Why are oysters so important to the sea environment?

These oysters are taking an epic journey.

They're going from Loch Ryan in south-west Scotland down to Spurn Point in Humber in Yorkshire.

The journey takes 6 hours and 200 miles but why do they have to move?

Well the Humber used to have lots of oysters of its own but with too many being caught, they've now become almost extinct in this part of the country.

But the shellfish play a vital role in keeping the water clean.

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