European eels must head to the sea in order to breed. We know that yellow eels can remain in our waterways for a very long time - eels have been aged at 85 years in freshwater - before the irresistible urge to migrate is upon them and the cycle starts afresh. They gradually turn into silver eels and start to adapt to a marine life whilst in freshwater. Their eyes and pectoral fins start to enlarge, their bodies become increasingly silver, and their behaviour changes. They develop an incredibly strong urge to migrate downstream. These migrations are often less than straightforward because of obstructions. There are other hazards too, they can become vulnerable to predators and water intakes.
Females and males are different sizes at the point of migration, the females being up to one metre long, males seldom being longer than 500mm.
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