East Asia Eel Resource Consortium
Head Office: Atmosphere and Ocean Research Institute, The University of Tokyo
277-8564 Kashiwa, Chiba, JAPAN. Tel: +81-4-7136-6416, Fax: +81-4-7136-6227

Statement of the East Asia Eel Resource Consortium forthe protection and conservation of the Japanese eel
Emergency EASEC Symposium, 19 March 2012
Glass eel recruitment and standing stock of Japanese eels have continued to decrease sincethe 1970’s and appear to have reached a historically critical situation in recent years.
Very low levels of glass eel catches throughout East Asia since 2009 suggested a possible
collapse of the Japanese eel stock, or even endangerment of the species. The industry
depends on wild caught glass eels for seed for aquaculture along with imported glass eelsof other species, mainly European eels. Declines in recruitment of the Japanese eel andthe export ban on glass eels in Europe due the regulation of wildlife trade for conservation
purposes by CITES have caused a crisis in this industry. Artificial seed production of theJapanese eel has been experimentally completed in 2010, but many technical problems still
remain to be solved before it can be realized at a commercial scale. Therefore, we needto solely depend on the natural Japanese eel stock, at least, until the artificial production
technique is finally established. The Japanese eel is an internationally very importantaquaculture species in the East Asian region such as Japan, Korea, Taiwan and mainland
China. The East Asia Eel Resource Consortium (EASEC), established in 1998, has been
holding an annual meeting to share the latest information for the conservation andsustainable use of the Japanese eel. This year, however, due to the crisis of the Japaneseeel stock in the last 3 years, the EASEC had an international emergency symposium on 19
March 2012 in Tokyo to discuss a possible strategy for the conservation of the Japanese
eel as summarized below.
1. Present status of the Japanese eel
The fishery statistics of the Japanese eel, including glass eels, in East Asia are fragmental
and are not sufficient in duration or accuracy to enable scientifically based management ofthe species. However, drastic declines of total amount of glass eels stocked in eel culture
ponds in East Asia (from more than 100 tons until 2004 to 41 tons in 2010 and 35 tons in
2011, data from The Nihon Yoshoku Shimbun, Japan) strongly show a negative trend ofthe stock. Further, rapid decline in recent years suggests that the Japanese eel will follow
the case of the European eel listed in the CITES in 2007.
2. Possible causes of the population decline
Our knowledge on the spawning ecology of the Japanese eel has been advanced recently,
however, many uncertainties still remain for clearly understanding the causes of thedecline of the Japanese eel, due to its spawning area being located far offshore in the oceanand recruitment success being determined by complex interaction between biological andenvironmental factors. Based on the scientific information presently available, thefollowing factors that occur at different time scales are proposed as possible reasons forthe decline of glass eel recruitment:
A. Short-term time scales (within several years)
・ Increased larval mortality due to alterations of the offshore environment, a shift in thespawning season, and changes in the larval migration period.
1East Asia Eel Resource Consortium
Head Office: Atmosphere and Ocean Research Institute, The University of Tokyo
277-8564 Kashiwa, Chiba, JAPAN. Tel: +81-4-7136-6416, Fax: +81-4-7136-6227

