CONSIDER A TALE of two fish. First, the orange roughy, known to most of us by its frozen or thawed filets in the local seafood market.
Fished from the frigid, black depths (up to 2,500 feet) off New Zealand and Australia, the roughy takes a century or more to reach 3 pounds and 16 inches. It takes 30 years just to reach reproductive age.
At the opposite end of the spectrum is the mahi mahi, featured at fine restaurants and also known as dorado or dolphin fish (not the mammalian dolphin).
Fished widely from tropical seas, the flashy, leaping mahi mahi speeds through life, reproducing, growing to as much as 6 feet and dying all within about four years.
Without knowing much more than that, you could predict that the slow growing and maturing roughy could be easily overfished -- and would take decades to recover.
Which is exactly the case, and is why orange roughy is deep in the red (avoid it) sector on my handy Audubon Society wallet guide to responsible seafood eating.
You could also predict that the fast growing, wide-ranging, prolific spawning mahi mahi could be fished fairly hard without calamity.
Which is why it's solidly in the green (go for it) sector of the Audubon guide, which ranks, along a red-yellow-green spectrum, more than two dozen popular seafoods.
A companion book, the Seafood Lover's Almanac, expands on the wallet card with life histories, fishing status, recipes and other details about where our fish, crabs and shellfish come from.
"Our rankings [the red-yellow-green scale] are fairly simple, but the assessments we do to determine them are not," explains Mercedes Lee, the almanac's editor and assistant director of Audubon's Living Oceans Program.
Into the rankings go such factors as species' abundance and vulnerability to overfishing (i.e., does it take a long time to grow and mature sexually?); also whether it is well managed -- is enough known about it to say if overfishing is occurring?
Other important factors include "by-catch" -- is other marine life destroyed in gathering it, as by heavy bottom trawl gear? Also, is the species' habitat intact or shrinking (say, as coastal development fills in marshes it needs)?
So what can we eat with a clean conscience? Striped bass gets a green light. It has recovered nicely in the Chesapeake after a several-year fishing ban and is well managed.
Also salmon from Alaska, where stocks are wild and healthy, farmed mussels and clams and oysters, catfish and albacore (white meat) tuna.
Clearly in the red sector: shrimp (trawling for them has a large by-catch of other species and destroys bottom habitat), codfish, grouper, shark, snapper and the popular Chilean sea bass.
Chilean sea bass is really a misnomer for the Patagonian toothfish, like the orange roughy a deepwater, slow growing and late maturing species that is close to becoming commercially extinct. Restaurant chefs love it, but after reading the Audubon Almanac, I would not order it again.
Any such rankings are bound to have species where it's just not that simple, and Audubon's are no exception. A toughie for me, because I have been buying lots of it, is farmed salmon, which is often bargain-priced at my local Giant.
Audubon says the farmed fish are a source of pollution (so much concentrated fecal matter), and are spreading disease to wild salmon, and possibly contaminating the wild gene pool.
Only in Maine are salmon farms doing a demonstrably better job, Audubon says, and their fish get a "yellow" rating.
Giant's senior seafood buyer, Bruce Steinberg, said their Atlantic salmon comes from Chile. He said Giant tries to be sensitive to environmental issues with fish and has stopped carrying the Patagonian toothfish/Chilean sea bass as a result.
Another tough call. Audubon's almanac rates blue crabs in the green sector -- except from the Chesapeake, where they are in decline enough to rate in the yellow.
Yet, I want to support local watermen. Perhaps it comes down to whether there is a recovery plan in place for our crabs (there is), and whether it looks like the plan will work (it's promising, but too soon to say).
I asked Almanac editor Lee how she decides about eating something in the yellow or yellow-green part of the spectrum.
"What I tell people is begin by removing the reds from your diet, choose from yellow and green, try green; moving up the scale from where you are now is the key," she said.
I'd recommend the Seafood Lover's Almanac as an addition to anyone's recipe shelf -- and keep one of the cards, updated annually, in your wallet.
Get the book ($19.95) or the cards (free) by calling 1-888-397-6649, or go to http://seafood.audubon.org; or write 550 South Bay Ave., Islip, NY 11751.