http://earthsave.org/news/fishwhat.htm
As vacuuming fish from the sea has grown easier and fleet sizes have ballooned, fishers have achieved the once unimaginable—they've begun to strip the seas of their genetic wealth. Industrial innovations permit fishers to scoop an astounding 80 to 90 percent of a given fish population from the ocean in any one year.[10] Individual species have been ushered to the brink of extinction, and predator-prey relationships that evolved over millennia have been grievously disrupted.[11]
There's more. As preferred species are overfished and lose commercial viability, fishers switch to less-desirable species lower in the food web. This robs larger fish, marine mammals and seabirds of food, creating additional havoc.[12] And since less-palatable species earn fishers less money, they must catch more of these fish just to maintain their incomes. Where will it all end?