India, Oct. 21 -- We all have made a seemingly smart choice at the time that later turned into a headache. Sweden did something like that in the 1960s. It brought in the signal crayfish, a species introduced to support fishing. According to the Swedish University of Agricultural Sciences (SLU), the move proved catastrophic for the native noble crayfish. Native populations have dropped by a factor of four since the newcomer arrived, and the newcomer carries a disease that is deadly to them.

The signal crayfish did deliver on fishing. It has provided good fishing opportunities in southern Sweden, and built fishable populations in lakes Hjalmaren and Vattern. Commercial catches there have increased sharply, mostly because there is more fish...