Decline of Japanese eels

The Japanese eel Anguilla japonica is a catadromous migratory fish that spawns in the open ocean northwest of the Mariana Islands and grows in the rivers, lakes and coastal waters of East Asia. In the three decades from 1982 to 2012, catches of glass eels used for farming fell by 93% and catches of eels in rivers dropped by 91%. In February 2013 the Ministry of Environment designated this species as Endangered (EN) and in June 2014 the International Union for Conservation of Nature (IUCN), which manages the global Red List of Threatened Species, designated it as the same level as the MOE’s ranking. The Japanese eel is without doubt facing the serious risk of extinction.

Three major factors possibly contribute the decline of the Japanese eel; changes of ocean environment, over exploitation, and the anthropogenic changes of growth habitats such as the rivers, lakes and coastal waters. The changes of ocean environment can have critical impacts on their spawning area and larval transportation, since they are born in the open ocean and passively carried by currents to their growth habitats.

As for over exploitation, present-day technology does not enable the cultivation of eels for food from artificially spawned eggs. Eel farming therefore entails catching and raising wild young glass eels born in the open ocean. But with any kind of animal, excessive consumption by humans leads to a decline in its population.

The environment of rivers and coastal waters in East Asia, growth habitats of Japanese eels, has changed significantly over the last several decades. Fresh and brackish water ecosystems are currently in a critical condition having been hugely impacted by floodplain wetland developments, the construction of structures across rivers such as dams and estuary barrages, the revetment upgrade, eutrophication caused by human sewage and agricultural drainage, alien organism invasion, and so on. Human activities are in response to various societal and economic demands of the times, which in itself should not just be rejected. Nevertheless, we do need to take account of the great impact these human activities have had on aquatic ecosystems.

Measures deemed necessary

The measures required for the recovery of Japanese eel stock are (1) fisheries management, (2) conservation and restoration of the habitat environment, (3) proper monitoring, and (4) information sharing throughout society.

Trial fisheries management led by the Ministry of Agriculture, Forest and Fisheries is underway, but it seems that achieving effective measures will take more time. In addition to the high economic value of eels, irregular channels of distribution are growing. Furthermore, allowable catches are difficult to calculate because stock and catches cannot be accurately determined. Proper fisheries management is undeniably difficult, but without it the sustainable utilization of Japanese eels will never be achieved.

Measures are also essential to conserve and restore the environment of the rivers and coastal waters where the eels spend their growth phase. It is important to increase the number of rivers that eels can enter, by removing any unnecessary estuary barrages and dams and fitting the necessary ones with fish passes. Also, reintroducing complexity into river environments that have been simplified by river straightening or revetment construction will enrich the whole ecosystem of the water and ensure sufficient living matter for the predatory Japanese eels to feed on.

In concurrence with fisheries management and the conservation and restoration of rivers and coastal waters, it is important to verify the results and impact through monitoring. We still do not fully understand nature. It is quite conceivable that some well-meaning measures may produce unexpected results. In fact, releasing eels in order to replenish their stock was found to have introduced the non-native European eel into rivers throughout Japan. Constant monitoring of results is needed alongside an adaptable management approach that is flexible enough to make corrections according to circumstances.

Promoting these measures will require strong leadership from the government. And it is only citizens who can elicit such strong leadership from their government. What stakeholders concerned with eels, including consumers of eels, need in order to be able to clarify their opinions is accurate and sufficient information. What is required of researchers is not only to gather necessary knowledge through surveys but also to actively disseminate that knowledge and encourage information sharing throughout the whole of society.

Social sustainability and eels

The problem of dwindling eel stock is not limited to the Japanese eel. The European eel, for example, which has been consumed in large quantities in Japan since the 1990s, is currently designated as Critically Endangered (CR) on the IUCN’s Red List, its highest rank, and is listed on Appendix II of CITES (making an export permit a requirement for its international trade), the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention.

When we think about the environment of rivers and coastal waters, it is not only eels that are affected by dams, estuary barrages and riverbank reinforcement works. Many other aquatic organisms are also impacted by human-induced environmental changes. Improving the environment of rivers and coastal waters for eels will help to restore the health of these ecosystems.

Can we utilize our limited resources sustainably, and can we achieve economic development while maintaining the integrity of the natural environment? The decline of the eel should be addressed as an issue not only of food culture but also of the sustainability of our society.

Note: In this article, I use the term “Japanese eel” when referring to Anguilla japonica and “eel” when including other species too such as the European eel or the Giant mottled eel.