Endangered eel tracker found in Lihou

Friday 06 March 2020

Lihou Island is at the centre of a marine biology research project, after a data logger tracking the endangered European Eel washed up there during recent storms.

The island's warden, Steve Sarre, discovered a small orange data logger whilst clearing up waste that had come ashore after Storm Ciara.

Among the rubbish he found something that piqued his interest - a tracking device which appeared to have become detached from some form of marine life. 

Seeing that it contained contact details, Mr Sarre sent an email describing what he had found and the tracker's ID number. 

He received a response from Pieterjan Verhelst from the Marine Biology Research group at Ghent University, who explained that it was part of a wider project tracking the critically endangered species. 

Pictured: The pop-off data storage tag (PDST) that Mr Sarre found on the island. 

"In Belgium, we study the seaward migration of these animals, since not much is known about the species when they venture into the sea," the researcher said. "To fill the knowledge gaps, we attach data loggers on their back which record temperature and depth, and pop-off after a pre-programmed time."

The eel is the subject of ongoing study by the Belgian Lifewatch project, which serves as a "virtual laboratory" for biodiversity research. 

It says the eel, which has a wide distribution stretching from Scandinavia to Northern Africa, tends to grow in coastal and freshwater habitats but spawn at sea.

The assumption is that these are spawn in the Sargasso Sea, as the youngest eel stage has been observed in that area. 

These larvae drift with currents towards continental Europe and metamorphose into transparent glass eels once they reach the continental shelf, before settling in coastal and freshwater habitats, where they grow as yellow eels.

Pictured: European Eels show sexual dimorphism, with female silver eels (upper limit 93 cm long) growing much larger than males, which do not exceed 45 cm total length. Picture credit: Pieterjan Verhelst.

After a couple of years they migrate back into the sea as silver eels and start their migration towards the spawning grounds to spawn and die.

"Since the 1970s, the recruitment of the European eel has declined by 90 - 99 %, leading to the critically endangered status of the European eel under the IUCN Red List and resulting into the European Eel Regulation in 2007," the website says. "The latter states that all European member states need to take management actions to restore the population."

The project was set up to better understand the eel's ecology using acoustic transmitters and pop-off data storage tags, which is what was discovered on Lihou Island.

The tracker found by Mr Sarre is one of only a hundred to be discovered and sent back to Mr Verhelst to date.