・ An increased proportion of larvae being transported out of the species range each year,
due to southward shifts of spawning sites or shifts of the bifurcation latitude in thewestward flowing North Equatorial Current region.
B. Middle-term time scales (within decades)
・ Overexploitations of both glass eels in the estuary and yellow or silver eels in inlandand coastal waters.
・ Decline of the population due to degradation and losses of growth habitat such as
rivers and coastal areas.
C. Long-term time scales (within hundreds of years)
・ Gradual changes in climate as well as oceanic environments may have changed somecharacteristics of the species life history and/or species range.
3. Conservation Measures
The management plan for European eels through EU regulation that was initiated in 2009
(Report of the 2011 session of the joint EIFAC / ICES working group on eels), explainsthat implementation of protection and conservation efforts for catadromous fish that spawn
and migrate in the vast open ocean, like anguillid eels, is quite difficult. The oceanic
migration process of the adult Japanese eels is still not understood because it is certainly
influenced by environmental factors that act at the global scale. This means that if somefactors globally affecting the ocean-ecosystem caused the recent sharp declines of theJapanese eel stock, it is out of our direct control and there are no feasible measures at themoment to stop the main cause of the declines. We also have no way to compensate forfactors with geological time scales, and the only possible management strategy is to copewith factors with limited temporal and spatial scales. Furthermore, there are still many
uncertainties about the ecology of the Japanese eel even in freshwater. Population traits
such as habitat selection and sex ratio of the Japanese eels in their freshwater growthhabitats are characterized by the environment in which they occur, but the mechanisms ofthis are not well known. Artificial interventions for the purpose of conservation may
disrupt the ecological balance of the natural population. The East Asia Eel Resource
Consortium has considered these factors and has proposed the following precautionary
directives as conservation measures for the Japanese eel.
3-1. Regulation of the eel fisheryAfter glass eels recruit to their growth habitats, they spend 4-15 years until they grow andmetamorphose into the silver eel stage and begin their downstream migration forreproduction. To ensure that a certain amount of eels can become spawning eels eachyear, regulations on capture of yellow or silver eels in their growth habitats must be
urgently controlled to allow escapement of spawners. So we propose, at first, temporal
restriction of eel fisheries in growth habitats as well as recreational fishing that probably
capture a considerable amount of eels. Capture of silver eels during their fall migration
would be of the highest priority. Glass eel fishing should also be strongly restricted,
however, considering the situation in which we solely depend on natural Japanese eelseedlings for aquaculture until the artificial production technique is completely established,2

East Asia Eel Resource Consortium
Head Office: Atmosphere and Ocean Research Institute, The University of Tokyo
277-8564 Kashiwa, Chiba, JAPAN. Tel: +81-4-7136-6416, Fax: +81-4-7136-6227

glass eel collection needs to be allowed for a while under strict regulatory observation inrelation to scientific monitoring. Geographic and seasonal patterns of glass eel
recruitment are known to drastically vary. This suggests that glass eel fishing regulations
should be flexibly modified and applied based on the real-time scientific monitoring. To
facilitate such fishery management as well as to have accurate statistics, an official systemthroughout the East Asian countries is required, instead of local governments that
presently regulate these fishing activities independently. Scientific monitoring of glass
eel recruitment throughout the East Asia, such as the EASEC has been conducting throughthe Eel River Project, should also be expanded and utilized for the stock management.
3-2. Growth habitat conservation and restoration
Habitat conservation and restoration in coastal and inland water is strongly needed toconserve the Japanese eel populations and it must be implemented according to a masterplan suitable for ecosystems and human societies in and around the target area. Fish passmust be constructed at all artificial structures, which prevent movements of eels and otheraquatic animals. In the EU management plan, "eel ladders" were used to make it possible
for glass eels or young eels to ascend a dam that has no fish pass. This should berecommended for dams that are located close to the estuary that prevent many eels fromtheir upstream migration. The eel ladders are not preferably recommended though,particularly in upper parts of rivers with very limited habitats available for young eels
beyond obstacles. Further, the setting of the eel ladder must always be accompanied witha way for the returning silver eels to descend past the dam for their downstream migration
to reproduce.
3-3. Improvement of restocking techniques and encouragement of other measures
The release of eels from aquaculture production facilities into natural river systems for thepurpose of stock enhancement, or sometimes for fisheries, have been frequently conducted
for more than 40 years. However, its efficiency for stock enhancement has never beencomprehensively evaluated.
Recent ecological studies showed that demographic
characters of eel populations such as size composition, sex ratio and distribution pattern
are different depending on the environment in which the eels occur. Restocking needs tobe carefully conducted under the official and scientific plans to check its effect on stockenhancement and impacts on the natural eel population and the local ecosystems.
Transplants of newly recruited glass eels are likely acceptable because of less artificial
influence on the fish. On the other hand, increasing effort on aquaculture of eel species
other than Japanese eel A. japonica, artificial invasion of exotic species must becompletely prevented. We therefore strongly recommend to make standard protocols forboth restocking and identifying exotic eel species and also to encourage relatively secureand effective management measures such as regulations on eel fisheries, anti-poaching
patrol, ecological monitoring of eel populations, and conservation and restoration of their
growth habitat.

3