Ever wonder what kind of fish end up in a Filet-O-Fish sandwich? The answer, according to the New York Times, is usually hoki, a bug-eyed sea creature found deep in the Pacific waters of New Zealand. 

But it turns out that exporting millions of pounds of the fish each year -- McDonald’s alone at one time used 15 million pounds annually -- is depleting the hoki supply and pitting conservationists against commercial interests.

The NY Times goes on to quote a critic of the practice: “We have major concerns,” said Peter Trott, the fisheries program manager in Australia for the World Wildlife Fund. In addition to population declines and ecosystem damage, he cited the accidental killing of other species, including skates and sharks. Managers let the fishing industry “get as much as it can from the resource without alarm bells ringing.” 

Industrial fishing is no stranger to regulations designed to protect species that have been overfished, such as red snapper, monkfish and tuna. But for years, fishing for hoki was thought to be safe.

In fact, hoki’s commercial popularity coincided with the over-harvesting of another deepwater fish, the orange roughy, in the early 1990s. Hoki, which can grow up to four feet long, became a popular replacement. Its 25-year lifespan and quick pace of reproduction promised sustainable harvests. McDonald’s, Denny’s and Long John Silver’s became repeat customers, SeaFood Business, a trade publication, reported in 2001.

At first, the New Zealand Ministry of Fisheries set high fishing quotas of roughly 275,000 tons a year, from 1996 to 2001. And restaurant fish buyers saw the fish with new eyes after 2001, when hoki won certification from the Marine Stewardship Council.

But signs of overfishing and a decline in hoki spawns came quickly.

So far, New Zealand has not formally acknowledged that hoki are being overfished. But it has cut its quotas from 275,000 tons in 2000 and 2001 to 100,000 tons in 2007 and 2008.

In 2007, when the matter came up before the stewardship council, which was deciding whether to recertify hoki fishery as sustainable and well managed, ecological groups spoke out. The World Wildlife Fund in Washington, D.C., opposed recertification, saying: “The impacts of bottom trawling by the hoki fishery must be reduced.”

The fund was overruled, but as New Zealand cut back its fishing quotas, restaurants cut back, too.

Now, Yum Brands, which owns Long John Silver’s, does not use hoki, a departure from a company report that previously praised the fish as “certified sustainable.” Denny’s only serves hoki in New Zealand.

As for McDonald’s, home of the Filet-O-Fish, hoki use was slashed to 11 million pounds annually from 15 million pounds as the company tried to mind the fish supply. The fast food chain also uses other whitefish for the sandwich.

New Zealand’s Ministry of Fisheries believes hoki are coming back. “If you look at the current state of the fishery, it’s apparent that the string of management actions that we’ve taken, which came at severe economic impact, have been effective,” Aoife Martin, manager of deepwater fishers, recently said.

But not everyone agrees. A New York-based conservation group called Blue Ocean Institute says the fish is less abundant overall and that hoki fishing “takes significant quantities of seabirds and fur seals.”