Today the Japanese consume around 100,000 tons, or 70 - 80 per cent of the worldwide eel catch, but in 2013 the Japanese Ministry of the Environment designated the fish as a species at risk of extinction, and in June 2014 it was placed on the International Union for Conservation of Nature (IUCN)'s Red List of Threatened Species.
In Japan, aquaculture is extremely important to the eel industry's success, with most eel caught in the wild as juveniles and then raised on fish farms. However, the overfishing of juvenile glass eels has now become a huge problem.
Fed on a diet of fishmeal and kept in fossil-fuel-heated greenhouses, eel are usually collected along the Pacific Coast between December and April and put into tanks where their chances of survival are improved thanks to heating apparatus that helps increase water temperature particularly during the winter, and a circulating filter system in which water is filtered and re-circulated.
Ponds or specialised tanks are then used to grow the eels in temperatures of around 23oC - 28oC, after which regular grading takes place in which the eels are separated according to size and harvested once they are large enough to have reached market value.
However, despite the existence of eel farms in Japan, breeding the fish is extremely difficult because its physiology, spawning behaviour and life history are not yet well understood.
Various studies are underway to address this, such as a set of hormone treatments that include a sex change (most farmed eels are male). Although the result is a supply of fertilized eggs, there are some risks involved such as stressing the fish with repeated shots.
According to the FAO, the Japanese eel market is nearly saturated but there is potential for expansion elsewhere such as in South Korea and Europe. The eel market has been shrinking somewhat, and large quantities farmed in Japan still remain in domestic as well as in Chinese and Taiwanese fish farms.
In 2014, Japan, China, Taiwan and South Korea drew up the first international attempt to manage and control Japanese eel stocks by agreeing to set limits on the amount of glass eels farmers can procure.
Under the agreement, eel farms must register with Japan's Fisheries Agency so the Agency can monitor their glass eel purchases and shipping volumes (Japan's annual limit for the procurement of glass eels was set at 21.6 tons).
Meanwhile in April 2015, the Fisheries Agency introduced a licensing system for eel farming in which eel farmers must obtain permission from the fisheries minister to farm Japanese eel.
The Agency is also aiming to promote resource management measures at home and abroad, and is aware of the need to further tighten the surveillance of trade in eels.
However, although significant action has been taken, problems still remain such as poaching and black market trading of glass eels that could threaten the effectiveness of the new regulations.
Efforts to protect wild eel resources must continue and it's crucial not to be entirely dependent on any future success of artificial propagation. Whether the Japanese allow eel, tuna or other species to disappear or take action to save these species from extinction depends on how sustainably the species are harvested.
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