Eel Group in the UK) , the issue of pollution from major cities has remained relatively unchecked. As a result, our project aimed to solve this problem by placing genetically modified E. coli bacteria into the sewers in order to break down cocaine. Please see our design for further details on the specifics of how we performed this.

References

  1. Verreycken, H., Belpaire, C., Van Thuyne, G., Breine, J., Buysse, D., Coeck, J., Mouton, A., Stevens, M., Van den Neucker, T., De Bruyn, L. and Maes, D. (2013) IUCN Red List of freshwater fishes and lampreys in Flanders (north Belgium). Fisheries Management and Ecology 21: 122–132.
  2. Why the once common European eel is now Critically Endangered (and what can be done about it). (2019). Wwt.Org.Uk. https://www.wwt.org.uk/news/2019/06/14/why-the-once-common-european-eel-is-now-critically-endangered-and-what-can-be-done-about-it/17073#
  3. Life Cycle of a European Eel. (2020, April 14). Forth Rivers Trust. https://forthriverstrust.org/life-cycle-of-a-european-eel/
  4. European eel. (2017). NatureScot. https://www.nature.scot/plants-animals-and-fungi/fish/freshwater-fish/european-eel
  5. Aarestrup, K., Okland, F., Hansen, M. M., Righton, D., Gargan, P., Castonguay, M., Bernatchez, L., Howey, P., Sparholt, H., Pedersen, M. I., & McKinley, R. S. (2009). Oceanic spawning migration of the European eel (Anguilla anguilla). Science (New York, N.Y.), 325(5948), 1660. https://doi.org/10.1126/science.1178120
  6. Reservoirs and dams. (2018). European Environment Agency. shorturl.at/aexFU.
  7. Europol announces increased effort to stop European eel trafficking. (2019). Seafoodsource.Com. https://www.seafoodsource.com/news/environment-sustainability/europol-announces-increased-effort-to-stop-european-eel-trafficking
  8. Eel smuggling ring busted in Spain. (2018). Seafoodsource.Com. https://www.seafoodsource.com/news/supply-trade/european-agencies-arrest-group-suspected-of-smuggling-eels-worth-eur-37-million
  9. Climate change pushing eels in Europe towards extinction, study shows. (2019, January 30). The Independent.
  10. Troiano, G., Mercurio, I., Golfera, M., Nante, N., Melai, P., Lancia, M., & Bacci, M. (2017). Cocaine contamination of banknotes: a review. European Journal of Public Health, 27(6), 1097–1101. https://doi.org/10.1093/eurpub/ckx100
  11. Tchobanoglous, G., Stensel, H., Tsuchihashi, R., Burton, F., & N/A Metcalf & Eddy, Inc. (2013). Wastewater Engineering: Treatment and Resource Recovery (5th ed., Vol. 1).
  12. Munro, K., Martins, C. P. B., Loewenthal, M., Comber, S., Cowan, D. A., Pereira, L., & Barron, L. P. (2019). Evaluation of combined sewer overflow impacts on short-term pharmaceutical and illicit drug occurrence in a heavily urbanised tidal river catchment (London, UK). Science of The Total Environment, 657, 1099–1111. https://doi.org/10.1016/j.scitotenv.2018.12.108
  13. Capaldo, A., Gay, F., Lepretti, M., Paolella, G., Martucciello, S., Lionetti, L., Caputo, I., & Laforgia, V. (2018). Effects of environmental cocaine concentrations on the skeletal muscle of the European eel (Anguilla anguilla). Science of The Total Environment, 640–641, 862–873. https://doi.org/10.1016/j.scitotenv.2018.05.357