Canadian cod recovering, but it's tricky.

Sampled sea life

20 years after the cod fishery collapsed, it has recovered to 37% of normal.  Cod like to eat small forage fish. Taking too many cod allowed the smaller ones to increase nine-fold. Those multitudes, in turn, ate so many baby cod, the cod couldn't recover, even after the fishermen hung up their nets.  As usually happens, the forage fish population began to crash back to normal numbers, re-opening a niche for cod.  Rest of the story at Science Daily News