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Q&A Biodiversity and Us

Eels

According to the old Japanese calendar, the days of the ox (doyo no ushi no hi) in the summer of 2015 are 24 July and 5 August. Having eels on the days of the ox has been a summer event in Japan. However, poor catches of young glass eels and price increases have been frequently reported recently. In February 2013, the Japanese Ministry of the Environment officially designated the Japanese eel (Anguilla japonica)as an endangered IB species on the country's Red List. And in June 2014, the Japanese eel was also added to the Red List of endangered species by the International Union for Conservation of Nature (IUCN). If the Japanese eel were also listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), effects on the Japanese lifestyle and related industries would be inevitable as Japan is highly dependent on the import of glass eels, and processed and unprocessed eels. Can Japanese continue to eat eels in the future?

Prof. Kenzo Kaifu of Chuo University who has conducted research on this topic answered our questions.

Questions answered by: Kenzo Kaifu
Assistant Professor, Faculty of Law, Chuo University
Member of the Anguillid Specialist Sub-Group (ASSG) of the International Union for Conservation of Nature

Q1

Why has the population of eels decreased?

A

Changes of the marine environment, overfishing, and the environmental degradation of habitats in rivers and coastal waters are considered to be the major reasons. However,the relative influences and interrelationships among the three factors have rarely been elucidated.

 

(1) Changes of marine environment: The Japanese eel spawns in the northwest open sea area of the Mariana Islands, and glass eels come to East Asia by being swept by currents. Accordingly, changes of the marine environment greatly affect the survival of glass eels.

(2) Overfishing: As it is still difficult to conduct artificial spawning and incubation of eels with present technologies, glass eels are captured in rivers and raised in enclosures (aquaculture ponds). Grown eels surviving in rivers or coastal waters are highly prized as “natural eels” and are fished as well.

(3) Environmental degradation of habitats in rivers and coastal waters: Surviving glass eels grow in rivers or coastal waters near river mouths in East Asia. However, rivers and coastal waters have been greatly damaged due to human activities. Recent research investigating 16 rivers in South Korea, Taiwan and Japan reported that 76.8% of effective habitats for the Japanese eel have been lost during the last 4 decades. Therefore, it is considered that the environmental degradation of habitats is strongly related to the population decrease of Japanese eels.

Q2

Why is it difficult to conduct artificial reproduction of eels?

A

The principal reason is the location of the Japanese eel’s spawning sites; they are located in the outer sea. Therefore it is very difficult to artificially create an environment for the Japanese eel to grow soundly. It is said that the commercial use of the artificial reproduction of eels might be realizable due to the efforts made by researchers and technologists, but there is no clear idea when it will be realized, whether in a few years or in decades.
Artificial reproduction technology would be a great contribution to the industry, but it would not directly solve the problems of the Japanese eel. The success of artificial reproduction would only be effective for a part of overfishing, the glass eel catch. Furthermore, if artificial reproduction is realized, it is quite unlikely that the prices of cultured glass eels will be cheaper than natural ones.
Recently, it is not unusual for the transaction price of glass eels to be more than 2 million yen/kg, but 20 years ago, it was about one tenth of this. As glass eel capturing is easy and costless, it is possible to lower prices when necessary. On the other hand, improvements of technologies and facilities are required for reducing the production costs of artificial reproduction. Man-made glass eels can only be supplementary for the shortfall of natural glass eels. Even if the commercialization of artificial reproduction technologies were successful, it is essential for humans to conduct fisheries management of glass eels with a high degree of responsibility.

Q3

What are the measures necessary for recovering the Japanese eel population?

A

It is essential to manage the fisheries including of glass eels and grown eels, and restore the habitats in rivers and coastal waters.
Among the abovementioned three factors related to the decrease of the Japanese eel, humans can only directly mange fisheries and the environmental management of rivers and coastal waters. Regarding fisheries, it is important to set upper limits for appropriate fish catches, and we should comply with these. If accurate upper limits for catches can be set, people dealing with eels can fairly and squarely practice their trades. Consumers can eat eels free from anxiety.
The environmental restoration of habitats in rivers and coastal waters is a bigger and deep-rooted problem. As the environment has been greatly degraded, a longer time and greater efforts will be necessary in order to restore the environment to a level to maintain a sound population of Japanese eels. In addition, the deterioration of the environment must be having adverse effects not only on Japanese eels but also on aquatic organisms. We have to take measures as soon as possible both for the Japanese eel and all other organisms in water ecosystems.
It is also important to aim at achieving a wide range of consensus when considering the measures. For example, it is not possible for science to present reliable threshold percentages for fish catches in order to switch the population from decrease to increase. Therefore, regarding which measures are to be taken, justification based on social consensus is necessary for the decision-making. It is also important to discuss with East-Asian countries where the Japanese eel is distributed. Appropriate discussions will be an opportunity to enhance peaceful relationships and collaboration among East Asian countries. The sustainable use of resources, conservation and restoration of the environment, and collaboration among adjacent countries are the keys. The eel problem containing various elements is one where we should create a sustainable society.

Thank you very much, Prof. Kaifu.

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