The environmental friendliness of shrimp trawling?

I’ve been setting up MythTV, and my test show was an episode of “Dirty Jobs” which I am watching now. The process for shrimp trawling is the current victim, and it seems to involve grabbing everything from the bottom of the ocean, and then throwing the vast majority of it back while looking for the relatively small number of shrimp in the catch.

So, does this suck environmentally or not?