Creative commons imageCredit: Work found at http://en.wikipedia.org / CC BY-SA 3.0 This week Saving Species looks at freshwater eels and Chinese mitten crabs.

Both American eels (Anguilla rostrata) and European eels (Anguilla anguilla) migrate to the Sargasso Sea to spawn, and although thought to be different species, both behave in the same way in terms of their lifecycles; migrating between ocean and river systems.

Due to this they both also face the same threats albeit in different parts of the world such as sluices, hydropower dams and commercial fishing.

Another threat comes in the form of flood prevention measures which impede on the eel’s migration routes into the river as very small glass eels and then again when swimming back out to sea some years later as silver eels on route to spawn in the Sargasso Sea.

The Chinese mitten crab (Eriocheir sinensis) first arrived in Europe nearly a century ago and since then has damaged river banks and invaded numerous waterways.

Named after the soft bristles covering its large claws, the mitten crab is native to Asia, migrating up to 1,500 kilometres along some rivers.

In the right conditions mitten crabs can spread rapidly, helped by their ability to leave the water, cross dry land and enter a new river systems.

Levels of mitten crabs in the UK did not at first expand like in mainland Europe but numbers are currently rising causing concern for many.

Also in the programme:

• News from around the world with regular news reporter, Kelvin Boot
• An update on the activities of the Open University's iSpot. A new iSpot app has been launched, making it possible to photograph wildlife, upload it to iSpot and get help with identifications while you’re still out in the field.

Listen to Saving Species

You can listen to this episode of Saving Species on BBC Radio 4 at 11:00am on Tuesday 29 January 2013. More information and a link to listen again can be found on the Radio 4 website.

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