This image:
National Geographic: Global Fisheries Crisis, APRIL 2007: Waste of Sea Life
is one of the most powerful I have seen demonstrating what commercial fishing methods can do.
Monterey Bay Aquarium Guide to Sustainable Seafood Guide to choosing sustainably harvested seafood. Some methods may surprise you: Alaskan wild caught salmon is a better choice than Atlantic farm-raised.
Pages with good overviews & descriptions of multiple methods:
Monterey Bay Aquarium Commercial Fishing Page
Monterey Bay Aquarium Longlining and Purse Seining Facts Card
Monterey Bay Aquarium Trolling Facts Card
New Jersey Scuba Diver Commercial Fishing Page
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS - Fishing Techniques
Statistics, Fish Counts, Landing Totals:
California 1999 Freshwater and Marine Commercial Landings Historical Trends of Tuna Catches in the World
Bycatch:
Bycatch described by the Monterey Bay Aquarium
Sharks:
UN Food and Agricultural Organization, US Elasmobranch Landings
News Clippings on Sharks from Florida Musuem of Naturals History
Commercial Sharks Caught, count by species, all US regions, 1994-2003
Trolling:
(good method, low or no bycatch)How to identify troll-caught tuna in ordinary cans Troll caught tuna have high omega 3, low mecury, and little or no bycatch.
Longliners from New Jersey Scuba Diver
Long Lines:
from Australia Albatross Conservation
Longliners from New Jersey Scuba Diver