Friday, 13 June 2014

Japanese Eel classified as Endangered.

The International Union for the Conservation of Nature published its annual update of its Red List of Threatened Species on Thursday 12 June 2014, marking the 50th year of the list's existence, and revising the status of a number of Plant and Animal species from around the world. The Japanese Eel, Anguilla japonica, has been included on the list for the first time, being believed to have lost over half its spawning population in the last 30 years, primarily due to overfishing. 

A Japanese Eel, Anguilla japoonica, in Hong Kong. HT Cheng/iNaturalist.

While named for Japan, the species is quite widespread, being found from Korea and Japan in the north, along the coasts of China, Taiwan and Hong Kong to the Philippines in the south, as well as sometimes being found in Thailand, Vietnam and Cambodia. However recent studies have shown that all the Eels across this range form a single population with a common breeding ground, to the west of the Mariana Islands. The Eel is also widely bred in captivity, with waterways stocked from captive-bred Eels across much of its range. However it is far from clear if these captive-bred Eels are capable of returning to the wild spawning grounds, and thereby contributing to the future of the species. 

The known range of the Japanese Eel, Anguilla japonica. ICUN Species Survival Commission.

Like most Eels the Japanese Eel has a complex life cycle, with adults migrating to breed at an oceanic breeding site remote from the land, and an ocean-going larval stage that migrates back to estuarine waters before metamorphosing into a juvenile that takes several years to mature to a full adult. Unusually the Japanese Eel seems to have two separate post-metamorphic lifestyles, with some juveniles migrating into rivers and other fresh water ecosystems to mature, while others remain in shallow marine waters around the coast. However all these Eels appear to be a single breeding population. 

The single breeding site for the species, combined with heavy levels of human consumption of all life-stages across its range, and uncertainty as to the extent to which each adult population contributes to the breeding population, together with the risk of the breeding cycle being disrupted by climate-change driven changes in ocean current, lead to a considerable degree of concern about the future of this species.

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Eels first appear in the fossil record about 100 million years ago, in the Mid Cretaceous. These Cretaceous forms are primitive compared to modern forms, with incomplete fusion of the dorsal, caudal and anal fins, scales on their bodies and many of the bones lost or fused still present. However they are still clearly eels, with elongate bodies and the loss and fusion of some bones associated with the group, in...


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