There are some new fish in town, and researchers want to know where they came from. The fish are Atlantic salmon (Salmosalar L.), and the town is London—or, more accurately, weirs located in the River Thames at the boundaries of London. It’s hard to find salmon in the Thames these days, and it’s even harder to find untagged salmon, which likely originate not from restocking efforts but from the wild. If this is the case, it may mean that the animals are finally repopulating the Thames after having been extirpated from the river in the 19thcentury—an impressive feat considering that teams of conservationists have been unable to achieve this goal despite decades of efforts.

follow link for whole story----> 

http://www.science20.com/anthrophysis/salmon_river_thames_result_restora...