Mackerel rates highly on all of the sustainable seafood websites because it seems to have bounced back from being over-fished in the 70s and 80s. It now is available in abundance, thanks to prolific and quick spawning (naughty little fish.)
It has high-fat, firm flesh with a savory, strong flavor. It can be cooked in a variety of ways, from grilling to smoking to broiling. The key to preserving its nice texture and strong flavor is to not overcook.
Now the not-so-great news. Unfortunately, because it is a large fish, especially "King Mackerel," it is susceptible to high levels of mercury, so it should not be eaten often, and should be completely avoided by certain populations, such as pregnant women, nursing mothers and young children.
For more on mercury advisories in fish, see the EPA's Fish Advisories and Oceans Alive's Consumption Advisories page.
Here's what the various seafood rating websites have to say about it, in terms of its environmental standing:
From the Monterey Bay Aquarium's Seafood Watch Program: "King mackerel is caught predominately using hook-and-line methods in both the Atlantic and Gulf of Mexico and can be considered a "Best Choice"."
From Environmental Defense's Oceans Alive Guide: "Mackerel are fast growing with a highly migratory behavior that makes them resilient to fishing pressure."
From Blue Ocean Institute's Guide to Ocean-Friendly Seafood: "Over fished in the mid-1980s, King Mackerel have rebounded to a high level of abundance today. "
• Here is a link to all the Mackerel recipes on epicurious.com
• One Fish, Two Fish, Crawfish, Bluefish: The Smithsonian Sustainable Seafood Cookbook (Smithsonian Books) by Carole C. Baldwin
• Ocean Friendly Cuisine: Sustainable Seafood Recipes from the World's Finest Chefs (Willow Creek Press) by James Fraioli