From myth to reason – Population structure and spawning area(s) of Pacific eels

Freshwater eels have fascinated both scientists and the general public because of their long migrations to mysterious offshore spawning areas, most of which are still unknown. A steep decline in stocks of economically important temperate eel species, such as the European (Anguilla anguilla), American (A. rostrata), and Japanese (A. japonica) eels and their recent Red listing of the International Union for Conservation of Nature as critically endangered or endangered will now intensify the demand for eels from undisturbed tropical populations. Locating the spawning areas of Pacific eels is a vital step for understanding their life cycles. After two years of tagging silver eels (giant mottled eel A. marmorata, Polynesian long-finned eels - A. megastoma, Polynesian short-finned eels - A. obscura) from Vanuatu with pop-up satellite archival transmitters (PSATs), a potential spawning area (460 x 250 km; 812S, 170175E) has been discovered in the western South Pacific (WSP) at the border of the South Equatorial Current and the South Equatorial Counter Current. Our genetic studies showed that A. marmorata and A. megastoma hybridize and thus spawn in the same area. A salinity maximum at eels upper nighttime migration depths (150 m) was discovered and may serve as a landmark to help eels locate the spawning area. We propose to sample the three Pacific eel species at three different locations throughout the WSP (Bougainville Island, Papua New Guinea; Gaua Island, Vanuatu; Upolu and Savaii Islands, Samoa) and study population genetics and screen for hybrids and backcrosses among eels, tag silver eels with PSATs to follow them to their spawning areas in the WSP, and explore the oceanographic conditions at the pop-up locations to potentially find landmarks that eels could use to find their spawning area. In addition, the results of the tagging campaign will be used to guide the search for larvae on board the Japanese research vessel Hakuho Maru scheduled to search for eel spawning areas during the same year. This will provide a unique opportunity to adjust the sampling grid for leptocephali to include our pop-up locations. This would be the first time that tagged silver eels would guide ship-based oceanographers to potentially discover a new spawning area. Until now, it had taken more than 20 years of intensive survey work to locate the spawning areas of European and Japanese eels. Once the spawning area has been found, the early life histories of eels in the ocean can be studied using ocean circulation and larval dispersal models.

The project leader works as a free TV Journalist for the Austrian Broadcasting Corporation (ORF). A 48 min documentary on the mysterious migrations of eels has been produced for ORF Enterprises: The Eels' Mysterious Journey The eels on the tropical South Sea Island of Gaua live in paradise, safe in a deep crater lake that is fed by an active volcano and full of freshwater shrimp. But in order to reproduce, they have to get to the sea. They have to run the gauntlet. After a 120-metre dive over a waterfall, they face fishermen with metal hooks, keen to spear them and drag them out of the river; hungry sharks lurking on the reef; and an exhausting migration of nearly one thousand kilometres into the blue expanse of the South Pacific, 800 m down, in icy temperatures and without food. The survival of these migratory fish hangs in the balance. No one knows what the tiny eel larvae eat in the sea and so they can't even be bred in the laboratory. German version: https://vimeo.com/388990431 The field work in Samoa has been broadcasted in Salzburg Heute (ORF): https://vimeo.com/386237158