Claire Corlett

Fish Food, Fish Tanks, and More
eel migration gaua

eel migration gaua

In early 2012 the Austrian scientist Robert Schabetsberger has spent 6 weeks on a South Pacific island. He has been sent half-way around the globe by the Austrian Academy of Sciences to help solve an old enigma in biology. To find the unknown spawning grounds of Pacific eels. They live in freshwater and migrate thousands of kilometres into the ocean for spawning. With modern technology scientist around the world are currently trying to follow their tracks. Many eel stocks are endangered. This research work will help to protect these enigmatic creatures. Approach to the island of Gaua in the South-West Pacific. The bush-pilots skilfully land the small plane on the grass runway. Our international team of biologist has brought 200 kg of equipment. We are cordially received by our host family. Our target is Lake Letas. The active volcano Mount Garet towers over the lake, which harbours many eels. We can only drive a few kilometres of bumpy road. Then all the equipment has to be carried. The local soccer team comes to our aid. We are not yet adapted to the tropical heat and the high humidity. After a three hours hike we reach the lake. Gaua belongs to the island nation of Vanuatu. Lake Letas is the largest volcanic lake in the South Pacific. On the next morning we paddle the outrigger canoe to the deepest point of the lake. We measure exactly 100 m depth. Water samples are taken to describe the eel habitat. They are instantly analysed in our jungle laboratory. For the first time we try to catch eels with our electrofishing machine. Not long, and the first eel is caught. The eels are anaesthetized with a substance related to heroin. They can grow to a size of more than two meters. Studying the dentition and the body proportions helps us to determine the species. We discover two different species in the lake. After the examination, the eels are released back into the lake. To reach the ocean, the eels have to surmount a big obstacle when going down the only outflowing river. They have to take a header down Siri Falls, to reach the ocean. They migrate thousands of kilometres to their spawning grounds presumed to be within the South Equatorial Current. Nobody knows the exact location. From a distance we can hear the thundering water fall. It is hard to believe that the elvers can surmount the wet, mossy rock face besides the water fall to reach Lake Letas. After several years in the lake they go over the 120 m high cascade. Only five kilometres separate them from the mouth of the river. From now on we want to follow their spawning migration with satellite pop-up tags. During the migration the tags store information about temperature, depth, and light conditions. The local fishermen have caught seven emigrating eels within the lower stretches of the river. Only for a few minutes are the animals unconscious. The tag has to be attached fast and precisely. A single tag costs 3000 Euros. The tag detaches after a pre-programmed time and surfaces. The stored information is sent to a network of satellites. From there it is transmitted to receiving antennae on earth. On a motorboat we take the tagged eels out into the open ocean. Too many hungry sharks would be waiting within the reef. Finally the moment of truth has come. The eels are released. They descend instantly into the deep blue. Hopefully they will lead us to their spawning grounds. In about one month the tags will surface. Then we will know more.

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